A self-excited half-bridge series-resonant ballast with automatic input current shaping

A single-stage electronic ballast for fluorescent lamps with power factor correction and soft switching is presented and analyzed. This circuit utilizes a half-bridge series-resonant power stage to obtain the zero-voltage-switching clamping-voltage merits. The input current waveform is automatically shaped by an additional high-frequency inductor. Near unity power factor can be achieved.