High-efficiency electronic transformer for low-voltage halogen lamp

Low-power dichroic halogen lamps, usually used for display lighting, have low-voltage filaments. The lightweight electronic transformer (ET), based on self-oscillating half-bridge high frequency inverters, are used to replace bulky and heavy conventional 50/60 Hz step-down transformers. However, their lamp currents are rectangular-like in shape, leading to generation of high electromagnetic noise and increased transformer core losses. This paper proposes a new, near sine lamp current, electronic transformer using class-D zero-voltage-switching (ZVS) inverter. The experimental results from a 50 W/12 V prototype show that efficiency is greater than 92% with unity power factor. Moreover, the dimmable feature and controlled starting current can be achieved by simply increasing the switching frequency without increasing the switching loss.