The AC/DC is to transform the communication to DC. Its power flow can be two -way. The power flow is called "rectification" from the power flow to the load. The power flow returns the power supply from the load and is called "active inverter". AC/DC converter input is an AC power of 50/60Hz. Because it must be rectified and filtered, the relatively large filter capacitor is essential. At the same time, due to safety standards (such as UL, CCEE, etc.) and EMC instructions Limitations (such as IEC, FCC, CSA), the AC input side must add EMC filtering and use components that meet the security standards, so as to limit the miniaturization of AC/DC power supply volume. The switching action makes it difficult to solve the problem of EMC electromagnetic compatibility. It also puts forward high requirements on the design of high -density installation circuit in the interior. Due to the same reason, high voltage and large current switches have increased the power consumption of the power supply, limiting AC to AC /DC converter's modular process, so the power system optimization design method must be adopted to make its work efficiency achieve a certain degree of satisfaction.