# Circuit Analysis Op amp

Discussion in 'Homework Help' started by damm1371, Mar 28, 2012.

1. ### damm1371 Thread Starter New Member

Feb 22, 2012
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This is a practice problem for a test. The objective is to find Vo of the following circuit. All op amps are ideal. I have attempted to start by separating the op amps and calculating Vo accordingly. Starting with the top right op amp as 1. Vo1 = V1(1+R5/R4) and Vo2 = V1( 1 + [(R2+R3)/R1) so Vo would be Vo1+ Vo2
this doesnt seem right. I am more interested in the process to get the answer than the answer.

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Last edited: Mar 28, 2012
2. ### Jony130 AAC Fanatic!

Feb 17, 2009
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Well see this method

Va = Vin

So

IR1 = Vin /R1

then

Vb = (IR1 * R2 ) + Vin = (Vin /R1 * R2) + Vin = Vin*( R2/R1 +1 )

And

Vo = Vc

IR3 + IR4 = IR1

(Vo - Vb)/R3 + (Vc - Vb)/R4 = Vin/R1

From this we solve for Vo

Vo = Vb + ( Vin * (R3||R4)/R1) ) = Vin*( (R2/R1 +1) + (R3||R4)/R1)

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3. ### bountyhunter Well-Known Member

Sep 7, 2009
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I believe you can "weld" R3 and R4 at the right ends (in parallel) since the voltages at the inputs of the second opamp are identical. Nodes which are the same voltage can always be shorted together.

Last edited: Mar 28, 2012
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4. ### damm1371 Thread Starter New Member

Feb 22, 2012
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so maybe you can help me with this one as well. I tried to create a new thread for this but keep getting server errors. anyways...

All components are Ideal for the following circuit. Calculate a value for R so that R dissipates maximum power. My first thought is to convert R2, R3, and R from Delta to Y, which gets very messy or is there a better way?

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5. ### vvkannan Active Member

Aug 9, 2008
138
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Remove R and calculate the thevenin equivalent resistance as seen by the open circuit.For maximum power transfer the value of R should be equal to the equivalent resistance calculated

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6. ### mlog Member

Feb 11, 2012
276
36
Sounds right. I don't think R1 even enters the equation. Does it?

7. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
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If R2, R3, R4 and R5 are the same ohmic value, "R" will dissipate ZERO power because there will be no current through it.

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8. ### damm1371 Thread Starter New Member

Feb 22, 2012
11
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let me know if this looks correct.

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9. ### mlog Member

Feb 11, 2012
276
36
Looks right to me. Delta-wye conversion. Obviously R1 is in the equation. And yes, bountyhunter has a good point.

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