Hello everyone,
Please help me find the output voltage formula for this operational amplifier circuit.


Thank you.

 

You need to show your best attempt to tackle your homework problems. We will not work it for you, but we will look over what you have done and help you see where you might be going wrong and help you get past the specific points that are blocking your progress.

 

You need to show your best attempt to tackle your homework problems. We will not work it for you, but we will look over what you have done and help you see where you might be going wrong and help you get past the specific points that are blocking your progress.

I know that R1 is useless, so does this mean that this is a non-inverting amplifier circuit?

 

I know that R1 is useless, so does this mean that this is a non-inverting amplifier circuit?

Yes, that is correct.

An opamp has such a high voltage gain that when negative feedback is added then the output of the opamp will do whatever it can to make its - input voltage the same as the + input voltage. Since both inputs have the same voltage then R1 is useless with no current in it.

 

Here is the essential behavior of an op-amp circuit with proper negative feedback.
+Vinput = -Vinput

Just like what ag says above.
Take it from there.

 

I know that R1 is useless, so does this mean that this is a non-inverting amplifier circuit?

I know and realize that - as it seems - the question comes from a beginner.
And - as far as an idealized opamp is concerned - I agree that R1 is "useless".

However, for real opamps with a frequency-dependent gain the resistor R1 is NOT useless. It resembles a special kind of external frequency compensation - thereby improving the phase margin as well as the step response. More than that, using such a resistor across the opamps input nodes allows us to use opamps which are not unity-gain stable even with 100% feedback (unity gain).

 

Hello everyone,
Please help me find the output voltage formula for this operational amplifier circuit.
View attachment 219235

Thank you.

Hello there,

Would you like to know a very general method for handling these op amp circuits?
Once you get the answer to this i would be happy to post if you like.

 

Hello there,

Would you like to know a very general method for handling these op amp circuits?
Once you get the answer to this i would be happy to post if you like.

Sure, why not?

 

Hello there,

Would you like to know a very general method for handling these op amp circuits?
Once you get the answer to this i would be happy to post if you like.

Hello there,

Would you like to know a very general method for handling these op amp circuits?
Once you get the answer to this i would be happy to post if you like.

Hi, MrAl,

Don't wait for the TS to solve his problem. I'm interested in your method, and others are probably also. Start a new thread in the general forum, Use some other circuits as examples.

 

Hi, MrAl,

Don't wait for the TS to solve his problem. I'm interested in your method, and others are probably also. Start a new thread in the general forum, Use some other circuits as examples.

Yes that is an interesting idea, thanks for the suggestion.
I wonder if it might be better as an article, or better yet, a new thread that might be able to be promoted as an article. I'll look into this.

 

Don't wait for the TS to solve his problem. I'm interested in your method, and others are probably also.

The usual method is to use the zero differential input theorem.

 

I know that R1 is useless, so does this mean that this is a non-inverting amplifier circuit?

For an ideal opamp (which I'm pretty sure is what you are assuming) R1 has no effect. For real opamps it can serve a purpose, but that's not where you are yet.

So, yes, it is just a classic non-inverting opamp-based amplifier.

But what is important is not that you realize that R1 can be removed, leaving you with a circuit that you happened to have seen before and can come with with a memorized formula for, but that you understand how to apply ideal opamp circuit analysis principles to an opamp-based circuit even if it is completely new to you.