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US 7,247,991 B2Granted
Dimming ballast and method
AssigneeGeneral Electric Company
InventorsTimothy Chen, Didier Rouaud, James K. Skully
Life of this patent
Estimating the term…
Abstract
A ballast lamp circuit and method of operation is disclosed. The ballast lamp circuit comprising an inverter circuit and cathode heating circuit, wherein a lamp current, generated by the inverter circuit, is inversely proportional to a lamp cathode voltage generated by the cathode heating circuit.
Claims29
A ballast lamp circuit comprising:
- an inverter circuit configured to convert a dc waveform to a first ac current waveform for driving a first lamp;
- and
- a cathode heating circuit operatively connected to the inverter circuit and configured to generate a second ac waveform for heating the electrodes of the first lamp, the RMS value of the second ac waveform decreasing as the RMS value of the first ac current waveform increases, and the RMS value of the second ac waveform increasing as the RMS value of the first ac current waveform decreases, wherein the RMS value of the second ac waveform is controlled with pulse width modulation.
A ballast lamp circuit comprising:
- a means for converting a dc waveform to one or more ac waveforms for driving, respectively, one or more lamps;
- and
- a means for generating one or more pulse width modulated ac waveforms for heating the electrodes of the one or more lamps, wherein the RMS value of the one or more ac waveforms for heating the electrodes decreases as the RMS value of the ac waveforms for driving the one or more lamps increases, and the RMS value of the one or more ac waveforms for heating the electrodes increases as the RMS value of the ac waveforms for driving one or more lamps decreases.
A method of operating a hot cathode lamp, comprising:
- driving one or more lamps with a lamp current to produce a lamp lumen output, the lamp lumen output decreasing as the lamp current is decreased and increasing as the lamp current is increased;
- and
- supplying a pulse width modulated cathode heating voltage to the electrodes of the one or more lamps, the cathode heating voltage decreasing as the lamp current is decreased and increasing as the lamp current is increased, the cathode heating voltage limited to a minimum voltage when the lamp current is less than a predetermined value and the cathode heating voltage is at a minimum or zero when the lamp current is more than a predetermined value.
Dependencies are inferred from the claim text.