Power-factor correction circuit of electronic ballast for fluorescent lamps

Abstract

A power-factor correction circuit of an electronic ballast for fluorescent lamps which includes an input full-wave rectification circuit for full-wave rectifying an AC input voltage from an AC input power source, a DC-link capacitor for supplying a DC-link voltage in response to an output voltage from the rectification circuit and a resonant inverter connected in parallel to the DC-link capacitor. The power-factor correction circuit comprises a charge pumping circuit disposed between the AC input power source and the rectification circuit, a valley-fill DC voltage supply circuit disposed between the rectification circuit and the DC-link capacitor, and a high-frequency full-wave rectification circuit disposed between the DC voltage supply circuit and the DC-link capacitor and connected to a secondary winding of a power transformer in the resonant inverter. The high-frequency full-wave rectification circuit includes a first pole connected to the secondary winding of the power transformer and a second pole connected to a common connection point of a plurality of stabilizing capacitors connected in series respectively to the fluorescent lamps. Therefore, a power factor of the ballast is improved and power supply is automatically controlled according to the number of fluorescent lamps being turned on.