Zero-Voltage Switching Two-Transformer Full-Bridge PWM Converter with Lossless Diode-Clamp Rectifier

Abstract

The two-transformer full-bridge (TTFB) PWM converter has series-connected two transformers which act as an output inductor as well as a main transformer, i.e. as the forward and the flyback transformer. Although the doubled leakage inductor of two-transformer makes it easier to achieve the zero-voltage switching (ZVS) of the lagging leg switch along the wide load range, it instigates a serious voltage ringing across the output rectifier diodes, which would require the dissipative snubber circuit, cause the serious power dissipation, and increase the voltage stress across those diodes. To overcome these problems, a new lossless diode-clamp rectifier (LDCR) is employed as the output rectifier, which helps the voltage across rectifier diodes to be clamped on a half the output voltage (Vo/2) or the output voltage (Vo). Therefore, no dissipative snubber for rectifier diodes is needed and a high efficiency as well as low noise output voltage can be realized. The operations, analysis and design consideration of proposed converter are presented in this paper. Also, a 425W, 385-170Vdc prototype is constructed and experimental results verified the validity of the proposed converter.