# How to determine numerically the diode current

1. Aug 1, 2006

### 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

2. Aug 3, 2006

### 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.

Last edited: Aug 3, 2006