US20020067139A1 - Electronic ballast with feed-forward control - Google Patents
Electronic ballast with feed-forward control Download PDFInfo
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- US20020067139A1 US20020067139A1 US09/730,430 US73043000A US2002067139A1 US 20020067139 A1 US20020067139 A1 US 20020067139A1 US 73043000 A US73043000 A US 73043000A US 2002067139 A1 US2002067139 A1 US 2002067139A1
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- 238000004804 winding Methods 0.000 claims description 18
- 239000002131 composite material Substances 0.000 claims description 3
- 239000003990 capacitor Substances 0.000 description 19
- 230000000295 complement effect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000000903 blocking effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
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- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000368 destabilizing effect Effects 0.000 description 1
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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
- H05B41/36—Controlling
- H05B41/38—Controlling the intensity of light
- H05B41/39—Controlling the intensity of light continuously
- H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/538—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration
- H02M7/53803—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration with automatic control of output voltage or current
-
- 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
- H05B41/2825—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 by means of a bridge converter in the final stage
- H05B41/2827—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 by means of a bridge converter in the final stage using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0016—Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters
- H02M1/0022—Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters the disturbance parameters being input voltage fluctuations
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- 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
- 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
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Definitions
- This invention relates to electronic ballasts for discharge lamps such as fluorescent lamps and, in particular, to such ballasts which are useful in applications where compact size is desirable.
- ballast circuitry If the operating frequency of ballast circuitry is increased sufficiently to achieve a substantial reduction in the sizes of magnetic and filtering elements, power losses tend to increase.
- an electronic ballast includes a source of power having a varying DC voltage, a self-oscillating converter powered by the DC voltage for producing pulses at a controlled frequency, a resonant tank for converting the pulses to an alternating current for powering a discharge lamp, and a feed-forward control circuit for effecting variation of the frequency in response to variations of the DC voltage, the resonant tank having a voltage drop which varies directly with said frequency.
- Such a ballast does not require a regulated DC power supply and will operate effectively with a filter capacitor that is much reduced in size from capacitors that are typically used to reduce ripple of the rectified DC power.
- a self-oscillating resonant converter circuit for operating discharge lamps, which does not require a regulated DC power supply, is described U.S. Pat. No. 6,072,710.
- that circuit utilizes a feed-back approach.
- a feed-forward approach is utilized which is inherently more stable and has a greater range of correction for variations of the DC source voltage.
- FIG. 1 is a combination block and schematic diagram of a system including a ballast in accordance with an embodiment of the invention.
- FIG. 2 is a detailed circuit diagram of a system including an exemplary ballast in accordance with the invention.
- FIGS. 3A and 3B are waveform diagrams illustrating operation of the exemplary ballast of FIG. 2.
- the exemplary system shown in FIG. 1 includes a source of AC power S, a discharge lamp L (e.g. a fluorescent lamp) and a ballast for controllably passing power to the lamp from the source S.
- the ballast includes an EMI filter 10 , a bridge rectifier DR 1 , a line-filter capacitor C f , a half-bridge converter 12 , a resonant tank 14 , a current transformer T 1 , a gate driver circuit 16 and a feed-forward control circuit 18 .
- the EMI filter 10 serves to isolate the AC power source S from interference signals generated within the ballast (e.g. high-frequency switching signals generated by the converter 12 ).
- the bridge rectifier DR 1 and the filter capacitor C f convert the AC power from the source S to rectified, but unregulated, DC power having a varying DC voltage V f .
- this rectifier and capacitor form a DC power source that is conventional except for its simplicity and the relatively small size of the filter capacitor that is possible because of the ripple compensation provided by the feed-forward control.
- a relatively simple voltage-step-up circuit can be substituted.
- the half-bridge converter 12 (including serially-connected transistors Q 1 and Q 2 ) operates together with the resonant tank 14 to provide power to the lamp L.
- the converter switches at a nominal high frequency (e.g. 120 kHz) relative to the frequency (e.g. 60 Hz) of the AC source S and alternately connects the resonant tank 14 (via a node N) to the varying DC voltage on the capacitor C f (through transistor Q 1 ) and then to ground (through transistor Q 2 ).
