An electronic ballast with multi-step constant-power starting control for small-wattage metal halide lamps

This paper develops an electronic ballast with multi-step constant-power control for small-wattage metal halide (MH) lamps supplied from a dc power source. The ballast circuit consists of a buck-boost/fly-back conversion circuit and a half-bridge inverter with commonly used two capacitors. The starting scenario with multi-step constant-power, can limit the starting current at relatively low levels, and can run up the transient period faster as compared to that started by a constant current. A laboratory circuit is designed for 35 W MH lamps. Experimental results have demonstrated satisfactory performances. A circuit efficiency higher than 91% is achievable.