Soft-switching and low-conduction loss full-bridge converter with auxiliary circuit for battery charging applications

Traditional phase-shift full-bridge (PSFB) converters have the problems of a narrow zero-voltage switching (ZVS) range, a large circulating current, and voltage oscillation. A PSFB converter with novel auxiliary circuits is proposed to solve these problems for a wide voltage output charging application. A simple passive circuit is connected to the primary tap of a transformer with unbalanced magnetic windings, which can provide two differentiated constant triangular currents for ZVS of the leading and lagging legs in the full-load range. Thus, both the external series large inductance and the duty cycle loss are avoided. In addition, the introduced reactive loss is reduced. Meanwhile, a center tap clamping circuit is added on the secondary side. The leakage inductance of the transformer is fully utilized to resonate with the clamping capacitor. Hence, reductions in the voltage stress of the rectifier diode and circulating current can be achieved. A circuit steady-state analysis of the three modes of the proposed converter is carried out. When compared with the conventional PSFB converter, the proposed converter improves efficiency and reduces the filter requirements. A 100 kHz/1.05 kW prototype is established to verify the theoretical analysis.