Explain the reverse characteristics of p-n junction diode by circuit diagram with graph.

Explanation

The circuit arrangement for reverse characteristics of the p-n junction diode is shown in the figure (b).

The battery is connected to the diode through a potentiometer or reheostat so that the applied voltage to the diode can be changed.
For different values of voltages, the value of the current is noted. A graph between V and I is obtained as in figure (c ) question 30. Here current is of the order of `muA`.
The current under reverse bias is essentially voltage independent upto a critical reverse bias voltage known as breakdown voltage `V_("br")`.
When reverse bias voltage becomes equal to break down voltage `(V=V_("br"))`, the diode reverse current increases sharply. Even or slight increase in the bias voltage causes large change in the current.
If the reverse current is not limited by an external circuit below the rated value, the p-n junction will get destroyed. Once it exceeds the rated value, the diode gets destroyed due to overheating.
For the diode in reverse bias, the current is very small `(-muA)` with opposite direction and almost remains constant with change in bias. It is called reverse saturation current.
The general purpose diode are not used beyond the reverse saturation current region.
For diode, a quantity called dynamic resistance as the ratio of small change in voltage `DeltaV` to a small change in current `DeltaI`
`r_(d)=(DeltaV)/(DeltaI)`
The resistance of the diode in forward bias mode is approximately between `10Omega` to `100Omega` in reverse bias mode it is about of the order `10^(6)Omega (M Omega)`.