WO2001076057A2

WO2001076057A2 - Cooling module incorporating communication port and related circuits

Info

Publication number: WO2001076057A2
Application number: PCT/US2001/010066
Authority: WO
Inventors: Ford Chapman Ii Mays
Original assignee: Ljm Products, Inc., D/B/A Jmc Products
Priority date: 2000-03-31
Filing date: 2001-03-29
Publication date: 2001-10-11
Also published as: AU2001251089A1; WO2001076057A3; US6545438B1

Abstract

A cooling module includes, for certain embodiments, a brushless DC fan and integral fan control circuitry which independently implements a self-contained start and run motor control loop and also includes a communications port to accept commands from a host processor and to provide status and other data in response to queries from the host processor. In one embodiment, a fan module interfaces with a two-wire serial bus, such as an I2C bus or SMbus, and accepts commands and provides status and data in a serial digital format. A variety of commands such as on/off, and various speed control settings may be received from the host system, and the actual speed of the fan may be reporter back when queried by the host system. In some embodiments a temperature within or near the fan housing or of the air flow through the fan may be reported back when queried. The entire fan control circuit may preferably be incorporated within the fan housing, including a serial interface and power terminals for the fan, resulting in a compact four-wire interface for the fan module.

Description

COOLING MODULE INCORPORATING COMMUNICATION PORT AND RELATED CIRCUITS

Technical Field

The present invention relates to cooling modules such as those incorporating brushless DC fans or thermo-electric cooling devices, and particularly relates to cooling modules of a type suitable for use in personal computers and similar electronic equipment.

Background Art

Brushless DC fans have found wide use in cooling electronic equipment such as personal computers. Such fans incorporate a brushless DC motor (BLDC motor) which includes a stationary armature. At least two winding stages are configured around an armature core to provide a predetermined number of poles, and permanent magnets are mounted on the rotor of the fan. Frequently such fans incorporate two winding stages which are arranged to generate four magnetic poles in the armature, although greater numbers are possible. A traditional two-terminal BLDC fan motor usually incorporates circuitry to electronically commutate the winding stages to operate the motor at its full speed for the particular power supply voltage applied. Such circuitry frequently incorporates a rotor sensor to determine when the rotor has rotated sufficiently for the next winding stage to be energized. BLDC motors are also frequently known as electronically commutated motors.

BLDC fans have significant advantages over other kinds of fans. There is no rotating commutator or brush assembly as with traditional DC motors. Consequently, much fewer dust particles are generated which, if shed, may contaminate the equipment. There are fewer parts to wear out, and there is much less ignition noise than with a brush assembly. Furthermore, the magnetic coils of a BLDC motor are mounted on a rigid frame which improves the thermal dissipation of the motor and provides for greater structural integrity of the motor. BLDC fan motors are also much more electrically quiet than other kinds of motors previously used.

Despite all of these advantages, BLDC motors typically still wear out faster than the electronic systems they are included to protect. Mainly, such wear-out is caused by a failure of the bearings supporting the rotor assembly. Also, any fan generates acoustic noise which may be ergonomically displeasing to an operator of equipment incorporating such a fan. Likewise, as with all fans, the fan may become blocked by foreign matter, or filters included in the air flow path generated by the fan may become increasingly clogged with particulate matter which results in a higher strain on the motor driving the fan, and ultimately, an inability of the fan to provide the air flow for which the system was designed.

To reduce the detrimental aspects of using BLDC fans, fan-speed management has proven useful to drive such fans only when needed and only at a speed sufficiently useful to cool the system within which the fan is incorporated. Such fan-speed management results in less acoustic noise, either because the fan is totally off at certain times or is throttled to a much lower speed for a typical operation than its maximum speed which is only driven in a worst-case cooling demand. By throttling back the power of a BLDC fan, significant power dissipation is also saved, which is particularly important in battery-powered systems. There are a variety of ways that BLDC motors, and particularly BLDC fans, have been controlled in attempt to provide fan-speed management. In its simplest implementation, such fans may be turned fully on or fully off. In a system incorporating such an on off technique, the fan is turned on typically when a measured temperature somewhere in the system exceeds a first threshold limit, and the fan is turned off when that same temperature is below a second threshold limit (usually lower than the first threshold limit to provide hysteresis). This technique is effective when the fan is unnecessary for most operating conditions and may, therefore, be left off except in the most unusual circumstances. Nonetheless, such control has its drawbacks. For example, when the fan is on, it usually runs at full speed, in which case the acoustic noise is at its worst. Furthermore, if the temperature of the system hovers near the threshold temperatures, a displeasing frequent cycling of the fan may occur as the temperature is driven below the second threshold and allowed to rise above the first threshold with frequent cycling of the power to the fan.

In many systems, a temperature proportional cooling method has been devised to variably increase the speed of a cooling fan as a function of the heat generation or the temperature of the system to be protected. One method of controlling the speed of a brushless DC motor is to regulate the voltage powering the motor to a lesser voltage than the nominal operating voltage that the motor is normally specified to require. Referring now to FIGURE 1, a standard brushless BLDC motor 40 ,is shown having one power terminal tied to ground, and the other power terminal connected to a triple darlington transistor circuit (i.e., transistors 41, 42 and 43) to a 12-volt positive power supply voltage. A variable control voltage, indicated in the figure as a variable voltage 44, is applied to the control terminal of transistor 41 and the current is amplified by transistor 42, and yet again, by transistor 43, to provide on the power terminal 45 of the BLDC motor 40 a substantially fixed voltage which is a function of the control voltage 44. Raising the control voltage 44 similarly raises the voltage applied to terminal 45, which is usually about 1.5 volts below the control voltage 44. The current drawn through BLDC motor 40 is generally proportional to the voltage applied across the motor. For example, if the current drawn by BLDC motor 40 at 12 volts is 300 milliamps, the current drawn through the BLDC motor 40 will usually be approximately 150 milliamps if terminal 45 is instead controlled to a 6-volt level. The linear voltage regulator circuit shown in FIGURE 1 has several advantages, not the least of which it is extremely easy to design. It provides for a fan speed decrease which is almost linear with decreasing voltage. However, the power dissipation in the voltage regulator itself is substantial. At low fan speeds, the power dissipation of the regulator circuit may actually exceed the power consumed by the fan. This suggests large transistors may be necessary, and external heat sinks may need to be provided to dissipate the heat generated by such a large amount of current flowing through a circuit with a large voltage drop across the same circuit. Generating all of this additional heat seems counter-productive to the purpose of having the fan incorporated within the system in the first place. Consequently, such a linear voltage regulator fan-speed control has found decreasing use in recent years. Nonetheless, such a circuit does extend fan life if the system is designed to rarely require the fan to operate at full speed. Likewise, controlling the fan in this fashion may reduce acoustic noise typically generated by the system.

Another method of controlling the speed of a brushless DC motor involves chopping the power to intermittently apply full power to the motor at certain times, and applying no power to the motor at other times. This is usually accomplished with a relatively low-frequency (30-250 Hz) pulse-width-modulated (PWM) signal. One terminal of the BLDC motor may be connected to one power supply, and the other terminal may be connected to ground through a power switching device which is driven appropriately by the PWM signal.

Referring now to FIGURE 2A, the brushless DC motor 40 discussed previously is here shown with one terminal connected to a +12 volt source of voltage and a second terminal 54 coupled through an MOS transistor 50 to ground. The gate of transistor 50 is generated by a pulse- width-modulated signal generator 51, which is responding to a control signal for controlling the speed of the BLDC motor 40. By using the pulse- width-modulated signal coupled to the gate of driver transistor 50, and assuming that transistor 50 is sized appropriately large, the average power consumed by transistor 50 is much lower than in the linear voltage regulator circuit described in FIGURE 1. This occurs because driver transistor 50 is either fully turned on or fully turned off. When it is turned on by the pulse-width-modulated signal coupled to its gate terminal, the drain to source voltage is quite low (e.g., 0.5 volts) because the fan motor terminal 54 is pulled nearly to ground. While there may be significant amount of current flowing through driver transistor 50, there is not a large voltage drop across driver transistor 50, and so the instantaneous power during this portion of a cycle is very low. When driver transistor 50 is off, of course, no current flows, and there is no power dissipated instantaneously by driver transistor 50. Such a pulse-width-modulated speed control of a brushless DC motor, such as for a fan, has found wide use because of the much lower power dissipation compared to linear voltage regulator schemes, and due to the fact that a pulse-width-modulated signal at a 30 to 250 Hz rate is easily generated in either hardware or software and at very low cost.

Referring now to FIGURE 2B, a similar circuit is shown incorporating a bipolar driver transistor 52, having a current limiting base resistor 53 connecting the output of the pulse-width-modula ed signal generator 51 to the base terminal of transistor 52 to set the drive current into the base terminal and, consequently, provide for sufficient collector to emitter current through driver transistor 52 to fully support the current flow necessary through brushless DC motor 40.

A great many commercially available integrated circuits have been developed to generate useful pulse-width-modulated signals for controlling, in configurations similar to those shown in FIGURE 2A and FIGURE 2B, the speed of a brushless DC motor. Some of these circuits include temperature sensors which may be configured in a closed loop fashion to automatically control the speed of such a connected fan as a function of the locally measured temperature. Others of these integrated circuits include provisions for communicating with the whole system. Some generate the PWM signal to drive (either directly or through a buffering circuit) one of the power terminals of a standard two-terminal BLDC fan. Others generate a simple on/off control which may be used to control current through a BLDC fan.

Some types of brushless DC fans include a brushless DC motor which provides a tachometer output terminal. A pulse signal is generated on the tachometer terminal by the fan as a function of the internal self- commutation of the winding stages occurring internal to the fan. By sensing the various pulses generated on the tachometer output, the rotational speed of the fan may be determined, and an RPM (revolutions per minute) indication may be computed, or a fault condition, such as a stuck or locked rotor, may also be detected. Other commercial devices have been developed which provide a similar tachometer output or tachometer capability when using standard Iwo-terminal brushless DC motors without a built-in tachometer output. Most such circuits generate the tachometer indication by including a low- valued resistor in the current path powering the fan motor. A voltage pulse across the resistor is generated when the commutation internal to the fan occurs because of the brief interruption of current flow through the winding stages within the fan motor.

