WO2016124956A1

WO2016124956A1 - Electronic device for powering a display unit

Info

Publication number: WO2016124956A1
Application number: PCT/IB2015/000107
Authority: WO
Inventors: Eric Chemisky; Joachim SIEGRIST; Sornam Viswanathan VENKATESWARAN; Anand VENKATRAMANI
Original assignee: Siemens Aktiengesellschaft
Priority date: 2015-02-03
Filing date: 2015-02-03
Publication date: 2016-08-11

Abstract

An electronic device configured, to supply at least one of a substantially constant voltage and a constant current for a display unit of a field device, comprising constant voltage driving unit comprising one or more voltage converters, one or more switching units, wherein at least one of the one or more switching units are electrically coupled in parallel with one or more voltage converters. The operation of the one or more voltage converters are controlled using the switching units based on a level of supply voltage. Further, a voltage step-up converter is configured to operate in a constant current mode, wherein the voltage step-up converter is activated using a pulsed configuration. Additionally, the voltage step-up converter is operated in a constant current mode by using a sense resistor to generate a feedback. The pulsed configuration is used to operate the display unit in a stable condition eliminating the variation in brightness due to low current operation.

Description

TITLE: Electronic device for powering a display unit

This invention relates to the field of powering display units of low power devices. More particularly, the invention relates to an electronic device for powering the display unit of a low power field device.

Generally, certain class of electronic devices are used in the industry for measuring physical process values such as pressure, temperature, flow and levels. An example of such electronic device may be a process transmitter, also known as a field device. The personnel working at the site may use the electronic control devices to measure various physical process parameters and communicate these values to a central server. Generally, electronic devices include a display unit, a logic unit, and an input unit. Such electronic devices usually contain an analog frontend including the sensors and a transmitter system, which is dedicated to the communication with the control system. The communication can be performed in an analog mode (4 - 20 mA) or a digital mode. The communication can be carried over bus systems which include ProfiBus, HART, Fieldbus foundation and the like.

Some advanced field devices include a Graphics LCD (GLCD) and backlight LEDs . GLCDs work in presence of backlight LEDs which provide ambient light in order to produce a visible image on the GLCD. The GLCD and the backlight LEDs together consume about 70% of the total allocated power for the. field device. Therefore, the remaining functions of the field device, which includes power supply and logic circuit, need to be configured to consume remaining 30% of the power. In field devices, the supply voltage may vary between a certain ranges of voltage. The GLCD consumes minimum power at a particular voltage level. Therefore, there is a need for regulating the supply voltage to the particular voltage level in order to power the GLCD.

Generally, LEDs are operated at a constant low current by using a boost converter. But such small currents cause charge variations across temperature and hence the brightness values. An exemplary implementation of constant current of 400 uA used in electronic devices is shown in FIG 1. FIG 1 illustrates an exemplary configuration 1 of an electronic device in accordance with prior art. In FIG 1, it can be seen tha the the backlight LEDs (4,6) are powered by a voltage step-up converter 2 operated in a constant current mode, using a feedback from sense resistor R. In this mode, the current provided to the backlight LEDs is a constant low current of 400 uA. As a result the backlight LEDs have varying brightness when there are changes in temperature.

Thus, there is a need for operating the display unit of a field device in an efficient manner without fluctuating in brightness values. It is also needed that the LEDs are operated at a point in the brightness curve where there is no variation due to temperature. Further, there is a need to increase the efficiency of the existing buck-boost circuitry in the field devices.

Accordingly, it is an object of the invention to disclose an electronic device for operating a display unit of a low power device in an efficient manner. The display unit needs to be operated with circuitry having higher efficiency and stability than the existing electronic devices. The object of the invention is achieved by providing an electronic device configured to supply at least one of a substantially constant voltage and a constant current for a display unit of a low power device, comprising a constant voltage driving unit comprising one or more voltage converters, one or more switching units. The one or more switching units are electrically coupled in parallel with one or more voltage converters, wherein the operation of the one or more voltage converters are controlled using the switching units based on a level of supply voltage. Further, the circuit includes a voltage step-up converter is configured to operate in a constant current mode, wherein the voltage step- up converter is activated using a high current pulsed configuration.

In an embodiment of the invention, the voltage step-up converter is operated in a constant current mode by using feedback generated from a sense resistor. The voltage step-up converter is

In another embodiment of the invention, . the pulsed configuration is used- to control an operation of the voltage step-up controller and an electronic switch.

In yet another embodiment, the pulses are generated by a microcontroller. The microcontroller is configured to generate pulses at 1 kHz with a duty cycle of 10%. The amplitude of the pulse is configured based on the type of lighting element that is used.

