Five kinds of PWM feedback control circuit diagram of switching power supply

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Overview:
The basic working principle of PWM switching regulator or steady current power supply is that under the condition of input voltage change, internal parameter change and external load change, the control circuit performs closed-loop feedback through the difference between the control signal and the reference signal to adjust the main circuit switching device. The on-pulse width is such that the output voltage or current of the switching power supply is stabilized by the control signal.

The switching frequency of the PWM is generally constant, and the control sampling signals are: output voltage, pleasant voltage, output current, output inductor voltage, and peak current of the switching device. These signals can form a single-loop, double-loop or multi-loop feedback system to achieve the purpose of voltage regulation, steady current and constant power. At the same time, some additional functions such as overcurrent protection, anti-biasing and current sharing can be realized.
There are currently five main PWM feedback control modes. The following is a steady-state step-down chopper composed of VDMOS switching devices. The development process, basic working principle, detailed circuit schematic diagram, waveform, characteristics and application points of the five PWM feedback control modes are illustrated to facilitate selection. Application and simulation modeling research.

Five kinds of feedback control modes of switching power supply PWM Generally speaking, the main circuit of the forward switching power supply can be simplified by the step-down chopper shown in Fig. 1, and Ug represents the PWM of the control circuit to drive the driving signal.
According to the different PWM feedback control mode, the input voltage Uin and the output voltage V in the circuit are selected. Ut, switching device current (from point b), inductor current (from point c or point d) can be used as sampling control signals. When the output voltage Uout is used as a control sampling signal, it is usually processed by the circuit shown in FIG. 2 to obtain a voltage signal Ue, which is then processed or directly sent to the PWM controller. The voltage operational amplifier (e/a) in Figure 2 has three functions:
1. Amplify and feedback the difference between the output voltage and the given voltage Uref to ensure the stability of the voltage at steady state. The DC release gain of the op amp is theoretically infinite, which is actually the open-loop amplification gain of the op amp.
2. Converting the DC voltage signal with the wider band switching noise component at the output of the main circuit of the switching power supply into a relatively "clean" DC feedback control signal (Ue) with a certain amplitude, that is, retaining the DC low frequency component and attenuating the AC high frequency. ingredient. Because the frequency of the switching noise is high, the amplitude is large, and the high-frequency switching noise attenuation is not enough, the steady-state feedback is unstable; if the high-frequency switching noise attenuation is too large, the dynamic response is slow. Although contradictory, the basic design principle for voltage error op amps is still "high frequency gain and low frequency gain".
3. Correct the entire closed loop system to make the closed loop system work stably.

When a signal such as a voltage or current is input as a sampling control signal, it is often processed. Since the processing methods are different, the following describes the different control modes.

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