The switching power supply is to obtain a high-voltage DC voltage (DC=1.4AC) after the input AC voltage (AC) is rectified and filtered. This voltage is connected to the switching element and used as a switch in the high-frequency state of 20KHZ~100KHZ. At this time, the DC high voltage will be cut into a high-frequency square wave signal. This square wave signal can obtain the preset voltage value at the secondary side through the power type NTC thermistor, and then obtain the required DC output voltage through rectification and filtering.
After NTC thermistor completes the function of suppressing surge current, the resistance value of power type NTC thermistor will drop to a very small extent due to the continuous action of its current, and the power consumed by it can be ignored, which will not affect the normal working current. Therefore, using power type NIC thermistor in the power circuit to suppress the surge during startup is the most simple and effective measure to protect electronic equipment from damage.