Modern switching power supplies are divided into two types: DC switching power supply and AC switching power supply. The former outputs high-quality direct current, and the latter outputs high-quality alternating current. The core of the switching power supply is the AC-DC converter. The converter is a device that uses power electronics to convert one type of electrical energy into another or multiple forms of electrical energy. According to the type of converted electrical energy, it can be divided into four types: 1. DC a DC converter, which is a converter that converts one DC power into another or a plurality of DC power, is a main component of a DC switching power supply; 2. An inverter is a power exchanger that converts DC power into AC power. It is the main component of the AC switching power supply and the uninterruptible power supply UPS; 3. The rectifier is the electric energy converter that converts the alternating current into the direct current; 4. The crossover is the direct conversion of one frequency of alternating current to another constant frequency. Or variable frequency AC, or a power converter that converts variable frequency AC directly into constant frequency AC. These four types of converters can be either single-row or bidirectional. The unidirectional power converter can only say that the electric energy is input from one direction and converted from the other direction; the bidirectional electric energy converter can realize the bidirectional flow of electric energy.