CA2472530C - Feedback circuit and method of operating ballast resonant inverter - Google Patents
Feedback circuit and method of operating ballast resonant inverter Download PDFInfo
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- CA2472530C CA2472530C CA2472530A CA2472530A CA2472530C CA 2472530 C CA2472530 C CA 2472530C CA 2472530 A CA2472530 A CA 2472530A CA 2472530 A CA2472530 A CA 2472530A CA 2472530 C CA2472530 C CA 2472530C
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- circuit
- ballast
- phase
- inverter
- output voltage
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Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/282—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices
- H05B41/285—Arrangements for protecting lamps or circuits against abnormal operating conditions
- H05B41/2851—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions
- H05B41/2856—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions against internal abnormal circuit conditions
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/2806—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without electrodes in the vessel, e.g. surface discharge lamps, electrodeless discharge lamps
- H05B41/2813—Arrangements for protecting lamps or circuits against abnormal operating conditions
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S315/00—Electric lamp and discharge devices: systems
- Y10S315/07—Starting and control circuits for gas discharge lamp using transistors
Abstract
A ballast resonant inverter with a self-oscillating driver IC powers and dims a gas discharge lamp. A feedback circuit automatically adjusts IC oscillator frequency for safe and stable inverter operation above the resonant frequency following changes in the resonant load. The feedback signal is derived from resonant inverter output voltage, by attenuating, programmed phase shifting and injecting the resulting signal in a timing circuit of the IC. The feedback circuit includes an active inverter circuit or passive RC phase boosting networks coupled in series. Phase control of the feedback signal by variable RC networks is used in transient modes of ballast-lamp operations.
Description
FEEDBACK CIRCUIT AND METHOD OF
OPERATING BALLAST RESONANT INVERTER
BACKGROUND OF THE INVENTION
The present invention relates to electronic ballasts for powering gas discharge lamps and particularly to DC/AC inverters for energizing and dimming gas discharge lamps, including inductively coupled gas discharge lamps.
A gas discharge lamp typically utilizes an electronic ballast for converting AC
line voltage to high frequency current for powering the lamp. Conventional electronic ballasts include an AC to DC converter and a resonant inverter converting DC
voltage to lamp high frequency current. The resonant inverter includes switching transistors generating a high frequency rectangular AC voltage that is applied to a voltage resonant circuit having an inductor and a capacitor in series. The gas discharge lamp is coupled in parallel to the capacitor. For high frequency electronic ballasts, a self-oscillating resonant inverter is a common part that generates AC voltage for starting and AC current for powering the lamp. Self-oscillating resonant inverters utilize a feedback transformer coupled between a resonant circuit and gates of the switching transistors to provide a sinusoidal voltage to the gates for sustaining the oscillations. Dead time intervals for the switching transistors are automatically formed when crossing near zero gate voltage providing zero voltage switching (ZVS). Self-oscillating resonant inverters are described, for example, in U.S. Patents 4,748,383, 5,962,987 and 5,982,108.
A typical voltage feedback self-oscillating circuit is shown in Figure 1. The self-oscillating inverter is self-adjusted to above resonant frequency. If resonant frequency __ _ changes with temperature, lamp inductance and load variations, the inverter will still operate above the resonant frequency. However, driving MOSFET's with a sinusoidal voltage causes dead time variations followed by lamp power variations and other disadvantages.
As shown in Figure 1, a prior art electronic ballast for powering a gas discharge lamp converts a standard AC line voltage to a high frequency current for lighting the lamp. An AC/DC converter is coupled to the AC line through an EMI filter. The AC/DC
converter includes a rectifier (not shown) and, optionally, a power factor corrector. An AC/DC converter output low frequency ripple is filtered out by an electrolytic storage capacitor C31 connected across a high voltage DC bus. The self-generating ballast inverter is connected to the DC bus and its output is connected to the lamp.
The storage capacitor C31 reduces the high frequency voltage ripple across the DC bus. Two series switching MOSFET's M1 and M2 are coupled across the DC bus. A resonant load includes series an inductor Li, a capacitor C3, and the lamp that is coupled in parallel to the capacitor C3. The resonant load is connected in parallel to the switching MOSFET
M2 via a DC blocking capacitor Cl. The switching transistors M1 and M2 are driven through resistors R16 and R15 via voltage feedback circuit that includes transformer T9 and an output voltage divider with capacitors C27 and C30. The ballast inverter in Figure 1 includes a starting circuit built with a starting capacitor C29, a resistor R19 charging the starting capacitor C29 from the DC bus, a discharge diac X28 coupled to the starting capacitor C29 and blocking diode D10 for discharging the starting capacitor C29 after inverter starting.
OPERATING BALLAST RESONANT INVERTER
BACKGROUND OF THE INVENTION
The present invention relates to electronic ballasts for powering gas discharge lamps and particularly to DC/AC inverters for energizing and dimming gas discharge lamps, including inductively coupled gas discharge lamps.
A gas discharge lamp typically utilizes an electronic ballast for converting AC
line voltage to high frequency current for powering the lamp. Conventional electronic ballasts include an AC to DC converter and a resonant inverter converting DC
voltage to lamp high frequency current. The resonant inverter includes switching transistors generating a high frequency rectangular AC voltage that is applied to a voltage resonant circuit having an inductor and a capacitor in series. The gas discharge lamp is coupled in parallel to the capacitor. For high frequency electronic ballasts, a self-oscillating resonant inverter is a common part that generates AC voltage for starting and AC current for powering the lamp. Self-oscillating resonant inverters utilize a feedback transformer coupled between a resonant circuit and gates of the switching transistors to provide a sinusoidal voltage to the gates for sustaining the oscillations. Dead time intervals for the switching transistors are automatically formed when crossing near zero gate voltage providing zero voltage switching (ZVS). Self-oscillating resonant inverters are described, for example, in U.S. Patents 4,748,383, 5,962,987 and 5,982,108.
