A single-stage high-power-factor dimmable electronic ballast with asymmetrical pulse-width-modulation for fluorescent lamps

A single-stage high-power-factor electronic ballast is designed to drive fluorescent lamps with dimming capability. The circuit configuration is originated from the integration of a half-bridge resonant inverter and a buck-boost converter. The buck-boost converter is designed to operate in discontinuous current mode (DCM) to achieve nearly unity power factor at a fixed switching frequency. With asymmetrical pulse-width-modulation (APWM), the lamp power can be controlled in a wider dimming range. The two power switches of the inverter exhibit zero-voltage-switching (ZYS) and zero-current-switching (ZCS), respectively, over the whole dimming range. Design equations are derived and computer analyses are performed based on a power-dependent lamp model and fundamental approximation. Design guidelines for determining circuit parameters are provided. A prototype circuit for a T8-36W fluorescent lamp is built and tested to verify the analytical predictions.