Inverting OP AMP analysis solution problem

In summary, the conversation is about a new member seeking help with a circuits exam. They are struggling with understanding a HW problem and are questioning a potential typo in the solution. They are also seeking clarification on the derivation of certain terms.
  • #1
sdusheyko
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Hello Physics Forums community, I'm a new member and this is my first post.

I have a circuits exam tomorrow, and though I grasp the majority of the material I'm having a hard time understanding the solution to a HW problem that I attached as a picture.

Problem: Show that the circuit has A=Vo/Vi= -k(R2/R1) where k= 1+ R4/R2 + R4/R3.

One of the issues is I have no clue how to derive: V1= -(R2/R1)VI

And also the KCL @ V1; I understand where -(V1/R2) comes from. and from where (V1-AV1)/R4 comes from. But I have no clue how the middle term, -V1/R1, is derived.
Shouldn't it instead be -V1/R3?? Could this be a typo or am I just a n00b? If so, please help me out.

Thanks very much.
 

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  • #2
sdusheyko said:
Hello Physics Forums community, I'm a new member and this is my first post.

I have a circuits exam tomorrow, and though I grasp the majority of the material I'm having a hard time understanding the solution to a HW problem that I attached as a picture.

Problem: Show that the circuit has A=Vo/Vi= -k(R2/R1) where k= 1+ R4/R2 + R4/R3.

One of the issues is I have no clue how to derive: V1= -(R2/R1)VI

And also the KCL @ V1; I understand where -(V1/R2) comes from. and from where (V1-AV1)/R4 comes from. But I have no clue how the middle term, -V1/R1, is derived.
Shouldn't it instead be -V1/R3?? Could this be a typo or am I just a n00b? If so, please help me out.

Thanks very much.

Welcome to the PF.

"V1= -(R2/R1)VI " -- Remember that the output of the opamp will do whatever it has to to try to get the - input to match the + input voltage (ground in this case). So that defines the current from the source Vi through R1, which has to ALL flow through R2 (why?)

"Shouldn't it instead be -V1/R3??" -- Yes, that looks like a typo to me too.
 

1. What is an inverting op amp?

An inverting op amp is a type of operational amplifier that produces an output that is the inverse of the input signal. This means that when the input voltage increases, the output voltage decreases, and vice versa.

2. How does an inverting op amp work?

An inverting op amp has two inputs, a positive and a negative. The positive input is connected to ground, while the negative input is connected to the input voltage. The op amp amplifies the difference between these two inputs and produces an output voltage that is the inverse of the input voltage.

3. What is the purpose of an inverting op amp?

An inverting op amp is commonly used in electronic circuits to amplify signals, perform mathematical operations such as integration and differentiation, and to create filters. It is also used in feedback circuits to stabilize and control the gain of the amplifier.

4. How do you analyze an inverting op amp circuit?

To analyze an inverting op amp circuit, you can use the principles of ideal op amp analysis. This involves assuming that the op amp has infinite input impedance, zero output impedance, and infinite open-loop gain. By applying Kirchhoff's laws and the virtual ground concept, you can easily calculate the output voltage and gain of the circuit.

5. What are common problems encountered with inverting op amp circuits?

One common problem with inverting op amp circuits is instability, which can be caused by insufficient feedback or a high gain value. Other issues include input offset voltage, noise, and bandwidth limitations. These problems can be addressed by using proper circuit design techniques and selecting appropriate op amps for the application.

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