Simple Diode Problem

  • #1
180
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Homework Statement



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.

Homework Equations



They are in the image below, written there.

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]
 
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Answers and Replies

  • #2
218
0
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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