- the resonant tank 14 converts the power provided through transistor Q 1 (in the form of DC pulses) to a sinusoidal AC waveform for powering the lamp L.
- the tank 14 operates at a resonant frequency which is determined primarily by inductance and capacitance in the tank itself and by the impedance of the lamp L.
- the current transformer T 1 senses the current flowing through the resonant tank and supplies a signal I res representative of this current to a first input of the gate driver circuit 16 .
- the gate driver applies signals to the gates of the transistors Q 1 and Q 2 to effect switching of these transistors at the same frequency as that of the sinusoidal AC waveform generated within the resonant tank 14 .
- the converter 12 , resonant tank 14 , current transformer T 1 and gate driver circuit 16 operated as described thus far, form a self-oscillating resonant converter.
- a known converter of this type is described in greater detail in U.S. Pat. No. 6,072,710, which is hereby incorporated by reference.
- control circuit 18 applies a feed-forward signal to a second input of the gate driver 16 to effect an offset of the driving signals applied to the gates, thereby compensating for the variations of the rectified DC supply voltage V f on the line-filter capacitor C f .
- Such feed-forward control enables compensation for substantially greater variations in the DC supply voltage, without destabilizing the self-oscillating operation of the resonant converter.
- a current-limiting resistor R 1 is inserted in series with the AC power source S to limit inrush current through the bridge rectifier DR 1 when power is initially applied.
- the EMI filter is formed by a capacitor C 2 for bypassing high-frequency interference signals (generated by the high-frequency switching of the half-bridge converter) to ground and by an inductor L 2 for blocking passage of the high-frequency interference signals.
- the line filter-capacitor C f reduces the magnitude of the ripple of the rectified AC power supplied to the converter 12 . Because of the compensation provided by the feed-forward control, the size of this capacitor can be substantially reduced. For example, a circuit having the component values specified in FIG. 2 and having a 3.3 ⁇ f capacitor C f was used to power a 28 Watt T8 fluorescent lamp at a nominal voltage of 142 Volts RMS. Without the feed-forward control, a 22 ⁇ f capacitor C f would be required to power the same lamp or the crest factor would substantially increase.
- the half-bridge converter 12 is substantially identical to that shown in FIG. 1, but further includes snubber capacitors C 3 and C 4 connected in parallel with the respective transistors Q 1 and Q 2 . These capacitors serve to reduce energy losses during turn off of the transistors Q 1 and Q 2 , as is well known in the art.
- the resonant tank is formed by an inductor L 1 , by a capacitor C 6 in parallel with the lamp L and by the capacitance of the lamp itself.
- the capacitor C 5 has an impedance which is very small compared to that of the lamp and functions primarily as a DC blocking impedance, as is well known in the art.
- the current transformer includes windings T 1 - 1 , T 1 - 2 , T 1 - 3 and T 1 - 4 .
- Winding T 1 - 1 acts as a primary winding for sensing the current I res flowing through the resonant tank.
- Windings T 1 - 2 and T 1 - 3 together with parallel pairs of serially-connected zener diodes Dz 1 -Dz 2 and Dz 3 -Dz 4 , respectively, form the gate driver circuit 16 .
- These zener diode pairs serve to convert current signals I Z produced by the windings T 1 - 2 and T 1 - 3 to voltage signals V Z for driving the transistors Q 1 and Q 2 , respectively.
- I Z 1 ⁇ 2 ⁇ [I S ⁇ (I mag +I C )].
- one of the transistors Q 1 /Q 2 is ON and the other is OFF.
- Q 1 is ON and Q 2 is OFF.
- I S (t) [N 1 /N] ⁇ I res (t)
- I mag (t) [V Z /L M ] ⁇ t
- I C (t) is determined by the feed-forward control circuit, where:
- N 1 , N 2 , N 3 , N 4 are number of turns of the windings T 1 - 1 , T 1 - 2 , T 1 - 3 , and T 1 - 4 , respectively
- L M is the magnetizing inductance of T 1 .
- the feed-forward control circuit 18 includes complementary first and second circuits for driving the winding T 1 - 4 .
