Help with Circuit function

Discussion in 'General Electronics Chat' started by Steven_Shi, May 13, 2009.

  1. Steven_Shi

    Thread Starter New Member

    May 12, 2009
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    Hello all :

    Could you help me check the SCH as follow, I just want to make

    Vouput=Vinput, but I'm not sure whether it is OK. Thank you.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    I don't think you've got the summing integrator stage U1-A right.

    One would normally add the input and feedback signals via equal resistors into the -ve input terminal. Then tie the +ve terminal to ground. Provided the total control loop feedback signal polarity is correct [trace it around the loop] then OK. I'd add a small resistance in the U1-A feedback path to give a P+I control rather than pure I control.

    You would also need to check the overall stability in closed loop so that you don't get unwanted self oscillation.
     
  3. t_n_k

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    Mar 6, 2009
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    Also to get Vo=Vin you would need an inverter stage in the feedback path - otherwise the magnitudes match but the sign is inverted. If you did this you would have change U1-B to an inverting stage to keep the relative input/output sign sense (phase?) around the closed loop correct.
     
  4. t_n_k

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    Mar 6, 2009
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    This is what I mean.....
     
  5. Steven_Shi

    Thread Starter New Member

    May 12, 2009
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    Thank you very much, t n k, I will make test for it. thank you.
     
  6. Ron H

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    Apr 14, 2005
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    I don't see anything wrong with the phase of the feedback. It's basically just a big voltage follower. Loop stability might be an issue.

    EDIT: The simulated circuit was stable. The .ASC file for LTspice is attached.
     
    Last edited: May 14, 2009
  7. Ron H

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    Steven, why did you make it so complex? A voltage follower doesn't need two op amps, or an integrator in the feedback loop
     
  8. Pich

    Active Member

    Mar 11, 2008
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    Agree with Ron supped up voltage follower
     
  9. mik3

    Senior Member

    Feb 4, 2008
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    Use an op amp with the input signal at its non inverting input and the feedback taken from the output (load) and connected on its inverting input.
     
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