A Novel Two-Transformer Full-Bridge Converter with Integrated Boost Converter for Hold-Up Time Compensation

This article presents a new full-bridge converter with two series-connected transformers (TTFB), designed to meet the hold-up time requirements in power systems. The conventional TTFB topology offers low root mean square (RMS) output current, clamped voltage stress across the primary switches, and zero-voltage switching (ZVS) capability. However, under a wide input voltage range, it suffers from a significant circulating current during the freewheeling period, leading to efficiency degradation. To mitigate this issue, a new converter is proposed by integrating the TTFB with a boost circuit, which operates during the hold-up state when the input voltage drops below the nominal level. Thus, the proposed converter can increase the duty ratio under nominal input voltage conditions, thereby reducing the primary-side RMS current and improving efficiency. To validate the effectiveness of the proposed method, a prototype with a 12 V/400 W output was implemented. The proposed converter achieved a peak efficiency of 92.1% at 50% load, and maintained a higher efficiency across the entire load range compared to the conventional design. Thus, the proposed converter offers a solution for applications demanding extended hold-up time with improved efficiency.