Explain the forward characteristics of the p-n junction diode by drawing circuit and graph.

Explanation

The configuration of the circuit for the p-n junction diode forward characteristics is shown in the figure.

The battery is connected to the diode through a potentiometer (or reheostat) so that the applied voltage to the directed can be changed.
For different values of voltages, the value of the current in noted. A graph between `V to I` is obtained in first quadrant for Si diode as shown in figure. Here, current is of the order of mA.

In forward bias, the current first increases very slowly, (almost neglibible) till the voltage across the diode crosses a certain value.
After the characteristic voltage, the diode current increases exponentially, even for a very small increase in the diode bias voltage. This voltage is called the thershold voltage or cut-in voltage.
`~0.2` V for germanium diode and `-07` V for silicon diode.
Usually the p-n junction diode current flow in one direction so it is used for rectification of A.C. voltage.
If the forward voltage is increased beyond the value of its safety voltage a very large current is generated so overheating can cause the p-n junction diode to be destroyed. Junction diodes of Ge or Si do not cause any damage to the `100^(@)C and 170^(@)C` temperatures respectively.