A typical voltage feedback self-oscillating circuit is shown in Figure 1. The self-oscillating inverter is self-adjusted to above resonant frequency. If resonant frequency __ _ changes with temperature, lamp inductance and load variations, the inverter will still operate above the resonant frequency. However, driving MOSFET's with a sinusoidal voltage causes dead time variations followed by lamp power variations and other disadvantages.
As shown in Figure 1, a prior art electronic ballast for powering a gas discharge lamp converts a standard AC line voltage to a high frequency current for lighting the lamp. An AC/DC converter is coupled to the AC line through an EMI filter. The AC/DC
converter includes a rectifier (not shown) and, optionally, a power factor corrector. An AC/DC converter output low frequency ripple is filtered out by an electrolytic storage capacitor C31 connected across a high voltage DC bus. The self-generating ballast inverter is connected to the DC bus and its output is connected to the lamp.
The storage capacitor C31 reduces the high frequency voltage ripple across the DC bus. Two series switching MOSFET's M1 and M2 are coupled across the DC bus. A resonant load includes series an inductor Li, a capacitor C3, and the lamp that is coupled in parallel to the capacitor C3. The resonant load is connected in parallel to the switching MOSFET
M2 via a DC blocking capacitor Cl. The switching transistors M1 and M2 are driven through resistors R16 and R15 via voltage feedback circuit that includes transformer T9 and an output voltage divider with capacitors C27 and C30. The ballast inverter in Figure 1 includes a starting circuit built with a starting capacitor C29, a resistor R19 charging the starting capacitor C29 from the DC bus, a discharge diac X28 coupled to the starting capacitor C29 and blocking diode D10 for discharging the starting capacitor C29 after inverter starting.
With the feedback circuit in Figure 1, the switching phase of the inverter transistors is locked with the phase of the output voltage oscillations load, thereby preventing the inverter from running below resonant frequency.
Ballasts with high frequency integrated circuit (IC) oscillating inverter controllers, such as the IR 215X series from International Rectifier or the L6579 series from ST
Microelectronics, do not have the drawbacks of self-oscillating circuits. With shutdown and restarting features, these IC driven inverters can be used for ON/OFF
pulse width modulation (PWM) dimming. However, with a preadjusted switching frequency that is not sensitive to transient variations and fluctuations of resonant frequency of the resonant load, direct application the above controllers has been troublesome. Without correction of switching frequency, MOSFET's could have cross conduction and fail when operating below resonant frequency in some steady-state conditions, dimming mode or at lamp starting.
A solution to this problem is described in Application Notes AN 995A
"Electronic Ballasts Using the Cost-Saving IR215X Drivers" issued by International Rectifier. Figure 2 illustrates a feedback circuit with two anti-parallel power diodes connected in series with the resonant load as zero current detectors. The diodes generate a rectangular AC pulse signal that forces the timing circuit for the IC to switch synchronously with this signal. A feedback signal indicates phasing of current in the resonant load. However, zero current sensing in any portion of the resonant load does not provide the necessary synchronization angle for optimized operation mode above the resonant frequency. In addition, when used as a source of synchronization signals, the power diodes add significant power losses to the ballast.
Ballasts with high frequency integrated circuit (IC) oscillating inverter controllers, such as the IR 215X series from International Rectifier or the L6579 series from ST
Microelectronics, do not have the drawbacks of self-oscillating circuits. With shutdown and restarting features, these IC driven inverters can be used for ON/OFF
pulse width modulation (PWM) dimming. However, with a preadjusted switching frequency that is not sensitive to transient variations and fluctuations of resonant frequency of the resonant load, direct application the above controllers has been troublesome. Without correction of switching frequency, MOSFET's could have cross conduction and fail when operating below resonant frequency in some steady-state conditions, dimming mode or at lamp starting.
A solution to this problem is described in Application Notes AN 995A
"Electronic Ballasts Using the Cost-Saving IR215X Drivers" issued by International Rectifier. Figure 2 illustrates a feedback circuit with two anti-parallel power diodes connected in series with the resonant load as zero current detectors. The diodes generate a rectangular AC pulse signal that forces the timing circuit for the IC to switch synchronously with this signal. A feedback signal indicates phasing of current in the resonant load. However, zero current sensing in any portion of the resonant load does not provide the necessary synchronization angle for optimized operation mode above the resonant frequency. In addition, when used as a source of synchronization signals, the power diodes add significant power losses to the ballast.
The prior art electronic ballast shown in Figure 2 includes a self-oscillating controller for driving switching transistors M1 and M2 of the resonant inverter. A
resonant load includes an inductor L, capacitor C2 and a fluorescent lamp coupled in parallel with capacitor C2. The resonant load is connected via DC blocking capacitor Cl in parallel to transistor M2. An IR2155 controller includes a timer (known as a "555"
timer), with timing capacitor CT and timing resistor RT being external components that determine the oscillating frequency. Anti-parallel diodes D46 and 11)51 connected in series circuit with the resonant inductor L are used as zero current detectors generating a rectangular pulse signal. This signal is injected between the timing capacitor CT and ground.
