Design of a novel APWM half-bridge DC-DC resonant converter with load-independent soft-switching and reduced circulating current

This paper presents a novel Asymmetrical-Pulse-Width-Modulated (APWM) half-bridge resonant converter with one additional active switching device at the secondary side of the transformer. The proposed converter features load-independent Zero-Voltage-Switching (ZVS) of both of the primary side switches with minimal magnetizing current. Empirical formulae are derived to design the resonant network and the high-frequency transformer systematically. The circulating current is minimized not only by operating the converter exactly at the resonant frequency, but also by reducing the magnetizing current. Moreover, the additional secondary-side switching device (which is a low-voltage and high-current rated MOSFET) achieves zero current turn-off at all load conditions. Thus the efficiency of the overall converter is significantly improved for wide load range. Simulation and experimental results are presented to validate the analysis and to prove the significance of the additional switching device at the secondary side of the transformer.