The working process of the switching power supply is quite easy to understand. In the linear power supply, the power transistor is operated in a linear mode. Unlike the linear power supply, the PWM switching power supply allows the power transistor to operate in the on and off states. In the state, the volt-ampere product applied to the power transistor is small (the voltage is low and the current is large when turned on; the voltage is high and the current is small when turned off) / the voltammetric product on the power device is the power semiconductor Losses generated on the device.
Compared with linear power supplies, PWM switching power supplies work more efficiently by “chopper”, which is to convert the input DC voltage into a pulse voltage with an amplitude 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 clamped into an AC square wave, its amplitude can be raised or lowered by the transformer. The voltage value of the output can be increased by increasing the number of secondary windings of the transformer. Finally, these AC waveforms are rectified and filtered to obtain a DC output voltage.
The main purpose of the controller is to keep the output voltage stable, and its operation is very similar to that of a linear controller. This means that the controller's function blocks, voltage references and error amplifiers can be designed to be identical to linear regulators. The difference is that the output of the error amplifier (error voltage) goes 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. Despite the small differences in the placement of the various parts, the work processes vary widely and have advantages in specific applications.