Many commercial devices, particularly those incorporating temperature sensing capability, include provisions for sensing the speed of a fan, but lack any ability to control the speed of a fan. These are mostly used to sense alarm conditions, such as a clogged filter or an actually stuck rotor. One device, available from National Semiconductor Corporation, is known as the LM75. This device includes a serial interface compatible with the I²C™ interface standard (initially developed by, and a trademark of Philips Corporation) for communicating with a host system, and includes a temperature sensor and an on/off output for a fan control. The I²C interface, which is also similar to, largely compatible with, and known by many as the SMBus interface (popularized by Intel Corporation, Santa Clara, California, and widely supported by many other companies), is a popular bi-directional two-wire serial interface, originally developed to provide power management control in battery-powered systems.

Other devices incorporate such an I²C interface and include a digital-to-analog converter (DAC) for generating on an output pin an analog voltage which can be used to control the speed of a brushless DC fan. For example, the THMC50, available from Texas Instruments, Inc., can be used to provide a controllable analog voltage on an output pin, which voltage may be used either in a linear voltage regulator, as described in relation to FIGURE 1, or to modulate the pulse width of a PWM signal for controlling fan speed, as described in relation to FIGURE 2.

One industry specification known as NLX calls for a zero to 10.5-volt analog signal which is used to set the fan speed. Controller integrated circuits are available to take this variable voltage signal and generate the pulse- width-modulated signal necessary to drive the power terminal of a fan motor. Such an analog control voltage may also be provided by a DAC output of a microcontroller or other device which may be incoφorated within the system. And yet another standard, known as the EISCA standard, provides for the sensing of a variety of system voltages and system temperatures measured at several locations within the system, provides for a fan speed indication, and includes an I²C interface to communicate with the host processor. A great many industry-available devices provide for local and remote temperature sensing with an I²C bus interface. In another device available from Tracewell Systems, a Chassis Management Module product includes an I²C interface for communication with the host processor and a PWM channel output for each of two fans, for controlling each fan in a fashion as described in FIGURE 2A and FIGURE 2B. Yet another device, the LM78, available from National Semiconductor Corp., monitors temperature, voltage and fan speed, and includes an I²C interface.

In spite of these seemingly highly-specialized commercial solutions for various temperature voltage sensing and fan speed sensing and/or control, a variety of problems remain. Most notably, the internal commutation of the winding stages within the BLDC motor is asynchronous to the external power modulation (i.e., the "power chopping") of the fan power by the PWM signal driving the motor. The electrical noise is consequently worse. Also, the tachometer output may only be generated when the motor is energized by the PWM signal. This makes RPM determinations more difficult, particularly when the fan speed is much slower than full rate. Worse, the tachometer signal may have spurious noise spikes associated with the beginning and the end of the power switching due to the PWM signal applied to the power terminals of the fan motor. This may result in erroneous determination of the actual fan rotational speed and RPM. Moreover, all of these solutions require additional integrated circuits and other discrete components hi addition to the fan itself to provide the cooling solution sought to be achieved.

Consequently, there is still a need for a better solution where thermal management, power control, sound level, and reliability are paramount.

DISCLOSURE OF THE INVENTION

An improved fan module includes integral fan control circuitry which independently implements a self-contained start and run motor control loop and also includes a communications port to accept digital commands from a host processor and to optionally provide status and other data in response to queries from the host processor. In one embodiment, the fan module interfaces with an internal system management bus, such as the SMbus or I C bus, and accepts commands and provides status and data in a serial digital format. In other embodiments, a fan module interfaces with a parallel bus. A variety of commands such as on/off, and speed control settings may be received from the host system. The actual speed of the fan may be reported back when queried by the host system. In some embodiments the temperature of the fan or of the air flow through or in the vicinity of the fan may be reported back when queried. In still other embodiments, the current through one or more fan motor windings may be measured and reported back when queried.

Such an improved fan module is highly useful for personal computers, workstations, servers, embedded systems, and other electronic systems incorporating fans for cooling. The entire fan control circuit may be incorporated within or attached to the fan housing and a simple serial two- wire interface may be provided in addition to the two power terminals for the fan, resulting in a compact four-wire interface for the fan module. In one embodiment of the invention, the power coupled to the BLDC motor is not regulated to lower voltages, nor is it chopped in a PWM fashion, but is maintained at the fixed power supply voltage provided to the fan module. The power supply voltage may be chosen from, for example, 5 volts to 30 volts. All speed control, as well as on/off control, is communicated to the fan via the serial interface, and the speed is controlled independently of the particular power supply voltage chosen.

A fan module in accordance with the present invention affords all of the benefits previously achieved by varying the speed of brushless DC fans, such as enhanced ergonomics and enhanced reliability due to operating the fan speed, at least for a significant percentage of the time, at less than its full rated speed. In addition, however, system reliability is further enhanced by eliminating the requirement of additional integrated circuits and discrete components otherwise necessary to achieve the previously discussed forms of speed control. Moreover, by directly converting a digital speed command to appropriate signals driving the internal winding stages of the BLDC motor within the fan module, much less electrical noise is generated compared to that generated by chopping the power to a standard brushless DC fan motor. The digital command may include, for example, an eight-bit control word to indicate the desired speed, and consequently a much greater degree of control over the fan speed may be achieved than with other methods. Alternatively, a fan module may be configured to respond to only a few different speed commands.

Provision for responding to a variety of different commands may be designed into such a fan module and other capabilities included within its design. For example, the fan module may be designed to initially provide a default speed when first powered up (e.g., full-rated speed) to ensure adequate cooling without requiring any digital commands communicated to the fan module. After reaching a run state at the default speed, the fan module may then be commanded to a different speed as required by the system. Other queries which may be incorporated within such a fan module include responding to a manufacture and model number request, responding to actual angular velocity or RPM of the fan, providing the delta between the commanded speed and the actual speed, winding currents, and others. This capability allows a host system to determine when the fan is unable to achieve the speed commanded, indicating a possible clogged filter or high bearing wear, and would further allow such a system to alert a maintenance provider to schedule periodic maintenance of the fan before an outright failure of the fan. The fan module may also be designed to respond to a command to operate in an automatic mode which increases fan speed appropriately as ambient airflow temperature or other self-determined temperature increases without requiring supervision by the host system. In some embodiments, the fan is configured to control the fan speed as a function of a temperature measured in the vicinity of the fan, and no interface with a host processor is required. In still other embodiments, additional memory locations may be included in the fan control circuitry to allow storing of operational or environmental parameters of a fan module. The memory may be implemented as non-volatile memory to permit retention of such stored data even when power is removed. A wide variety of data may be measured and stored, such as peak and/or average winding current, cumulative rotations of the fan motor, current and/or peak temperatures within or nearby the fan module, cumulative operating time of the fan, cumulative time operated at each possible operating speed, and many others.

The teachings of the present invention may be utilized to achieve a variety of different embodiments. For example, a cooling device in accordance with the present invention may incorporate a thermo-electric cooler rather than a fan. In another embodiment, a clock signal may be used to convey a desired speed to a fan module, which desired speed is proportional to the frequency of the clock signal. Several such fan modules may be operated at precisely the same speed, thus eliminating distracting audible "beat" frequencies otherwise present when nearby fan modules operate at similar but not identical speeds. The fan control circuits may or may not be incorporated as a part of the fan module. If separate from the module, such circuits may include more than one set of outputs for controlling more than one fan motor or other cooling device. Moreover, the control circuits may be incorporated to control a brushless DC motor used for other than a fan. Such control circuits may also be incorporated into a molded connector having one or more sets of motor control output connectors or wires, or may be implemented on a separate printed wiring board. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIGURE 1, labeled Prior Art, is a schematic drawing illustrating a linear voltage regulation method of controlling the speed of a brushless DC motor.

FIGURE 2A, labeled Prior Art, is a schematic drawing illustrating a pulse-width-modulated technique for chopping the power applied to a brushless DC motor to achieve speed control of the motor.

FIGURE 2B, labeled Prior Art, is a schematic drawing illustrating another embodiment of a pulse- width-modulated technique similar to that shown in FIGURE 2A.

FIGURE 3 is a three-dimensional drawing illustrating a fan module in accordance with the present invention.

FIGURE 4 is a block diagram illustrating major functional components of the fan module depicted in FIGURE 3.

FIGURE 5 is a schematic diagram illustrating one embodiment of fan control circuitry useful for the present invention.

FIGURE 6 is a flowchart diagram illustrating, for an exemplary embodiment, a portion of the software incorporated within a microcontroller depicted in FIGURE 5.

FIGURE 7 is a flowchart diagram illustrating, for an exemplary embodiment, the processing of an interrupt by the microcontroller depicted in FIGURE 5, and is a companion flowchart to that shown in FIGURE 6.

FIGURE 8 is a flowchart diagram illustrating, for an exemplary embodiment, various steps performed to adjust the speed of the brushless DC motor.

FIGURE 9 is a flowchart diagram illustrating, for an exemplary embodiment, the steps performed to respond to a command received by the microcontroller depicted in FIGURE 5.

FIGURE 10 is a flowchart diagram illustrating, for an exemplary embodiment, various steps performed to service an interrupt request within the microcontroller depicted in FIGURE 5.

FIGURE 11 is a schematic diagram for a portion of a motor control block which includes additional capability to detect current flow through each winding stage within the brushless DC motor.

FIGURE 12 is a schematic diagram for a portion of a motor control block which includes another circuit for detecting current flow through the winding stages within the brushless DC motor. FIGURE 13 is a block diagram illustrating major functional components of a fan module having additional register memory for storing operating and/or environmental parameters.

FIGURE 14 is a block diagram of a fan module responsive to a synchronous clock signal for setting the desired operating speed of the fan.

FIGURE 15 is a block diagram illustrating major functional components of a fan module which includes an integral communications port and a power control circuit for a brushless DC motor.

FIGURE 16 is a block diagram of a generalized cooling module in accordance with the present invention.

FIGURE 17 is a schematic diagram of a cooling module incorporating a thermo-electric cooler (TEC) device.

FIGURE 18 is a three-dimensional diagram for a fan module incorporating a heat sink.

FIGURE 19 is a diagram representing a fan speed profile as a function of measured temperature useful for a fan module in accordance with the present invention.

FIGURE 20 is a three-dimensional diagram for a control module useful for controlling one or more external fans.

FIGURE 21 is a three-dimensional diagram for a control module useful for controlling a single external fan.

The use of the same reference symbols in different drawings indicates similar or identical items.

