Switching power supply is substantially made up by the four parts: the main circuit, control circuit, test circuit and auxiliary power supply.

1）The main circuit
Inrush current limiter:  limit the inrush current of the instantaneous power input.
Input filter:  its role is filtering the clutter waveform of the power grid and hindering the clutter waveform of the machine produces itself feedback to the power grid.
Rectifier and filter:  rectifier the AC power of the power grid directly to smooth DC power.
Inverter:  The DC rectified into a high-frequency alternating current, which is the core part of the high-frequency switching power supply.
Output rectifier and filter:  provide a stable and reliable DC power according to the load required.

2）Control circuit
On the one hand, sample from the output and compare with the set value, then controlling the inverter to change the pulse width and pulse frequency to make the output stability. On the other hand,

3）Detection circuit
Provide all kinds of parameter and instrument data that running in the protection circuit.

4）Auxiliary power
Realize software (remote) starting of the power supply to give the protection circuit and control circuit (such as PWM IC) power to work.