Push-pull switching regulated power supply schematic diagram

The push-pull converter circuit is a double-terminal conversion circuit. Its high-frequency transformer works on both sides of the hysteresis loop. It is a circuit with simple design and reasonable operation, and has a wide range of applications. Its typical circuit is shown in the figure. The switching transistors VTl and VT2 are alternately turned on and off by the base drive circuit, and the input DC voltage Ui is converted into a high-frequency square wave AC voltage. When VTl is turned on, Ui is added to the primary winding N1 of transformer T1 through VTl. Due to the action of the transformer, the cut-off transistor VT2 will be applied to 2 times the input voltage, that is, 2U;. When the base excitation disappears, both VTl and VT2 tubes are cut off. The voltage applied by its collector is the input voltage Ui. In the second half of the cycle, VT2 is turned on, VTl is turned off, VTl applies 2 times the input voltage, then the two tubes are turned off, and the next cycle starts again. The main disadvantage of the push-pull circuit is that the switching transistor's withstand voltage must reach 2 times the input power supply. For the peak voltage, taking the grid voltage of 220±10%V as an example, the maximum steady-state cut-off voltage is 680V. Adding the peak voltage during the dynamic process, the switching transistor must withstand a voltage of more than 800V.