Working principle of switching power supply

The working process of switching power supply is quite easy to understand. In linear power supply, the power transistor works in linear mode. Different from linear power supply, PWM switching power supply makes power transistors work in on and off States. In these two States, the volt-ampere product added to the power transistor is very small (when conducting, the voltage is low and the current is large; The volt-ampere product on the power device is the loss produced on the power semiconductor device. Compared with linear power supply, the more effective working process of PWM switching power supply is realized by chopping, that is, chopping the input DC voltage into pulse voltage with the same amplitude as the input voltage. The duty cycle of the pulse is adjusted by the controller of the switching power supply. Once the input voltage is chopped into an AC square wave, its amplitude can be increased or decreased by a transformer. By increasing the number of transformer secondary windings, the number of output voltage groups can be increased. Finally, these AC waveforms are rectified and filtered to obtain DC output voltage. The main purpose of the controller is to keep the output voltage stable, and its working process is very similar to that of a linear controller. That is, the functional block, voltage reference and error amplifier of the controller can be designed to be the same as the linear regulator. The difference between them is that the output of the error amplifier (error voltage) has to pass through a voltage/pulse width conversion unit before driving the power tube.