A New Soft-Switched DC-DC Buck Converter with Large Step Down Ratio

This paper proposes a new soft-switched dc-dc buck converter with large step-down ratio. The proposed converter uses a switched coupled-inductor to achieve high step-down ratio and a switched resonant-inductor cell for soft-switched transition of the semiconductor devices. The semiconductor switch turns on under ZV-ZCS condition and turns off with ZVS, while the diodes recover softly. The proposed converter is controlled with adaptive pulse frequency modulation (PFM) for soft-switched operation over a wide load range. Performance of the proposed converter has been verified with laboratory scale hardware prototype, rated with 42V-48V input and 5V, 25W output. The experimental results have endorsed the theoretical predictions.