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.
     
    Last edited: Mar 28, 2012
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    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)
     
    Last edited: Mar 28, 2012
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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?
     
  5. vvkannan

    Active Member

    Aug 9, 2008
    138
    11
    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
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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
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    let me know if this looks correct.
     
  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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