DETAILED DESCRIPTION Referring now to FIGURE 3, a fan module 100 in accordance with one embodiment of the present invention is depicted. A fan housing 102 is shown and provides the traditional frame for the fan assembly. A rotor 104 is shown with a plurality of fan blades (one of which is labeled as 106) connected radially around the circumference of the rotor 104. Such a fan may include greater or lesser numbers of fan blades than depicted in FIGURE 3. A stationary armature (not shown) is located in the center of fan housing 102, and in FIGURE 3 is located below the rotor 104. The fan control circuitry, including a communications port for receiving digital commands, is integral to the fan module 100 and may be located within or attached to the fan housing 102, or may be wholly or partially located within the stationary armature in the center of the fan housing 102. In other embodiments, the fan control circuitry may be external to the fan housing 102. A cable 110 is shown which provides a connection to terminal pins 112 (shown here with five terminal pins 112) which are connected to a connector 108. This connector 108 is plugged into a receiving socket to provide power to the fan module and to provide connections to the communication port as well. Other numbers of terminal pins 112 may also be advantageously implemented. All of the necessary control circuitry is preferably wholly contained within the fan module, and no external components are necessary to provide any direct control of the speed of the fan, nor for the actual confrol loop of the winding stages themselves. Alternatively, rather than a cable 110, a connector may be integrated within the fan housing 102 to receive a cabled connector.

Referring now to FIGURE 4, a functional block diagram is shown corresponding to the fan module 100 depicted in FIGURE 3. A fan control circuit 121 includes a communication port 124 and a motor control circuit 127. Power for the fan confrol circuit 121 is provided on terminal 112a and the reference potential, ground, is provided on terminal 112b. The communications port 124, for this embodiment, preferably provides for a bidirectional two-wire serial interface. A serial clock is provided to the fan control circuit on terminal 112c and a bi-directional serial data signal is communicated to and from the fan control circuit 121 on terminal 112d. The serial clock and serial data signals are communicated directly to a serial interface 125 which communicates with a command interpreter and control block 126, both of which are included within the communication port 124. An optional temperature sensor 134 may be included within the fan control circuit 121 to provide the capability of ascertaining a localized temperature within the fan module 100. Examples of various particularly useful commands include a Set-Desired-Fan-Speed command (indicating a desired speed setting which is chosen from a plurality of available speed settings), a Query-Actual-Fan-Speed command, a Fan-Off command, a Query- Actual-Temperature command, and others.

The motor confrol circuit 127 includes a commutation control 128 which generates pulse-width- modulated signals on its outputs 129a and 129b, which are buffered by a driver 130 and coupled to energize the BLDC motor winding stages 122 by way of outputs 131a and 13 lb of the driver 130. Proper commutation of the motor winding stages 122 results in rotor movement which is sensed by a rotor position sensor 132 and communicated via node 133 to the commutation control 128. Consequently the commutation confrol 128, the driver 130 and the rotor position sensor 132, along with the motor winding stages 122, form a closed loop motor control. A FAULT signal may optionally be generated by the commutation control 128 to directly provide at an optional terminal pin 112e an indication of a fault condition such as a stuck rotor or a rotor whose actual rotational speed differs significantly from that commanded.

One of many potential implementations of the functional block diagram shown in FIGURE 4 is illustrated in FIGURE 5. In this circuit, many of the functional blocks are implemented within a single integrated circuit programmable microcontroller 146. In particular the serial interface 125 and the command interpreter 126 of the communication port 124, and the commutation control 128 of the motor control circuit 127 are all implemented within the microcontroller 146. Suitable microcontrollers are well known in the art. One such device is an 8-bit microcontroller known as the PIC16C62B, available from Microchip Technology, Inc., located in Chandler, Arizona. This particular microcontroller includes 2048 words (each 14 bits wide) of one-time programmable program memory, 128 bytes of random access read/write memory (RAM), several programmable timers, and a serial I/O interface compatible with the I²C interface. The SMBus interface was based upon the earlier I²C interface, and the use of each is widely known in the art. The SMBus specification revision 1.1, dated December 11, 1998, is incorporated herein by reference in its entirety. Other microcontrollers having fewer bytes of RAM and/or having factory programmed read-only memory instead of one-time programmable memory may easily be utilized instead, particularly to provide for lower production costs when manufactured with high unit volumes.

The rotor position sensor 132, previously shown in FIGURE 4, may be implemented using a hall sensor 148. Suitable Hall-effect devices are well known in the art. One especially suitable device is the TLE4935G Hall-effect sensor, available from Infineon Technologies Corp, located in Cupertino, California. A pull-up resistor 150 is included on the open collector output 170 of the hall sensor 148, which output is communicated to an interrupt pin of the microcontroller 146. A transition on the output of the hall sensor 170 (in response to movement of the rotor) generates an interrupt request within the microcontroller 146, which is described in greater detail below.

A positive power supply voltage is conveyed to the fan control circuit 121 using terminal 112a.

Nominally, this may be a 12-volt power supply, although voltages ranging from, for example, 5 volts to 30 volts may be easily accommodated. The voltage regulator 142 is provided which receives the input voltage and generates a regulated output of 5 volts (for this embodiment) on output node 144. Suitable voltage regulators are well known in the art. One especially suitable device is the LM78L05M voltage regulator, available from Fairchild Semiconductor Corp, located in Santa Clara, California. This 5-volt internal "power supply" voltage on node 144 is used to power both the integrated microcontroller 146 and the hall sensor 148.

A crystal 152 and two capacitors 154, 156 are provided to form a parallel resonant circuit between nodes 172, 174 for an internal oscillator within the microcontroller 146, which provides a timing reference for the internal clock generator contained within microcontroller 146. An 8 MHz crystal may be advantageously selected, along with 22 pF capacitors, to provide an 8 MHz clock rate. This clock rate provides adequate cycle times to implement the algorithms described herein. As before, the serial clock and serial data signals are communicated by way of terminals 112c and 112d, respectively, to nodes 176, 178 and communicated directly to the microcontroller 146, which implements the serial interface internally. An output of the microcontroller 146 or a configurable input/output pin is appropriately configured to generate the FAULT output which is communicated via node 180 to terminal 112e. The driver 130 is implemented with a pair of MOS driver transistors 158a, 158b. These driver transistors 158a, 158b receive on men respective gate terminals 182a, 182b respective pulse-width-modulated signals generated by the microcontroller 146. Each of these signals, when active, causes a low impedance path to ground through the respective driver transistor 158a, 158b, which provides a current path for energizing a respective winding stage 122a, 122b of the BLDC motor. The two driver transistors 158a, 158b are preferably implemented using an integrated pair of driver transistors, indicated by dashed line 158. Many suitable devices are available, including the Si4936DY Dual N-Channel 30-volt power MOSFET pair, available from Vishay Siliconix, located in Santa Clara, California. Alternatively, two individual discrete transistors (e.g., MOSFETs or bipolar) could be implemented. In other cases, a microcontroller may be utilized which can directly drive the winding stages without using an external buffer.

Zener diodes 160a and 160b are provided to swallow the inductive voltage kick otherwise generated by the winding stages 122a, 122b when the respective driver transistor 158a, 158b suddenly shuts off during normal commutation of the winding stages 122a, 122b. Zener diodes with 20-volt zener voltages may be advantageously used to provide adequate over-voltage protection for the outputs of the power transistors (which, for this embodiment, are 30-volt MOSFETs). Diode 162 is provided to ensure that current does not flow back into the positive 12- olt power supply node (connected to terminal 112a) when the winding stages 122a, 122b are commutated. Capacitor 164 is a filtering capacitor to help stabilize the voltage on node 166 when the various winding stages 122a, 122b are energized and de-energized during normal commutation. The movement of the rotor is indicated by dashed line 190 and the rotor position is sensed by the hall sensor 148. A transition on the output node 170 of the hall sensor is generated every time the rotor rotates 90 degrees. This transition then generates an interrupt request within the microcontroller 146, which when serviced, commutates the winding stages by energizing the next winding stage to keep the rotor rotating.

Referring now to FIGURE 6, a flowchart diagram is shown which illustrates the initialization and main control loop of exemplary firmware programmed into the microcontroller 146 shown in FIGURE 5. This flowchart is but one of many possible flowcharts which could be implemented to carry out the functions required within the microcontroller 146. During power up, the microcontroller 146 is automatically reset (flowchart step 200). Confrol then proceeds to step 202, which is the start of the main confrol portion of this firmware. Control first passes to step 204 where the controller is initialized. Examples of such initialization include setting internal timer configuration and default/preload values, configuring timer prescalers and watchdog timers, configuring I/O ports to select one of several modes of operation and particular I/O characteristics, initializing programming variables, and similar operations depending upon the particular microcontroller chosen and other implementation decisions. Control then passes to step 205 wliich sets the default fan speed. This is provided so that, in the absence of any communication via the communication port, the fan module will power up to a default speed rather than awaiting a command merely to turn the fan on. The default speed may advantageously be set to the maximum normal operating speed of the fan (e.g., 4000 RPM) to provide adequate cooling prior to or in the absence of a command from a system. After setting the default fan speed, control passes to step 206 wliich checks the rotor position. This is done by interrogating the output of hall sensor 148. In the circuit shown in FIGURE 5, the interrupt (INT) pin on the microcontroller 146 to which the hall sensor 148 is connected operates as a traditional interrupt (generating the interrupt on a transition of the input signal), but the input signal can also be sampled using a level-sensitive input buffer. The appropriate winding stage is then energized in step 208 to initiate movement of the rotor and, optionally, a watchdog timer is set. A control loop is then entered in step 210 which checks for each of two specific flags being set. Each of these flags is set, for example, by an interrupt service routine as described below. At step 210 the ROTATION flag is checked; if it is set, control passes to flowchart A, labeled as 212. If not set, confrol passes to step 214 which interrogates the COMMAND flag. If set, confrol passes to flowchart B, labeled as 216. If not, control returns to step 210. Each of these flowcharts A and B execute and return to the main control loop at step 218, which returns control to step 210 to repeat the flag interrogations.

Referring now to FIGURE 7, the basic interrupt service processing is depicted in this flowchart at step 230. Whenever an interrupt occurs, indicated in this flowchart at step 230 as a test for such an interrupt occurring, control passes to an interrupt service routine ISR, labeled as 232, which ascertains the nature of the interrupt and processes the interrupt accordingly. Confrol then returns at step 234 from the interrupt service routine 232, and passes back to step 230 to await further interrupts. The flowchart depicted in FIGURE 7 for most microcontrollers is not explicitly programmed (other than an interrupt service routine address or vector), but represents the typical functionality of microcontrollers that support interrupts and which may be configured to vector to a particular interrupt service routine whenever the interrupt occurs.

