Design and implementation of an LLC resonant converter with saturable resonant inductor

An LLC resonant converter with saturable resonant inductor, which could reduce obviously switching frequency changes and enhance the extreme light-load efficiency, is proposed in this study. The LLC resonant converter is operated with variable frequency that the switching frequency is extremely high and the conversion efficiency is lower when operating in light-load. For reducing the light-load switching frequency, it would be lower in full-load that the magnetic component design would be difficult and does not present economical benefits. In this case, a saturable resonant inductor is proposed in the paper. When operating in light-load, the resonant tank appears larger resonant inductance that the resonant frequency is low and the switching frequency is lowered. On the contrary, the additional resonant inductor being saturated in high-load, the resonant and switching frequencies are increased. As a result, light and high loads efficiencies would be taken into account and the switching frequency variation would be reduced.