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What will be the output signal of op-amp?

Discussion in 'Electronics Homework Help' started by za_slovom, Jun 20, 2017.

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  1. za_slovom

    za_slovom

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    Apr 20, 2017
    Hi everyone. I am stuck on op-amp. There are some problems that I can deal with, and some thay I can't. I know that if our signal is applied into inverting input then there will be phase shift of 180 degrees in the output. For the example below, this rule doesn't work. The signal applied to the non-invering input doesn't have to change in the output. What am I doing wrong?
    bandicam 2017-06-20 20-14-43-072.jpg
     

    Attached Files:

  2. davenn

    davenn Moderator

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    double ended output ???
    what is the op-amp ?

    what I see in that diag. doesn't even make sense
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The input signal is the difference between the two input voltages.
     
  4. Audioguru

    Audioguru

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    Sep 24, 2016
    Your opamp has no power supply.
    Its inputs have no biasing.
    It has no negative feedback.
    It has an extra output (opamps have only one output). Some audio power amplifiers have a differential outputs (two outputs) and some have built-in biasing and negative feedback.

    Here are two opamp circuits that amplify AC signals. One has a single polarity power supply and the other has a dual polarity power supply.
    They are biased at half the supply voltage so their outputs can swing up and down.
    They have negative feedback.
    They have only one output.
     

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  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Perhaps you should Google for op amps with differential output.

    The other points are not relevant either.

    There is no suggestion that this is a practical circuit, and it is not uncommon to omit the power supply connections.
     
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  6. Audioguru

    Audioguru

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    I explained why his circuit did not work and I showed all the details on my schematic that works perfectly.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's not a working circuit. It's a demonstration of how the device works.

    You've probably never seen the equation Vo = a(V+ - V-)
     
  8. Laplace

    Laplace

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    Apr 4, 2010
    Texas Instruments has an application note (sboa092b.pdf) that covers operational amplifiers with balanced output.
    Screenshot from 2017-06-21 22-19-04.png
     
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  9. davenn

    davenn Moderator

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    cool

    I have never had need to play with those
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

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    An opamp with differential output needs feedback, too, which is missing in the circuit from post #1.
    Assuming the amplifier shown in post #1 has finite gain (e.g. internal feedback or feedback simply not shown). one would still expect the differential output voltage
    Vd = Vo1-Vo2 to be in phase with the input voltage Vi.
    The graphical representation in the figure suggests that the definition of Vd is Vd = Vo2-Vo1 which explains the 180 ° phase shift. In fact, this is the only exlanation I can think of lacking more information from the op. The app note shown by @Laplace in post #8 supports this.
     
  11. Audioguru

    Audioguru

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    Sep 24, 2016
    The OP says that his input is applied to the inverting input but it is shown applied to the non-inverting input!
    Another problem is that his inverting output is not indicated.
     

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  12. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    does he?


    Right, which leads to my questioning the definition of Vd.
     
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