Electrical Engineering ⇒ Topic : Diode Resistance

DIODE RESISTANCE

The ratio V/I of the volt ampere characteristics of the diode gives the static diode resistance. It is the reciprocal of the slope of a line joining the operating point to origin.

The dynamic resistance is given by

                                ........(1)

                         .                ......... (2)

             ...........(3)

     ........ (4)

      [Using Eq. (1)]            ............. (5)

For a reverse bias greater than a few tenths of a volt, V/ηV_T >> I. Therefore, g is very small, forward resistance R_f is very high which is of the order of megaohms. For a forward bias greater

than a few tenths of a volt, I >> I₀, so that

                  ............. (6)

Substituting η = 1, and V_T = 0.026 V, forward resistance is obtained as:

                           .............. (7)

For a current of 1 mA, the forward resistance is 26 Ω and for 26 mA it is 1 Ω.

The ratio of backward to forward resistance in germanium is 400,000 : 1 and in silicon is 1,000,000: 1.