A Non-Resonant ZVS Four-Switch Flyback Converter

The four-switch flyback (FSF) converter has the advantages of low switch voltage stress and zero-voltage-switching (ZVS) with the leakage inductance energy. However, if the clamping capacitor is too small, its voltage will oscillate, and the negative magnetizing current for realizing ZVS is difficult to be accurately obtained since it is generated by resonance. In this article, the clamping capacitor is intentionally designed quite large so that its voltage keeps nearly constant. The resultant converter is called nonresonant ZVS FSF converter. The operating principle of the converter is analyzed, and the method to accurately control the negative magnetizing current is proposed, which not only minimizes the magnetizing current ripple, but also realizes ZVS for all the power switches. Finally, a 400-W prototype is built and tested in the lab, and experimental results are provided to verify the operating principle of the FSF converter and the proposed control method.