AC-DC switching power supply is the use of transistors, field effect tubes, thyristor and other electronic switching devices, through the control circuit, so that the electronic switching device is constantly "on", "off", so that the electronic switching device pulse modulation of the input voltage, so as to realize the voltage conversion between AC-DC, and automatically regulate the output voltage. Ac-dc power chip AC conversion is to convert AC into DC, its power flow can be bidirectional, when the power flow from the power supply to the load is called "rectification", when the power flow from the load back to the power supply is called "active inverter". The converter input 50/60 AC, because it must be rectified, so the relatively large AC capacitor is necessary, and because of the safety standards (such as UL,CCEE, etc.) and EMC directive restrictions (such as IEC,FCC,CSA), the AC input side must be equipped with EMCU and use components that meet the safety standards. In this way, the AC/MCU capacity is small. AC-DC switching power supply function: 1. Adjust the output voltage and keep it consistent so that the output voltage is stable. 2. Simplify circuit design and improve reliability;