As the name suggests, the switching power supply is using electronic switching devices (such as transistors, FET, SCR thyristors, etc.), by the control circuit to make the electronic switching device constantly "on" and "off" so that electronic switching device on the input voltage pulse modulation, in order to achieve DC / AC, DC / DC voltage converter, as well an output voltage adjustable and automatic voltage regulator.

Switching power supply generally has three operating modes: fixed frequency and pulse width mode, fixed frequency and pulse width variable mode, frequency and pulse width variable mode. The former mode of operation is used for the DC / AC inverter or DC / DC voltage converter; the latter two modes of operation are used for the switching power supply. In addition, the switching power supply output voltage also has three operating modes: Direct output voltage mode, average output voltage mode, amplitude of the output voltage mode. Similarly, the former way of working is mostly used in DC / AC inverter or DC / DC voltage converter; the latter two works are used for switching power supply.

According to the connection way of switching device connected in the circuit mode，Switching power supply can be divided into tandem switching power supply, parallel switching power supply, transformer switching power supply and other three categories. Among them, the transformer switching power supply can be further divided into push-pull, half-bridge, full-bridge, and others; According to the transformer excitation and output voltage phase, Can be divided into forward, flyback, single-excited, double excited and so on; if you come from the use, but also can be divided into more categories.