Switching mode power supply, also known as switching power supply and switching converter, is a high-frequency electric energy conversion device and a kind of power supply. Its function is to convert a standard voltage into the voltage or current required by the user through different forms of architecture. The input of switching power supply is mostly AC power supply (such as mains power) or DC power supply, while the output is mostly equipment requiring DC power supply, such as personal computer, and switching power supply converts the voltage and current between the two.

Switching power supply is different from linear power supply. Most of the switching transistors used by switching power supply are switched between fully open mode (saturation zone) and fully closed mode (cut-off zone). Both modes have the characteristics of low dissipation. The conversion between switching will have high dissipation, but the time is very short. Therefore, it saves energy and produces less waste heat. Ideally, the switching power supply itself will not consume electric energy. Voltage stabilization is achieved by adjusting the on and off time of the transistor. On the contrary, when the linear power supply generates the output voltage, the transistor works in the amplification region and will consume electric energy itself. The high conversion efficiency of switching power supply is one of its advantages. Moreover, because the switching power supply has high working frequency, small-size and light-weight transformers can be used. Therefore, the switching power supply will be smaller and lighter than the linear power supply.

Switching power supply is better than linear power supply when high efficiency, volume and weight are the key points. However, the switching power supply is complex, and the internal transistors will switch frequently. If the switching current has not been processed, it may produce noise and electromagnetic interference and affect other equipment. Moreover, if the switching power supply is not specially designed, its power factor may not be high.

There are two kinds of modern switching power supply: one is DC switching power supply; The other is AC switching power supply. Only DC switching power supply is mainly introduced here. Its function is to convert the original ecological power supply (crude power) with poor power quality, such as municipal power supply or battery power supply, into high-quality DC voltage (refined power) meeting the equipment requirements. The core of DC switching power supply is DC / DC converter. Therefore, the classification of DC switching power supply depends on the classification of DC / DC converter. In other words, the classification of DC switching power supply is basically the same as that of DC / DC converter, and the classification of DC / DC converter is basically the classification of DC switching power supply.