Due to the trend to higher power and smaller volume, 22-kW on-board chargers with integrated planar magnetics have become more and more popular recently. CLLC converters are widely used in the DC-DC stage because of their isolation ability and high efficiency. However, several challenges remain because of this trend. The first one is to integrate the resonant inductance into the transformer for higher power density. The second one is the high current stress induced by the high power. Therefore, the integration of the planar inductor and transformer and the current distribution between the parallel transformers are analyzed in this paper. At last, a transformer with naturally perfect current sharing and built-in resonant inductance is developed in this paper. The concepts are verified in a 22-kW CLLC resonant converter with PCB based silicon-carbon (SiC) devices. Because of the planar devices and transformers, the converter can reach 10.3 kW/L power density and 98.4% peak efficiency.
