Half-bridge converter power circuit

Among high-voltage switching power supplies, those with large power output generally use half-bridge converter circuits. Its circuit is shown in the figure. It consists of two capacitors and two high-voltage transistors. When both transistors are turned off, if the capacitances of the two capacitors are equal and the circuit is symmetrical, the voltage at the midpoint A of the capacitor is half of the input voltage. When VTl is turned on, capacitor C01 will be discharged through VTl and the primary winding N1 of the transformer; at the same time, capacitor C02 will be charged through the input power supply, VTl and the primary winding N1 of T1. The potential of midpoint A will decrease exponentially during the charging and discharging process. At the end of VTl conduction, the potential of point A is (1/2) Ui-ΔUi, and both transistors are turned off. The voltages between the collectors and emitters of the two capacitors and the two transistors are basically equal, both close to half of the input power supply voltage. On the contrary, when VT2 is turned on, C02 is discharged and C0l is charged, and the potential of point A will increase to (1/2) Ui + ΔUi, that is, the potential of point A will be at the potential of (1/2) Ui during the switching process. The amplitude of ±△U changes exponentially. It can be seen that in the half-bridge circuit, current flows through the primary coil of the transformer throughout the cycle, and the core is more fully utilized. The main advantage of the half-bridge converter circuit is that the power switching transistor used in the circuit has a low withstand voltage and will never exceed the peak value of the input voltage; the saturation voltage of the transistor is also reduced to a minimum; the withstand voltage of the input filter capacitor is also reduced. can be reduced. However, because the voltage amplitude applied to the high-frequency transformer is only half of the input voltage, compared with the push-pull circuit, in order to output the same power, the transformer switch must flow twice as much current.