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The working principle of a switch power supply.
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The working process of a switch power supply is quite easy to understand. In a linear power supply, the power transistor operates in linear mode. Unlike linear power supplies, PWM switch power supplies allow the power transistor to operate in on and off states. In these two states, the volt-ampere product applied to the power transistor is very small (when on, the voltage is low and the current is high; when off, the voltage is high and the current is low). The volt-ampere product on the power device is the loss generated on the power semiconductor device.
The working process of a switch power supply is quite easy to understand. In a linear power supply, the power transistor operates in linear mode. Unlike linear power supplies, PWM switch power supplies operate the power transistor in an on and off state. In these two states, the volt-ampere product applied to the power transistor is very small (when on, the voltage is low and the current is high; when off, the voltage is high and the current is low). The volt-ampere product on the power device is the loss generated by the power semiconductor device.
Compared to linear power supplies, the more efficient working process of PWM switch power supplies is achieved through 'chopping', which means converting the input DC voltage into a pulse voltage with an amplitude equal to the input voltage amplitude. The duty cycle of the pulse is adjusted by the controller of the switch power supply. Once the input voltage is chopped into an AC square wave, its amplitude can be increased or decreased through a transformer. By increasing the number of turns in the secondary winding of the transformer, the output voltage value can be increased. Finally, these AC waveforms are rectified and filtered to obtain a DC output voltage.
The main purpose of the controller is to maintain a stable output voltage, and its working process is very similar to that of linear controllers. In other words, the functional blocks of the controller, voltage reference, and error amplifier can be designed to be the same as those of linear regulators. The difference is that the output of the error amplifier (error voltage) must pass through a voltage/pulse width conversion unit before driving the power transistor.
There are two main operating modes for switch power supplies: forward conversion and boost conversion. Although the arrangement of their components is very similar, the working processes differ significantly, each having its advantages in specific applications.
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2024-11-29
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