How to judge whether the operational amplifier of this circuit is in the amplification state

hsfx

How to judge whether the operational amplifier of this circuit is in the amplification state [Copy link]

This is a parallel voltage regulator circuit, but I don't understand how to judge whether the op amp is in the amplification state, and how the feedback circuit works? Please help experts

maychang

『How does the feedback circuit work? 』

Vout is high-->sampling voltage divider is high-->op amp output is high-->Q1 collector voltage is low.

The result is that the voltage divided by R3R4 on Vout is equal to Vref.

chunyang

To judge the feedback state of the op amp, you only need to analyze the impact of output changes on the input. For details, see the analysis above. The transistor is included in the op amp circuit, so the "op amp output" actually refers to the output of the transistor. The transistor common emitter circuit is inverted, so the feedback signal is connected to the same-phase input to form negative feedback.

hsfx

chunyang posted on 2022-8-11 18:23 To determine the feedback state of the op amp, you only need to analyze the impact of output changes on the input. For details, see the analysis above. The transistor is included in the op amp circuit, ...

Thanks

jiangbianyeren

After coming from the sampling circuit, how is it fed back to the input end of the comparison detection? Is it simply amplified?

jimtien

jiangbianyeren posted on 2022-8-12 16:55 After coming from the sampling circuit, how is it fed back to the input end of the comparison detection? Is it simply amplified?

The basics of op amps need to be reviewed. The feedback voltage is input to the op amp's inverting terminal, and the non-inverting terminal is the reference voltage. The two are subtracted and amplified by the op amp.

jimtien

The only way to determine whether the op amp is in the amplification state is to analyze whether the op amp can respond to the input signal by "amplification". When does the op amp lose its amplification function? When the op amp output is close to the power supply voltage or 0 volts, the op amp cannot output a higher voltage or a lower voltage, that is, it cannot respond to the input signal by "amplification" (this is unidirectional, because although the op amp cannot output a higher voltage, it can output a slightly smaller voltage). The above two states are the so-called "saturation" and "cutoff" states.