Switching power supply is a kind of power supply that uses modern power electronics technology to control the principle of switching transistor on and off to maintain stable output voltage. From the composition of the switching power supply, it is mainly composed of two parts: power level and control stage. The main task of power level is to choose different topology according to different applications and requirements, taking into account the design cost of semiconductor components, and the main task of the control level is to choose the appropriate control mode according to the circuit electrical signal, the current switching power supply is mostly in the form of PWM control.