A Control Method for the Problem of Losing the ZVS in CCM Mode LLC Converter Caused by Rectifier Parasitic Capacitance

In recent years, the power consumption of data center and communication equipment has increased rapidly. LLC resonant converter is widely used in the DC-DC power conversion part of high efficiency and high power density communication power supply. Si MOS devices are widely used as the synchronous rectifier of LLC converter. However the parasitic junction capacitance will affect the realization of the primary zero-voltage switching (ZVS). To solve this problem, this paper considers that the main reason for losing the primary ZVS is that the resonant current decreases and crosses zero in advance due to the rectifier parasitic capacitance voltage converting process, and proposes an asymmetrical dead time control method for the CCM mode LLC converter. By appropriately giving unequal dead time in one switching period, the problem can be solved without adjusting the hardware design. The experimental results show that the proposed control method can effectively solve the problem of losing the primary ZVS and significantly improve the efficiency of the converter.