Zero-Voltage-Switching Two-Switch Forward Converter with Asymmetric Two Transformers

Abstract

In this paper, a zero-voltage switching (ZVS) two-switch forward converter with asymmetric two transformers and an active-clamp circuit is proposed to satisfy wide ZVS range, wide input voltage range and high efficiency requirements. Each transformer acts not only the power transformer but also an inductor during different times of the switching period. The asymmetric two transformers can result in wide ZVS range and reduce the conduction losses in the primary side. The active-clamp circuit can help the transformer reset and recycle the energy stored in the leakage and magnetizing inductances of the transformers. The output capacitances of power switches and the leakage inductance are utilized to realize the ZVS operation for all the switches to reduce the switching losses. Since the proposed converter does not have the duty cycle limitation, the converter is suitable for wide input voltage range. The operating principles and design considerations of the proposed converter are given. Finally, the experimental results of a 300 W prototype are provided to verify the validity of the proposed converter.