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Homework Help: How to determine numerically the diode current

  1. Aug 1, 2006 #1

    can anybody pls show me how to determine numerically the diode current
    I(D) for t<0 and t>0

  2. jcsd
  3. Aug 3, 2006 #2
    First of all, there is NO given time-dependent information. Why do you want I(D) for t<0 and t>0? I assume you want the I(D) for the diode's working point.

    It would be better understood if we plug in some values. Here we go:




    [tex]I_{0}=24\ mA[/tex]

    By considering the open (oc) and short circuits (sc), you will obtain two values where:

    [tex]I_{oc}=0[/tex] as [tex]V_{oc}=V_{Th}=1.2\ V[/tex]

    [tex]I_{sc}=\frac{V_{Th}}{R_{Th}}=8.0\ mA[/tex]

    Here is the I-V source characteristic, the red line:


    Now, if the characteristic of the diode is given by


    Then plotting the characteristic on the same graph gives the green line:


    A. Graphically
    So you know that the intersection is the working point for the diode and there you can write down the value of [tex]V_{D}=0.9\ V[/tex] and [tex]I_{D}=2.0\ mA[/tex].

    B. Numerically
    Find the equation of the I-V source characteristic using the famous [tex]Y=mX+C[/tex] where you will expect C = 0.008 A and and negative slope m. Then, solving the simultaneous equations proves the values obtained in A. That's simple.
    Last edited: Aug 3, 2006
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