Zener Diode

A semiconductor device that causes the current to flow in a backward or forward direction is the Zener diode which is usually doped to a large extent and possesses a p-n junction. It is specifically designed so that the flow of current happens in a reverse direction when a particular voltage is reached. 

The features of the Zener diode are that it has a reverse breakdown voltage. What does this mean? Current that is conducted by the diode is constant in the reverse mode and the voltage drop is also constant, notwithstanding the amount of voltage or force applied. Hence it is thought in electronics that the Zener diode is extremely useful for voltage regulation in circuits.

How is the Zener Diode Circuit Depicted?

As we already know, the Zener diode functions in a reverse-bias mode. Hence, the negative terminal of the power supply is connected to the p-type material and the positive terminal is connected to the n-type material in the Zener diode. Because it has semiconductor material that is heavily doped, the diode has a thin depletion region.

How does the Zener Diode Work? 

To enhance its conductivity, the Zener diode is doped with lots of impurities in the semiconductor material. Hence the depletion region thins out. So the application of electric fields across this depleted region is intensified even when a small voltage is applied to the system. 

Now, what happens when there is no biassing in the Zener diode? The p-type semiconductor material has a valence band where electrons come together. This results in zero current flow across the diode. This band is then called the valence band electron. Once external energy is applied to this valence band, electrons start making their journey from one band to the next. 

What is the situation when a reverse bias is applied across the Zener diode? It so happens that the diode conducts itself in a reverse-bias mode when the Zener voltage equals the supply voltage. We must remember that the voltage which is known as the Zener voltage is when the depletion region not only thins out but completely vanishes. 

When a reverse bias is applied across the diode, the electric field intensifies as the depletion region has thinned out. The electrons thus move from the valence band of the p-type semiconductor material to the conduction band of the n-type semiconductor material. This movement destroys the barrier between the two materials. At this voltage and level of the current field, the diode conducts the current in a reverse bias direction.

VI Characteristics of the Zener Diode

When the diode is in forwarding bias mode, the Zener diode is nothing but an ordinary diode. However, when the reverse bias is applied, the reverse voltage rises. This causes a complete breakdown in the Zener diode. 

This breakdown causes the current to flow in a reverse direction, at what is called a breakdown voltage. Graphs show us that the Zener diode possesses quite a bit of resistance and that the breakdown is not linear or vertical. 

Hence, the Zener diode’s voltage is given by the following equation - V = VZ + IZRZ

Applications of the Zener Diode

Zener diodes are mainly used in industrial as well as commercial settings. A voltage stabiliser is used to regulate voltage. The fluctuating voltage here is converted to a constant voltage to be supplied to the power load. So the Zener diode is usually connected parallel to the load. Because it is able to maintain a constant voltage, it acts as a voltage regulator or stabiliser. 

Commercial and industrial buildings use huge power-metre systems which are easily prone to metre overloads. However, these multimeters are connected parallel to the Zener diode which prevents accidental overloads upon the system. When an overload does occur, the majority of the current passes through the diode, hence the metre is protected. 

Two Zener diodes are connected back to back and in opposite directions in a series with the resistance of the circuit, because of which a sine wave is easily converted into a square wave. 

The Zener diode also has certain specifications for values such as Zener voltage, the minimum current required for the breakdown and maximum current, the power that can be dissipated by the Zener diode, temperature stability of the diode and the Zener resistance.