Switching Transformer-Based LLC Resonant Converter for Efficiency Improvement in Wide Range of Light Load

Traditional LLC resonant converter takes the rated power as the design requirement to calculate the resonant parameters. Although voltage gain in full load range is guaranteed, the problem of low efficiency under light load is ignored at the same time. This paper proposes a switching transformer-based LLC resonant converter (ST-LLC). Combined with the corresponding strategy of high-frequency transformer switching control, the efficiency of ST-LLC resonant converter is improved, especially in light load conditions. The design procedure of main component parameters is given in detail, and an optimal load partition control strategy is proposed to further broaden the optimized range of light load efficiency. Finally, a prototype about 1kW based on ST-LLC topology was built to verify the proposed scheme. It is shown that the efficiency of the prototype is achieved at 95% maximally, and maintains 90% in 82% of the full load range.