Mumbai University > Electronics ana telecommunication engineering > Sem 3 > Analog electronics 1

Marks: 4M

Years: Dec 2014, May 2016

The diode current depends on the voltage applied to it. The relationship between applied voltage V and the diode current I is exponential and is mathematically given by the equation called diode current equation. It is expressed as,

I = $I_0 (e^\frac{V}{(ηV_T )} -1) A$

Where $I_0$ = Reverse saturation current in amperes

V = Applied voltage

η = 1 for germanium diode

= 2 for silicon diode

$V_T$ = Voltage equivalent of temperature in volts

The voltage equivalent of temperature indicates dependence of diode current on temperature. The voltage equivalent of temperature $V_T$ for a given diode at temperature T is calculated as,

$V_T$ = kT volts

Where k = Boltzmann's constant = $8.62 x10^(-5) eV/° K$

T = Temperature in °K.

Thus at room temperature of 27 °C i.e. T = 27 + 273 = 300 ° K the value of $V_T$ is,

$V_T= 8.62 x 10^(-5) x 300 $= 0.02586 V = 26 mV

The value of V_T also can be expressed as,

$V_T= \frac{T}{\frac{1}{K}}= \frac{T}{\frac{1}{8.62x10^(-5)}}= \frac{T}{11600}$

Thus at room temperature of T = 300 ° K, we get $V_T$ = 26 mV.

The diode current equation is applicable for all the conditions of diode i.e. unbiased, forward biased and reverse biased.

When unbiased, V = 0 hence we get,

$I = I_0 (e^0 -1) A = 0 A$

Thus there is no current through diode when unbiased.