How to determine numerically the diode current

[teng125]

http://www.sendspace.com/file/qhojgm

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

thanx

 

[Meson]

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:

Given:

R_{1}=R_{2}=R_{3}=100\Omega

I_{0}=24\ mA


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

I_{oc}=0 as V_{oc}=V_{Th}=1.2\ V

I_{sc}=\frac{V_{Th}}{R_{Th}}=8.0\ mA


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 V_{D}=0.9\ V and I_{D}=2.0\ mA.

B. Numerically
Find the equation of the I-V source characteristic using the famous Y=mX+C 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.