Voltage mode and current mode control of switching power supply

Voltage mode control and current mode control refer to different sampling methods for feedback signals , The voltage type control takes the output voltage of the power supply as the feedback signal , The deviation between the feedback signal and the given value is amplified by the comparator and compared with the sawtooth wave to generate a control pulse . The current mode control uses the output current of the primary side of the high frequency transformer as the sampling feedback signal to form a current closed loop , The outer voltage loop is composed of voltage feedback signals , The output deviation of the outer voltage loop is taken as the given value of the inner current loop , The control pulse is generated by comparing with the current feedback signal , The system structure block diagram of the two control modes is shown in Figure 1 and 2 Shown ：

The implementation principle of the two control modes is shown in the figure 3 Shown ：

The voltage type control combines the output voltage with VR Reference voltage Vref Deviation signal of e the PI Type a error amplifier is processed and compared with the sawtooth wave generated by the oscillator , produce PWM Control pulse , The output waveform is shown in the figure 5 Shown .

Current mode control has two closed-loop channels , Voltage and VR Reference voltage Vref Deviation signal of e the PI The V-type error amplifier can generate voltage Ve, The voltage is compared with the drain output current of the switch , produce PWM Control pulse , The output waveform is shown in the figure 6 Shown .