Referring now to FIGURE 8, a flowchart diagram is shown which is executed whenever the

ROTATION flag is detected at earlier step 210 as being set. In this exemplary embodiment, the ROTATION flag is set by an interrupt service routine which responds to a rotation interrupt which is generated whenever the hall sensor 148 senses that the rotor has rotated 90 degrees (i.e., one-quarter of the rotation period), as described in greater detail below. After entering at step 212, control first passes to step 240 which compares the "measured quarter-period" with the "desired quarter-period" (which variable is set based upon a received fan speed command). If the measured quarter-period is greater than the desired, control passes to step 242 which decreases the value of a pulse width variable. This variable controls the duration of both pulse-width- modulated signals generated on the two outputs of the commutation control 128, which thus controls the volt- ampere (V-A) product of an energized winding stage. Confrol then returns at step 218 to the main control loop shown in FIGURE 6. If at step 240 the test fails, confrol passes to step 244, and if the measured quarter-period is less than the desired quarter-period, control passes to step 246 which increases the pulse width of the pulse- width-modulated output signals. Again, control returns at step 218 to the main control loop. If the measured quarter-period is equal to the desired quarter-period, which is tested at step 248, then no adjustment is necessary to the timing of the pulse-width-modulated commutation output signals (i.e., neither the pulse width (duty cycle) nor the period), and confrol immediately returns at step 218. If all three tests fail, namely, the test performed at steps 240, 244 and 248, then control passes to step 250 which may be configured to report a fault, either by a dedicated fault pin, such as terminal 112e, or through the communication of a fault indication by way of the communication port to an external system connected thereto.

In other embodiments a full period of rotation may be measured and compared to a desired period, rather than measuring and comparing quarter periods. Alternatively, the average quarter period may be computed over, for example, a half-rotation or a full-rotation, and compared to the desired quarter period. In either case, any asymmetry in the output signal of the hall sensor 148, which might otherwise lead to inaccurate quarter-period measurements, may be cancelled out and a truer representation of actual rotational speed (i.e., rotational period) achieved.

Referring now to FIGURE 9, a flowchart diagram is shown which is executed whenever the

COMMAND flag is detected at step 210 as being set. Confrol enters at step B, labeled 216, and proceeds to step 260 to validate the command received. At step 262 the command is tested and, if determined to be a command to adjust the fan speed, control passes to step 264 which updates the "desired quarter-period" variable used to set the timing of the pulse-width-modulated commutation signals used to drive the motor winding stages within the fan. (Alternatively, a "desired period" variable could be used.) Otherwise the command is tested again at step 266 and, if determined to be a REPORT STATUS (i.e., QUERY) command, control passes to step 268 which writes the appropriate status data to the host by way of the communication port 124. If not a report status command, then confrol passes to step 270 to report a fault, again, either by way of a hard-wired pin and/or by a status word communicated to the host processor by way of the communication port.

Referring now to FIGURE 10, an exemplary embodiment of a suitable interrupt service routine 232 is depicted. Upon entering at step 232, the nature of the interrupt is determined by steps 280, 284 and 292. There are at least three types of interrupts explicitly processed by this routine: a duty cycle interrupt, a rotation interrupt, and a command interrupt. Additionally, other types, such as a watchdog timer interrupt, may also be processed, as described below.

Regarding a duty-cycle interrupt, each of the pulse-width-modulated commutation signals is controlled by an internal variable which sets the duty cycle (i.e., pulse width) of the signal. When each PWM signal is driven active, an internal timer is loaded with a value corresponding to the present pulse width setting.. When the timer "times out," an interrupt request is generated to indicate that the PWM signal should be driven inactive (thereby de-energizing the winding stage). This internal timer-generated interrupt request is herein referred to as a duty-cycle interrupt. Initially at step 280, if the interrupt is determined to be a duty-cycle interrupt, then confrol passes to step 282 which de-energizes the currently-driven winding stage, and control then returns at step 218 to await further interrupts. During startup of the fan, the duty cycle of the PWM signals is set for maximum speed to provide maximum torque to ensure that the fan begins rotation and spins up. For example, a value of 30 ms per winding stage may be set for the PWM signals. Such a long value ensures that, at startup, a winding stage will stay energized until the rotation of the rotor causes the next winding stage to be energized.

The second type of interrupt is a rotation interrupt. For every 90 degrees of rotor rotation, the hall sensor 148 generates a transition on its output node 170 which, being coupled to an external interrupt pin of the microcontroller 146, generates an interrupt request within the microcontroller 146. This type of interrupt indicates when the next winding stage should be driven to continue proper commutation of the motor. If the interrupt is determined, at step 284, to be a rotation interrupt, then control passes to step 286 which captures the measured quarter-period by storing the elapsed time since the previously-driven winding stage was earlier energized. This may be done in a variety of ways, including using programmable timers, software timing loops, or specialized hardware. At step 288, the currently-driven winding stage is de-energized if still found to be energized (as would typically occur at a full-speed setting or during fan startup), and the opposite winding stage is energized. The ROTATION flag is set at step 290, a watchdog timer (used for detecting, if timed-out, a stuck^"rotor) is reset, and control returns at step 218 to await further interrupts.

Lastly, if the interrupt is a command interrupt (caused by, for example, the serial interface detecting a received command), confrol passes from step 292 to step 294 which sets the COMMAND flag and then control returns at step 218 to await further interrupts. If the interrupt is other than one of these three types, confrol passes to step 296, which reports a fault condition. An example of such a fault is a stuck rotor. A watchdog timer may be configured to time out well after (e.g., 500 ms) a winding stage is energized unless reset by a rotation interrupt. Consequently, if the rotor does not begin to rotate and start generating rotation interrupts, the fan may detect its stuck rotor and alert a host system to take necessary action. The microcontroller 146 may be configured with a variety of registers. Some of these registers hold variables wliich may either be written by a host system or read by the host system. In a preferred protocol, a pointer register selects which register is read from or written to. At power-up, the default value of the pointer register may be set to reference the Commanded Speed (CS) register. The CS register is preferably a write- only register, and is used to dictate the desired speed of the fan. Another register may be the Reported Speed (RS) register, a preferably read-only register used to report the actual speed of the fan. Under normal operating conditions, the values found in the two registers are identical. In the event that the fan motor cannot operate at the commanded speed, the RS register indicates the actual speed. In a system that commands and reads fan speed, a mismatch of the CS and RS registers may indicate a blocked fan or clogged filter, thus causing an alert condition in the system logic.

For an exemplary embodiment compatible with the I²C interface, a write by the system host to the fan module 100 includes the address byte and the pointer byte to set the desired Pointer Register contents, as follows:

Pointer Byte:

Register Select Truth Table:

If the pointer register contents are correct, then a read or a write is performed by the host system issuing the correct address byte followed by a data byte (for a write) or alternatively for a read, by the host system issuing the correct address byte followed by the retrieval of the data byte. Other pointer byte values may be used to access additional registers, such as a localized temperature within the fan module 100, and other possible features. By setting the pointer register once, sequential read or write commands to the same register may be executed over the I²C bus without re-transmitting an "address" of the register for each access, thus reducing bus traffic.

As described above, the speed of the fan may be controlled by the value written into the CS register. In an exemplary embodiment, there are 255 valid speed values that may be written to the CS register. The speed of the fan is linearly proportional to the value contained in the CS register as described in the table below:

In addition, the value 0x00 may be used as a FAN OFF command. Reported speed values may be arranged to correspond to the commanded speed values one to one, making system comparison logic very simple. In other embodiments, a smaller set of possible speeds is very adequate. For example, a fan module may be configured to respond to any of three possible fan speed commands and an "off command (e.g., 1100, 2500, and 4000 RPM, and OFF).

As described above, the fan module 100 provides a communications port having a two-wire serial interface. Commands received are converted directly into a plurality of commutation signals which energize the winding stages of the BLDC motor to achieve variable speed control of the fan without varying the voltage across the winding stages when energized. The total parts count is very low, and facilitates incorporating the entire fan control circuit integrally with the fan module. A fan module in accordance with the present invention is well-suited for use in a microprocessor-based system, such as a personal computer, workstation, embedded system, etc.

Referring now to FIGURE 11, low- valued series resistors may be included between the driver transistors 158a, 158b and the respective winding stages 122a, 122b so that the magnitude of the current flow through each of the winding stages may be ascertained. For example, resistors 200a, 200b are respectively included between winding stages 122a, 122b and driver transistors 158a, 158b. The voltage drop across each of these resistors 200a, 200b may be measured by a respective differential analog-to-digital (ADC) circuit 204a, 204b, which may be incorporated within certain available integrated circuit microcontrollers (as shown here within microcontroller 146) or may be implemented externally to a microcontroller. In particular, to sense the current flowing through winding stage 122a, one input of the differential ADC circuit 204a (shown here as the positive input) is connected to node 168a, and the other input (shown here as the negative input) is connected to node 202a. Likewise, the current flowing through winding stage 122b may be determined by connecting the positive input of differential ADC circuit 204b to node 168b, and the negative input to node 202b. By including a capability such as this, the magnitude of the current flow through the winding stages may be determined, and if excessive, or alternatively if non-existent, an appropriate status or fault indication may be communicated.

Referring now to FIGURE 12, a single low-valued series resistor may be included between the driver transistors 158a, 158b and their respective source terminal connections to ground so that the magnitude of the current flow through either winding stage may be ascertained. For example, resistor 206 is included between node 208 and ground. The source terminal of each driver transistor 158a, 158b is connected to node 208 rather than directly to ground so that the current flowing through an energized winding stage also flows through resistor 206. The voltage drop across this resistor 206 (and inferentially, the current flow through the winding stages) may be measured by a single analog-to-digital (ADC) circuit 210, which preferably may be incorporated as shown here within the integrated circuit microcontroller 146 (using, for example, an internally generated reference voltage, VREF, as is found in several commercially available microcontrollers) or may be implemented externally to a microcontroller. By including a capability such as this, the magnitude of the current flow through the winding stages may be determined in a manner which requires fewer circuit resources than that shown in FIGURE 11. As before, if the current is either excessive or non-existent, an appropriate status or fault indication may be generated and or communicated to a host.

Another exemplary embodiment of a fan module may include seven registers to facilitate storage and retrieval of operating and/or environmental fan parameters. In this embodiment, the two primary operating fan parameters are fan speed and motor winding current. A localized temperature within or near the fan module could also be advantageously measured and stored as another parameter.

