Patent ID: 7432661

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; a control circuit coupled to the 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 so 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, said ballast power supply coupled to said inverter and operable to provide current to said inverter when said rectified voltage is lower than said predetermined level; wherein said inverter is operable to convert said DC voltage of said ballast power supply to said high-frequency AC drive voltage when said rectified voltage is lower than said predetermined level and to convert said bus voltage to said high-frequency AC drive voltage when said rectified voltage is more than said predetermined level.