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Homework Help: Simple Diode Problem

  1. Sep 16, 2007 #1
    1. The problem statement, all variables and given/known data

    Find the parameters of a piecewise linear model of a diode with the following known values:

    v_d = 0.7V
    i_D = 1mA
    n = 2.

    Make your model fit at 1mA.

    2. Relevant equations

    They are in the image below, written there.

    3. The attempt at a solution

    Here's my attempt. I drew out the piecewise linear equivalent, which can be seen to the right of the equal sign. The eq. that I need are on the far left top, and I start putting values in.

    I also assumed the saturation current was 10^-11. That's another question I had, they never specified it, so should I assume that 10^-11 is it? It seems that the other ex. in this book uses that value, so...

    http://img45.imageshack.us/img45/1165/untitledkp4.jpg [Broken]
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Sep 16, 2007 #2
    You found the correct value for [tex]r_{d}[/tex] but then you used the value 0.921 for [tex]V_{d}[/tex] when you are told that the value of [tex]V_{d}[/tex] is 0.7. In this problem you are given the value of the forward voltage (Vd = 0.7) at a specific forward current (Id = 1mA) so you don't need to assume any value for Is, because it's value results from the equation [tex]I_{d} = I_{s}e^{\frac{V_{d}}{nV_{T}}}[/tex] where you know both [tex]I_{d}[/tex] and [tex]V_{d}[/tex].
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