Interleaving Controlled Three-Leg Electronic Ballast for Dual-HID-Lamps

This paper presents a novel electronic ballast for dual high-intensity-discharge (HID) lamps. The electronic ballast is composed of a boost preregulator to achieve high power factor and a three-leg inverter to drive two HID lamps. One leg of the inverter is operated at a low frequency with a 50% duty ratio to drive the HID lamps with low-frequency square-wave current in order to avoid acoustic resonance. The other two legs of the inverter are operated at a high frequency to modulate the lamp current with constant lamp power. Also, interleaving control is applied to the high-frequency legs to decrease the current stress on the low-frequency leg. To verify the feasibility of the proposed methodology, a laboratory prototype is implemented to drive two 35-W HID lamps. The overall efficiency of the proposed electronic ballast is about 90%.