Understanding the Equalizing Nature of Negative Feedback in Op Amps

[sidvelu]

I understand how to apply op amps, but one thing about op amps had bugged me for some time. I want to know what about an op amp in negative feedback forces both the posotive and negative inputs to be equal. And could your explanation be for both an inverting and non inverting op amp.

Thanks! :)

 

[Redbelly98]

I understand how to apply op amps, but one thing about op amps had bugged me for some time. I want to know what about an op amp in negative feedback forces both the posotive and negative inputs to be equal.

Welcome back to PF.

If the (-) input were significantly lower than the (+) input, that would drive the output high, since V_{out}=A\cdot(V_+-V_-). And because of the feed back to the (-) input, driving the output high would raise the voltage at (-) input, driving it closer to the voltage at the (+) input.

A similar argument applies to considering if the (-) input were significantly higher then the (+) input.

And could your explanation be for both an inverting and non inverting op amp.

Not sure what you mean here. Op amps are not "inverting" or "non inverting", those terms refer to the two inputs of any op amp. The explanation only works for feedback to the inverting input, that I refer to as (-) above.

 

[sidvelu]

oh okay, that makes more sense now. I should've drawn that conclusion on my own, but i guess i was just being stupid.

Thanks a lot!