- the first winding-driver circuit includes an NPN transistor Q 3 , a resistor R 3 connected in series with the collector, a diode D 3 connected in series with the emitter, and the series combination of a diode D 1 and a resistor R 5 connected in series between the base of Q 3 and a node M.
- the second winding driver circuit includes a PNP transistor Q 4 , a resistor R 4 connected in series with the collector, a diode D 4 connected in series with the emitter, and the series combination of a diode D 2 and a resistor R 6 connected in series between the base of Q 3 and the node M.
- Control circuit 18 further includes a bandpass filter which is formed by the serially-connected combination of a resistor R 7 and a capacitor C 7 (connected between nodes N and M) and by the parallel-connected combination of a capacitor C 8 and resistor R 8 (connected between node M and ground).
- This bandpass filter serves to convert a square-wave signal produced at node N (and having a voltage alternating between approximately V f and ground) to a triangular-wave signal which is produced at node M.
- This triangular-wave signal has an amplitude proportional to V f and varies substantially symmetrically above and below ground potential.
- the first and second winding-driver circuits operate to produce the control current I C in the winding T 1 - 4 , which is an alternating triangular-wave current having an instantaneous polarity determined by the polarity of the voltage at the node M.
- FIGS. 3A and 3B illustrate signals produced, during operation of the exemplary ballast shown in FIG. 2, for two different values of V f .
- V f the exemplary ballast shown in FIG. 2
- the square-wave signal represents the voltage at node N (which is substantially equal to the voltage V f when the transistor Q 1 is conducting);
- the triangular-wave signal represents the sum of the magnetizing current I mag and the control current I C ;
- the sinusoidal-wave signal represents the current I res passing through the winding T 1 - 1 .
- the feed-forward control circuit 18 cooperates with the gate-driver circuit 16 to vary the switching frequency of the converter 12 in response to variations of the DC voltage V f . This is done by producing a contributory drive current through the winding T 1 - 4 which varies directly with the magnitude of the triangular waveform signal at node M. Note that the converter transistors Q 1 and Q 2 change state whenever the sum of the magnetizing current I mag and the control current I C is equal to the sensed resonant inductor current I S . The contributory drive current through winding T 1 - 4 tends to increase the rate at which the magnetizing current reaches the value of the resonant inductor current.
- the operating frequency of the converter (and thus of the current I res through the resonant tank) varies directly with the amount of the contributory drive current through the winding T 1 - 4 .
- the voltage drop across the resonant inductor L 1 varies directly with frequency. Consequently, as the voltage V f supplied to the tank 14 by the converter 12 varies, the resonant inductor regulates the voltage supplied to the lamp L by dropping more voltage for higher values of V f and by dropping less voltage for lower values of V f .
- This causes a lower converter frequency f ⁇ and a lower voltage drop across the resonant inductor L 1 .
- FIG. 2 represents only one exemplary embodiment of specific circuitry that may be utilized to implement an electronic ballast in accordance with the invention.
- compactness of the ballast might be further improved by forming the resonant tank with an integral device rather than discrete circuit components.
- One particularly interesting device is a multi-layered piezoelectric transformer, such as that described in U.S. Pat. No. 58344882, which is hereby incorporated by reference.
- a fluorescent lamp ballast utilizing such a piezoelectric transformer is described in Ray L. Lin et al., Inductor-less Piezoelectric Transformer Ballast for Linear Fluorescent Lamps, 2000 CPES Power Electronics Seminar Proceedings, Sep. 17-19, 2000, which is hereby incorporated by reference.
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- Engineering & Computer Science (AREA)
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- Circuit Arrangements For Discharge Lamps (AREA)
Abstract
An electronic ballast is provided which is capable of compactly powering a discharge lamp from a source of rectified, but unregulated, power having a varying DC voltage. The ballast includes a self-oscillating converter powered by the DC voltage for producing pulses at a nominal operating frequency which is determined by a resonant tank. The resonant tank converts the pulses to a sinusoidal current for powering the discharge lamp and includes an inductive impedance in series with the lamp for providing a voltage drop which varies with the operating frequency. A feed-forward control circuit is coupled to the converter for varying the operating frequency directly with variations in the DC source voltage. The voltage drop across the inductive impedance is substantially proportional to the magnitude of the DC source voltage. This enables regulation of the voltage supplied to the discharge lamp by the ballast without sensing the lamp voltage itself.
