Apparatus and method for controlling the filament voltage in...

Electric lamp and discharge devices: systems – With cathode or cathode heater supply circuit – Pulsating or a.c. supply to the cathode or heater circuit

Reexamination Certificate

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C315S224000, C315S274000, C315S312000

Reexamination Certificate

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07843139

ABSTRACT:
An electronic dimming ballast comprises a filament turn-off circuit for controlling the magnitudes of filament voltages supplied to the filaments of a gas discharge lamp. Each of a plurality of filament windings is directly coupled to one of the filaments and is operable to supply a small AC filament voltage to the filaments. The plurality of filament windings and a control winding are loosely magnetically coupled to a resonant inductor of an output circuit of the ballast. A controllably conductive device is coupled across the control winding. When the controllably conductive device is conductive, the voltage across the control winding and the filament windings falls to zero volts. The controllably conductive device is driven with a pulse-width modulated (PWM) signal so as to control the magnitudes of the filament voltages. The filament voltages are provided to the filaments before striking the lamp, and when dimming the lamp near low end.

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European Patent Office, International Search Report and Written Opinion for International Patent Application No. PCT/US2006/046793, Mar. 26, 2007, 10 pages.

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