Resonant LLC DC-DC Converter Employing Fixed Switching Frequency Based on Dual-Transformer with Wide Input-Voltage Range

In this article, a dual-transformer-based LLC resonant converter is proposed, which is a hybrid combination of a full-bridge and half-bridge LLC circuits. The output voltage is regulated through fixed-frequency phase-shift pulsewidth modulation control scheme, whereas the switching frequency is equal to the resonant frequency, which helps to design the magnetic components. The turns-ratio design of the two transformers is analyzed by the current stress and power distribution of both transformers with two different cases. The proposed converter is capable of realizing soft switching over wide input-voltage and whole load range. Finally, a prototype converter of 1 kW is built and the experiments are conducted under wide input-voltage and full load range. The experimental results show that the proposed converter can achieve high efficiency throughout the full load range.