Other prior art IC driven ballasts are disclosed in U.S. Patents 5,723,953 and 5,719,472. Both patents teach IC feedback control with a resistor, placed in a manner similar to the anti-parallel diodes D46 and D51 in Figure 2. The resistor signal indicates both the level of current in the resonant load and the phasing of this current. According to these two patents, the feedback signal is injected into the IC timing circuit during lamp starting. As a result, inverter frequency is reduced to a level of the resonant frequency and, accordingly, inverter output voltage increases for lamp starting. The higher the resistor signal, the lower the inverter switching frequency, the higher the output inverter voltage, and accordingly, the resistor signal. It was found that the prior art inverter feedback circuit may cause excessive starting voltage and operation below the resonant frequency. If it is used in a steady state mode, this positive feedback circuit creates instability.
resonant load includes an inductor L, capacitor C2 and a fluorescent lamp coupled in parallel with capacitor C2. The resonant load is connected via DC blocking capacitor Cl in parallel to transistor M2. An IR2155 controller includes a timer (known as a "555"
timer), with timing capacitor CT and timing resistor RT being external components that determine the oscillating frequency. Anti-parallel diodes D46 and 11)51 connected in series circuit with the resonant inductor L are used as zero current detectors generating a rectangular pulse signal. This signal is injected between the timing capacitor CT and ground.
Other prior art IC driven ballasts are disclosed in U.S. Patents 5,723,953 and 5,719,472. Both patents teach IC feedback control with a resistor, placed in a manner similar to the anti-parallel diodes D46 and D51 in Figure 2. The resistor signal indicates both the level of current in the resonant load and the phasing of this current. According to these two patents, the feedback signal is injected into the IC timing circuit during lamp starting. As a result, inverter frequency is reduced to a level of the resonant frequency and, accordingly, inverter output voltage increases for lamp starting. The higher the resistor signal, the lower the inverter switching frequency, the higher the output inverter voltage, and accordingly, the resistor signal. It was found that the prior art inverter feedback circuit may cause excessive starting voltage and operation below the resonant frequency. If it is used in a steady state mode, this positive feedback circuit creates instability.
_________________________________________________ .60.=097M.PM
_________________________ The present inventor has found, when synchronizing prior art inverters with an open feedback loop from an independent sinusoidal control signal source and optimizing inverter switching frequency above the resonant frequency, that the signal injected into the IC
timing circuit is significantly out of phase from the signals generated across the above-described current sensors. The phase difference between the inverter output voltage and the external synchronization signal is typically in a range from 150 to 200 depending on resonant load, type of IC and selected operating frequency.
It is desirable, for reliable phase lock and before closing the loop, that the injected feedback signal be generated with a minimum phase difference between the inverter output voltage and the external synchronization signal to provide an optimum mode for the loop inverter. In this case, the injected signal will dominate the ramp signal and the inverter will operate at this optimum mode after closing the loop. It is also desirable that power components, such as diodes and resistors, not be used as sensors in the resonant load to avoid additional power losses.
In any obvious possible connection of current sensing diodes (in series with resonant capacitor, inductor, or lamp), it is difficult, or even impossible to achieve an optimum mode phase lock in a resonant inverter driven by self-oscillating AC.
Therefore, there is still a need for improvements in inverter controls, in particular with more advanced controller integrated circuits.
SUMMARY OF THE INVENTION
It is desirable to provide a novel method for optimized and stable operation of a ballast driven by a self-oscillating driver.
_________________________ The present inventor has found, when synchronizing prior art inverters with an open feedback loop from an independent sinusoidal control signal source and optimizing inverter switching frequency above the resonant frequency, that the signal injected into the IC
timing circuit is significantly out of phase from the signals generated across the above-described current sensors. The phase difference between the inverter output voltage and the external synchronization signal is typically in a range from 150 to 200 depending on resonant load, type of IC and selected operating frequency.
It is desirable, for reliable phase lock and before closing the loop, that the injected feedback signal be generated with a minimum phase difference between the inverter output voltage and the external synchronization signal to provide an optimum mode for the loop inverter. In this case, the injected signal will dominate the ramp signal and the inverter will operate at this optimum mode after closing the loop. It is also desirable that power components, such as diodes and resistors, not be used as sensors in the resonant load to avoid additional power losses.
In any obvious possible connection of current sensing diodes (in series with resonant capacitor, inductor, or lamp), it is difficult, or even impossible to achieve an optimum mode phase lock in a resonant inverter driven by self-oscillating AC.
Therefore, there is still a need for improvements in inverter controls, in particular with more advanced controller integrated circuits.
SUMMARY OF THE INVENTION
It is desirable to provide a novel method for optimized and stable operation of a ballast driven by a self-oscillating driver.
It is also desirable to provide a novel feedback phase lock circuit with adjustable phase shifting and to provide a novel ballast with a feedback circuit with passive components.
It is also desirable to provide ballast/lamp current/voltage control through a novel controllable feedback circuit.
It is also desirable to provide a novel feedback circuit generating an advanced phase internal synchronization signal that limits ballast output voltage during lamp starting.
It is also desirable to provide reliable inverter operation in a periodical ON/OFF
mode with pulse width modulation (PWM) dimming.
An efficient method is disclosed for controlling a resonant inverter that may be driven by a self-oscillating integrated circuit with a small sinusoidal signal derived from an output inverter voltage. This method may include attenuating an output voltage, phase shifting the attenuated signal, and injecting the attenuated signal into the timing circuit for the driver.
One of embodiments of the present invention provides a feedback circuit with a signal inverter for phase shifting of an attenuated output voltage.
A second embodiment of the present invention includes a feedback circuit with combinations of RC phase-shifting networks.
A third embodiment of the present invention includes a feedback circuit with controllable phase of the output signal for limiting ballast output voltage.
A fourth embodiment of the present invention, preferably for inductively coupled lamps, includes a synchronization circuit with a controllable number of RC
phase-shifting networks in which an additional RC network is switched ON during lamp starting to limit lamp starting voltage.
Advantageously, an embodiment of the present invention can enable IC
oscillations to be locked with a frequency that is above the free oscillation frequency of the ballast resonant load including the lamp. When lamp impedance and resonant frequency vary, the switching frequency will vary accordingly, so the ballast inverter will continue to operate in a safe area above resonant frequency. An embodiment of the invention can also provide PWM dimming with permanently changed impedance of the dimmed lamp and variable resonant frequency.
