Patent ID: 8143796

Claim:
An electronic ballast comprising: a power converting circuit further comprising a plurality of switching elements and configured to receive DC power from a DC power source and output AC power to a discharge lamp; a starting circuit connected between output ends of the power converting circuit, and configured to generate a high voltage for starting the discharge lamp; a half-wave discharge detecting circuit configured for detecting an absolute value for each polarity peak of a current across the lamp, calculating an asymmetrical current value from the detected peaks and with respect to a predetermined current threshold, and detecting a half-wave discharge of the lamp wherein an absolute value of the asymmetrical current value is equal to or more than the current threshold for a predetermined determination time or longer; and a control circuit configured for controlling the switching elements of the power converting circuit in accordance with each of a starting operation wherein the starting circuit generates a high voltage and starts the lamp, a steady state operation wherein the power converting circuit outputs AC power for maintaining lighting of the discharge lamp, an filament heating operation wherein the power converting circuit provides an output frequency higher than that in steady state operation for heating each filament of the discharge lamp; wherein the control circuit is further configured to perform a half-wave control process for reducing a half-wave discharge detected by the half-wave discharge detecting circuit during the filament heating operation and prior to steady-state operation.