In still yet another embodiment, in the voltage step-up converter is electrically coupled in series with a lighting element of the display unit. In a further embodiment, the lighting elements are activated using high current pluses to eliminate brightness variations due to forward current effect. Instead of operating the lighting elements at a constant low voltage which results in flickering, the lighting elements are activated using high current pulses.

In yet another embodiment, the pulsed signals are configured to have 10% duty cycle pulsed at 1 kHz.

In still yet another embodiment, the display unit comprises a Graphics LCD display and one or more backlight LEDs .

In a further embodiment, the one or more voltage converters comprise a voltage step-up converter and a voltage step-down converter. The voltage step-up and step-down converter is used separately. A set of voltage converters along with switching elements are used for supplying a constant voltage to the graphics LCD display and the another step-up voltage controller is operated in a constant current mode to power one or more backlight LEDs.

The invention further provides method steps for achieving the object of supplying at least one of a substantially constant voltage and a constant current for a display unit of a field device. The method comprises a step of controlling the activation and deactivation of one or more voltage converters based on a level of a supply voltage, wherein the one or more voltage converters are configured to provide a constant voltage to a display element of the display unit. The method advantageously comprises regulating the supply voltage, using pulsed configuration of at least one voltage step-up converter, to provide a constant input current for a lighting element of the display unit. In an exemplary embodiment, the step of controlling the activation and deactivation of the voltage converters comprises controlling an operation of one or more switching units, for at least one of enabling and disabling the voltage converters, based on the level of the supply voltage. The switching units are coupled in parallel with the voltage converters . Based on the level of supply voltage appropriate switching units are turned on in order to bypass one of the voltage converters and activate the other.

In another embodiment, the step of regulating the supply voltage to provide a constant input current comprises generating the constant input current by providing a constant current configuration to at least one voltage converter. The constant current configuration is provided by electrically coupling the sense resistor in series with the lighting element. The voltage across the sense resistor is maintained constant thereby maintaining a constant current through the lighting elements.

In yet another embodiment, the constant input current of 10 mA having a 10% duty cycle pulsed at 1 kHz is provided to the lighting element of the display unit. Effectively, it results in an average current of 1 mA which operates the lighting element without varying the brightness .

In still yet another embodiment, the lighting elements are operated in at a constant point in the forward current curve to avoid variation in brightness.

In a further embodiment, the display element is a LCD display and the lighting element includes a plurality of Light Emitting Diodes. The LCD display may be a Graphics LCD and the LEDs may be backlight LEDs.

The above mentioned and other features of the invention will now be addressed with reference to the accompanying drawings of the present invention. The illustrated embodiments are intended to illustrated, but not limit the invention.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:

- FIG 1 - -illustrates an exemplary configuration

electronic device in accordance with art, in accordance with an embodiment;

FIG 2 illustrates an exemplary block diagram of a working of the electronic device in a first mode of operation, in accordance with an embodiment ;

FIG 3 illustrates an exemplary block diagram of a working of the electronic device in a second mode of operation, in accordance with an embodiment;

FIG 4 illustrates an exemplary block diagram of a the electronic device, in accordance with an embodiment; illustrates exemplar block diagram of the working of the voltat step-up converter in a pulsed configuration in accordance with an embodiment; and FIG 7 illustrates exemplary block diagram of method steps involved in powering the display unit of the electronic device, in accordance with an embodiment .

Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer like elements throughout. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details.

In an embodiment, the electronic device for powering a display unit includes voltage converters . Voltage converters are DC to DC converters and include, for example, voltage step-up converters and voltage step-down converters. Further, the electronic device includes one or more switching units for controlling the operation of the voltage converters. The voltage converters are configured to power the display unit of the electronic device. In accordance with the embodiment, the display unit includes a Liquid Crystal Display and a plurality of the Light Emitting Diodes (LEDs).

FIG 2 illustrates an exemplary block diagram of a working of the electronic device in a first mode of operation, in accordance with an embodiment. The block diagram shown in FIG 2 includes a power source 12, a voltage step-down converter 14, a voltage step-up converter 18, switching units (16 and 20), a voltage step-up converter 24, a load 22 and a LED unit 26. The power source 12 may be a current loop with supply current ranges vary based on the standard used for communication. For example, the current values may range from 4-20 mA in a preferred embodiment. The current source can be converted into a voltage source using a shunt resistor, which is well known in the art. The voltage range of the power supply 12 may vary from 1-10 volts. Further, the switching unit 16 is coupled in parallel with the voltage step-down converter 14. The load 22, which may be an LCD display, is be configured to operate at a constant voltage of 5 V. Therefore, the voltage converters and the switching units are configured to provide the constant voltage to the LCD display 22. The switching unit 20 is coupled in parallel with the voltage step-up unit 18. In the first mode of operation the supply voltage is in the range of VI to V2 , i.e. 1 < V_s < 5. In the first mode, the supply voltage V_s is in the range of V3 to V4. For example, the exemplary votlage range may be IV- 5V. For this range of the supply votlage, the voltage step-up unit is enabled whereas the votlage step-down converter is disabled. The switching unit 16 is enabled which provides an alternative path for current thereby by passing the voltage step-down converter. On the other hand, the switching unit 20 is disabled thereby enabling the votlage step-up unit 6. The votlage step-up unit 18 regulates the supply voltage to a value of V_A which is provided as input volatage to the load 7. in this embodiment, the Vi is held constant at 5V which is the supply voltage for which the load 22 is configured.

