Compared with the linear power supply, the more effective working process of the PWM switching power supply is achieved by "chopping", that is, chopping the input DC voltage into a pulse voltage whose amplitude is equal to the input voltage amplitude.

The duty cycle of the pulse is regulated by the controller of the switching power supply. Once the input voltage is chopped into an AC square wave, its amplitude can be raised or lowered through the transformer. The output voltage value can be increased by increasing the number of secondary windings of the transformer. Finally, these AC waveforms are rectified and filtered to get the DC output voltage.

The main purpose of the controller is to keep the output voltage stable, and its working process is very similar to the linear form of the controller. This means that the controller's functional block, voltage reference and error amplifier can be designed to be the same as the linear regulator. They differ in that the output of the error amplifier (error voltage) passes through a voltage/pulse width conversion unit before driving the power tube.

Switching power supplies have two main modes of operation: forward conversion and boost conversion. Although the arrangement of each part of them is very different, the working process is very different, and each has its advantages in specific applications.

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