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Ideal diode question

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  1. Feb 10, 2017 #1
    1. The problem statement, all variables and given/known data
    I am trying to prepare for an exam that is tomorrow, my professor gave sample questions but did not give us any solutions or answers. I have trouble with this question:
    upload_2017-2-10_19-21-19.png

    2. Relevant equations


    3. The attempt at a solution
    I don't know what to do. I would maybe try to figure out if the diode should be on or off. I would assume on in this case and then try to write vout as a function of vin? This isn't homework, I just really need to understand for my exam can someone please explain the steps to me ?
     
  2. jcsd
  3. Feb 10, 2017 #2

    gneill

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    Staff: Mentor

    Don't assume that the diode will always be on: the input is varying with time. Pick several locations along the input curve as test values and see what the circuit is doing for each. After one or two judiciously chosen points it should become clear how to sketch in the whole thing.
     
  4. Feb 10, 2017 #3
    What equation do I test those points in though ?
     
  5. Feb 10, 2017 #4

    gneill

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    Staff: Mentor

    It's up to you to write equations for the circuit. You have two cases: diode conducting and diode not conducting. So two circuits to analyze.
     
  6. Feb 10, 2017 #5
    If it is on, then vin=vout? and the other case I don't know
     
  7. Feb 10, 2017 #6
    If I am going to have two equations, then which one am I going to draw ? Do I at least have the right idea, trying to express Vout as a function of Vin ? Or am I completely lost
     
  8. Feb 10, 2017 #7

    gneill

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    Staff: Mentor

    Sure. For what parts of the input signal is it on?
    Why not? What is the path of the current in that case? What components does it flow through? What are the potential drops?
    Just pick a few individual values that the input can assume, like 0 V, 10 V, -10 V. See what the circuit is doing for each case. You'll be plotting points for BOTH versions of the circuit depending upon what the circuit is doing (diode conducting or not) at any particular time.
     
  9. Feb 10, 2017 #8
    Ok, so when it is off vout = vin/2 ?
     
  10. Feb 10, 2017 #9

    gneill

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    Staff: Mentor

    Yes, It's a simple voltage divider when the diode is off.
     
  11. Feb 10, 2017 #10
    Would it look something like this?
    upload_2017-2-10_20-2-32.png
     

    Attached Files:

  12. Feb 10, 2017 #11

    gneill

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    Staff: Mentor

    No. That doesn't show the action of the diode. It looks like a "pure" voltage divider, affecting the whole input waveform equally.

    Edit:
    However, if you choose the appropriate portions of both curves using the conclusions you've drawn earlier, you should be able to piece together the entire output signal.
     
    Last edited: Feb 10, 2017
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