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Basic components of switching power supply

Basic components of switching power supply

Switching power supplies are different from linear power supplies. Most of the switching transistors used in switching power supplies are switched between fully-on mode (saturation zone) and fully-closed mode (cut-off zone). Both modes have the characteristics of low dissipation. The conversion will have higher dissipation, but the time is very short, so it saves energy and generates less waste heat.


The switching power supply is roughly composed of four parts: the main circuit, the control circuit, the detection circuit, and the auxiliary power supply.

1. Main circuit

Impulse current limit: limit the impulse current on the input side when the power is turned on.

Input filter: Its function is to filter the clutter that exists in the power grid and prevent the clutter generated by the machine from being fed back to the power grid.

Rectification and filtering: Directly rectify the AC power of the grid into a smoother DC power.

Inverter: Convert the rectified direct current into high-frequency alternating current, which is the core part of the high-frequency switching power supply.

Output rectification and filtering: According to the needs of the load, provide a stable and reliable DC power supply.

2. Control circuit

On the one hand, samples are taken from the output terminal and compared with the set value, and then the inverter is controlled to change its pulse width or pulse frequency to stabilize the output. On the other hand, according to the data provided by the test circuit, it is identified by the protection circuit to provide The control circuit carries out various protection measures for the power supply.

3. Detection circuit

Provide various parameters and various instrument data in operation in the protection circuit.

4. Auxiliary power supply

Realize the software (remote) start of the power supply, and supply power for the protection circuit and the control circuit (chips such as PWM).