# Diode current

1. Jun 4, 2010

### sudec

1. The problem statement, all variables and given/known data

I have the following circuit:
[PLAIN]http://elementdesign.sk/dioda.jpg [Broken]

I would need to calculate the current and voltage through the diode.

I now that I can calculate the current by the following formula:

$$I=I_{0}(e^{U/U_{0}}-1)$$

I know that $$I_{0}=10^{-17}$$ and $$U_{0}=20mV$$

I have been looking for another formula to calculate the curent and the voltage through the diode, but I was not able to find anything.

Could anyone please help me out here how to get the I and U for the diode.

Thanks a lot.

Last edited by a moderator: May 4, 2017
2. Jun 4, 2010

### vk6kro

You would have to get that data from the manufacturer's data sheets. These are available on Internet by using Google to search. Diodes usually have a number on them to identify the exact type of diode. Something like "1N4148" would identify this diode.

If the diode was Silicon and it was forward biased, the voltage across it would be about 0.6 Volts to 1 Volt, depending on the current.

You can subtract this voltage from the supply voltage to get the voltage across the 13 ohm resistor. Hence you can calculate the current flowing in the resistor and in the diode since they are in series.

If the diode was a LED, the voltage across it will be much higher. LEDs have voltage drops of 1.2 to 4.0 volts mostly depending on their color. The procedure is the same, though.

Because you have a fairly high supply voltage, the error due to not knowing the diode voltage exactly is not very high. Much the same current will flow, regardless.

3. Jun 4, 2010

### xcvxcvvc

uhh, i think this problem comes from a small intro on the topic and isn't for a lab project or anything.

just write the KVL:

$$V_S = I_D R + V_D$$
where Vs is the voltage source. You can substitute the equation for diode voltage to solve for diode current. I believe you will end up with a transcendental equation, so you'll need to use an iterative method or a solver to find the answer.

It's valid to assume the diode is on with a 32V source hooked up to it like that (unless otherwise noted, diodes turn on ~.6V)