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Diodes Circuits Problem

  1. Nov 13, 2013 #1
    1. The problem statement, all variables and given/known data
    In the circuit below, determine the current through the diode
    http://img12.imageshack.us/img12/152/jar0.jpg [Broken]

    2. Relevant equations
    V:IR
    3V: Va+Vb


    3. The attempt at a solution
    This is my first time trying to solve a circuit problem involving diodes. I first tried to use previous equations I knew, (Ohm's Law & Kirchoff's Laws) but I don't see how I'm suppose to use these equations. I asked my professor if the problem was accidentally not given enough information but he corrected me wrong.

    How should I approach this problem?
    sorry I'm too noob :)
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Nov 13, 2013 #2

    gneill

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    Staff: Mentor

    KVL, KCL, Ohm's law, etc., will all work fine. You just need to know the properties of a diode. What are they?
     
    Last edited by a moderator: May 6, 2017
  4. Nov 13, 2013 #3
    Properties? What do you mean?
     
  5. Nov 13, 2013 #4

    gneill

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    Staff: Mentor

    What do you know about diodes?
     
  6. Nov 13, 2013 #5
    I know that there are three types of diodes. For the LED diode, the voltage needs to have at least 0.7 for it to be on.
     
  7. Nov 13, 2013 #6

    gneill

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    Staff: Mentor

    Okay. Here you're interested in just a run of the mill diode. The 0.7V forward bias voltage is typical of a silicon-based diode (diodes made from other materials will have slightly different characteristic turn-on voltages).

    So, how might you determine if the diode in your circuit is actually forward biased (and thus allowing current to flow)?
     
  8. Nov 13, 2013 #7
    By testing the two diodes whether they are on or off or both? (that's what I remember doing in class)
     
  9. Nov 13, 2013 #8

    gneill

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    Staff: Mentor

    Well, the circuit you've shown for this problem has only the one diode. But sure, test to see if it is "on". How will you do that?
     
  10. Nov 13, 2013 #9
    Sorry, I meant should I test that out?
    Well, I think I need to find the voltage of the diode if it's less/more than 0.7, right?
     
  11. Nov 13, 2013 #10

    gneill

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    Staff: Mentor

    Yup, and make sure it's "pointing" in the right direction; diodes only conduct in one direction.
     
  12. Nov 17, 2013 #11

    NascentOxygen

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    Let's assume the diode voltage is precisely 0.7V here. Then how much battery voltage does that leave for the resistors in your circuit?
     
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