Fan speed is controlled by writing the appropriate value to the Commanded Speed (CS) Register. The actual speed of the fan is reported in the Reported Speed (RS) Register, which may be read by way of the communication port. Under normal conditions, the value of both registers is the same. However, if there is a difference between commanded speed and reported speed, a problem with the fan may be detected by the host system. In addition, a Speed Threshold (ST) Register may be written and if the difference in commanded and reported speed exceeds the speed threshold, an Alarm Condition is triggered which may illuminate an alarm lamp on the module or may directly drive an alarm signal, if provided. Alternatively, the ST Register may be configured in a fan module to represent the actual speed below which an Alarm Condition is triggered, rather than a maximum allowable difference between actual and desired speed.

Similarly, the measured motor winding current is reported in a Winding Current (WC) Register. For each "on" cycle of the motor windings (i.e., typically four such cycles per revolution), the winding current is measured and the value stored in the WC Register. Excessive winding current may indicate a problem with the fan such as, for example, shorted windings, or worn bearings. If the reported winding current stored in the WC Register exceeds the value stored in a Current Threshold (CT) Register, an Alarm Condition is triggered which, as before, may illuminate an alarm lamp on the module or may directly drive an alarm signal, if provided.

The Slave Address (SA) Register stores the fan modules I²C slave address. This address preferably has a default value that may be overwritten to support multiple fans on the same bus segment. A unique address can be written to the fan in systems that support "clock blocking," which isolates all but the fan whose address is being written from the bus segment by holding the clock high during the slave address write. Similar techniques using an I C bus are well known in the art.

In a particular embodiment compatible with the I²C interface, a write by the system host includes a pointer byte specifies one of these six other registers described above, as follows:

Pointer Byte:

Register Select Truth Table:

An Alarm Condition may illuminate a light or lamp (e.g., an LED) if one is provided. While many various schemes may be supported, one particularly advantageous lamp scheme includes three possible states: (1) fully on; (2) blinking; and (3) off. If the fan fails to operate, the Alarm light is set to be fully on. Such a fan module should be replaced. If one or more of the thresholds has been exceeded, the Alarm light is set to blink. Such a fan module should be replaced, although less urgently so, and likely could be replaced when convenient. If the fan is operating properly (or the power to the fan module has been removed), the Alarm light is turned off. Other schemes, such as those incorporating different blink rates or patterns, may alternatively be utilized to encode even more information into a single indicator lamp.

In certain embodiments of the present invention, a fan module may be configured to operate at a lower power supply voltage than normal, albeit at a lower speed. Such a capability allows a user to reduce the operating voltage to achieve a low power mode. For example, a fan module configured to nominally operate at a power supply voltage of 12 volts may also be operated with the power supply voltage equal to 5 volts. The fan speed will likely be far lower than the desired speed value stored in the Commanded Speed (CS) Register, and the Alarm Condition may be triggered if the Speed Threshold (ST) Register has been loaded with certain values, but the fan will continue to operate. During such a low power mode, a different value may be stored into the ST Register to prevent such an Alarm Condition. Thereafter, when the power supply voltage is raised to the nominal value, the speed achieved will return to the normal value as loaded into the CS Register.

In certain embodiments, the registers thus far described are implemented within an integrated microcontroller as volatile storage registers. Consequently, whenever power is removed from a fan module or other motor controller containing such a microcontroller, the values previously stored in the registers will be lost, and new values must be written after power is restored if an operating condition other than the default condition is desired. In other embodiments, these or other registers may be implemented using non-volatile registers that • maintain their values through a loss of power. Such non-volatile registers may be implemented by using a commercially available microcontroller having non-volatile memory capabilities, or by adding one or more commercially available non-volatile memory devices to the fan confrol circuitry. Referring now to FIGURE 13, a functional block diagram is shown>corresponding to another embodiment of a fan module in accordance with the present invention. A fan control circuit 250 includes a communication port 252, a control block 254, and a motor control circuit 127. Power for the fan control circuit 250 is provided on terminal 112a and the reference potential, ground, is provided on terminal 112b. The communications port 252, for this embodiment, preferably includes a bi-directional two-wire serial interface having a serial clock conveyed on terminal 112c and a bi-directional serial data signal conveyed on terminal 112d. The serial clock and serial data signals are communicated directly to a serial interface within the communication port 252. A command interpreter may be implemented either within the communication port 252 or the confrol block 254. A temperature sensor 134 is included within the fan confrol circuit 250 to provide the capability of ascertaining a localized temperature within or nearby the fan module. A memory block 256 is also included to provide storage registers. The motor confrol circuit 127 is substantially identical (for this embodiment) to that shown in FIGURE 4 and need not be explained further here. An ALARM signal is generated to indicate one or more alarm conditions of the fan module, as described elsewhere herein. The memory block 256 may be implemented as non-volatile memory, such as E²PROM or flash memory, which are widely available commercially and which use is widely known by those skilled in the art.

Certain embodiments of a fan module may include even more registers to facilitate storage and retrieval of operating and/or environmental fan parameters. If such registers are implemented using a nonvolatile memory technology, the values of such registers survives the removal or loss of power. Moreover, other types of parameters, such as historical parameters, may be advantageously measured and/or computed and stored for retrieval by the host system. Examples of such historical parameters include cumulative rotations (possibly rounded to represent larger numbers at the expense of precision), total hours of operation, hours of operation at each possible speed range, total on-time of the fan, average and/or peak temperature, and others. Examples of present parameters include winding current, present power supply voltage value, present fan speed (or cooling value), present temperature within or near the fan module (or at a remote location), and others.

By capturing such information, a fan module in accordance with the present invention may be able to estimate remaining life of the fan module. For example, the fan may be rated for a predetermined number of cumulative rotations, and tracking the actual cumulative rotations may provide a metric for estimating remaining life, particularly if the average RPM or average rotations per unit time is known. Other examples of predictive parameters include estimated life remaining, estimated rotations remaining, an indication suggesting immediate replacement of the fan module, and others.

While the embodiments described thus far include a communication port having, for example, a serial or parallel interface for communicating one or more digital words to the fan module, an embodiment is shown in FIGURE 14 that responds to a synchronous clock to set the fan speed. In this embodiment a fan control circuit 280 includes a motor confrol circuit 127 that includes an optional tachometer output signal TACH conveyed on terminal 112d and an optional LOCKED ROTOR signal conveyed on terminal 112e. A control block 282 receives a synchronous clock signal SYNC_CLK conveyed on node 112c to provide a reference frequency for the fan speed, which is controlled to be proportional to the period of the SYNC_CLK signal. For example, the period of the fan may be equal to the period of the SYNC_CLK signal (i.e., a fan speed of 2200 RPM for a 2200 Hz SYNC_CLK signal). Alternatively, the fan period may be a multiple of fraction of the received SYNC_CLK period (e.g., a fan speed of 2200 RPM for a 550 Hz received SYNC CLK signal). Consequently, the fan speed is directly controlled by the incoming synchronous clock signal. Internally, the commutation may be controlled in a similar fashion as described above, wherein the control block 282 times the period of the incoming SYNC_CLK signal and sets the appropriate internal register accordingly (e.g., the Commanded Speed (CS) register), and wherein the motor control circuit 127, as before, adjusts the timing of the two output signals 129a, 129b to commutate the motor to run at the desired speed.

Referring now to FIGURE 15, a functional block diagram of another fan module is shown. A communication port 124 includes a serial interface 125 coupled to a command interpreter 126, as before. In this particular fan module, a fan control circuit 226 is more typical of the type utilized in a stand-alone two- terminal industry-standard brushless DC fan motor. It includes a commutation control circuit 228 for generating at least two commutation signals which are buffered by driver 230 to drive the motor winding stages 122. A position sensor 232 detects the position of the rotor, and provides an input to the commutation control circuit 228 for commutating the winding stages and for energizing the next winding stage. The speed of the motor driven by the fan confrol circuit 226 may be controlled by controlling the power applied to the entire fan confrol circuit 226. This is done by power confrol circuit 222, which is controlled by speed control circuit 220. The power control circuit 222 may include a linear voltage regulator circuit which is used to vary the voltage impressed across the fan control circuit 226 as a function of the desired rotational speed of the rotor. Alternatively, the power control circuit may include a pulse-width-modulating circuit to chop the power impressed across fan control circuit 226. In either case, the fan module includes, as shown, a communication port integrated with the fan module for directly responding to fan control commands. Moreover, the voltage coupled to the fan module by a system into wliich the fan module is incorporated is a constant voltage. By incorporating the power control circuit 222 into the fan module, the user is relieved of the burden of providing additional external components for controlling a separate fan module. Moreover, system reliability is improved.

The embodiment shown in FIGURE 15 may be generalized and depicted by the embodiment shown in FIGURE 16. Here, a cooling module 300 includes a communication port 302 having a digital interface (e.g., a serial or parallel interface). The communications port 302 communicates with a confrol block 304, wliich then communicates with a power confrol circuit 306 to control the current through (or voltage across) a cooling device 310. Such a cooling device 310 may be a fan, a thermo-electric cooling device, or another such device arranged to provide a source of cooling when appropriately driven by suitable signals. The amount of cooling may frequently be controlled by controlling the power applied to the cooling device 310. This is done by the power confrol circuit 306. The power confrol circuit 306 may include a linear voltage regulator circuit that is used to vary the voltage impressed across (or alternatively the current conducted through) the cooling device 310 as a function of the desired amount of cooling. Alternatively, the power control circuit may include a pulse-width-modulating circuit to chop the power impressed across the cooling device 310. In either case, the cooling module 300 includes, as shown, a communication port 302 integrated with the cooling module for directly responding to control commands. Moreover, the voltage coupled to the cooling module by a system into which the cooling module is incorporated is a constant voltage independent of the amount of cooling desired. By incorporating the power control circuit 306 into the cooling module, the user is relieved of the burden of providing additional external components for controlling a separate cooling module and system reliability is improved.

One of many potential implementations of this functional block diagram is illustrated in FIGURE 17, which shows a cooling module 320 utilizing a thermo-electric cooling device rather than a BLDC fan. In this circuit, many of the functional blocks are implemented within a single integrated circuit programmable microcontroller 146. In particular the communication port 302 (including a serial interface), the control block 304, and the power control circuit 306 are all implemented within the microcontroller 146. Suitable microcontrollers are well known in the art. One such device is the 8-bit microcontroller PIC16C62B, described above. Other microcontrollers having fewer bytes of RAM and/or having factory programmed readonly memory instead of one-time programmable memory may easily be utilized instead, particularly to provide for lower production costs when manufactured with high unit volumes.

