Patent ID: 7288898

Claim:
An electronic for driving a high intensity discharge (HID) lamp, the electronic ballast comprising: a voltage boost stage for receiving a DC input voltage and outputting a boosted DC output voltage with a controlled current; a switching stage for converting said boosted DC output voltage to a switched AC voltage which is capable of driving the HID lamp; an IC controller coupled to the voltage boost stage and the switching stage for controlling both, wherein the IC controller includes: a circuit for setting ON time and OFF time of a PWM signal, the PWM signal increasing or decreasing the boosted DC output voltage current by controlling a controlled switch of the voltage boost stage in accordance with the set ON and OFF times; a driver for providing control signals to the switching stage, the switching stage being provided with said boosted DC output voltage and providing AC power to the HID lamp; a lamp power control circuit comprising a sensing circuit for sensing an output current from the switching stage and the boosted DC output voltage; and a circuit for setting a duty cycle of said PWM signal thereby to control either or both the ON-time or the OFF-time of said controlled switch, said circuit being responsive to said output current and said boosted DC output voltage for controlling the power provided to said lamp.