According to one aspect of the invention there is provided a ballast for a discharge lamp, comprising: a self oscillating driver circuit (10); a timing circuit (12) for programming the oscillation frequency of the driver circuit (10) connected to the driver circuit (10); a resonant inverter (MI, M2, Li, C3) connected to the driver circuit (10) and having an output voltage (Vout); and a feedback circuit (14, 16) that connects the output voltage (Vout) from the resonant inverter (M1, M2, Li, C3) to the timing circuit (12), the feedback circuit (14, 16) including a phase shifting circuit (16) that selectively shifts a phase of the output voltage (Vout) from the resonant inverter (MI, M2, Li, C3) in a range from 150 to 200 degrees depending on a selected operating frequency of the ballast.
According to another aspect of the invention there is provided a method of operating a ballast for a discharge lamp that includes a self oscillating driver circuit (10), a timing circuit (12) for programming the oscillation frequency of the driver circuit (10), connected to the driver circuit (10), and a resonant inverter (M1, M2, Li, C3) connected to the driver circuit (10) and having an output voltage (Vout), the method comprising the steps of:
feeding back the output voltage (Vout) from the resonant inverter (M1, M2, Li, C3) to the timing circuit (12); and selectively shifting a phase of the output voltage (Vout) being fed back from the resonant inverter (M1, M2, L 1, C3) in a range from 150 to 200 degrees, depending on a selected operating frequency of the ballast.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a circuit diagram of a conventional ballast with self-oscillating inverter.
Figure 2 is a circuit diagram of a conventional ballast with a self-oscillating driver IC.
Figure 3 is a circuit diagram of a ballast of the present invention with a self-oscillating driver IC synchronized by a voltage feedback circuit.
Figure 4 is a circuit diagram of the ballast of the present invention utilizing active phase shifting in the feedback circuit.
Figure 5 is a circuit diagram of the ballast of the present invention with a feedback circuit utilizing signal attenuation and phase shifting by plural RC phase-shifting networks.
7a Figure 6 is a circuit diagram of the invention with a phase controlled feedback circuit.
Figure 7 is a circuit diagram of the invention in a lamp dimming application.
DESCRIPTION OF PREFERRED EMBODIMENTS
With reference now to Figure 3, a self-oscillating driver IC 10 drives half bridge power stages with transistors M1 and M2 generating an AC voltage across the input of a resonant load. IC 10 has a built-in oscillator that is, or is similar to, the "555" timer of the prior art. Oscillator frequency can be programmed with a timing circuit 12 coupled to pins Rt, Ct and common "corn".
The feedback circuit includes blocks 14 and 16 that couple inverter high voltage output LH to timing circuit 12. Block 14 attenuates the output voltage signal and block 16 phase shifts the output voltage signal from 1500 to 200 to compensate for the phase difference between the inverter output voltage and the external synchronization signal.
Timing circuit 12 may include a timing capacitor Ct and resistor Rt (see Figure 2) and switches when the timing capacitor is charged to 2/3 Vcc and discharged to 1/3 Vcc.
In a standard IC application, the timing capacitor voltage waveform is an exponential ramp that is superposed on the DC voltage. By mixing in a small phase shifted signal to the ramp, the IC oscillator correlates its frequency. Preferably, a source of this signal is coupled between ground and the timing capacitor.
In an embodiment of the device shown in Figure 4, which is particularly suited for high frequency application (200-270 kHz), attenuating block 14 (Figure 3) includes a capacitive divider with capacitors C4 and C5 connected to inverter high voltage output LH. Phase shifting block 16 includes an active signal inverter that includes transistor M3 and resistors R3, R4, R6 and R7. The output of the capacitive divider is connected to the input of the active signal inverter. The output of the active signal inverter is connected to the Ct pin of IC 10 via a second timing capacitor Ct2 and timing circuit 12.
The active signal inverter provides a stable phase shift of about 1800 at any frequency.
Thus, the active signal inverter compensates for about 180 of phase difference between the input and output of the open loop inverter operating above resonant frequency.
In one embodiment for electrodeless lamp ballasts, the circuit of Figure 4 may include the following components: IC 10 - IR21531D, M3 ¨ BC337, C4 and Ct2 -22pF, Ctl ¨ 250pF, C5 ¨ 4.7nF, Rtl ¨ 10K, R3 ¨ 100k, R7 ¨750. R4 ¨ 15k, R6-15k, R15 and R16 ¨ 22k, C26 and C28 - 0.1uF. The ballast inverter switches at 250 kHz. With an open loop circuit, the ballast inverter switches at 242 kHz. Resonant frequency of the inverter resonant load is about 220 kHz. The sinusoidal signal injected to pin Ct of IC
10 via timing capacitor Ct2 dominates above the ramp signal generated by the timer even though it has a much smaller level than the ramp signal. The switching frequency of the inverter depends on the resonant load as in self-generated resonant ballasts without an IC.
In other embodiments of the present invention, resistive means may be connected between timing capacitor Ctl and common "coin" of IC 10. Figure 5 shows two anti-parallel diodes D53 and D55 that may serve as the resistive means, although resistor(s) can be used instead of diodes (for example, see R10 in Figure 6).
With further reference to Figure 5, the feedback circuit may include two RC
phase-shifting networks that perform the functions of blocks 14 and 16. The first network includes a capacitor C6 coupled to high voltage output LH and a resistor R8 coupled to common. The second network includes a capacitor C7 and the resistive means. The second network is connecter in parallel to resistor R8 of the first network.