FIG 3 illustrates an exemplary block diagram of a working of the electronic device in a second mode of operation, in accordance with an embodiment. In the second mode of operaiton, the votlage range of the supply voltage V_s is in the range of 5-10V. The electronic device is configured to enable the votlage step-down converter 14 and disable the votlage step-up unit 18 in the second mode. For the voltage range in the fist mode, the switching unit 16 is disabled and a the switching unit 20 is enabled. When enabled, the switching unit 20 provides an easier path for the current, as a result, by-passes the votlage step-up converter 18. Therefore, a constant input voltage of Vi is supplied to the load 22.

In the first and the second modes of operation of the electronic device, the enabling and disabling of the switching units includes providing a control signal from a microcontroller. The microcontroller is configured to generate control signals, for example, logic "HIGH" and logic "LOW", based on the level of supply voltage. The switching units are composed of electronic switching units like MOSFETs and diodes in an antiparallel confgiuration with the OSFET. The control signlas are provided to one of the MOSFETs to enable/disable the switching units.

FIG 1 and FIG 2 further include a voltage step-up converter 24 configured to provide a constant current the LED unit 26 of the display unit of the electronic device. The voltage step-up converter 24 is operated in a constant current mode. In the constant current mode, voltage step-up converter 24 is provided with a sense resistor which is electrically coupled in series with the LED unit 26. Advantageously, the voltage step-up converter 24 is operated in a high current plused configuration, which enables the voltage step-up converter 24 to provide high current pulses to operate the LED unit 26 in a stable manner without fluctuations in brightness. The details of the implementation is explained in conjunction with FIG 5.

FIG 4 illustrates an exemplary block diagram of a the electronic device, in accordance with an embodiment FIG 4 illustrates an additional voltage converter 24 which is used for supplying current to the logic unit 26 of the electronic device. The logic unit 28 may include a microprocessor, a memory and an input/output unit. In the memory of the logical unit, processor readable instructions may be stored. The processor readable instructions enable the logical unit to perform various functions such as displaying values and communicating with a central server. In an embodiment, the ^■voltage converter 26 is a voltage step-down converter configured to supply a constant voltage to the logic unit 26.

FIG 5 illustrates exemplary block diagram of the working of the voltage step up converter 26 in a pulsed configuration, in accordance with an embodiment. FIG 5 includes a voltage step-up converter 42, . a buffer 44, a plurality of LEDs

(46, 48), a MOSFET Tl and a sense resistor R_senSe - The LEDs are electrically coupled in series with the output of the voltage step-up converter 42 as shown in FIG 5. Further, the MOSFET Tl and the sense resistor Rsense are electrically coupled in series with LEDs. The MOSFET Tl may be an N-channel MOSFET, electrically coupled in series with LEDs . The voltage step-up converter 42 is operated in a pulsed configuration, where the pulse is generated by a microcontroller (not shown) associated with the logic unit. The pulse signal LED_EN generated by the microcontroller is provided to the buffer 44. The output from the buffer 44 is provided to an ENABLE

(EN) pin of the voltage step-up converter 42 and the source terminal of MOSFET Tl. In effect, the ENABLE pin of the voltage step-up converter 42 and the source terminal of MOSFET Tl are pulsed at a certain frequency. In an exemplary embodiment, the frequency of the pulse may be fixed at 1 kHz and the duty cycle may be set to 10%.

The voltage step-up converter 42 is configured to receive a voltage feedback from the sense resistor R_sense - The votlage feedback is provided to a feedback (FB) pin of the voltage step-up converter 42. The votlage feedback V_sense enables the voltage step-up converter 42 to maintain a constant voltage across the sense resistor R_sense - Due to the constant voltage maintained across R_sense , a constant current flows through the LEDs . In an exemplary scenario, the sense resistor R_sense has a value of 50 Ω, which results in a constant current of 10 mA pulsed at 1 kHz passing through the LEDs. The high current passes through the LEDs in a pulsed manner. Based on the frequecny and duty cycle of the pulse, an average current of 1 mA passes through the LEDs (46,48) . Due to pulsed excitation of the LEDs, the LEDs are activated for a short duration with a high current value. The high current pulsed excitation of the LEDs eliminates the charge variation over change in temperature thereby providing a constant brightness. Generally, charge variation due to temperature results in variation of brightness, which is observed in LEDs which are excited with a continuous low current.

