The principle of switching power supply is to convert alternating current (AC) into direct current (DC), and then control the output voltage and current size through switching control circuit. The principle of switching power supply is to convert alternating current into direct current, and then control the output voltage and current size by switching control circuit. The output voltage and current of the switching power supply can be adjusted by changing the on and off time of the switch, so as to achieve the purpose of regulating the output voltage and current.