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Op-Amp, finding value of resistors

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Date Posted: 7/9/2008 2:13:24 AM  Status: Live
Op-Amp, finding value of resistors
Course Textbook Chapter Problem
Analog Circuits Electric Circuits (8th) by Nilsson 7 N/A
Question Details:
Can anyone help me explain the steps i would need to find the value of all three resistors individually?

I appreciate your help!
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Answers:

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Date Posted: 7/9/2008 6:50:49 AM  Status: Live
Asker's Rating: Lifesaver   
Response:
Dear User,
 
In the given circuit you have not specified any input or output parameters.
Or at least you have not specified any op-amp parameters.
So I will given you expressions for input and output voltages in terms required resistors.
So that it will be helpful to you if you have any parameters related to the above circuit.
 
For analysis given circuit will be represented as below:

     
 
From this circuit by applying KCL at inverting terminal we can get
................ (1)
By applying KCL at op-amp output terminal we can get
............. (2)
From equation (1), we can write equation (2) as below:
............. (3)
From this equation we can say that it is a inverting operational amplifier with a gain of .
If you have any parameters related to this amplifier you get exact values fo  and  form the above equation (3). 
 
I hope this helps you.................
fja3's Comment:
wow...great help

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Date Posted: 7/9/2008 6:08:38 PM  Status: Live
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Response:
If we have R1 and R2 and we put a load resistance RL after R3. Let Output voltage before RL be Vo. How do we find R3 using VL , Vo, RL and using Iin ?

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Date Posted: 7/10/2008 12:02:40 AM  Status: Live
Asker's Rating: Helpful   
Response:
According to your description the circuit is modified as below:

        

From this circuit by applying KCL at inverting terminal we can get

................ (1)
By using potential divider rule we can write
...................... (2)
From equation (1), we can modify equation (2) as below:
................ (3)
From (2) and (3) equations we can found the value of resistor .
 
I hope this helps you............



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