FIG 7 illustrates exemplary block diagram 55 of method steps involved in powering the display unit of the electronic device, in accordance with an embodiment. The method discloses steps for supplying of a substantially constant voltage and a constant current for a display unit of a field device. At step 56, the activation and deactivation of one or more voltage converters is controlled based on a level of a supply voltage. The one or more voltage converters are configured to provide a constant voltage to a display element of the display unit. Further, the operation of one or more switching units is controlled, for enabling and disabling the voltage converters, based on the level of the supply voltage. The operation of the switching units may be controlled based on a control signal generated by a microcontroller.

At step 58, the supply voltage is regulated, using pulsed configuration of at least one voltage step-up converter, to provide a constant input current for a lighting element of the display unit. Step 58 further, comprises exciting the step-up voltage converter and an electronic switch simultaneously with pulsed signals. The electronic switch may be an N-channel MOSFET.

The method and device described in the invention is advantageous as it provides an optimal price to performance ratio. The efficiency of the electronic device is increased due to reduced input/output voltage differential. Further, the electronic device has a reduced complexity and consumes less board space. Further, since the components are easily available in the market, it results in convenient second sourcing options .

While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those embodiments. In view of the present disclosure, many modifications and variations would be present themselves, to those skilled in the art without departing from the scope of the various embodiments of the present invention, as described herein. The scope of the present invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

Claims

1. An electronic device (10) configured to supply at least one of a substantially constant voltage and a constant current for a display unit, wherein the display unit comprises a display element (22) and a lighting element (26), comprising:

constant voltage driving unit comprising one or more voltage converters (14, 18), one or more switching units (16, 20), wherein at least one of the one or more switching units are electrically coupled in parallel with one or more voltage converters, wherein the operation of the one or more voltage converters are controlled using the switching units based on a level of supply voltage;

characterized in that;

a voltage step-up converter (24) is configured to operate in a constant current mode to supply constant current to the lighting element, wherein the voltage step-up converter (24) is activated using a pulsed configuration .

2. The electronic device of claim 1, wherein the pulsed configuration includes providing pulse signals to the voltage step-up controller (24) and an electronic switch (Tl) simultaneously.

3. The electronic device of claim 1, wherein the voltage step-up converter (24) is electrically coupled in series with the lighting element (26) .

4. The electronic device of claim 1, wherein the lighting element (26) is activated using high current pluses to eliminate brightness variations.

5. . The electronic device of claim 1, wherein the pulsed signals are configured to have 10% duty cycle pulsed at 1 kHz.

6. The electronic device of claim 1, wherein the pulses are generated by. a microcontroller.

7. The electronic device of claim 1, wherein the voltage step-up converter (24) is operated in a constant current mode based on a feedback generated by sense resistor ( R_sehse ) ·

8. The electronic device of claim 1, wherein the display unit comprises a LCD display (22) and the lighting element (26) comprises one or more LEDs.

9. The electronic device according to any of the preceding claims, wherein the one or more voltage converters comprise a voltage step-up converter (18) and a voltage step-down converter (14).

10. The electronic device according to any of the preceding claims, wherein the supply voltage is in the range of IV - 10V.

11. A method for supplying at least one of a substantially constant voltage and a constant current for a display unit of a field device, comprising:

controlling the activation and deactivation of one or more voltage converters (14,18) using one or more switching unit (16,20) based on a level of a supply voltage, wherein the one or more voltage converters are configured to provide a constant voltage to a display element (22) of the display unit ; characterized in that;

regulating the supply voltage, using high current pulsed configuration of at least one voltage step-up converter, to provide a constant input current for a lighting element (26) of the display unit.

12. The method of claim 11, wherein controlling the activation and deactivation of the voltage converters comprises:

controlling an operation of one or more switching units (16, 20), for at least one of enabling and disabling the voltage converters, based on the level of the supply voltage.

13. The method of claim 11, wherein regulating the supply voltage to provide a constant input current comprises:

exciting the at least one step-up voltage converter (24) and an electronic switch (Tl) simultaneously with pulsed signals .

14. The method of claim 11, wherein the pulsed signals have 10% duty cycle at 1 kHz.

15. The method of claim 11, wherein a voltage feedback is used to maintain a constant current through the lighting element (26) .

16. The method of claim 11, wherein the lighting element (26) is operated using high current pulses to avoid variation in brightness.