Because the +3 volts is going into the inverting input so it will come out reversed polarity.

 

The output is (Va - Vb) x amplifier gain, where Va is the non-inverting input and Vb is the inverting input.

Hence,
Vout = (0V - 3V) x gain = -Vs

Oh ok.

To summarize it and if you can correct me if I'm wrong but If I'm not then like it

When I have Op Amp with positive feed back it will be saturated.
By the way can I check if it will work ? Like this equation for Vout = Va-Vb x amplifier ? for 4V on the negative inpute ? And undetermined on the positive input ?

 

Because the +3 volts is going into the inverting input so it will come out reversed polarity.

Yes but I was said that input polarity doesn't matter

Those statements are incorrect.
It is not the polarity that matters. It is the voltage difference that matters.

(+IN) - (-IN)

 

When I have Op Amp with positive feed back it will be saturated.

Yes.

And undetermined on the positive input ?

What do you mean "undetermined".
The voltage to both inputs is always determined.
If one of the input's voltage is undetermined, than the output voltage is also undetermined.

 

Yes.
What do you mean "undetermined".
The voltage to both inputs is always determined.
If one of the input's voltage is undetermined, than the output voltage is also undetermined.

I was just curious if I can tell if the Vout equations works here.
Because I don't know what is in positive input I know only negative input that is 4V

 

Operational Amplifier Circuits

Operational amplifiers or op-amps are difference or differential amplifiers.

Memorize this circuit configuration.



Assume,
R1 = R3
R2 = R4
Vin = v1 - v2
voltage gain Av = -R2/R1
Vout = Av x Vin = -R2/R1 x (v1 - v2)





Unity gain non-inverting buffer

 

Can I do it the same with this :



You know make this equation Vout ?
Because in your example there are only negative feedbacks.
And can I do it for positive feedback ? Vout = Va-Vb * A ?
I wanted to see if it is going into saturation because this Vout is negative.

Oh and is it possible to have positive output while having a positive voltage on negative input ? (while having negative feedback) ?

 

Because I don't know what is in positive input I know only negative input that is 4V

That's because a bistable circuit has two stable states but you know it has to be in one of the two states.
Which of the two states it's in is determined by the past history of the control input.
So you need to know the past history of the circuit to know which state it is in.

 

555 Bistable Multivibrator
The 555 Projects
Wendy's Index
this circuit uses a 555 as a Schmitt trigger and will toggle when the button is pressed, any Schmitt trigger would work for this application.

 

Oh and is it possible to have positive output while having a positive voltage on negative input ? (while having negative feedback) ?

What negative feedback?
So far we've been talking about positive feedback.

 

Oh and is it possible to have positive output while having a positive voltage on negative input ? (while having negative feedback) ?

Vout = -R2/R1 x (v1 - v2)

or

Vout = R2/R1 x (v2 - v1)

If v1 is positive input, then the output will be positive if v2 > v1.

 

What negative feedback?
So far we've been talking about positive feedback.

Yes we were talking about positive feedback.
But I was also curious about that one input doesn't determine what is the output.

Like I have talked 2 pages ago. Positive input on the negative input gave me positive output.

 

Taking a theoretical op amp(with infinite gain), if the positive input is greater than the negative input then the output would be positive if the negative input is greater than the positive input then the output is negative.

In reality it only takes a few microvolts of difference.

 

Schmitt trigger

But I was also curious about that one input doesn't determine what is the output.

We have explained to you that its the differential input voltage, not the voltage on one pin that determines the output.
Do you not understand that?
Or are you trolling us?

 

Vout = -R2/R1 x (v1 - v2)

If the positive input is v1, then the output will be positive if v2 > v1.

Oh cool. Something like that ?


Positive on the negative inpute and positive output. Heh

I guess I get it now.

But I want to still know if I can calculate Vout = Va-Vb *A. And why the output is negative for positive voltage on negative input?
I want to somehow make sure that it will stay negative Or maybe in different words. I know that positive feedback will be always saturated but how to prove it ?

 

Treat positive feedback circuit as a different case altogether.

Study negative feedback circuit alone and master it.



The current in R1 and R2 are equal and opposite.
No current flows in the inverting input.
The voltage on the inverting input is equal to the voltage on the non-inverting input.

Iin = Vin / R1 = - Vout / R2

Vout = -Vin x R2/R1

 

Treat positive feedback circuit as a different case altogether.

Study negative feedback circuit alone and master it.

View attachment 272659

Vout = -Vin x R2/R1

Ok.
So Vout is a different case. I thought that I can use this equation like Vout = Va-Vb * A. And prove it that it is saturated.

 

Ah yes more more thing.
What will happen if I have 2 feedbacks ? Positive and Negative ? How do I know if it works as a "forever saturated" or a OpAmp that wants to be stable like for only negative feedback ?

 

Vout = (V1 - V2) x ∞

 

View attachment 272660


Vout = (V1 - V2) x ∞

?
This shows why positive feedback is saturated ?