A high power factor electronic ballast of projector lamps with variable frequency control

A variable-frequency electronic ballast to shorten the projector startup transition with feature of power factor correction is proposed in this paper. The circuit topology is composed of a boost converter as 1^st stage and a half-bridge series-resonant parallel-load inverter together with a single-stage step-up igniter as 2^nd stage. A 120 W prototype was built to test and verify the characteristics of the proposed projector lamp ballast at start-up and steady state conditions. It was found that start-up time was reduced by nearly 50% and a high power factor above 0.98 could be achieved. In addition, the power converter is designed to operate at zero-voltage-switching to reduce power losses. Experimental results show good performance, verifying the functionality of the proposed ballast.