A new LLC resonant converter with resonant frequency change for high conversion efficiency and high power density

A LLC resonant converter is a converter, which achieves Buck or Boost gain with Pulse Frequency Modulation, and it is a suitable topology for high power density. This LLC resonant converter has many advantages, such as wide soft-switching range, high switching frequency capability, and low voltage stress of active devices, however, it also has large RMS current and circulating current. From these results, the usage of LLC resonant converter had been limited in low voltage and high current output applications. In this paper, a new LLC resonant converter, which can achieve high conversion efficiency while maintaining high power density, is proposed. Since the proposed converter can be reduced the conduction loss and turn-off loss by large magnetizing inductance, it can achieve higher conversion efficiency than the conventional converter. In addition, in order to regulate the output voltage, the proposed converter changes the resonant frequency using the small size of auxiliary circuit under hold-up time condition. Therefore, the proposed converter is a topology that can satisfy both high conversion efficiency and high power density.