Three-Switch Active-Clamp Forward Converter With Low Switch Voltage Stress and Wide ZVS Range for High-Input-Voltage Applications

In low-to-medium power applications, an active-clamp forward (ACF) converter is popular for its simple structure and zero-voltage switching (ZVS) capability. However, the high voltage stress on switches can be a burden in high-input-voltage applications. To relieve this, a three-switch ACF (TS-ACF) converter, which employs two main switches for a forward converter and one auxiliary switch for an active-clamp circuit (ACC), is proposed in this paper. With a repositioned ACC, all the switches of TS-ACF converter have relatively low voltage stress compared to the conventional one. In addition, one of the main switches always ensures ZVS during the transformer reset. Consequently, the TS-ACF converter can be promising for high-input-voltage applications with high efficiency.