Electronic ballast with feed-forward control
First Claim
1. 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.
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Accused Products
Abstract
An electronic ballast 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 selfoscillating 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 automatically 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.
34 Citations
19 Claims
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1. An electronic ballast for powering a discharge lamp, said ballast comprising:
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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. - View Dependent Claims (2, 3, 4)
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.
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4. A ballast as in claim 3 where:
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a. the self-oscillating converter includes alternatelyconducting 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.
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- 5. 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.
- 12. 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 automatically 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.
Specification