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Real diode analysis question

  1. Jan 15, 2014 #1
    1. The problem statement, all variables and given/known data
    9XUbpS3.png

    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. jcsd
  3. Jan 15, 2014 #2

    ehild

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    Homework Helper
    Gold Member

    You ignored VT in the exponent.

    ehild
     
  4. Jan 15, 2014 #3
    Isn't the VT value the same (approximately 0.025V at room temperature)?
     
  5. Jan 15, 2014 #4

    gneill

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    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.
     
  6. Jan 16, 2014 #5

    ehild

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

    ehild
     
  7. Jan 17, 2014 #6

    mezarashi

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    Homework Helper

    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.
     
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