# Homework Help: Real diode analysis question

1. Jan 15, 2014

### theBEAST

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

2. Relevant equations
I=Ise(V/VT)

3. The attempt at a solution
The solution I got is wrong. Does anyone know why?

Here is my attempt, the image was too large for this forum so here is the link:
http://i.imgur.com/4tuGxdO.jpg

2. Jan 15, 2014

### ehild

You ignored VT in the exponent.

ehild

3. Jan 15, 2014

### theBEAST

Isn't the VT value the same (approximately 0.025V at room temperature)?

4. Jan 15, 2014

### Staff: Mentor

The approximation is just that, an approximation. It is a good "typical" value for run-of-the-mill diodes. The actual value for a given diode depends upon the details of the diode doping. You should determine its true value for this problem.

5. Jan 16, 2014

### ehild

Even in case it is, I1/I2 = e(V1-V2)/VT

ehild

6. Jan 17, 2014

### mezarashi

You may need to run a few simultaneous equations. Here's my suggestion: Use the generic information provided to solve for Is and VT before proceeding further. Then from there you can solve for R using the fact that both sides of the circuit must equate 10mA.