A secondary-side phase-shift-controlled soft-switching DC/DC converter utilizing two transformers with wide voltage gain for high step-down applications

A soft-switching DC-DC converter with secondary-side phase-shift control strategy is proposed for applications requiring wide voltage range and isolated step-down power conversion such as battery charger. Two transformers and a three-leg hybrid rectifier (one MOSFET-leg and two diode-legs) are employed. The primary windings of the two transformers are in-series and the secondary windings are in parallel. Zero voltage switching is achieved for both the primary- and secondary-side power MOSFETs while zero current switching is achieved for the secondary-side diodes in a wide load range. Leakage inductance of the transformers is utilized for power transferring. The voltage stresses of all the devices are clamped automatically. Besides, the converter can operates in the buck, balance and boost modes to achieve a relatively wide input or output voltage range. The secondary-side rectifier can be extended to multiple transformers configuration for high step-down applications. The operation principles are analyzed and experimental results of a 1-kW 100-kHz prototype are provided to verify the effectiveness of the proposed converter.