Q.Write the Shockley diode equation for the current through the power diode and explain its terminology.

The V-I characteristics of a power diode describe how its current depends on the applied voltage. Like a signal diode, the current follows the Shockley diode equation

where $I_S$ is the reverse saturation current, $V$ the applied voltage, $q = 1.6\times10^{-19}\ \text{C}$ the electron charge, $k = 1.381\times10^{-23}\ \text{J K}^{-1}$ Boltzmann's constant and $T$ the absolute temperature. Both the forward and reverse curves shift with junction temperature.

When a power diode conducts in the forward direction, its anode-to-cathode voltage has two parts: the drop $V_j$ across the p+ n- junction, and the ohmic drop across the resistive drift region. Writing the ohmic term as $R_{ON} I_F$ gives

$V_{AK} = V_j + R_{ON} I_F$ …