0
\$\begingroup\$

I've got a question about feedback factor. Because I don't know how to calculate it. I've been talking with some people and they say that feedback factor here is equal -R1/R2. Which is the reverse of closed loop gain = -R2/R1.

enter image description here

Also I read that Feedback factor for inverting is V-/Vout. But V- is 0 V so how is it posible to have Vout*B("B" stand for feedback factor). And from it I have 0 V? Vout isn't 0 V also B is also a certain value not 0. So how does it work?

\$\endgroup\$

1 Answer 1

2
\$\begingroup\$

The feedback factor is the fraction of the output that appears at the inverting input and, for your circuit it's solved by looking at the potential divider of R1 and R2 with the input grounded.

Hence it's simply \$\dfrac{R_1}{R_1+R_2}\$.

If you did the same analysis on a non-inverting amplifier, the answer would be the same.

enter image description here

\$\endgroup\$
10
  • 1
    \$\begingroup\$ In the answer there is only R1/R1+R2. I am talking about feedback factor V-/Vout. Many sites tell the same. I'll ask again the equation also for feedback factor is V-/Vout. So 0V = Vout*B ??? and it will be still 0V ?How? \$\endgroup\$
    – user331990
    Aug 6 at 12:39
  • 2
    \$\begingroup\$ So, who are you going to trust? And try and be more mathematically correct in your equations for instance R1/R1+R2 = 1 + R2 and I'm sure you didn't mean that. Stop and think and don't keep blasting comments because, at the end of the day, my answer is correct and anyone in doubt will just have to take that on-board. \$\endgroup\$
    – Andy aka
    Aug 6 at 12:41
  • 1
    \$\begingroup\$ I don't know to be honest because many people tells me many versions. Like closed loop gain = Vin/Vout electronics-tutorials.ws/opamp/opamp_2.html \$\endgroup\$
    – user331990
    Aug 6 at 12:43
  • 1
    \$\begingroup\$ I'm not going to try and explain why other sites may say this. If you want to know why other sites say different things then you should raise that problem as a new question. YOU asked what feedback factor is and I have supplied an answer. End of. \$\endgroup\$
    – Andy aka
    Aug 6 at 12:45
  • 3
    \$\begingroup\$ No, I've made my answer to your question and that's it. Ask a new question if you have other problems. This site is not a progressive learning experience, a talking shop or a forum; it's a Q and A site where you supply the Q and someone like me supplies the A. \$\endgroup\$
    – Andy aka
    Aug 6 at 12:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.