A novel constant power control circuit for HID electronic ballast

This paper presents a constant power control circuit for a three-stage high intensity discharge (HID) electronic ballast. The three-stage electronic ballast is composed of a boost pre-regulator to achieve high power factor, a dc-dc buck converter to regulate lamp current with constant lamp power, and a full-bridge inverter to drive the HID lamp with a low frequency ac square wave current. The buck converter operating in current mode utilizes current sense level-shift technique to achieve constant power output. The proposed constant power control circuit is easily designed and implemented for the three-stage HID electronic ballast. Finally, a laboratory prototype of a 70-W HID electronic ballast is implemented. The measured results show that the proposed ballast can be applied for various HID lamps with low lamp power variation (less than 0.6%).