Description
- 1. Field of the Invention
- This invention relates to electronic ballasts for discharge lamps such as fluorescent lamps and, in particular, to such ballasts which are useful in applications where compact size is desirable.
- 2. Description of Related Art
- There is an ever-increasing demand for smaller electronic ballasts. In order to achieve this goal, a variety of problems must be overcome, for example:
- If the operating frequency of ballast circuitry is increased sufficiently to achieve a substantial reduction in the sizes of magnetic and filtering elements, power losses tend to increase.
- Decreasing the size of filtering components tends to have a negative impact on circuit performance.
- It is an object of the invention to provide an electronic ballast for discharge lamps which can be made compact without substantially increasing cost or adversely affecting performance.
- In accordance with the invention, an electronic ballast includes a source of power having a varying DC voltage, a self-oscillating converter powered by the DC voltage for producing pulses at a controlled frequency, a resonant tank for converting the pulses to an alternating current for powering a discharge lamp, and a feed-forward control circuit for effecting variation of the frequency in response to variations of the DC voltage, the resonant tank having a voltage drop which varies directly with said frequency.
- Such a ballast does not require a regulated DC power supply and will operate effectively with a filter capacitor that is much reduced in size from capacitors that are typically used to reduce ripple of the rectified DC power.
- A self-oscillating resonant converter circuit for operating discharge lamps, which does not require a regulated DC power supply, is described U.S. Pat. No. 6,072,710. However, that circuit utilizes a feed-back approach. In accordance with the invention, a feed-forward approach is utilized which is inherently more stable and has a greater range of correction for variations of the DC source voltage.
- FIG. 1 is a combination block and schematic diagram of a system including a ballast in accordance with an embodiment of the invention.
- FIG. 2 is a detailed circuit diagram of a system including an exemplary ballast in accordance with the invention.
- FIGS. 3A and 3B are waveform diagrams illustrating operation of the exemplary ballast of FIG. 2.
- The exemplary system shown in FIG. 1 includes a source of AC power S, a discharge lamp L (e.g. a fluorescent lamp) and a ballast for controllably passing power to the lamp from the source S. The ballast includes an
EMI filter 10, a bridge rectifier DR1, a line-filter capacitor Cf, a half-bridge converter 12, aresonant tank 14, a current transformer T1, agate driver circuit 16 and a feed-forward control circuit 18. - The
EMI filter 10 serves to isolate the AC power source S from interference signals generated within the ballast (e.g. high-frequency switching signals generated by the converter 12). - The bridge rectifier DR1 and the filter capacitor Cf convert the AC power from the source S to rectified, but unregulated, DC power having a varying DC voltage Vf. Together, this rectifier and capacitor form a DC power source that is conventional except for its simplicity and the relatively small size of the filter capacitor that is possible because of the ripple compensation provided by the feed-forward control. Alternatively, in a ballast for powering a lamp requiring a higher DC voltage than can be provided by a simple bridge rectifier, a relatively simple voltage-step-up circuit can be substituted.
