Solve Simple Diode Problem: v_d, i_D, n, Fit at 1mA

[DefaultName]

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

 

[antonantal]

You found the correct value for $$r_{d}$$ but then you used the value 0.921 for $$V_{d}$$ when you are told that the value of $$V_{d}$$ 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 $$I_{d} = I_{s}e^{\frac{V_{d}}{nV_{T}}}$$ where you know both $$I_{d}$$ and $$V_{d}$$.