Patent ID: 8299723

Claim:
An electronic ballast comprising: a power converter arranged to receive DC power input thereto and to convert said DC power input into an AC power output; a resonant circuit coupled with a discharge lamp and further coupled between output terminals of the power converter; and a controller configured for controlling the power converter with respect to a mode of operation, wherein the controller in a starting operation is configured to set the output frequency of the power converter to a predetermined start frequency upon starting the discharge lamp to make the discharge lamp begin discharging, and the controller is further configured to shift from the starting operation to a steady-state operation by setting the output frequency of the power converter at a predetermined steady-state frequency lower than the start frequency, the steady-state operation providing alternating current power to the lamp for maintaining lighting of the lamp, wherein the predetermined start frequency is set to a frequency identical or close to 1/(n) of the resonant frequency of the resonant circuit with the discharge lamp unlit, and also to a frequency identical or close to the resonant frequency of the resonant circuit with the discharge lamp lit, wherein (n) is an odd whole number greater than or equal to five, and wherein the resonant frequency of the resonant circuit with the discharge lamp unlit is greater than or equal to five times the resonant frequency of the resonant circuit with the discharge lamp lit, and wherein the predetermined start frequency is set to a frequency sufficient to make the discharge lamp start discharging, and to a frequency sufficient to raise a temperature of each electrode of the discharge lamp after startup of the discharge lamp and by an end of the starting operation.