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Homework Help: Small signal approximation diode model

  1. Apr 14, 2009 #1
    hello all im new here so i dont know if this is the correct place for this topic so sorry for any inconvenience caused.

    this is my question:
    Use the small-signal model of the diode to predict the output voltages for the input voltages given. Plot a graph of | vout(t) | based on the small signal model.

    Input Voltage 1 = 0.65 + 0.04cos(2*pi*200*t) V
    Input Voltage 2 = 0.68 + 0.01cos(2*pi*200*t) V
    0 ≤ t ≤ 20ms

    i know vout = -Is*R*exp(vin/Vt)

    How would you solve this? what basically is the small signal model? is it like a formula that I have to substitute these values in? And for the graph what goes on the x-axis and what goes on the y-axis?

    I've got a diagram of the circuit if it helps for you to see:
    http://www.flickr.com/photos/24949707@N07/3430348460/ [Broken]

    Thank You.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 19, 2009 #2


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    Staff Emeritus
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    Homework Helper

    Welcome to Physics Forums ... and sorry about the delayed response.

    This explains the small-signal model for diodes:

    For Input 1 you'll need to figure out:
    • The diode current when Vdiode = 0.65V
    • dI/dV for the diode, when Vdiode = 0.65V

    Use that information to get a linear relation between I and V, that is the small-signal model for the diode.
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