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Homework Help: How to correctly redraw a circuit?

  1. May 31, 2014 #1
    1. The problem statement, all variables and given/known data

    Redraw the following circuit:


    2. Relevant equations

    Identifying nodes and drawing skills maybe :S

    3. The attempt at a solution

  2. jcsd
  3. May 31, 2014 #2

    Simon Bridge

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    Redraw the circuit as what?
    Why can't all the 5V blobs get joined together so you only need one battery?
    Shouldn't the back-end of each diode be earthed?
    What was your question?
  4. May 31, 2014 #3
    Your attempt looks good. But you can simplify this circuit further. Notice that all voltage source are 5V.
    So you can use one 5V voltage source on your diagram.
  5. May 31, 2014 #4
    Simon Bridge:

    I don't know whether I should ground the diodes or not. Anyway, the original question was: "Determine whether the diodes are forward biased or reverse biased if: 1) V1=V2=5V 2) V1=5V, V2=0V 3) V1=V2=0V "


    I missed that, the all three sources are in parallel, can I put one source in place of V1?
  6. May 31, 2014 #5

    Simon Bridge

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    You ground the diode if one end of the diode is connected to a "ground" symbol on the diagram - go look!

    This is an exercise in reading a circuit diagram.
    If you are having trouble telling if two components are connected or not, run your finger along a "wire" line.

    V1 is already one source.
    The 3 sources you drew in your modified diagram are not in parallel with each other - they have other components with them. Go back to the original diagram. You can draw a line connecting all parts of the diagram that are held at the same voltage ... try it for all the +5V dots. That line has to be held at +5V - how do you do that?

    Then why are you bothering with redrawing the diagram?

    What does it mean to forward or reverse bias a diode?
  7. May 31, 2014 #6
    Okaaay. I understand now, looks like I have to basics at all. :S

    I want to evaluate Vo in case V1=V2=0.

    Forward bias means there's a current flowing and reverse bias means there isn't any current.
  8. May 31, 2014 #7

    Simon Bridge

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    You do not need to redraw the diagram to do that.

    No. Diodes may conduct when reverse biased. Some, like Zener diodes, do this at low voltages.

    Treat the symbol for a diode as an arrow.
    Compare the voltages on each side of the diode symbol.
    Current flows from higher voltage to lower voltage.
    If the current is in the same direction as the arrow, then the diode is "forward biased".
  9. May 31, 2014 #8


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    The original schematic is the clearest, stay with it :wink:

    Vo appears to be the diodes' anode voltage. That is a poorly-drawn arrow, not a connection to ground! Erase the arrow, and focus on that schematic.

    The approach to analyzing circuits with diodes is to, in turn, imgine this diode is conducting in this direction....That means current must be flowing along this path, and the voltages along this branch will be .. Do these voltage levels confirm the initial assumption that the diode is conducting? Yes/no. If not, then the assumption that that diode is conducting must be wrong.

    For circuits with multiple diodes, it's a trial-and-error technique until you become adept at it.
  10. Jun 18, 2014 #9
    Ok, I just to make sure of something. When V1=V2=5V, the two diodes are reverse biased, then Vo would be 5V, isn't?
  11. Jun 18, 2014 #10


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    You're renaming the voltage sources now, are you? :confused:

    Anyway, if all 3 voltage sources are +5V then the output will be +5V. But in this state the diodes won't be reverse-biased; neither will they be forward-biased. With identical potential on each side, a diode won't be biased at all! It won't be conducting current, either, because across the diode there is no voltage difference to push current along.

    I'm assuming that black line at Vo does not denote a connection to ground
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