Application of Cascode GaN HEMT in LLC Soft Switching Converter

After decades of development, the performance of Si-based power switching devices is approaching its material limits. The power electronic converter is limited to further growth in the direction of high frequency, high efficiency, and high power density. As an outstanding representative of the third generation of wide bandgap semiconductor devices, the cascode GaN HEMT utilizes a cascode structure to achieve the normally-off nature of GaN devices, with unmatched steady-state and dynamic performance of Si-based devices. In order to promote its replacement of Si devices and give full play to the performance advantages, the cascode GaN HEMT is applied to the soft-switching topology of the LLC resonant converter in this paper. The relationship between the output capacitance and the dead-time of the switching device is analyzed. The effects with root mean square values of the first and second side currents are also considered. Taking advantage of the small output capacitance of the cascode GaN HEMT, the circulating current of the converter is reduced, which leads to further reduction of the conduction and transformer loss. Thus, the efficiency of the converter is improved. An LLC converter with 97% maximum efficiency and 96.2% total load efficiency was built to prove the correctness and effectiveness of the analysis.