High-efficiency electronic transformer for low-voltage halogen lamp

Low-power dichroic halogen lamps, usually used for display lighting, have low-voltage filament. The lightweight electronic transformer (ET), based on self-oscillating half-bridge high frequency inverter, are used to replace bulky and heavy conventional 50160 Hz step-down transformer. But their lamp current are rectangular like shape, leading to generate high electromagnetic noise and increase 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 5OW/12V prototype show the efficiency is greater than 92% with unity power factor. Moreover, the dimmable feature and controlled starting current can be achieved by simply increase the switching frequency without increasing the switching loss.