Pulse width modulated dimming arrangement for fluorescent lamps

Abstract

An energy-efficient ballast or energizing circuit for fluorescent lamps which is relatively uncomplicated and which can be manufactured relatively simply and inexpensively. An on-off switch and dimming means are connected in a low-voltage portion of the circuitry to permit less expensive wiring to be utilized. A base-driven, high frequency push-pull transistorized inverter circuit is utilized for energizing the lamps. The inverter drive is pulse width modulated to effect dimming, and to save energy additional transistor circuitry is provided for ensuring rapid turn-on and turn-off of the inverter transistors. A photo-responsive means senses ambient light and lamp light at a surface being illuminated by both and controls pulse width in accordance therewith. Thermostat means are mounted on the heat sinks of the inverter transistors and are connected in parallel with the on-off switch to effect shut-off if overheating occurs.