EXTERNALLY DIMMABLE ELECTRONIC BALLAST

摘要

An electronic ballast includes a converter coupled to a variable frequency inverter and a series resonant, parallel loaded output coupled to the inverter. The frequency of the inverter increases when the supply voltage from the converter decreases. The converter includes a full wave rectifier (17) producing a first voltage and an unregulated boost circuit (Q1, Q2) producing a second voltage which is combined with the first voltage to produce the supply voltage. The amount of boost, and therefore the magnitude of the supply voltage, is varied to provide dimming. Dimming is controlled mechanically, via a potentiometer (126), or electrically, via a control input (132). Dimming also occurs in response to changes in the first voltage, i.e. from changes in the voltage on an AC power line or from changes in the voltage provided by a capacitive dimmer coupled between the ballast and an AC power line.