- The half-bridge converter12 (including serially-connected transistors Q1 and Q2) operates together with the
resonant tank 14 to provide power to the lamp L. The converter switches at a nominal high frequency (e.g. 120 kHz) relative to the frequency (e.g. 60 Hz) of the AC source S and alternately connects the resonant tank 14 (via a node N) to the varying DC voltage on the capacitor Cf (through transistor Q1) and then to ground (through transistor Q2). - The
resonant tank 14 converts the power provided through transistor Q1 (in the form of DC pulses) to a sinusoidal AC waveform for powering the lamp L. Thetank 14 operates at a resonant frequency which is determined primarily by inductance and capacitance in the tank itself and by the impedance of the lamp L. - The current transformer T1 senses the current flowing through the resonant tank and supplies a signal Ires representative of this current to a first input of the
gate driver circuit 16. In response to this signal, the gate driver applies signals to the gates of the transistors Q1 and Q2 to effect switching of these transistors at the same frequency as that of the sinusoidal AC waveform generated within theresonant tank 14. - Collectively, the
converter 12,resonant tank 14, current transformer T1 andgate driver circuit 16, operated as described thus far, form a self-oscillating resonant converter. A known converter of this type is described in greater detail in U.S. Pat. No. 6,072,710, which is hereby incorporated by reference. Contrary to the feed-back control described in that patent, however,control circuit 18 applies a feed-forward signal to a second input of thegate driver 16 to effect an offset of the driving signals applied to the gates, thereby compensating for the variations of the rectified DC supply voltage Vf on the line-filter capacitor Cf. Such feed-forward control enables compensation for substantially greater variations in the DC supply voltage, without destabilizing the self-oscillating operation of the resonant converter. - In the exemplary circuit embodiment shown in FIG. 2, corresponding parts are indicated by the same reference indicia as in FIG. 1. In addition to the circuit elements shown in FIG. 1, a current-limiting resistor R1 is inserted in series with the AC power source S to limit inrush current through the bridge rectifier DR1 when power is initially applied.
- The EMI filter is formed by a capacitor C2 for bypassing high-frequency interference signals (generated by the high-frequency switching of the half-bridge converter) to ground and by an inductor L2 for blocking passage of the high-frequency interference signals.
- The line filter-capacitor Cf reduces the magnitude of the ripple of the rectified AC power supplied to the
converter 12. Because of the compensation provided by the feed-forward control, the size of this capacitor can be substantially reduced. For example, a circuit having the component values specified in FIG. 2 and having a 3.3 μf capacitor Cf was used to power a 28 Watt T8 fluorescent lamp at a nominal voltage of 142 Volts RMS. Without the feed-forward control, a 22 μf capacitor Cf would be required to power the same lamp or the crest factor would substantially increase. - The half-
bridge converter 12 is substantially identical to that shown in FIG. 1, but further includes snubber capacitors C3 and C4 connected in parallel with the respective transistors Q1 and Q2. These capacitors serve to reduce energy losses during turn off of the transistors Q1 and Q2, as is well known in the art. - The resonant tank is formed by an inductor L1, by a capacitor C6 in parallel with the lamp L and by the capacitance of the lamp itself. The capacitor C5 has an impedance which is very small compared to that of the lamp and functions primarily as a DC blocking impedance, as is well known in the art.
- The current transformer includes windings T1-1, T1-2, T1-3 and T1-4. Winding T1-1 acts as a primary winding for sensing the current Ires flowing through the resonant tank. Windings T1-2 and T1-3, together with parallel pairs of serially-connected zener diodes Dz1-Dz2 and Dz3-Dz4, respectively, form the
gate driver circuit 16. These zener diode pairs serve to convert current signals IZ produced by the windings T1-2 and T1-3 to voltage signals VZ for driving the transistors Q1 and Q2, respectively. These are composite signals of opposite polarity, each representing the sensed instantaneous tank current IS=[N1/N]·Ires, the transformer magnetizing current Imag, and a control current IC produced by the feed-forward control circuit 18. - The magnitude of the current IZ produced by each of the windings T1-2 and T1-3 (and passing through the respective zener diode pairs) is equal to one-half of the difference between the sensed tank current IS and the sum of the magnetizing current Imag plus the control current Ic, that is IZ=½·[IS−(Imag+IC)]. Depending on the instantaneous polarity of IZ in each of the windings T1-2 and T1-3, one of the transistors Q1/Q2 is ON and the other is OFF. For the polarities of IZ shown in FIG. 2, Q1 is ON and Q2 is OFF. For the circuit shown in FIG. 2, IS(t)=[N1/N]·Ires(t), Imag(t)=[VZ/LM]·t, and IC(t) is determined by the feed-forward control circuit, where:
- N1, N2, N3, N4 are number of turns of the windings T1-1, T1-2, T1-3, and T1-4, respectively
- N=N2=N3=N4; and
- LM is the magnetizing inductance of T1.