Capacitor C6 may be a high voltage capacitor connected to LH while other components may be low voltage, low power components. As previously explained, a phase shift angle of about 150-200 degrees is needed for optimizing the feedback phase lock. The two series RC networks provide attenuation of the feedback signal more than 100 times and a programmable phase shifting up to around 1800. The ballast inverter starts with a programmed initial switching frequency determined by timing capacitor Ctl and resistor Rtl . As soon as a voltage appears at LH, the inverter will be internally synchronized as the feedback signal will dominate the "555" timer ramp signal of IC 10.
Inverter frequency will be automatically corrected so that input/output phase difference at selected switching frequency will be automatically compensated by the RC phase boosting networks in the feedback circuit.
Figure 6 shows a modification of the embodiment of Figure 5 with a third RC
phase-shifting network that is added during lamp starting. The third RC
network includes capacitor C8, resistor R9 and a switching means connected in series with resistor R9.
The switching means may include two series Zener diodes D3 and D4 connected in opposite directions. During lamp starting, voltage that is applied across the circuit comprising resistor R9 and Zener diodes D3 and D4 is much higher than the Zener diodes' threshold voltage. During steady-state operation, the peak of this voltage is lower than the Zener diodes' threshold. The Zener diodes provide a switching function by adding a third RC phase-shifting network during lamp starting to limit starting voltage.
Ballast components should be protected from overstressing in starting and no-load ____ ...e=P
operation modes. In feedback circuit of Figure 6, two anti-parallel diodes (such as in Figure 5) can be used instead resistor R10 for better stability.
A self-oscillating dimmed ballast circuit is shown in Figure 7. The ballast inverter includes a feedback circuit with a variable structure having three RC
phase-shifting networks. The first RC-network includes high voltage capacitor C9 and resistor R11. The second RC network includes capacitor C10, resistor R12 and Zener diodes D5 and D6. The third RC network includes capacitor C11 and anti-parallel diodes D53 and D55 connected between timing capacitor Ctl and IC 10 common terminal "corn".
Resistor R13 connected across anti-parallel Zener diodes D5 and D6 is provided when more than 1800 phase-shifting is needed in the feedback circuit for optimized steady-state operation of the inverter (for example 2000 phase shifting). PWM signal controlled switching means (for example, transistor M4 in Figure 7) is connected to the Ct pin of IC
It is also desirable to provide ballast/lamp current/voltage control through a novel controllable feedback circuit.
It is also desirable to provide a novel feedback circuit generating an advanced phase internal synchronization signal that limits ballast output voltage during lamp starting.
It is also desirable to provide reliable inverter operation in a periodical ON/OFF
mode with pulse width modulation (PWM) dimming.
An efficient method is disclosed for controlling a resonant inverter that may be driven by a self-oscillating integrated circuit with a small sinusoidal signal derived from an output inverter voltage. This method may include attenuating an output voltage, phase shifting the attenuated signal, and injecting the attenuated signal into the timing circuit for the driver.
One of embodiments of the present invention provides a feedback circuit with a signal inverter for phase shifting of an attenuated output voltage.
A second embodiment of the present invention includes a feedback circuit with combinations of RC phase-shifting networks.
A third embodiment of the present invention includes a feedback circuit with controllable phase of the output signal for limiting ballast output voltage.
A fourth embodiment of the present invention, preferably for inductively coupled lamps, includes a synchronization circuit with a controllable number of RC
phase-shifting networks in which an additional RC network is switched ON during lamp starting to limit lamp starting voltage.
Advantageously, an embodiment of the present invention can enable IC
oscillations to be locked with a frequency that is above the free oscillation frequency of the ballast resonant load including the lamp. When lamp impedance and resonant frequency vary, the switching frequency will vary accordingly, so the ballast inverter will continue to operate in a safe area above resonant frequency. An embodiment of the invention can also provide PWM dimming with permanently changed impedance of the dimmed lamp and variable resonant frequency.
According to one aspect of the invention there is provided a ballast for a discharge lamp, comprising: a self oscillating driver circuit (10); a timing circuit (12) for programming the oscillation frequency of the driver circuit (10) connected to the driver circuit (10); a resonant inverter (MI, M2, Li, C3) connected to the driver circuit (10) and having an output voltage (Vout); and a feedback circuit (14, 16) that connects the output voltage (Vout) from the resonant inverter (M1, M2, Li, C3) to the timing circuit (12), the feedback circuit (14, 16) including a phase shifting circuit (16) that selectively shifts a phase of the output voltage (Vout) from the resonant inverter (MI, M2, Li, C3) in a range from 150 to 200 degrees depending on a selected operating frequency of the ballast.
According to another aspect of the invention there is provided a method of operating a ballast for a discharge lamp that includes a self oscillating driver circuit (10), a timing circuit (12) for programming the oscillation frequency of the driver circuit (10), connected to the driver circuit (10), and a resonant inverter (M1, M2, Li, C3) connected to the driver circuit (10) and having an output voltage (Vout), the method comprising the steps of:
feeding back the output voltage (Vout) from the resonant inverter (M1, M2, Li, C3) to the timing circuit (12); and selectively shifting a phase of the output voltage (Vout) being fed back from the resonant inverter (M1, M2, L 1, C3) in a range from 150 to 200 degrees, depending on a selected operating frequency of the ballast.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a circuit diagram of a conventional ballast with self-oscillating inverter.
Figure 2 is a circuit diagram of a conventional ballast with a self-oscillating driver IC.
Figure 3 is a circuit diagram of a ballast of the present invention with a self-oscillating driver IC synchronized by a voltage feedback circuit.
Figure 4 is a circuit diagram of the ballast of the present invention utilizing active phase shifting in the feedback circuit.
Figure 5 is a circuit diagram of the ballast of the present invention with a feedback circuit utilizing signal attenuation and phase shifting by plural RC phase-shifting networks.
7a Figure 6 is a circuit diagram of the invention with a phase controlled feedback circuit.
Figure 7 is a circuit diagram of the invention in a lamp dimming application.
