Patent ID: 8294385

Claim:
An electronic ballast comprising: a rectifier circuit coupled to receive an AC power signal and rectify said AC signal into a rectified DC signal; a DC step-up chopper circuit coupled to said rectifier circuit and arranged to convert the rectified DC signal into a desired DC output signal; an inverter circuit coupled to the DC chopper circuit and further comprising a plurality of switching elements for converting said DC output signal into a rectangular wave AC signal and supplying the AC signal to a high pressure discharge lamp; a starting circuit including an LC resonant circuit, the starting circuit arranged to generate a starting voltage sufficient for producing electrical breakdown of the high pressure discharge lamp; and a control circuit configured for controlling on/off positions for said switching elements dependent on an operating mode, the control circuit further configured to shift operation of the starting circuit and the inverter circuit among at least three operating modes comprising an electrical breakdown mode for producing electrical breakdown of the high pressure discharge lamp, a high frequency preheat mode for supplying a preheat current to the high pressure discharge lamp and preheating lamp electrodes, and a rectangular wave lighting mode for supplying the rectangular wave AC to the high pressure discharge lamp to maintain steady state lighting of the high pressure discharge lamp, wherein the control circuit in the electrical breakdown mode is further configured to control at least one of the switching elements to switch on and off around a first switching frequency which is 1/(n) of a resonant frequency of the LC circuit at no load, wherein (n) is an odd integer, and further wherein a first voltage is generated that is sufficient for starting the lamp, and wherein the control circuit in the high frequency preheat mode is further configured to control at least one of the switching elements to switch on and off around a second switching frequency which is 1/(n) of the resonant frequency of the LC circuit at no load, wherein (n) is an odd integer, the second switching frequency lower than the first switching frequency, wherein a second voltage is generated that is effective for restarting the lamp.