Isolated High-Voltage-Gain Full-Range Soft-Switching DC/DC Converter Using Built-In Transformer and Coupled Inductors With Minimum Design Constraints

We propose an isolated high-voltage-gain full-range soft-switching DC/DC converter, incorporating a built-in transformer (BT) and coupled inductors (CLs), with minimal design constraints of magnetic components for achieving zero-voltage switching (ZVS) operation. A state-plane trajectory analysis is adopted to evaluate the ZVS conditions of main switches, providing precise ZVS boundaries and an exact dead-time margin. On the primary side, the proposed converter employs an interleaved interface utilizing CLs to reduce input current ripple and increase voltage gain. An active-clamping technique with the BT is also implemented to realize full-range ZVS operation with minimal constraints. On the secondary side, a voltage doubler configuration easily doubles the voltage gain. Moreover, the equivalent inductance reflected from the BT and CLs, together with the output capacitors of the main switches, enables zero-current switching (ZCS) of rectifier diodes, thereby mitigating reverse-recovery problems. A 400 W prototype, operating with input voltage of 26–34 V and output voltage of 400 V, is fabricated and evaluated to verify the effectiveness of the proposed converter.