DESCRIPTION OF PREFERRED EMBODIMENTS
With reference now to Figure 3, a self-oscillating driver IC 10 drives half bridge power stages with transistors M1 and M2 generating an AC voltage across the input of a resonant load. IC 10 has a built-in oscillator that is, or is similar to, the "555" timer of the prior art. Oscillator frequency can be programmed with a timing circuit 12 coupled to pins Rt, Ct and common "corn".
The feedback circuit includes blocks 14 and 16 that couple inverter high voltage output LH to timing circuit 12. Block 14 attenuates the output voltage signal and block 16 phase shifts the output voltage signal from 1500 to 200 to compensate for the phase difference between the inverter output voltage and the external synchronization signal.
Timing circuit 12 may include a timing capacitor Ct and resistor Rt (see Figure 2) and switches when the timing capacitor is charged to 2/3 Vcc and discharged to 1/3 Vcc.
In a standard IC application, the timing capacitor voltage waveform is an exponential ramp that is superposed on the DC voltage. By mixing in a small phase shifted signal to the ramp, the IC oscillator correlates its frequency. Preferably, a source of this signal is coupled between ground and the timing capacitor.
In an embodiment of the device shown in Figure 4, which is particularly suited for high frequency application (200-270 kHz), attenuating block 14 (Figure 3) includes a capacitive divider with capacitors C4 and C5 connected to inverter high voltage output LH. Phase shifting block 16 includes an active signal inverter that includes transistor M3 and resistors R3, R4, R6 and R7. The output of the capacitive divider is connected to the input of the active signal inverter. The output of the active signal inverter is connected to the Ct pin of IC 10 via a second timing capacitor Ct2 and timing circuit 12.
The active signal inverter provides a stable phase shift of about 1800 at any frequency.
Thus, the active signal inverter compensates for about 180 of phase difference between the input and output of the open loop inverter operating above resonant frequency.
In one embodiment for electrodeless lamp ballasts, the circuit of Figure 4 may include the following components: IC 10 - IR21531D, M3 ¨ BC337, C4 and Ct2 -22pF, Ctl ¨ 250pF, C5 ¨ 4.7nF, Rtl ¨ 10K, R3 ¨ 100k, R7 ¨750. R4 ¨ 15k, R6-15k, R15 and R16 ¨ 22k, C26 and C28 - 0.1uF. The ballast inverter switches at 250 kHz. With an open loop circuit, the ballast inverter switches at 242 kHz. Resonant frequency of the inverter resonant load is about 220 kHz. The sinusoidal signal injected to pin Ct of IC
10 via timing capacitor Ct2 dominates above the ramp signal generated by the timer even though it has a much smaller level than the ramp signal. The switching frequency of the inverter depends on the resonant load as in self-generated resonant ballasts without an IC.
In other embodiments of the present invention, resistive means may be connected between timing capacitor Ctl and common "coin" of IC 10. Figure 5 shows two anti-parallel diodes D53 and D55 that may serve as the resistive means, although resistor(s) can be used instead of diodes (for example, see R10 in Figure 6).
With further reference to Figure 5, the feedback circuit may include two RC
phase-shifting networks that perform the functions of blocks 14 and 16. The first network includes a capacitor C6 coupled to high voltage output LH and a resistor R8 coupled to common. The second network includes a capacitor C7 and the resistive means. The second network is connecter in parallel to resistor R8 of the first network.
Capacitor C6 may be a high voltage capacitor connected to LH while other components may be low voltage, low power components. As previously explained, a phase shift angle of about 150-200 degrees is needed for optimizing the feedback phase lock. The two series RC networks provide attenuation of the feedback signal more than 100 times and a programmable phase shifting up to around 1800. The ballast inverter starts with a programmed initial switching frequency determined by timing capacitor Ctl and resistor Rtl . As soon as a voltage appears at LH, the inverter will be internally synchronized as the feedback signal will dominate the "555" timer ramp signal of IC 10.
Inverter frequency will be automatically corrected so that input/output phase difference at selected switching frequency will be automatically compensated by the RC phase boosting networks in the feedback circuit.
Figure 6 shows a modification of the embodiment of Figure 5 with a third RC
phase-shifting network that is added during lamp starting. The third RC
network includes capacitor C8, resistor R9 and a switching means connected in series with resistor R9.
The switching means may include two series Zener diodes D3 and D4 connected in opposite directions. During lamp starting, voltage that is applied across the circuit comprising resistor R9 and Zener diodes D3 and D4 is much higher than the Zener diodes' threshold voltage. During steady-state operation, the peak of this voltage is lower than the Zener diodes' threshold. The Zener diodes provide a switching function by adding a third RC phase-shifting network during lamp starting to limit starting voltage.
Ballast components should be protected from overstressing in starting and no-load ____ ...e=P
operation modes. In feedback circuit of Figure 6, two anti-parallel diodes (such as in Figure 5) can be used instead resistor R10 for better stability.
A self-oscillating dimmed ballast circuit is shown in Figure 7. The ballast inverter includes a feedback circuit with a variable structure having three RC
phase-shifting networks. The first RC-network includes high voltage capacitor C9 and resistor R11. The second RC network includes capacitor C10, resistor R12 and Zener diodes D5 and D6. The third RC network includes capacitor C11 and anti-parallel diodes D53 and D55 connected between timing capacitor Ctl and IC 10 common terminal "corn".
Resistor R13 connected across anti-parallel Zener diodes D5 and D6 is provided when more than 1800 phase-shifting is needed in the feedback circuit for optimized steady-state operation of the inverter (for example 2000 phase shifting). PWM signal controlled switching means (for example, transistor M4 in Figure 7) is connected to the Ct pin of IC
10 via resistor R14. By turning ON transistor M4, IC 10 shuts OFF the ballast inverter.
