Tuesday, August 24, 2010

Equivalent Circuit for an LED

The deviation of the measured characteristic from an ideal diode at higher currents can be explained by an internal resistance within the diode. If one allows for an internal resistance one gets an almost perfect fit with the ideal diode equation for all values of the measured current. So the diode equation does appear to work.

The results suggest the following equivalent circuit for a real diode. There appears to be an interval voltage source, V0, an ideal diode characterized by I0 and the thermal voltage and an internal resistance.

I do not know enough about the internal structure of the diode to explain the internal voltage barrier. It may to due to a Fermi energy which is associated with the chemical potential, μ, a measure of the free energy of the charge carriers in the diode.

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