Phase-shifted full-bridge switching power supply module circuit design

　　This soft switching power supply adopts a full-bridge converter structure and uses MOSFET as a switch tube with a parameter of 1000V/24A. It adopts phase-shifted ZVZCSPWM control, that is, the leading arm switch tube realizes ZVS and the lagging arm switch tube realizes ZCS. The circuit structure diagram is shown in Figure 1. VT1~VT4 are four MOSFET switch tubes of the full-bridge converter. VD1 and VD2 are the reverse-parallel ultra-fast recovery diodes of the leading arm switch tubes VT1 and VT2 respectively. C1 and C2 are high frequencies set to realize ZVS of VTl and VT2 respectively. VD3 and VD4 are reverse current blocking diodes used to realize ZCS of lagging arms VT3 and VT4. Llk is the transformer leakage inductance, Cb is the blocking capacitor, T is the main transformer, and the secondary side is composed of a high-frequency rectifier circuit composed of VD5~VD8 and filter components such as Lf, C3, and C4.

　　Circuit principle: When the switch tubes VT1, VT4 or VT2, VT3 are turned on at the same time, the circuit works in the same way as the hard switch working mode of the full-bridge converter, and the primary side of the main transformer provides energy to the load. Through phase shift control, VT4 is not turned off immediately when VT1 is turned off, but the phase shift angle is determined according to the output feedback signal, and VT4 is turned off after a certain period of time. Before turning off VT1, since VT1 is turned on, the voltage on its parallel capacitor C1 is equal to the conduction voltage drop of VT1, and its value is zero under ideal conditions. When VT1 is turned off, C1 starts to charge. Since the capacitor voltage cannot change suddenly, VT1 is turned off at zero voltage. Due to the role of the transformer leakage inductance L1k and the secondary side rectifier filter inductor, after VT1 is turned off, the primary current cannot change suddenly, and Cb continues to be charged. At the same time, C2 is also discharged through the primary side. When the voltage of C2 drops to zero, VD2 is naturally turned on. At this time, VT2 is turned on, and VT2 is turned on at zero voltage. When C1 is fully charged and C2 is discharged, since VD2 is turned on, the voltage applied to the primary winding and leakage inductance of the transformer is the voltage across the blocking capacitor Cb, and the primary current begins to decrease, but Cb continues to be charged until the primary current is zero. At this time, due to the blocking effect of VD4, capacitor Cb cannot be discharged through VT2, VT4, and VD4, and the voltage across Cb remains unchanged. At this time, the current flowing through VT4 is zero, and turning off VT4 is zero current shutdown.