Patent ID: 7825609

Claim:
An electronic ballast for driving a gas discharge lamp, said ballast drawing an input current from an AC power supply, said ballast comprising: a rectifier for rectifying an AC input voltage from said AC power supply to produce a rectified voltage; a filter circuit for converting said rectified voltage to a filtered bus voltage; an inverter for converting said bus voltage to a high-frequency AC drive voltage to drive said lamp; an output circuit for filtering said high-frequency AC drive voltage in order to supply an essentially sinusoidal voltage to said lamp; a control circuit coupled to said inverter for controlling the operation of said inverter; and a ballast power supply coupled to receive said rectified voltage for selectively drawing current from said AC power supply when said rectified voltage is lower than a predetermined value such that said input current to said ballast is essentially sinusoidal, said ballast power supply operable to generate a substantially DC voltage for powering said control circuit; wherein said ballast power supply is coupled to said inverter and is operable to provide current to said inverter when the magnitude of said rectified voltage is less than said predetermined value.