hot key words：

(1) According to the driving method, there is self-excitation. (2) According to the composition of the circuit, there are resonance and non-resonance

(3) According to the working mode of DC/DC converter: 1) single-ended forward and flyback, push-pull, half-bridge, full-bridge, etc.; 2) buck, boost and boost.

(4) According to the control method, it is divided into: pulse width modulation (PWM), pulse frequency modulation (PFM), PWM and PFM mixing. (5) According to the power isolation and feedback control signal coupling, there are problems such as isolation, non-isolation, transformer coupling, and optoelectronic coupling. These combinations can form a variety of switch mode power supplies. Therefore, designers need to effectively combine the characteristics of various modes to produce high-quality switching power supplies to meet the needs.

The PWM circuit has already shouldered the task of voltage rectification. The input voltage will be corrected again before passing through the switch, and the voltage entering the transformer has become a square wave. Therefore, the waveform of the transformer output is also a square wave, not a sine wave. Since the waveform is already a square wave at this time, the voltage can be easily converted into a DC DC voltage by the transformer. That is, after the voltage is recalibrated by the transformer, the output voltage has become a DC DC voltage. This is why switching power supplies are often referred to as DC-DC converters.

The loop feeding the PWM control circuit is responsible for all required adjustment functions. If the output voltage is wrong, the PWM control circuit changes the duty cycle control signal to accommodate the transformer and eventually corrects the output voltage. This situation often occurs when the power consumption of the PC rises. At this time, the output voltage tends to decrease, or when the power consumption of the PC decreases, the output voltage tends to rise.