AC/DC transformation is the conversion of alternating current, the power flow can be two-way, power flows from the power supply to the load known as "rectifier ", power flow by the load back to the power of the so-called "active inverter ". AC/DC converter input for 50/60hz alternating current, because must be rectified, filter, so the relatively large volume of filter capacitor is essential, at the same time because of the safety standards (such as UL, CCEE, etc.) and the limitations of the EMC directive (such as IEC,, FCC, CSA), The AC input side must be added with EMC filtering and using components that meet safety standards, this restricts the size of AC/DC power supply miniaturization, in addition, due to internal high-frequency, high voltage, large current switch action, making it difficult to solve EMC electromagnetic compatibility problem, but also on the internal high-density installation circuit design put forward a very high demand,
Because of the same reason, high voltage and large current switch make the power supply work loss increase, restrict the process of the AC/DC converter modularization, so it is necessary to use the Power system optimization design method in order to achieve a certain degree of satisfaction. AC/DC conversion circuit wiring can be divided into half-wave circuit, full-wave circuit. According to the power supply phase number can be divided into single-phase, three-phase, multiphase. According to the circuit work quadrant can be divided into one quadrant, two quadrants, three quadrants, four quadrants.