Zener diode

A diode is an electrical component which is used for the conduction of electrical current in a single direction. A diode is known to have lower resistance in one direction and higher resistance in the other direction. A Zener diode has a special kind of electrical diode that has the ability to make the electrical current flow in the reverse direction. This flow of current in the reverse direction occurs when a certain voltage known as the Zener voltage is achieved by the circuit. For a variety of Zener voltages, a variety of Zener diodes are manufactured. Some of these diodes work for a variable amount of voltage.

Zener diode

Normally diodes allow the flow of current only from anodes to cathodes but in the case of Zener diodes working the flow of current takes place from cathodes to anodes as well. Due to this functionality of these diodes they are one of the most commonly used semiconductors for various industrial purposes. The Zener diode is also commonly known as the breakdown diode. This is because the Zener diode working is based on the breaking of the circuit when the voltage reaches a point known as the Zener voltage or the knee point. At this point the diode is reversed and the current starts to flow in the reverse direction. This effect is also known as the Zener effect. This type of diode is heavily doped and is formed especially to work in the reverse direction. The Zener diode was invented by the physicist Clarence Melvin Zener. He discovered the breakdown effect of the diode that could be used to move the electrical current in the opposite direction.

Working principle of Zener Diode-

The Zener diode working principle is based on the widening of the depletion layer due to the increase in the flow of current. Due to the continuous increase in voltage the depletion layer keeps on getting wider. Consequently there is an increase in the reverse current and it eventually reaches its saturation point. Once the saturation point is reached the minority carriers of charge get enough energy to knock out the electrons that are still present in their external orbitals. This cycle keeps on repeating and the cumulative effect of all the collisions that are taking place amongst the electrons leads to the conversion of the entire diode into a conductor. When the voltage reaches its saturation point, the circuit breaks down. However the structuring of the Zener diode is done in a way that allows the current to flow in the opposite direction as well.

 Working of Zener Diode-

The Zener diode acts as a normal diode when it is working in the forward bias. On the other hand when it is placed in the reverse bias, the diode experiences the flow of small leakage current throughout the circuit. Eventually the reverse voltage is increased to the predetermined level of the diode, current starts to flow in the reverse direction. During this process the current increases and reaches at its highest value but it is controlled by a resistor. Eventually the flow of current stabilises and the diode starts to work over a variety of voltages. The breakdowns that are experienced by the Zener diode can be further classified into two categories namely, Avalanche breakdown and Zener breakdown.

Avalanche Breakdown-

As the name suggests, avalanche breakdown occurs in a diode when the voltage is very high. The process occurs when a high voltage is applied to the circuit which gives sufficient energy to the electrons to accelerate at a higher velocity. These electrons that move at such high velocities collide with other electrons and provide them with energy to move. Due to this continuous collision of electrons, a considerable amount of energy is produced that allows the current to increase in the diode. In normal conditions, such an increase in the electric current can lead to the destruction of the diode. However, a  Zener diode has been made in such a way that it can withstand the increase in current.

Zener Breakdown-

Zener breakdown is another type of breakdown that can be seen in a Zener diode. In case of a Zener diode, when the voltage moves in the reverse direction and it is close to reaching the Zener voltage, the electric field gets strong enough to pull the electrons from their outermost orbital. When the electrons are set free they increase the flow of current which subsequently increases the voltage leading to Zener breakdown. 

Advantages of zener diode-

• Dissipation power is really high.
• High precision
• Small in size 
• low cost

Applications-

• As a voltage reference, it is frequently employed.
• Shunt regulators and voltage stabilisers employ Zener diodes.
• In switching processes, Zener diodes are employed.
• Clipping and clamping circuits use Zener diodes, which are sometimes referred to as zeners.
• Protection circuits rely on Zener diodes.

Conclusion 

Zener diodes are available in a wide range of voltages, some of which are adjustable. This is known as the Zener effect, after Clarence Zener, because electron quantum tunnelling happens in the narrow gap between the p and n regions of a Zener diode, resulting in reverse conduction. Higher Zener voltage diodes have a more progressive junction and use avalanche breakdown in their operation. With the Zener effect predominating at lower voltages and avalanche breakdown occurring at higher voltages, Zener diodes have both breakdown types. Electronic devices of various kinds rely on Zener diodes, which are the building blocks of electronic circuits.They are, for example, used to generate low-power stabilised supply rails from a higher voltage and to provide reference voltages for circuits, notably stabilised power supplies. Overcurrent and electrostatic discharge can also be prevented by using these devices (ESD).