Oh no now I have noticedWhat is (-1 V) - (10 V) ?
I mean I can understand the part with only negative feedback.The better way to think about the condition at the inputs of the opamp is not that it is a "virtual ground", because that only applies if one of the inputs is tied to ground, but rather that there is a "virtual short" between the two since they are held at the same voltage, like a real short would, but no current flows between them, and hence it is only virtual, not real.
I belive I do follow.hi X,
I have split the circuit into two circuits, showing the plot for each type of input, now do you follow.?
Which circuit are you talking about now? PLEASE, we are NOT mind readers. There are a number of different circuits in this thread, you need to make it clear which one you are talking about.But what if both feedback ? For non inverting OPA it was positive feedback, for inverting OPA the gain was negative. With both feedback it seems a bit scatchy.
Because increasing Vin I will increase Vp but I will also increase Vn, So where will go Vout ? Will it decrease or will it increase? If one of them then why ?
Sorry form the Post#1.Which circuit are you talking about now? PLEASE, we are NOT mind readers. There are a number of different circuits in this thread, you need to make it clear which one you are talking about.
Pretty complicated.hi X,
This is Joeys circuit with the 'positive' feedback and without it.
Note how the positive feedback increases the gain.
E
Hi X,But what about the both feedback post I've posted ?
I mean more like a concept.Hi X,
Please some values for your circuit and I will try it.
E
The problem I have is that why it has positive gain.This is your circuit with typical components values, works as expected.
I don't see why you have a problem with it.
Which part ?Sadly, with respect, you are talking deliberate nonsense.
I thought I am doing progressPerhaps someone else will step forward and try to help you, I am stepping down.
I'll say it yet again.The problem I have is that why it has positive gain.
Maybe I said it incorrectly.
For inverting and non inverting we can say what is the gain right ?
Increasing Vin in non inverting will increase the Vp, while Vn is constant. So Vout will increase just to increase Vn to make them equal.
For inverting increasing Vin will increase the Vn but Vp is constant so Vout will decrease to decrease Vn to make Vn equal to Vp.
For both feedback increasing Vin will increase both of them Vn and Vp. So I don't know why acutally positive gain works here but negative gain doesn't. There is no constant value. Like in inverting or non inverting. Why it doesn't work like increasing Vin could decrease Vout (negative gain). But it works this way increasing Vin increases Vout (positive gain). There is no constant value like in inverting or non inverting Op Amp
Aha I thought that Vn would also change. I thought that the path is like this : Vin -> Vp -> Vout (which is for this moment 0V) -> Vn and -> GND.or the dual-feedback circuit you keep referring to, increasing Vin increases Vp.
Vn hasn't changed yet, because Vout hasn't changed yet.
Because Vp has gone up while Vn hasn't changed, there is an increase in the differential voltage (Vp-Vn), which in turn results in Vout starting to increase.
by Jake Hertz
by Duane Benson