1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do I find the forward resistance of a diode using diode law?

  1. Oct 9, 2011 #1
    1. The problem statement, all variables and given/known data

    I must find the resistance of a diode inside the piecewise model using the diode law equation.

    I am given variables VD = .75V, Is = 5*10^-13 A, and VT = .026 A. n = 1


    2. Relevant equations

    The Diode Law equation: ID = IS(e(VD/nVT) - 1)


    3. The attempt at a solution

    We were told that to find the resistance, we are to find the derivative of this equation to find the conductance, and then the inverse of this would be the resistance. I'm not sure what to derive with respect to or if even this explanation is correct. Can anyone help explain how to find resistance using this equation?
     
  2. jcsd
  3. Oct 9, 2011 #2

    gneill

    User Avatar

    Staff: Mentor

    One measure of resistance is the one that describes the operating point of the device: operating voltage divided by operating current. So if you're given the voltage across the device and can calculate the resulting current, then R = V/I.

    A second measure of resistance is the 'small signal resistance', which describes how a change in voltage across the device (at the operating point) affects the current: r = Δv/ΔI. This one you might find by taking the derivative of your diode law w.r.t. voltage to find di/dv, and hence dv/di.

    It looks like it's the first version of resistance you're after in this case.
     
  4. Oct 10, 2011 #3

    NascentOxygen

    User Avatar

    Staff: Mentor

    Poster needs to find the small signal resistance. (Probably what you meant to say.)

    The variables are ID and VD, being the diode current and voltage, all other terms are constants.
     
  5. Oct 10, 2011 #4

    gneill

    User Avatar

    Staff: Mentor

    You're probably right! :approve:
    Thanks for he catch.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How do I find the forward resistance of a diode using diode law?
Loading...