"Soft start" circuit diagram of DC switching power supply

This article introduces the " soft start " circuit diagram of a DC switching power supply . As shown in the figure (a) below, at the moment when the power is turned on, the input voltage charges the capacitor C through the rectifier bridge (D1~D4) and the current limiting resistor R1 to limit the inrush current. When the capacitor C is charged to approximately 80% of the rated voltage, the inverter operates normally. The thyristor trigger signal is generated through the auxiliary winding of the main transformer , causing the thyristor to conduct and short-circuit the current limiting resistor R1, and the switching power supply is in normal operation. In order to improve the accuracy of the delay time and prevent the relay from jittering and oscillating, the delay circuit can use the circuit shown in Figure (b) instead of the RC delay circuit.