Switching power supply principle

2018-11-08 23:08:25

The working process of the switching power supply is quite easy to understand. In the linear power supply, the power transistor works in the linear mode. Unlike the linear power supply, the PWM switching power supply makes the power transistor work in the on-off and on-off state. 

 

In these two states, the V-A product added to the power transistor is very small. On-time, low voltage, high current; on-off, high voltage, low current) / Volt-ampere product on power devices is the loss on power semiconductor devices. Compared with linear power supply, PWM switching power supply works more effectively by chopping the input DC voltage into a pulse voltage whose amplitude equals 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, the amplitude can be raised or reduced through the transformer. By increasing the number of two windings of the transformer, the number of output voltage groups can be increased. 

 

Finally, these AC waveforms get DC output voltage after rectification and filtering. The main purpose of the controller is to keep the output voltage stable. Its working process is very similar to that of the linear controller. That is to say, the function block, voltage reference and error amplifier of the controller can be designed to be the same as the linear regulator. Their difference is that the output of the error amplifier (error voltage) passes through a voltage/pulse width conversion unit before driving the power transistor.