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.

 

[piercas]

I can provide you with the following steps to determine the diode current numerically:

1. Begin by understanding the characteristics of a diode. A diode is a semiconductor device that allows current to flow in one direction and blocks it in the opposite direction.

2. For t<0, the diode is considered to be in reverse bias, meaning the voltage applied to it is in the opposite direction of the current flow. In this case, the diode current (I(D)) is assumed to be zero.

3. For t>0, the diode is considered to be in forward bias, meaning the voltage applied to it is in the same direction as the current flow. In this case, the diode current can be determined using the diode equation:

I(D) = I_s (e^(V_D/nV_T) - 1)

where I_s is the reverse saturation current, V_D is the voltage across the diode, n is the ideality factor (typically around 1 for silicon diodes), and V_T is the thermal voltage (approximately 26 mV at room temperature).

4. Substitute the values of I_s, V_D, n, and V_T into the diode equation to calculate the diode current at t>0.

5. If you have a circuit with multiple diodes, you can use Kirchhoff's current law to determine the total current in the circuit. This can help you determine the individual currents for each diode.

6. Alternatively, you can also use a multimeter to measure the current in the circuit and compare it to the calculated value to verify your results.

I hope this helps you determine the diode current numerically. If you have any further questions, please feel free to ask.