A positive power supply voltage is conveyed to the cooling module 320 using terminal 112a. Nominally, this may be a 12-volt power supply, although voltages ranging from, for example, 5 volts to 30 volts may be easily accommodated. The voltage regulator 142 is provided which receives the input voltage and generates a regulated output of 5 volts (for this embodiment) on output node 144. Suitable voltage regulators are well known in the art. One especially suitable device is the LM78L05M voltage regulator, available from Fairchild Semiconductor Corp, located in Santa Clara, California. This 5-volt internal "power supply" voltage on node 144 is used to power the integrated microcontroller 146.

A crystal 152 and two capacitors 154, 156 are provided to form a parallel resonant circuit between nodes 172, 174 for an internal oscillator within the microcontroller 146, which provides a timing reference for the internal clock generator contained within microcontroller 146. An 8 MHz crystal may be advantageously selected, along with 22 pF capacitors, to provide an 8 MHz clock rate. This clock rate provides adequate cycle times to implement the algorithms described herein. As before, the serial clock and serial data signals are communicated by way of terminals 112c and 112d, respectively, to nodes 176, 178 and communicated directly to the microcontroller 146, which implements the serial interface internally. An MOS driver transistor 158 receives on its gate terminal 182 a pulse- width-modulated signal generated by the microcontroller 146. This signal, when active, causes a low impedance path to ground through the driver transistor 158 which provides a current path for energizing the thermo-electric cooler device 322.

Referring now to FIGURE 18, another embodiment of a cooling module is shown. Here a fan module

500 includes a BLDC fan 502 mounted upon a heat sink 504. Several individual vanes of the heat sink 504 are shown, two of which are labeled 514. The fan control circuitry, including a communications port for receiving digital commands, is preferably integral to the fan module 500 and preferably located within or attached to the fan housing 502, or may be wholly or partially located within the stationary armature in the center of the fan housing 502. In other embodiments, the fan control circuitry may be external to the fan housing 502. A cable 510 is shown which provides a connection to terminal pins 512 (shown here with five terminal pins 512) which are connected to a connector 508. This connector 508 is plugged into a receiving socket to provide power to the fan module and to provide connections to the communication port as well. Other numbers of terminal pins 512 may also be advantageously implemented. All of the necessary control circuitry is preferably wholly contained within the fan module, and no external components are necessary to provide any direct control of the speed of the fan, nor for the actual control loop of the winding stages themselves. Alternatively, rather than a cable 110, a connector may be integrated within the fan housing 102 to receive a cabled connector.

A temperature sensor (e.g., a thermocouple) is preferably mounted remotely from the fan 502 at a location suitable to sense more closely the temperature of a semiconductor package in physical contact with the bottom surface 506 of the heat sink 504. A cable 516 connecting such a thermocouple (not shown) is shown routed from the fan housing 502 through a hole 518 in the heat sink 504.

Another useful embodiment of such a fan module 500 dispenses with a communications port and provides a fan module and heat sink combination to automatically confrol the fan speed, under self-control of the fan control circuitry and without any system intervention, to provide a desired temperature profile. Such a fan module preferably incorporates a remote temperature sensor in close proximity to the semiconductor package in contact with the heat sink to control the temperature profile near the semiconductor package. A particularly useful fan speed profile for such a fan module, as well for other embodiments, is depicted in FIGURE 19. At temperatures below a lower threshold temperature (labeled Tjj, the fan speed is maintained at a first speed S which is preferably a slow speed useful to keep a minimum amount of airflow passing through the system protected by such a fan module. At temperatures above an upper threshold temperature (labeled T₂), the fan speed is maintained at a second speed S₂, which is preferably the maximum normal speed for the fan. At temperatures between the lower and upper threshold temperatures, the fan speed is controlled to increase with increasing temperature. A linear relationship is shown in FIGURE 19 which is preferred, although other relationships, such as discrete stair steps, may be advantageously chosen.

While other embodiments have shown fan modules or cooling modules incorporating control circuitry as a part of the cooling module itself, the confrol circuitry variations described herein may also be advantageously provided for use with an external fan or other cooling device. Referring now to FIGURE 20, a control module 600 includes a control circuit module 602 within which the fan control circuitry is contained. A group of electrical pins 603 provide power to the confrol circuit module 602and to provide connections to a communications port for the module 602 as well. A first cable 606 couples the control circuit module 602 to a first connector 604 that is provided to connect to a first BLDC fan (not shown), and an optional second cable 610 couples the control circuit module 602 to an optional second connector 608 that is provided to connect to a second BLDC fan (also not shown). Consequently, the confrol circuit module 602 may be configured to control more than one external fan. Another embodiment of a control module 622 is shown in FIGURE 21 wliich is arranged to receive a connector 624 from a single external fan (or other cooling device).

While the invention has been largely described with respect to the embodiments set forth above, the invention is not necessarily limited to these embodiments, which are given by way of example only. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope and spirit of the invention as set forth in the following claims. For example, suitable implementations may be fashioned in hardware or software, or a combination thereof. Portions may be implemented using a programmable microcontroller, a general purpose microprocessor, dedicated hardware, a microcontroller core mapped into a custom integrated circuit, gate array, standard cell array, an ASIC, or any of several widely available circuit forms which can be chosen which meet the necessary performance requirements. Software timing loops may be used rather than or in combination with hardware interrupts. A serial interface may be provided in some commercially available microcontrollers, may be fashioned using hardware, or may even be implemented using largely software methods executing on relatively general purpose hardware. A variety of well-known serial interfaces may be chosen, including an SMBus or I²C interface, an RS-232 interface (or its military or ITU equivalent), a 3-wire SPI interface, a

Universal Serial Bus (USB) interface, or others. A power supply voltage other than +12 volts may be chosen according to system availability and designer choice. Rotation sensors other than hall sensors may be chosen such as, for example, optical sensors.

Moreover, the block diagrams described herein are provided as examples to aid the understanding of the invention, but are not to be construed as restricting the invention to the specific block diagrams shown. One skilled in the art will immediately recognize other equivalent arrangements which capitalize upon the teachings of the present invention. For example, a communication port block need not necessarily provide a command interpreter, which may be provided within other, more general, confrol blocks. Moreover, for many embodiments, the distinctions between the various functional blocks are, at best, somewhat arbitrary and the functions implied by each such block may be variously implemented within other blocks. As used herein , a communication port implies some kind of interface and some ability to process commands or other signals received thereby, although not necessarily within a single functional block ascribed as a communication port.

Accordingly, other embodiments, variations, and improvements not described herein are not necessarily excluded from the scope of the invention, which is defined by the following appended claims.

Claims

WHAT IS CLAIMED:

1. A fan module comprising: a fan housing; an electronically commutated motor mounted to the fan housing, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and further including a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; a plurality of fan blades coupled to the rotor; and a fan control circuit including a communication port for operably receiving digital commands, at least one of which for controlling the rotational speed of the rotor; and a motor control circuit coupled to the communication port and having at least two outputs, each respectively coupled to a respective winding stage, said motor control circuit for generating on each respective output a respective pulse-width-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to rotate the rotor with a rotational speed responsive to a received digital command.

2. A fan module as recited in claim 1 wherein the motor confrol circuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of the rotational speed of the rotor.

3. A fan module as recited in claim 1 wherein the motor control circuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of any received digital command.

4. A fan module as recited in claim 1 wherein the motor control circuit includes: a rotor position sensor for generating a signal indicative of rotor position relative to the magnetic poles established by the winding stages.

5. A fan module as recited in claim 4 wherein the fan control circuit is arranged to determine actual fan speed by observation of changes in the rotor position sensor signal as a function of time.

6. A fan module as recited in claim 5 wherein the fan confrol circuit is arranged to determine actual fan speed by observation of changes in the rotor position sensor signal corresponding to rotor rotation through at least two magnetic poles established by the winding stages.

7. A fan module as recited in claim 5 wherein the fan confrol circuit includes: a provision for responding to a fan speed query command received by way of the communication port by providing a data word to indicate actual fan speed.

8. A fan module as recited in claim 1 wherein: the fan control circuit is arranged to respond to any of a plurality of digital commands, each corresponding to a respective rotational speed of the rotor, by adjusting the timing and duration of the respective pulse-width-modulated signals to adjust the rotational speed in accordance with a digital command received.

9. A fan module as recited in claim 8 wherein: the fan confrol circuit is arranged to respond to a "fan off' digital command by preventing the respective pulse-width-modulated signals from occuring.

10. A fan module as recited in claim 1 wherein the communication port comprises a serial interface.

11. A fan module as recited in claim 2 wherein the communication port comprises a serial interface.

12. A fan module as recited in claim 10 wherein the serial interface comprises an I C bus compatible interface.

13. A fan module as recited in claim 12 further comprising: a first power supply terminal for operably receiving a source of voltage which is substantially independent of fan rotor speed; a second power supply terminal for operably receiving a reference voltage; a first signal terminal for operably receiving a clock signal for the serial interface; and a second signal terminal for operably receiving a bi-directional data signal for the serial interface.

14. A fan module as recited in claim 10 wherein: the serial interface comprises an RS-232 interface.

15. A fan module as recited in claim 1 wherein the communication port comprises a parallel interface.

16. A fan module as recited in claim 15 wherein the fan confrol circuit comprises: a first power supply terminal for operably receiving a source of voltage which is substantially independent of fan rotor speed; a second power supply terminal for operably receiving a reference voltage; a first signal terminal for operably receiving a clock signal for the parallel interface; and a plurality of signal terminals for operably receiving a data word signal for the parallel interface.

17. A fan module as recited in claim 1 wherein: the fan control circuit is either enclosed within or attached to the fan housing.

18. A fan module comprising: a fan housing; an electronically commutated motor mounted within the fan housing, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and having a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; a plurality of fan blades coupled to the rotor; and a fan control circuit including a communications port having a serial interface, for controlling at least the rotational speed of the rotor in accordance with a digital command operably received by way of the serial interface.

19. A fan module as recited in claim 18 wherein the fan confrol circuit includes: a motor control circuit coupled to operably receive a substantially constant voltage between a first power terminal and a second power terminal, said motor control circuit having at least two outputs, each respectively coupled to a respective winding stage, for generating on each respective output a respective pulse-width-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to both commutate the winding stages in a preselected sequence to rotate the rotor and with a rotational speed that is responsive to the digital command.

