An electronic ballast for driving a gas discharge lamp includes a rectifier to convert an AC mains input voltage to a rectified voltage, a filter circuit for producing a DC bus voltage, an inverter for converting the bus voltage to a high-frequency AC voltage for driving the lamp, an output circuit for supplying an essentially sinusoidal voltage to the lamp, a control circuit for controlling the inverter, and a flyback cat-ear power supply for powering the control circuit. The power supply supplies current to the inverter when the rectified voltage is less than a predetermined level, and draws current only when the inverter is not drawing current directly from the AC mains, so as to make the input current to the ballast substantially sinusoidal. The ballast thus has substantially improved power factor and THD, and operates more efficiently.