Two-Transformer Phase-Shift Full-Bridge Converter With a New Rectifier for Reducing Conduction Loss

A two-transformer phase-shift full-bridge (PSFB) converter has features of zero-voltage switching (ZVS) capability, clamped voltage stress of the primary switches, and small RMS current. However, when a wide input voltage range is required, the two-transformer PSFB converter operates with extended freewheeling mode. As a result, a large freewheeling current is reflected on the primary side, and it increases the primary RMS current. In addition, the freewheeling current flows through high voltage rating diodes, resulting in a large conduction loss. To mitigate this problem, a two-transformer PSFB converter with a new rectifier is proposed in this article. By employing a diode in the secondary side, the proposed converter reduces the conduction loss. This is because the path of the output current is changed to the freewheeling diode having a low voltage stress. As a result, the proposed converter can use a low voltage rating diode with a low forward voltage drop. In addition, it eliminates the circulating current in the primary side, which reduces the RMS current. Therefore, the proposed converter achieves a high efficiency by reducing the conduction loss. The proposed converter has been verified for a laboratory prototype with 300–400 V input and 12 V/400 W output.