Diode's internal resistance

Discussion in 'General Electronics Chat' started by buzaiandras, Oct 24, 2011.

  1. buzaiandras

    Thread Starter Member

    Jul 18, 2011
    Hello all,

    I am trying to correctly learn about diodes and I have some questions related to them.
    Does a diode, a non-linear device, have internal resistance?
    In case it has it is so small that it can be neglected?
    Is the voltage drop of the diode caused by by it's internal resistance or by its semiconductor structure?

    Thank you :),

    Buzai Andras
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    Yes at low currents.
    Semicondoctor structure.
    As you increase the current, the slope of voltage increase after that point is the internal resistance.
  3. crutschow


    Mar 14, 2008
    A semiconductor diode has a logarithmic relationship between voltage and current for any current above it's leakage current to amps. Added to that is a small ohmic resistance. This resistance is smaller for high current diodes and is one of the main differences between small and large diodes.

    If you plot a diode voltage versus current with current on a logarithmic scale it will be a straight line except for the deviation cause by the ohmic resistance.
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    The effect of the ohmic resistance can sometimes be seen in curves shown in device data-sheets.


    In this 1N914 data sheet, Figures 3 & 4 on Page 2 show the voltage-current characteristic following a logarithmic slope up to 10mA. In Figure 5 on Page 3, the curve can be seen curving upwards at higher currents. This becomes evident as the current approaches 100mA. You might like to estimate how much ohmic resistance would be required to explain this deviation.
  5. buzaiandras

    Thread Starter Member

    Jul 18, 2011
    Thank you all for clarifying this :D

    Best regards,