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Finding voltage change for current change for diode

  1. Jul 14, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the change in diode voltage if the current changes from 0.1 mA to 10 mA. Ans. 120 mV


    2. Relevant equations
    V2-V1=VTln(I1/I2)


    3. The attempt at a solution
    That is all the information given. The only equation I can think to use is the diode voltage/current relationship, but a value for initial voltage is not given. The calculation assuming V1=0.7 V V2=0.025ln(10/0.1)+0.7 = 0.8151.

    Thanks for the help.
     
    Last edited by a moderator: Jul 14, 2016
  2. jcsd
  3. Jul 14, 2016 #2

    berkeman

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    Staff: Mentor

    But the problem statement only asks for the change in voltage, not the final voltage...
     
  4. Jul 14, 2016 #3
    The only other equation in the section is i = IseV/VT. How would I find change in voltage?
     
  5. Jul 14, 2016 #4

    berkeman

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    Staff: Mentor

    What is the diode equation?
     
  6. Jul 14, 2016 #5
    i = IseV/VT is the only equation and Is is not given.
     
  7. Jul 14, 2016 #6

    berkeman

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    Staff: Mentor

    I_s is a constant...
     
  8. Jul 14, 2016 #7
    From what i researched it depends on the diodes physical characteristics. The information above is all that is provided. I could not find a constant value for Is.
     
  9. Jul 14, 2016 #8

    berkeman

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    Just assume it is the same for the test diode for the two test currents. Can you write the two equations and solve them to get the delta-V?
     
  10. Jul 14, 2016 #9
    V2-V1=VTln(I1/I2) = 0.025 ln (10/0.1) = 115.1 mV ?
     
  11. Jul 14, 2016 #10

    berkeman

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    Looks good. The only thing I would change would be to use 25.85mV for Vt (at room temperature). :smile:
     
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