Patent ID: 7863827
Filing Date: 2011-01-04
Classification: H05B

Abstract:
1. A method of controlling an oscillator of a high frequency ballast to drive a metal halide lamp at a constant power, said method comprising: monitoring a voltage of the oscillator, wherein the voltage is a direct current (DC) voltage provided to the oscillator by an alternating current (AC) to DC converter of the ballast; monitoring a current of a power supply loop of the oscillator driving the lamp; operating the oscillator at a first frequency during ignition of the lamp and operating at the first frequency or a second frequency following ignition, wherein the second frequency is different than the first frequency; determining a duty cycle as a function of the monitored current and voltage, wherein the duty cycle indicates a percentage of a given time period during which the oscillator is to operate at the first frequency versus operating at the second frequency; and switching the oscillator between the first frequency and the second frequency as a function of the determined duty cycle.