A Soft-Switching Boost-Type Resonant Forward Converter With Load-Adaptive Efficiency Optimization

This paper presents a fully soft-switching resonant forward converter, whose primary side adopts an active-clamp structure to achieve adjustable on-time of the main switch, and the secondary side adopts a boost switch to achieve boost-type voltage gain regulation and high efficiency. Based on proper resonant parameter design, the voltage across the resonant capacitor, as well as the drain-source voltage of the secondary boost switch, can decrease to zero each cycle, allowing zero voltage switching for the boost switch. Therefore, the penalty associated with the widened gain range is alleviated. To further improve efficiency, two optimization schemes are proposed to reduce the conduction loss of the boost switch and the core loss of the forward transformer. The experimental comparison with a conventional structure effectively validates that the proposed converter can achieve better efficiency performance, reduced noise, and lower cost while accommodating a wide input voltage range.