Practical circuit of half-bridge switching power supply

The picture shows a practical circuit of a half-bridge switching regulated power supply. The half-bridge converter is mainly composed of VTl, VT2, T2, C6 and C7. After the control signal is power amplified by VT3 and VT4, it drives the switching tube VT1 through the transformer T1, and the switching tube VT2 is turned on and off alternately. The two ends of the primary coil of T2 are respectively connected to the midpoints of C6 and C7 and the midpoints of VTl and VT2, so it can couple the power signal to the secondary of T2 through VDl6 and VDl7 full-wave rectification and L5, C26 and L6 and C28 Two-stage filtering to output stable DC. The control circuit is mainly composed of three double NAND gate integrated circuits. JD2 is a timer and generates a 20kHz square wave. JD3 and JD4 form two monostable flip-flops, which form a pulse width regulator. The synthesized signal is amplified by VD5 and VT6 and sent to the converter. The error comparison is performed by the integrated circuit JDl. After the output voltage Uo rises (or falls) through the sampling resistor, when the voltage obtained by pin 2 of JDl is higher (or lower) than its threshold, the output pin 6 of the NOT gate 2 of JDl is Correspondingly, it becomes low level (or high level), and this changed voltage is used to control the pulse width regulator to achieve voltage stabilization. The main technical properties of this power supply are as follows: Input voltage: 220V±10%; Voltage frequency: 50~200Hz; Switching frequency: 18~20kHz; Output voltage: 5V; Output current: 0~20A; Voltage stabilizer: 7×100- 3; Load stability: 7×10-3; Temperature drift: <5×10-4/0C; Overcurrent protection: ≤28A; Overvoltage protection: 6V; Efficiency: 60% ~ 70%.