20. A fan module as recited in claim 18 wherein the fan confrol circuit includes: a temperature sensor arranged to be responsive to a localized temperature within the fan module.

21. A fan module as recited in claim 18 wherein the serial interface comprises: a two-wire bi-directional interface.

22. A fan module as recited in claim 18 wherein the serial interface comprises: a three-wire bi-directional interface.

23. A fan module as recited in claim 21 wherein the serial interface comprises: an I²C compatible interface.

24. A fan module as recited in claim 18 wherein the serial interface comprises: an RS-232 compatible interface.

25. A fan module as recited in claim 21 wherein the fan control circuit includes: a provision for responding to a fan speed query command received by way of the serial interface by providing a serial data word to indicate actual fan speed.

26. A fan module as recited in claim 21 wherein the fan confrol circuit includes: a temperature sensor arranged to be responsive to a localized temperature within the fan module; and a provision for responding to a temperature query command received by way of the serial interface by providing a serial data word to indicate the temperature as sensed by the temperature sensor.

27. A computer system comprising: a fan module including a fan speed confrol circuit for controlling the rotation of the fan in response to a digital fan command received by way of a serial interface; computing circuitry which can execute stored instruction programs and which can generate a plurality of digital fan commands under program control; and a control bus for communicating a digital fan command from the computing circuitry to the fan module.

28. A computer system as recited in claim 27 wherein: the confrol bus comprises a serial bus.

29. A computer system as recited in claim 27 wherein: the confrol bus comprises an I²C compatible serial bus.

30. A computer system as recited in claim 27 wherein the fan module comprises: a fan housing; an electronically commutated motor mounted to the fan housing, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and further including a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; a plurality of fan blades coupled to the rotor; and a fan control circuit including a communication port for operably receiving digital commands, at least one of which for controlling the rotational speed of the rotor; and a motor control circuit coupled to the communication port and having at least two outputs, each respectively coupled to a respective winding stage, said motor control circuit for generating on each respective output a respective pulse- idth-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to rotate the rotor with a rotational speed responsive to a received digital command.

31. A method of controlling an electronically commutated motor that includes a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and having a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages, said method comprising the steps of: receiving a digital command; and generating at least two pulse- idth-modulated (PWM) signals, each respectively coupled to energize a respective winding stage at respective times for respective durations of time to commutate the winding stages in a preselected sequence to rotate the rotor with a rotational speed responsive to the received digital command.

32. A method as recited in claim 31 further comprising: impressing across each winding stage, when energized, a voltage which is substantially independent of the rotational speed of the rotor.

33. A method as recited in claim 31 further comprising: generating a signal indicative of rotor position relative to the magnetic poles established by the winding stages, from which current rotational speed may be inferred; receiving one of a plurality of digital commands, each corresponding to a respective rotational speed of the rotor; and adjusting the timing and duration of the respective pulse- width-modulated signals to adjust the desired rotational speed in accordance with the digital command received.

34. A method as recited in claim 31 further comprising: responding to a fan speed query digital command by providing a data word to indicate actual fan speed.

35. A method as recited in claim 31 wherein: the digital command is received by way of a serial interface.

36. A method as recited in claim 31 wherein: the digital command is received by way of a parallel interface.

37. A method as recited in claim 35 wherein: the serial interface comprises an I²C compatible interface.

38. A method as recited in claim 33 further comprising: generating a rotor position signal from which the current rotational speed of the rotor may be inferred; and adjusting the at least two pulse-width-modulated signals in accordance with both the digital control signal and the current rotational speed inferred from the rotor position signal, to urge the rotational speed closer to a desired rotational speed.

39. A fan module comprising: a fan housing; an electronically commutated motor mounted to the fan housing, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and further including a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; a plurality of fan blades coupled to the rotor; means for operably receiving digital commands for controlling at least the rotational speed of the rotor; and means for energizing each respective winding stage at respective times for respective durations of time to rotate the rotor with a rotational speed in accordance with a received digital command.

40. A fan module as recited in claim 39 wherein the energizing means is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of the rotational speed of the rotor.

41. A fan module as recited in claim 39 wherein the energizing means is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of the received command.

42. A fan module as recited in claim 39 further comprising: means for generating a signal indicative of rotor position relative to the magnetic poles established by the winding stages.

43. A fan module as recited in claim 39 further comprising: means for determining actual fan rotor speed.

44. A fan module as recited in claim 43 further comprising: means for providing a data word to indicate actual fan speed in response to a fan speed query command received by the fan module.

45. A fan module as recited in claim 39 wherein: the energizing means is arranged to respond to a "fan off command by preventing the energizing of the winding stages.

46. A fan module as recited in claim 39 wherein the means for operably receiving commands comprises a serial interface.

47. A fan module as recited in claim 39 wherein the means for operably receiving commands comprises a parallel interface.

48. An electronically commutated motor assembly comprising: a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles; a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; and a confrol circuit including a communication port for operably receiving digital commands, at least one of which for controlling the rotational speed of the rotor; and a motor control circuit coupled to the communication port and having at least two outputs, each respectively coupled to a respective winding stage, said motor confrol circuit for generating on each respective output a respective pulse-width-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to rotate the rotor with a rotational speed responsive to a received digital command.

49. A motor assembly as recited in claim 48 wherein the motor control circuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of the rotational speed of the rotor.

50. A motor assembly as recited in claim 48 wherein the motor control circuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of any received digital command.

51. A motor assembly as recited in claim 48 wherein the motor confrol circuit includes: a rotor position sensor for generating a signal indicative of rotor position relative to the magnetic poles established by the winding stages.

52. A motor assembly as recited in claim 51 wherein the confrol cfrcuit is arranged to determine actual rotor speed by observation of changes in the rotor position sensor signal as a function of time.

53. A motor assembly as recited in claim 52 wherein the control circuit is arranged to determine actual rotor speed by observation of changes in the rotor position sensor signal corresponding to rotor rotation through at least two magnetic poles established by the winding stages.

54. A motor assembly as recited in claim 52 wherein the confrol circuit includes: a provision for responding to a rotor speed query command received by way of the communication port by providing a data word to indicate actual rotor speed.

55. A motor assembly as recited in claim 48 wherein: the confrol circuit is arranged to respond to any of a plurality of digital commands, each corresponding to a respective rotational speed of the rotor, by adjusting the timing and duration of the respective pulse-width-modulated signals to adjust the rotational speed in accordance with a digital command received.

56. A motor assembly as recited in claim 55 wherein: the confrol circuit is arranged to respond to a "motor off digital command by preventing the respective pulse-width-modulated signals from occurring.

57. A motor assembly as recited in claim 48 wherein the communication port comprises a serial interface.

58. A motor assembly as recited in claim 48 wherein the communication port comprises a parallel interface.

59. A motor assembly as recited in claim 49 wherein the communication port comprises a serial interface.

60. A motor assembly as recited in claim 57 wherein the serial interface comprises an I²C bus compatible interface.

61. A motor assembly as recited in claim 60 wherein the control circuit comprises: a first power supply teπninal for operably receiving a source of voltage which is substantially independent of rotor speed; a second power supply terminal for operably receiving a reference voltage; a first signal terminal for operably receiving a clock signal for the serial interface; and a second signal terminal for operably receiving a bi-directional data signal for the serial interface.

62. A motor assembly as recited in claim 57 wherein: the serial interface comprises an RS-232 interface.

63. A motor assembly as recited in claim 48 wherein: the confrol cfrcuit is either enclosed within or attached to a housing for the motor.

64. A confrol circuit for at least one electronically commutated motor that includes a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and that further includes a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages, said control circuit comprising: a communication port for operably receiving digital commands, at least one of which for controlling the rotational speed of the rotor; and a first motor control circuit coupled to the communication port and having at least two outputs, each for respectively coupling to a respective winding stage of a particular motor, said first motor control circuit for generating on each respective output a respective pulse-width-modulated (PWM) signal to energize a respective winding stage when coupled thereto at respective times for respective durations of time to rotate the rotor with a rotational speed responsive to a received digital command.

65. A control circuit as recited in claim 64 wherein the first motor confrol circuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of the rotational speed of the rotor.

66. A confrol cfrcuit as recited in claim 64 wherein the first motor confrol cfrcuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of any received digital command.

.

67. A confrol circuit as recited in claim 64 wherein the motor confrol circuit includes: a rotor position sensor for generating a signal indicative of rotor position relative to the magnetic poles established by the winding stages.

68. A confrol circuit as recited in claim 67 further comprising circuitry to determine actual rotor speed by observation of changes in the rotor position sensor signal as a function of time.

69. A confrol circuit as recited in claim 68 wherein the control circuit is arranged to determine actual rotor speed by observation of changes in the rotor position sensor signal corresponding to rotor rotation through at least two magnetic poles established by the winding stages.

70. A confrol cfrcuit as recited in claim 68 further comprising: a provision for responding to a rotor speed query command received by way of the communication port by providing a data word to indicate actual rotor speed.

71. A confrol circuit as recited in claim 64 wherein: the confrol circuit is arranged to respond to any of a plurality of digital commands, each corresponding to a respective rotational speed of the rotor, by adjusting the timing and duration of the respective pulse-width-modulated signals to adjust the rotational speed in accordance with a digital command received.

72. A confrol cfrcuit as recited in claim 71 wherein: the confrol circuit is arranged to respond to a "motor off digital command by preventing the respective pulse-width-modulated signals from occurring.

73. A confrol cfrcuit as recited in claim 64 wherein the communication port comprises a serial interface.

74. A confrol circuit as recited in claim 64 wherein the communication port comprises a parallel interface.

75. A confrol circuit as recited in claim 65 wherein the communication port comprises a serial interface.

76. A confrol circuit as recited in claim 73 wherein the serial interface comprises an I²C bus compatible interface.

77. A confrol cfrcuit as recited in claim 76 further comprising: a first power supply terminal for operably receiving a source of voltage which is substantially independent of rotor speed; a second power supply terminal for operably receiving a reference voltage; a first signal terminal for operably receiving a clock signal for the serial interface; and a second signal terminal for operably receiving a bi-dfrectional data signal for the serial interface.

78. A control circuit as recited in claim 73 wherein: the serial interface comprises an RS-232 interface.

79. A control cfrcuit as recited in claim 64 wherein: the control circuit is either enclosed within or attached to a housing for the first motor.

