You cannot have both.



It is like a nuclear reactor. You can have criticality less than 1 (C), equal to 1 (B), or greater than 1 (A).

 

But I have seen some examples where there are used two feedbacks at the same time.


So I was curious how people are solving it. Because I know how it works with only positive or only negative. But if there is both? Is it like one of them is dominating or what? Or how does it work ?

 

But I have seen some examples where there are used two feedbacks at the same time.

Yes, that is a differential amplifier, which has both positive and negative feedback.
You can read about it here, for example.

 

Yes, that is a differential amplifier, which has both positive and negative feedback.
You can read about it here, for example.

The one you send me has only one feedback. Not two.

 

He might be thinking of a differential input and differential output amplifier.
This is still negative feedback on both arms of the circuit.

 

He might be thinking of a differential input and differential output amplifier.
This is still negative feedback on both arms of the circuit.

View attachment 272764

Ok this is wierd I didn't know there would be two outputs.

But still I didn't get the answear to my question :



The link didn't consist the circuit with two feedbacks and 1 output.

Because this one has one output.



Like here 2 feedbacks 1 output.

 

The answer is:
It is a theoretical example in a text book. It has no practical application.

 

The answer is:
It is a theoretical example in a text book. It has no practical application.

Oh.
So theoretically there is no solution ?
I've found something like this :

 

The one you send me has only one feedback. Not two.

Sorry I misread the circuit.

 

But to be sure.
Why they are giving this circuit to calculate when there is no practical use?
By the way is it even possible to calculate it ? I'm just curious because maybe I will meet something like this and I will be "bamboozled"

 

You can write an equation for it, but it might not have a single stable solution.

 

I think basically the circuit operates in the linear region if the negative feedback is greater than the positive feedback, and latches (bistable) if the positive feedback is greater than the negative feedback.

 

I think basically the circuit operates in the linear region if the negative feedback is greater than the positive feedback, and latches (bistable) if the positive feedback is greater than the negative feedback.

You are probably right.

How to calculate which feedback is greater ? Is there a tutorial with 2 feedbacks ?

You can write an equation for it, but it might not have a single stable solution.

Yea but I don't know how to calculate it. I just need a tutorial. Video or a circuit with 2 feedbacks on the weebsite step by step.

 

Can you write an equation for Vx in your post #106?

 

Can you write an equation for Vx in your post #106?

All I know from this Vx is that it is a positive feedback.
If the negative feedback was dominant then Vx = V_negative. But as I said I don't know.

 

Forget whether it is positive or negative. Can you write an equation for it?

 

Vx = Vin - I*R1

I don't know.

 

Vx = Vin - I*R1

I don't know.

There is no I in the diagram. Try to write an equation in terms of Vin and Vout.

 

I know there was a method method of nodal potentials but I haven't mastered it yet.
I just don't know how this circuit even works. Where to current flow.

I've found something like this :

https://electronics.stackexchange.c...dback-of-opamps-so-different-how-to-analyse-a

The guys is trying to solve it by saying it is negative feedback when in lim Av -> infinite (Vout/Vin) is infinite then it is positive feedback. But I don't know if this is also the same here.

 

You seem to be asking a lot of questions to which you could easily find answer on your own, rather than engaging in long, drawn-out discussions those who would like to help you. This is not only true of this thread, but others on this site.

For your op-amp questions, I have some suggestions.
On this site: https://www.allaboutcircuits.com/textbook/semiconductors/
Burr-Brown Operational Amplifier Handbook
Handbook Of Operational Amplifier Active RC Networks

If you have difficulty with any particular terms or concepts in these tomes you are welcome to ask for specific help on this site. Dragging individuals with good intentions into endless conversations are frowned upon.