In a p-n junction diode, the current I can be expressed as
$I=I_{0} \exp \left(\frac{e V}{2 k_{B} T}-1\right)$
where $I_{0}$ is called the reverse saturation current, $V$ is the voltage across the diode and is positive for forward bias and negative for reverse bias, and I is the current through the diode, $k_{B}$ is the Boltzmann constant $\left(8.6 \times 10^{-5} \mathrm{eV} / \mathrm{K}\right)$ and $\mathrm{T}$ is the absolute temperature. If for a given diode $\mathrm{l}_{0}=5$ $\times 10^{-12} \mathrm{~A}$ and $\mathrm{T}=300 \mathrm{~K}$, then
(a) What is the dynamic resistance?
(b) What will be the current if reverse bias voltage changes from $1 \mathrm{~V}$ to $2 \mathbf{V}$ ?

3 years ago

The expression for current in a p-n junction diode, is given as

$I=I_{0} \exp \left(\frac{e V}{2 k_{B} T}-1\right)$

Here, $l_{0}=5 \times 10^{-12} \mathrm{~A}$

$\mathrm{T}=300 \mathrm{~K}$

$\mathrm{k}_{\mathrm{B}}$ is the Boltzmann constant with a value of $8.6 \times 10^{-5} \mathrm{eV} / \mathrm{k}=8.6 \times 10^{-5} \times 1.6 \times 10^{-19}=1.376 \times 10^{-23} \mathrm{~J} / \mathrm{K}$

(a) Dynamic resistance $=$ Change in voltage/ Change in current
$=0.1 / 1.23$

$=0.081 \Omega$

(b) The current will nearly always be equal to $I_{o}$ if the reverse bias voltage is changed from 1V to 2V. As a result, with the reverse bias, the dynamic resistance will be infinite.