When transistor M4 is OFF, the ballast inverter turns ON. A duty ratio of transistor M4 switching is controlled by a PWM dimmer (not shown in Figure 7). In an ON/OFF
dimming mode, resonant frequency of the resonant load is not stable, as it depends on PWM frequency, duty ratio, temperature, etc. However, the internal synchronization circuit shown herein tracks all current variations of the resonant frequency providing operation of the resonant inverter in the safe area above resonant frequency.
In a particular embodiment for a 150W electrodeless lamp with PWM dimming, the feedback circuit in Figure 7 was utilized in a 250 kHz ballast with the following components: IC 10 -IR21531D, Rtl -10k, Ct1-270pF, D53 and D55-1N4148, M4-BC337, C9-22pF, R11-1.3k, C10-1nF, R12-1.8k, D5 and D6-16V, 0.5W Zener, and C11-47pF.
When transistor M4 is OFF, the ballast inverter turns ON. A duty ratio of transistor M4 switching is controlled by a PWM dimmer (not shown in Figure 7). In an ON/OFF
dimming mode, resonant frequency of the resonant load is not stable, as it depends on PWM frequency, duty ratio, temperature, etc. However, the internal synchronization circuit shown herein tracks all current variations of the resonant frequency providing operation of the resonant inverter in the safe area above resonant frequency.
In a particular embodiment for a 150W electrodeless lamp with PWM dimming, the feedback circuit in Figure 7 was utilized in a 250 kHz ballast with the following components: IC 10 -IR21531D, Rtl -10k, Ct1-270pF, D53 and D55-1N4148, M4-BC337, C9-22pF, R11-1.3k, C10-1nF, R12-1.8k, D5 and D6-16V, 0.5W Zener, and C11-47pF.
__ 0.111614ØMSOMAIMS,WWZMWSweir...Meximavaaamoansm The circuit could provide dimming in the range of 10-100% with up to a 10 kHz PWM
signal with high efficiency.
While embodiments of the present invention have been described in the foregoing specification and drawings, it is to be understood that the present invention is defined by the following claims when read in light of the specification and drawings.
signal with high efficiency.
While embodiments of the present invention have been described in the foregoing specification and drawings, it is to be understood that the present invention is defined by the following claims when read in light of the specification and drawings.
owl apialfaMain=II÷WOOSKS4 = __ Vo otypolomeme Apor ___________ aoPm=nwarem
Claims (14)
1. A ballast for a discharge lamp, comprising:
a self oscillating driver circuit;
a timing circuit for programming the oscillation frequency of the driver circuit connected to said driver circuit;
a resonant inverter connected to said driver circuit and having an output voltage;
and a feedback circuit that connects the output voltage from said resonant inverter to said timing circuit, said feedback circuit including a phase shifting circuit that selectively shifts a phase of the output voltage from said resonant inverter in a range from 150 to 200 degrees depending on a selected operating frequency of the ballast.
a self oscillating driver circuit;
a timing circuit for programming the oscillation frequency of the driver circuit connected to said driver circuit;
a resonant inverter connected to said driver circuit and having an output voltage;
and a feedback circuit that connects the output voltage from said resonant inverter to said timing circuit, said feedback circuit including a phase shifting circuit that selectively shifts a phase of the output voltage from said resonant inverter in a range from 150 to 200 degrees depending on a selected operating frequency of the ballast.
2. The ballast of claim 1, wherein said phase shifting circuit comprises a further inverter connected to an input to said timing circuit.
3. The ballast of claim 2, wherein said feedback circuit further comprises an attenuation circuit that includes a capacitive divider connected between the output voltage and an input to said further inverter.
4. The ballast of claim 1, wherein said phase shifting circuit comprises plural RC phase-shifting networks.
5. The ballast of claim 4, wherein a first of said phase-shifting networks comprises a first capacitor coupled to the output voltage and a first resistor coupled to said driver, and a second of said phase-shifting networks comprises a second capacitor and resistive means coupled to said timing circuit, said second network being connected in parallel with said first resistor.
6. The ballast of claim 5, wherein said resistive means comprises one of a resistor and anti-parallel diodes and is connected between said first resistor and said timing circuit.
7. The ballast of claim 5, further comprising a third RC network that includes a switch that connects said third RC network to said timing circuit during starting of a lamp that includes the ballast.
8. The ballast of claim 1, further comprising a switch operated by a pulse width modulation input and connected to said timing circuit.
9. A method of operating a ballast for a discharge lamp that includes a self oscillating driver circuit, a timing circuit for programming the oscillation frequency of the driver circuit, connected to the driver circuit, and a resonant inverter connected to the driver circuit and having an output voltage, the method comprising the steps of:
feeding back the output voltage from the resonant inverter to the timing circuit; and selectively shifting a phase of the output voltage being fed back from the resonant inverter in a range from 150 to 200 degrees, depending on a selected operating frequency of the ballast.
feeding back the output voltage from the resonant inverter to the timing circuit; and selectively shifting a phase of the output voltage being fed back from the resonant inverter in a range from 150 to 200 degrees, depending on a selected operating frequency of the ballast.
10. The method of claim 9, further comprising the step of attenuating the fed back output voltage with a capacitive divider connected between the output voltageand the timing circuit.
11. The method of claim 9, wherein the phase shifting step includes the step of phase shifting with plural RC phase-shifting networks.
12. The method of claim 11, wherein a first of the phase-shifting networks includes a first capacitor coupled to the output voltage and a first resistor coupled to the driver, and a second of the phase-shifting networks includes a second capacitor and resistive means coupled to the timing circuit, where the second network is connected in parallel with the first resistor.
13. The method of claim 12, wherein the RC networks further include a third RC network that includes a switch and the method further comprises the step of connecting the third RC network to the timing circuit only during starting of a lamp that includes the ballast.
