Zener Diode - Practice Questions & MCQ

Zener diode-

It is invented by C. Zener.

A Zener diode is a p-n junction semiconductor device designed to operate in the reverse breakdown region.

It is a highly doped p-n junction which is not damaged by high reverse current. It can operate continuously, without being
damaged in the region of reverse background voltage. It forms a very thin depletion region and an extremely high electric field across the junction even for a small reverse bias voltage (~5 V).

In the forward bias, the Zener diode acts as an ordinary diode.

Symbol of Zener diode-

The symbol of the Zener diode is shown in the below figure.

VI characteristics of Zener diode-

Zener Breakdown-

When a reverse bias is increased the electric field at the junction also increases. At some stage, the electric field becomes so high
that it breaks the covalent bonds creating electron, hole pairs. Thus a large number of carriers are generated.
This causes a large current to flow. This mechanism is known as Zener breakdown.

Avalanche breakdown-
At high reverse voltage, due to the high electric field, the minority charge carriers, while crossing the junction acquire very high velocities.

These by collision breaks down the covalent bonds, generating more carriers. A chain reaction is established, giving rise to high current.

This mechanism is known as Avalanche breakdown.

The VI characteristics of a Zener diode are shown in the below figure.

When forward-biased voltage is applied to the Zener diode, it works like a normal diode.

When reverse-biased voltage is applied to a Zener diode, it allows only a small amount of leakage current until the voltage is less than Zener voltage (V_z). As the reverse bias voltage (V) reaches the breakdown voltage of the Zener diode (Vz), there is a large change in current. Also, note that for a negligible change in the reverse bias voltage, a large change in current is produced.