Lamp ballast circuit with cathode preheat function

Details Lamp ballast circuit with cathode preheat function Lamp ballast circuit with cathode preheat function

1996-10-01

1999-01-12

Pascal, Robert

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Automatic regulation

315 94, 315DIG5, 315105, 315106, H05B 4100, H05B 4136

Patent

active

058595040

ABSTRACT:
A ballast circuit for a gas discharge lamp contained within a resonant load circuit has resistively heated cathodes. A d.c.-to-a.c. converter circuit supplyies a.c. current to the resonant load circuit. The converter circuit comprises first and second switches serially connected between a bus conductor at a d.c. voltage and a reference conductor, and has a common node through which the a.c. current flows. In an arrangement for controlling the converter switches, a comparator circuit compares a signal on a first input node with a periodic reference signal on a second input node, and produces a comparator output signal that changes state when a first one of the compared signals becomes greater than the second of the compared signals, and that further changes state when the second of the compared signals then becomes greater than the first of the compared signals. A circuit generates the periodic reference signal in response to the comparator output signal. A first circuit produces a signal on the first input node upon initial converter energization, for preventing lamp ignition while the lamp cathodes become heated. A second circuit for producing a signal on the first input node for allowing lamp ignition comprises a feedback circuit for sensing a.c. current in the resonant load circuit and producing a feedback signal in proportion to the a.c. current. The feedback signal is coupled to the first input node after a predetermined period of time from initial energizing of the converter circuit, during which period the lamp cathodes become heated.

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(Product Note), "Ballast IC Applications Information," International Rectifier Corporation, Oct. 1994, 3 pages.
(Product Note), "Compact Fluorescent Lamp," SGS-Thompson Microelectronics, Oct. 1995, 2 pages.

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