14. The method of claim 9, further comprising the step of controlling the timing circuit with a switch operated by a pulse width modulation input during a dimming operation of a lamp that includes the ballast.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US10/649,898 US6906473B2 (en) | 2003-08-26 | 2003-08-26 | Feedback circuit and method of operating ballast resonant inverter |
| US10/649,898 | 2003-08-26 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2472530A1 CA2472530A1 (en) | 2005-02-26 |
| CA2472530C true CA2472530C (en) | 2014-08-05 |
Family
ID=34104689
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2472530A Expired - Fee Related CA2472530C (en) | 2003-08-26 | 2004-06-25 | Feedback circuit and method of operating ballast resonant inverter |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US6906473B2 (en) |
| EP (1) | EP1511364B1 (en) |
| CN (1) | CN1592531B (en) |
| CA (1) | CA2472530C (en) |
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| US7471427B2 (en) * | 2004-06-22 | 2008-12-30 | Lite-On Technology Corporation | Warm-up circuit for CCFLs |
| US7619368B2 (en) * | 2005-07-05 | 2009-11-17 | Chao-Cheng Lu | Power source apparatus |
| US7498751B2 (en) * | 2006-06-15 | 2009-03-03 | Himax Technologies Limited | High efficiency and low cost cold cathode fluorescent lamp driving apparatus for LCD backlight |
| TW200812436A (en) * | 2006-08-22 | 2008-03-01 | Beyond Innovation Tech Co Ltd | Electronic ballast and method for driving fluorescent lamp |
| US8018173B2 (en) * | 2006-09-03 | 2011-09-13 | Fulham Company Ltd. | Ballasts for fluorescent lamps |
| US8736189B2 (en) * | 2006-12-23 | 2014-05-27 | Fulham Company Limited | Electronic ballasts with high-frequency-current blocking component or positive current feedback |
| US8058811B2 (en) * | 2007-03-26 | 2011-11-15 | International Rectifier Corporation | HID lamp ballast circuit |
| US20090200964A1 (en) * | 2008-02-08 | 2009-08-13 | King Ray J | Methods And Apparatus For Dimmable Ballasts With A High Power Factor |
| US20090200952A1 (en) * | 2008-02-08 | 2009-08-13 | Purespectrum, Inc. | Methods and apparatus for dimming light sources |
| US20090200951A1 (en) * | 2008-02-08 | 2009-08-13 | Purespectrum, Inc. | Methods and Apparatus for Dimming Light Sources |
| US20090200953A1 (en) * | 2008-02-08 | 2009-08-13 | Ray James King | Methods and apparatus for a high power factor ballast having high efficiency during normal operation and during dimming |
| US20100176733A1 (en) * | 2009-01-14 | 2010-07-15 | Purespectrum, Inc. | Automated Dimming Methods and Systems For Lighting |
| US20100225239A1 (en) * | 2009-03-04 | 2010-09-09 | Purespectrum, Inc. | Methods and apparatus for a high power factor, high efficiency, dimmable, rapid starting cold cathode lighting ballast |
| US8749162B2 (en) * | 2011-02-10 | 2014-06-10 | Osram Sylvania Inc. | Two level lighting ballast |
| CN102694473A (en) * | 2011-03-21 | 2012-09-26 | 国琏电子（上海）有限公司 | Power supply system |
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| GB2501539B (en) * | 2012-04-27 | 2018-10-24 | Nidec Control Techniques Ltd | Power control system |
| US20140035480A1 (en) * | 2012-08-02 | 2014-02-06 | Tsvi Blumin | Method for the control of luminance of gas discharge lamps |
| CN104105284A (en) * | 2013-04-15 | 2014-10-15 | 阮雪芬 | Double-half-bridge injection phase-locking power synthesis black light lamp group |
| CN104105280B (en) * | 2013-04-15 | 2018-01-05 | 张妙娟 | DC low-voltage is double to push away injection phase-locking power combing halogen tungsten lamp |
| CN104105294A (en) * | 2013-04-15 | 2014-10-15 | 阮树成 | Direct-current low-voltage power supply four-push-pull injection-locking power synthesis metal halide lamp |
| CN104105319A (en) * | 2013-04-15 | 2014-10-15 | 阮树成 | Solar power supply four-full-bridge injection locking power synthesis fluorescent lamp set |
| CN103327702B (en) * | 2013-04-15 | 2015-01-28 | 张根清 | Solar energy power source double half-bridge injection locked power synthesis halogen lamp set |
| CN104105253B (en) * | 2013-04-15 | 2017-12-01 | 梅玉刚 | Enjoy a double blessing bridge injection phase-locking LED array lamp |
| CN104105292A (en) * | 2013-04-15 | 2014-10-15 | 阮树成 | Solar power supply four-full-bridge injection-locking power synthesis electrodeless lamp group |
| CN104105325A (en) * | 2013-04-15 | 2014-10-15 | 张妙娟 | DC low-voltage double-push injection phase-locking power synthesis electrodeless lamp |
| CN104105295A (en) * | 2013-04-15 | 2014-10-15 | 梅玉刚 | Double-full-bridge injection phase-locking power-synthesizing metal halide lamp |
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-
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- 2004-07-14 EP EP04016556.5A patent/EP1511364B1/en not_active Expired - Fee Related
- 2004-08-26 CN CN2004100685429A patent/CN1592531B/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US20050046359A1 (en) | 2005-03-03 |
| EP1511364A1 (en) | 2005-03-02 |
| US6906473B2 (en) | 2005-06-14 |
| EP1511364B1 (en) | 2013-05-08 |
| CN1592531A (en) | 2005-03-09 |
| CA2472530A1 (en) | 2005-02-26 |
| CN1592531B (en) | 2012-02-08 |
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