Patent ID: 7489090
Filing Date: 2009-02-10
Classification: H05B

Abstract:
1. An electronic ballast for driving a gas discharge lamp, the ballast comprising: an inverter operable to convert a substantially DC bus voltage to a high-frequency AC voltage having an operating frequency and an operating duty cycle; a resonant tank operable to couple the high-frequency AC voltage to the lamp to generate a present lamp current through the lamp; a control circuit operable to control the operating frequency and the operating duty cycle of the high-frequency AC voltage of the inverter and operable to receive a target lamp current signal representative of a target lamp current; and a current sense circuit operable to provide to the control circuit a present lamp current signal representative of the present lamp current; wherein the control circuit is operable to control the operating duty cycle of the high-frequency AC voltage of the inverter in response to the target lamp current signal and the present lamp current signal; and the control circuit is operable to control the operating frequency of the high-frequency AC voltage of the inverter in response to the operating duty cycle and a target duty cycle, such that the control circuit is operable to minimize the difference between the operating duty cycle and the target duty cycle.