Two-transformer-based full-bridge soft-switching DC-DC converter with improved characteristics

A novel two-transformer-based full-bridge soft-switching DC-DC converter is proposed. The primary-windings of the two transformers are connected in series, while the two secondary windings of the two transformers are connected to the output through a semi-active full-bridge rectifier and a passive full-bridge rectifier, respectively, in parallel. The voltage stress on the primary windings of the transformers is reduced, as well as the current stresses of the secondary windings of the transformers and the rectifying devices. Zero-voltage-switching is realised for the MOSFETs, while zero-current switching is achieved for all the diodes by adopting the secondary side phase-shift control. In comparison with existing topologies, the turn-off current and loss of the secondary side MOSFETs are reduced, because only half of the output current flows through these switches. The circulating current is effectively suppressed, which leads to less conduction loss. The proposed converter also offers some advantages, such as smaller value and size of high-frequency-link inductor and reduced output current ripple. The converter can operate in the buck and boost modes to fulfil the application demands with wide input/output voltage ranges. The operating principle of the proposed converter is analysed in detail and verified with experimental results.