- The feed-
forward control circuit 18 includes complementary first and second circuits for driving the winding T1-4. The first winding-driver circuit includes an NPN transistor Q3, a resistor R3 connected in series with the collector, a diode D3 connected in series with the emitter, and the series combination of a diode D1 and a resistor R5 connected in series between the base of Q3 and a node M. The second winding driver circuit includes a PNP transistor Q4, a resistor R4 connected in series with the collector, a diode D4 connected in series with the emitter, and the series combination of a diode D2 and a resistor R6 connected in series between the base of Q3 and the node M. -
Control circuit 18 further includes a bandpass filter which is formed by the serially-connected combination of a resistor R7 and a capacitor C7 (connected between nodes N and M) and by the parallel-connected combination of a capacitor C8 and resistor R8 (connected between node M and ground). This bandpass filter serves to convert a square-wave signal produced at node N (and having a voltage alternating between approximately Vf and ground) to a triangular-wave signal which is produced at node M. This triangular-wave signal has an amplitude proportional to Vf and varies substantially symmetrically above and below ground potential. The first and second winding-driver circuits operate to produce the control current IC in the winding T1-4, which is an alternating triangular-wave current having an instantaneous polarity determined by the polarity of the voltage at the node M. - FIGS. 3A and 3B illustrate signals produced, during operation of the exemplary ballast shown in FIG. 2, for two different values of Vf. In each of these figures:
- the square-wave signal represents the voltage at node N (which is substantially equal to the voltage Vf when the transistor Q1 is conducting);
- the triangular-wave signal represents the sum of the magnetizing current Imag and the control current IC; and
- the sinusoidal-wave signal represents the current Ires passing through the winding T1-1.
- In operation, the feed-
forward control circuit 18 cooperates with the gate-driver circuit 16 to vary the switching frequency of theconverter 12 in response to variations of the DC voltage Vf. This is done by producing a contributory drive current through the winding T1-4 which varies directly with the magnitude of the triangular waveform signal at node M. Note that the converter transistors Q1 and Q2 change state whenever the sum of the magnetizing current Imag and the control current IC is equal to the sensed resonant inductor current IS. The contributory drive current through winding T1-4 tends to increase the rate at which the magnetizing current reaches the value of the resonant inductor current. The operating frequency of the converter (and thus of the current Ires through the resonant tank) varies directly with the amount of the contributory drive current through the winding T1-4. As is well known in the art, the voltage drop across the resonant inductor L1 varies directly with frequency. Consequently, as the voltage Vf supplied to thetank 14 by theconverter 12 varies, the resonant inductor regulates the voltage supplied to the lamp L by dropping more voltage for higher values of Vf and by dropping less voltage for lower values of Vf. - By comparison of FIGS. 3A and 3B, operation of the ballast of FIG. 2 at exemplary higher and lower values, respectively, of the DC voltage Vf can be seen. At a higher value of Vf + (Refer to FIG. 3A.) the complementary transistors Q3 and Q4 supply a higher value of triangular drive current to the winding T1-4 resulting in a current IC ++Imag + which rapidly reaches the magnitude of the sensed resonant inductor current IS +=[N1/N]·Ires +. This causes a higher converter frequency f+ and a higher voltage drop across the resonant inductor L1. At a lower value of Vf − (Refer to FIG. 3B.) the complementary transistors Q3 and Q4 supply a lower value of triangular drive current to the winding T1-4 resulting in a current IC −+Imag − which less rapidly reaches the magnitude of the sensed resonant inductor current IS −=[N1/N]·Ires −. This causes a lower converter frequency f− and a lower voltage drop across the resonant inductor L1.
- Note that FIG. 2 represents only one exemplary embodiment of specific circuitry that may be utilized to implement an electronic ballast in accordance with the invention. For example, compactness of the ballast might be further improved by forming the resonant tank with an integral device rather than discrete circuit components. One particularly interesting device is a multi-layered piezoelectric transformer, such as that described in U.S. Pat. No. 58344882, which is hereby incorporated by reference. A fluorescent lamp ballast utilizing such a piezoelectric transformer is described in Ray L. Lin et al., Inductor-less Piezoelectric Transformer Ballast for Linear Fluorescent Lamps, 2000 CPES Power Electronics Seminar Proceedings, Sep. 17-19, 2000, which is hereby incorporated by reference.
