What is Zener Diode?

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Zener diode in a nutshell

Some junction diodes are developed for different applications. The Zener diode is also a special type of junction diode. It was invented by Clarence Melvin Zener. It is a special type of silicon diode which is designed to operate optimistically in the reverse breakdown voltage region continuously without being damaged. A zener diode allows current to flow from its anode to cathode like a normal semiconductor diode, but it also permits current to flow in the reverse direction when its “Zener Voltage” is reached. It has a highly doped p-n junction. Its special characteristic of being reliably operated in the breakdown region make it a special type of p-n junction diode. Zener diodes have a sharp breakdown voltage. By varying the doping level of silicon diodes, a manufacturer can produce zener diodes with breakdown voltages from about 2 to 200 V. Now that you have known what a zener diode is, you would be thinking how a zener diode works, what are its characteristics and its uses. So, let’s find out all the answers to our curious questions. First of all, we will have a look through the working principle of the zener diode.

Working principle of a Zener Diode

The basic principle behind the working of zener diode lies in the cause of breakdown for a diode in reverse biased condition. Normally, there are two types of breakdown-Zener and Avalanche.

Zener breakdown occurs for a reverse bias voltage between 2 to 8V. Even at this low voltage, the electric field intensity is strong enough to exert a force on the valence electrons of the atom such that they are separated from the nuclei. This results in the formation of mobile electron-hole pairs, increasing the flow of current across the device. Approximate value of this field is about \( 2\times { 10 }^{ 7 } \)

This type of breakdown occurs normally for the highly doped diode with low breakdown voltage and larger electric field. As temperature increases, the valence electrons gain more energy to disrupt from the covalent bond and less amount of external voltage is required. Thus zener breakdown voltage decreases with temperature.

Avalanche breakdown occurs at the reverse bias voltage above 8V and higher. It occurs for the lightly doped diode with large breakdown voltage. As minority charge electrons flow across the device, they tend to collide with the electrons in the covalent bond and cause the covalent bond to disrupt. As voltage increases, the kinetic energy (velocity) of the electrons also increases and the covalent bonds are more easily disrupted, causing an increase in electron-hole pairs. The avalanche breakdown voltage increases with temperature. Now let’s have a look on some of the characteristics of the zener diode.

Characteristics of a Zener Diode:-

  • Its characteristics are similar to an ordinary rectifier diode with the exception that it has a sharp breakdown voltage called zener voltage \( V_{ z }\).
  • It can be operated in any of three regions i.e., forward, leakage or breakdown. But usually, it is operated in the breakdown.
  • The voltage is almost constant \(\left( { V }_{ z } \right)\) over the operating system.
  • Usually, the value of \( V_{ z }\) at a particular test current \(I_{ZT}\) is specified in the data sheet.
  • During operation, it will not burn as long as the external circuit limits the current flowing through it below the burnout value i.e. \(I_{ZM}\) (the maximum rated zener current).

Zener Diode Circuit Diagram

A specially designed silicon diode which is optimized to operate in the breakdown region is Zener Diode. The Zener Diode Circuit Diagram is embedded below:-Zener Diode

Usually, It is denoted by the symbol given below:-Zener Diode Symbol

Application of Zener Diodes

Zener Diodes find wide commercial and industrial applications. Some of the important applications are pointed below:-

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