80. A confrol circuit as recited in claim 64 wherein: the confrol circuit is enclosed within a module having an integral connector for a bus to wliich the communication port connects.

81. A confrol circuit as recited in claim 64 further comprising: a second motor confrol circuit coupled to the communication port and having at least two outputs, each for respectively coupling to a respective winding stage of a second motor, said second motor control circuit for generating on each respective output a respective pulse-width- modulated (PWM) signal to energize a respective winding stage of the second motor when coupled thereto at respective times for respective durations of time to rotate the rotor of the second motor with a rotational speed responsive to a received digital command.

82. A cooling module comprising: an electrically-powered cooling device having at least two electrical terminals; and a module confrol circuit including a communications port having a serial interface, said module confrol cfrcuit for controlling the cooling device in accordance with digital commands operably received by way of the serial interface.

83. A cooling module as recited in claim 82 wherein the cooling device comprises: a thermo-electric cooling device.

84. A cooling module as recited in claim 82 wherein the cooling device comprises: a brushless DC fan including an elecfronically commutated motor, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and further including a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages, said brushless DC fan further including a plurality of fan blades coupled to the rotor.

85. A cooling module as recited in claim 84 wherein the module control circuit includes: a motor confrol circuit coupled to operably receive power from a first power terminal and a second power terminal, said motor control circuit having at least two outputs, each respectively coupled to a respective winding stage of the brushless DC fan, for generating on each respective output a respective signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to commutate the winding stages in a preselected sequence to rotate the rotor; and a power control circuit for controlling the voltage on at least one of the first and second power terminals to provide for a rotational speed of the motor which is responsive to a received digital command.

86. A cooling module as recited in claim 85 wherein the power control circuit comprises: a linear voltage regulator circuit for developing on the at least one of the first and second power terminals a variable voltage, in accordance with a received digital command, thereby providing for a rotational speed of the motor which is responsive to the received digital command.

87. A cooling module as recited in claim 85 wherein the power control circuit comprises: a pulse- width modulating circuit for periodically coupling, in accordance with a received digital command, the at least one of the first and second power terminals to a source of voltage, thereby providing for a rotational speed of the motor which is responsive to the received digital command.

88. A cooling module as recited in claim 84 wherein the module control circuit includes: a motor confrol circuit coupled to operably receive a substantially constant voltage between a first power teπrrinal and a second power terminal, said motor confrol circuit having at least two outputs, each respectively coupled to a respective winding stage, for generating on each respective output a respective pulse-width-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to both commutate the winding stages in a preselected sequence to rotate the rotor and with a rotational speed that is responsive to the digital command.

89. A cooling module as recited in claim 82 wherein the module control circuit includes: a temperature sensor arranged to be responsive to a localized temperature within the cooling module.

90. A cooling module as recited in claim 82 wherein the module control circuit includes: non-volatile memory for storing at least one operational or environmental parameter of the cooling module; and a provision for responding to a parameter query command received by way of the serial interface by providing a serial data word corresponding to the value of the parameter.

91. A cooling module as recited in claim 82 wherein the serial interface comprises: a bi-directional interface.

92. A cooling module as recited in claim 84 wherein the module control circuit includes: a provision for responding to a fan speed query command received by way of the serial interface by providing a serial data word to indicate actual fan speed.

93. A cooling module as recited in claim 91 wherein the module confrol circuit includes: a temperature sensor arranged to be responsive to a localized temperature within the module; and a provision for responding to a temperature query command received by way of the serial interface by providing a serial data word to indicate the temperature as sensed by the temperature sensor.

94. A computer system comprising: a cooling module including a module control circuit having a serial interface, said module control cfrcuit for controlling the degree of cooling provided by the cooling module in response to a digital command received by way of the serial interface; computing cfrcuitry which can execute stored instruction programs and which can generate a plurality of digital module commands under program confrol; and a confrol bus for communicating a digital module command from the computing circuitry to the cooling module.

95. A computer system as recited in claim 94 wherein: the control bus comprises a serial bus.

96. A computer system as recited in claim 94 wherein: the control bus comprises an I²C compatible serial bus.

97. A computer system as recited in claim 94 wherein: the module control circuit is adapted to sense a temperature in the system and confrol the cobling module accordingly.

98. A computer system as recited in claim 94 wherein: the computing cfrcuitry is adapted to sense a temperature in the system and control the cooling module accordingly by way of the control bus.

99. A computer system as recited in claim 94 wherein the cooling module comprises: a fan housing; an elecfronically commutated motor mounted to the fan housing, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and further including a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; a plurality of fan blades coupled to the rotor; and a fan control circuit including a communication port for operably receiving digital commands, at least one of which for controlling the rotational speed of the rotor; and a motor confrol circuit coupled to the communication port and having at least two outputs, each respectively coupled to a respective winding stage, said motor confrol circuit for generating on each respective output a respective pulse-width-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times for respective durations of time to rotate the rotor with a rotational speed responsive to a received digital command.

100. A cooling module comprising: an electrically-powered cooling device having at least two electrical terminals; and a module confrol circuit including a communications port for communicating digital commands over a bus between the cooling module and an external device; and non-volatile memory for storing at least one operational or environmental parameter of the cooling module; said module control circuit for controlling the cooling device in accordance with digital commands operably received by way of the communications port, and for digitally communicating at least one operational or envfronmental parameter by way of the communications port.

101. A cooling module as recited in claim 100 wherein the at least one operational or environmental parameter comprises: a current parameter representing a current value of an observable condition of the cooling module.

102. A cooling module as recited in claim 100 wherein the at least one operational or envfronmental parameter comprises: a historical parameter representing a historical value of an observable condition of the cooling module.

103. A cooling module as recited in claim 102 wherein the historical parameter comprises: an average or integrated value of an observable condition computed over some period of time.

104. A cooling module as recited in claim 102 wherein the historical parameter comprises: a maximum or minimum peak value of an observable condition over some period of time.

105. A cooling module as recited in claim 102 wherein the historical parameter comprises: a cumulative value of an observable condition over some period of time.

106. A cooling module as recited in claim 100 wherein the at least one operational or envfronmental parameter comprises: a predictive parameter representing a predictive condition of the cooling module.

107. A cooling module as recited in claim 106 wherein the at least one operational or environmental parameter comprises: a predictive parameter representing estimated remaining operating life of the cooling module.

108. A cooling module comprising: a brushless DC fan; a temperature sensor for sensing an operating temperature in the vicinity of the fan; and a module control circuit for determining the operating temperature and for controlling the brushless DC fan accordingly.

109. A cooling module as recited in claim 108 further comprising: a heat sink attached to and providing a mounting base for the fan.

110. A cooling module as recited in claim 109 wherein: the temperature sensor is attached to the heat sink at a location removed from the location where the fan is mounted.

111. A cooling module as recited in claim 109 wherein: the heat sink provides a surface to which an integrated circuit package may be contacted; and the temperature sensor is attached to the heat sink in close proximity to the surface providing contact with the integrated circuit package.

112. A cooling module as recited in claim 111 wherein the temperature sensor comprises a thermistor.

113. A cooling module as recited in claim 108 wherein the module control cfrcuit is arranged to provide a locked rotor output signal.

114. A cooling module as recited in claim 108 wherein the module confrol cfrcuit is arranged to provide a tachometer output signal.

115. A cooling module as recited in claim 108 wherein the module confrol cfrcuit is arranged to provide both a tachometer output signal and a locked rotor output signal.

116. A cooling module as recited in claim 108 wherein the module confrol cfrcuit is arranged to operate the brushless DC fan: when the sensed temperature is below a lower temperature threshold, at a predetermined minimum RPM; and when the temperature sensed is above the lower temperature threshold, at an RPM generally increasing with increasing temperature.

117. A cooling module as recited in claim 108 wherein the module confrol cfrcuit is arranged to operate the bmshless DC fan: when the sensed temperature is below a lower temperature threshold, at a predetermined minimum RPM; when the temperature sensed is above an upper temperature threshold, at a predetermined maximum

RPM; and when the temperature sensed falls between the lower and upper temperature threshold, at an RPM generally increasing with increasing temperature.

118. A fan module comprising: a fan housing; an elecfronically commutated motor mounted to the fan housing, said motor including a stationary armature having a core and at least two independently energizable winding stages arranged to establish a predetermined number of magnetic poles, and further including a permanent magnet rotor adapted to rotate in response to the magnetic poles established by the winding stages; a plurality of fan blades coupled to the rotor; and a fan confrol circuit including an input port for operably receiving a periodic control signal for controlling the rotational speed of the rotor; and a motor control circuit coupled to the input port and having at least two outputs, each respectively coupled to a respective winding stage, said motor control cfrcuit for generating on each respective output a respective pulse- idth-modulated (PWM) signal to energize the respective winding stage coupled thereto at respective times • for respective durations of time to rotate the rotor with a rotational speed proportional to the periodic control signal.

119. A fan module as recited in claim 118 wherein the motor control cfrcuit is arranged to impress across each winding stage, when energized, a voltage which is substantially independent of the rotational speed of the rotor.

120. A fan module as recited in claim 118 wherein the motor confrol circuit includes: a rotor position sensor for generating a signal indicative of rotor position relative to the magnetic poles established by the winding stages.

121. A fan module as recited in claim 120 wherein the fan control circuit is arranged to determine actual fan speed by observation of changes in the rotor position sensor signal as a function of time.

122. A fan module as recited in claim 121 wherein the fan control circuit is arranged to deteπriine actual fan speed by observation of changes in the rotor position sensor signal corresponding to rotor rotation through at least two magnetic poles established by the winding stages.

123. A fan module as recited in claim 118 wherein: the fan confrol circuit is arranged to respond to the periodic confrol signal by adjusting the timing and duration of the respective pulse-width-modulated signals to adjust the rotational speed proportional to the periodic confrol signal.

124. A fan module as recited in claim 123 wherein: the fan confrol circuit is arranged to respond to an absence of the periodic confrol signal by preventing the respective pulse-width-modulated signals from occurring.

125. A fan module as recited in claim 118 further comprising: a first power supply terminal for operably receiving a source of voltage which is substantially independent of fan rotor speed; a second power supply terminal for operably receiving a reference voltage; a first signal terminal for operably receiving the periodic control signal.

126. A fan module as recited in claim 118 wherein: the fan control cfrcuit is either enclosed within or attached to the fan housing.