Claims (8)
1. An electronic ballast comprising a source of power having a varying DC voltage, a self-oscillating converter powered by the DC voltage for producing pulses at a controlled frequency, a resonant tank for converting the pulses to an alternating current for powering a discharge lamp, and a feed-forward control circuit for effecting variation of the frequency in response to variations of the DC voltage, the resonant tank having a voltage drop which varies directly with said frequency.
2. A ballast as in claim 1 where the resonant tank comprises a piezoelectric transformer.
3. An electronic ballast comprising a source of power having a varying DC voltage, a self-oscillating converter including alternately-conducting first and second switching devices powered by the DC voltage for producing pulses at a controlled frequency, a resonant tank for converting the pulses to an alternating current for powering a discharge lamp, and a feed-forward control circuit coupled to the switching devices for effecting variation of the switching rate of the switching devices directly with variations of the DC voltage, the resonant tank including an inductive impedance having a voltage drop which varies directly with said frequency.
4. A ballast as in claim 3 where the resonant tank comprises a piezoelectric transformer.
5. An electronic ballast for powering a discharge lamp, said ballast comprising:
a. a source of power having a varying DC voltage;
b. a self-oscillating converter powered by the DC voltage for producing pulses at a controlled operating frequency;
c. a resonant tank for converting the pulses to an alternating current for powering a discharge lamp, said resonant tank being coupled to the converter to control said operating frequency;
d. a feed-forward control circuit coupled to the converter for effecting variation of said operating frequency in response to variations of the DC voltage;
said resonant tank including an inductive impedance having a voltage drop which varies directly with variations in said operating frequency.
6. A ballast as in claim 5 where the resonant tank comprises a piezoelectric transformer.
7. A ballast as in claim 5 including driver circuitry coupled to the converter for controlling the converter operating frequency in response to:
a. a first signal from the resonant tank representative of the alternating current; and
b. a second signal from the feed-forward control representative of the varying DC voltage.
8. A ballast as in claim 7 where:
a. the self-oscillating converter includes alternately-conducting first and second switching devices having respective first and second control inputs;
b. the driver circuitry includes a first transformer winding coupled to the first control input for applying a composite signal representative of the alternating current and of the varying DC voltage and a second transformer winding coupled to the second control input for applying a corresponding composite signal of opposite polarity.
Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/730,430 US6424101B1 (en) | 2000-12-05 | 2000-12-05 | Electronic ballast with feed-forward control |
PCT/IB2001/002312 WO2002047442A1 (en) | 2000-12-05 | 2001-12-05 | Electronic ballast with feed-forward control |
JP2002549034A JP2004515893A (en) | 2000-12-05 | 2001-12-05 | Electronic ballast with feedforward control |
CN01804478A CN1397150A (en) | 2000-12-05 | 2001-12-05 | Electronic ballast with feed-forward control |
EP01270085A EP1352546A1 (en) | 2000-12-05 | 2001-12-05 | Electronic ballast with feed-forward control |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/730,430 US6424101B1 (en) | 2000-12-05 | 2000-12-05 | Electronic ballast with feed-forward control |
Publications (2)
Publication Number | Publication Date |
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US20020067139A1 true US20020067139A1 (en) | 2002-06-06 |
US6424101B1 US6424101B1 (en) | 2002-07-23 |
Family
ID=24935328
Family Applications (1)
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US09/730,430 Expired - Fee Related US6424101B1 (en) | 2000-12-05 | 2000-12-05 | Electronic ballast with feed-forward control |
Country Status (5)
Country | Link |
---|---|
US (1) | US6424101B1 (en) |
EP (1) | EP1352546A1 (en) |
JP (1) | JP2004515893A (en) |
CN (1) | CN1397150A (en) |
WO (1) | WO2002047442A1 (en) |
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Also Published As
Publication number | Publication date |
---|---|
US6424101B1 (en) | 2002-07-23 |
WO2002047442A1 (en) | 2002-06-13 |
EP1352546A1 (en) | 2003-10-15 |
CN1397150A (en) | 2003-02-12 |
JP2004515893A (en) | 2004-05-27 |
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