There are many kinds of switching regulated power supply, but the basic circuit is composed of linear filter, rectifier filter, DC / DC converter and regulated control circuit.

The AC voltage of 220V / 50h: passes through the linear filter to filter the pulse interference in the power grid and then enters the rectification filter circuit. The output DC high voltage is applied to the DC / DC converter for power conversion, and the DC voltage meeting the requirements is output to the load. The voltage stabilization control circuit includes sampling, comparison and amplification, reference and control adjustment circuits, etc. when the input voltage is unstable for some reason, the on-off time ratio of the switching elements in the DC / DC converter can be automatically adjusted by the operation of the voltage stabilization control circuit to achieve the purpose of automatically adjusting the output voltage and keep the output voltage stable.

A DC / DC converter is a conversion circuit that converts one DC voltage into another DC voltage. Generally, the power supply voltage required by various electronic equipment is different. By using DC / DC converter, the DC voltage output by the rectifier can be converted into the DC voltage required by the electronic equipment.

Compared with linear regulated power supply, the main characteristics of switching power supply are:

(1) High efficiency and low power consumption. The regulator of the switching power supply works in the switching state, so the power consumption of the regulator is very small and the efficiency is over 80%.

(2) Wide range of voltage stabilization. When the AC input voltage of the linear regulated power supply is lower than 160V, the output voltage cannot be stable, and when the input AC voltage is high, the efficiency will be reduced. When the AC input voltage of the switching power supply changes in the range of 130-260v, it can achieve a good voltage stabilization effect.

(3) High stability and reliability. The low power consumption makes the internal temperature rise of the electronic equipment low, reduces the high temperature damage rate of the surrounding components, and greatly improves the thermal stability and reliability of the equipment.

(4) Small size and light weight. The switching power supply can directly rectify the AC voltage input from the power grid, and then obtain various AC voltages through the high-frequency transformer, eliminating the heavy power frequency transformer and greatly reducing the weight of the power supply. In addition, due to the high operating frequency of the switching power supply, the filter capacitor and inductance can be used as components with smaller values, which can also reduce the volume and weight.

(5) Safe and reliable. Switching power supply can design automatic protection circuit conveniently. In case of circuit fault or short circuit, it can automatically cut off the power supply to prevent the expansion of fault range.

The main problems of switching power supply are complex circuit, high output ripple voltage and poor transient response. At present, countries around the world are vigorously developing new switching power supplies to meet the needs of miniaturization and high efficiency of various electronic equipment.