High efficiency electronic lamp ballast with unity power factor

A soft-switched single-phase AC/AC power converter for a high-frequency electronic ballast is presented which includes one controlled switch only. In spite of its simplicity, the power converter provides high-frequency lamp current with small amplitude fluctuations, lamp power control, low-distorted and in-phase input current, and high efficiency due to soft switching both at turn-on and turn-off. Two different circuit topologies, suitable for discontinuous and continuous current operation, are presented. Their behaviour is analyzed and design criteria are given. Simulated and experimental results are reported, showing the actual circuit performance in terms of lamp behavior, AC power factor, and efficiency.