# Op Amp how does the feedback factor works ?

#### Xenon02

Jul 18, 2021
4
Hello !
I've got a problem because I don't understand the feedback factor in Op Amp.
All I know is that it is equal V-/Vout for negative feedback.
But what if V- is equal 0V ? Like here :

Also I heard that feedback factor is the reverse of the closed loop gain A = 1/B.
So is it -R1/R2 ? I've seen on some sites that it is R1/(R1+R2). I've even talked with some people and they say the same that feedback factor is equal -R1/R2.

And I'm confused but even if feedback factor is equal -R1/R2 or R1/(R1+R2). They how is it possible that it is equal 0V? I mean V-/Vout = B ("B" is for feedback factor). So 0V/Vout = B => 0V = B*Vout. It doesn't make any sense.

Moderator
Nov 8, 2019
3,320

#### Audioguru

Sep 24, 2016
3,656
The biasing of the + input of an opamp depends on the type of its power supply:

#### Attachments

• opamps.png
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#### crutschow

May 7, 2021
846
And I'm confused but even if feedback factor is equal -R1/R2 or R1/(R1+R2). They how is it possible that it is equal 0V?
You are confusing the feedback factor (gain) with the output voltage from that gain.
If the input is 0V, then the output will be the gain x 0V = 0V.
The voltage being amplified has no effect on the gain of the circuit.

Make sense?

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