Patent ID: 8067902

Claim:
An electronic ballast for driving a gas discharge lamp having first and second electrodes with a lamp current between the electrodes, the ballast comprising: an inverter circuit having an input for receiving a substantially DC bus voltage and first and second output terminals, the inverter circuit further comprising a main transformer having a primary winding coupled between the first and second output terminals, the primary winding having a center tap coupled to the DC bus voltage at the input, the inverter circuit operable to convert the bus voltage to a high-frequency AC voltage across the primary winding of the main transformer of the inverter circuit; and a symmetrical resonant tank circuit operable to couple the high-frequency AC voltage to the lamp to drive the lamp with the lamp current, the resonant tank circuit comprising: a split resonant inductor having first and second windings magnetically coupled together, the first winding adapted to be electrically coupled between the first output terminal of the inverter circuit and the first electrode of the lamp, the second winding adapted to be electrically coupled between the second output terminal of the inverter circuit and the second electrode of the lamp, the first and the second windings each having an output terminal across which output terminals an output of the resonant tank circuit is formed, such that the first and second windings are adapted to couple the high-frequency AC voltage of the inverter circuit to the electrodes of the lamp to drive the lamp with the lamp current; and first and second resonant capacitors coupled in series electrical connection, the series combination of the first and second resonant capacitors coupled across the output of the resonant tank circuit; wherein the junction of the first and second resonant capacitors is coupled to the center tap of the primary winding of the main transformer of the inverter circuit.