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 th e fluorescent lamp in a wide dimmable range. The electronic ballast with an embedded buck-boost converter can effectively regulate tile lamp power by asymmetrical pulse-width-modulation. With carefully designed circuit parame ters, the proposed electronic ballast can achieve a high power factor by op erating the buck-boost converter at discontinuous conduction mode operation , and high efficiency by controlling the active switches operated at either zero-voltage switching or zero-current switching over the whole dimming ra nge. Design equations are derived and computer analyses are performed based on fundamental approximation and a power-dependent lamp model. A prototype circuit for a T8-36W fluorescent lamp is built and tested to verify the an alytical predictions.