Zener Diode Tutorial

The Zener diode is widely used as a reference, but to gain the best performance it is necessary to understand how it works and the breakdown mechanisms within the diode

Zener / Reference Diode Tutorial Includes:
Zener diode     Zener diode theory of operation     Zener diode datasheet specs     Zener diode circuits    

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TheZener diodes is a form of semiconductor diode that is widely used in electronics circuits as a voltage references.

The Zener diode or voltage reference diode provides a stable and defined voltage. As a result Zener diode circuits are often used in power supplies when regulated outputs are needed.

Zener diodes / voltage reference diodes are cheap and they are also easy to use and as a result they are used in many applications and many circuits.

Zener diode history

Zener diode history has its foundations in the development of the first semiconductor diodes. Although early detectors such as cat's whisker, point contact diodes had been available since around 1905, much work on semiconductors and semiconductor diodes was undertaken during and after the Second World War.

The first person to describe the electrical properties utilised by the Zener diode were described by Clarence Melvin Zener (born 1 Dec 1905, died 15 July 1993).

Clarence Zener was a theoretical physicist who worked at Bell Labs and as a result of his work, Bell named the Zener diode after him. He first postulated the breakdown effect that bears his name in a paper that was published in 1934.

Zener diode basics

Zener diodes are sometimes referred to as reference diodes as they are able to provide a stable reference voltage for many electronics circuits. The diodes themselves are cheap and plentiful and can be purchased in virtually every electronics components store.

Zener diodes have many of the same basic properties of ordinary semiconductor diodes. They conduct in the forward direction and have the same turn on voltage as ordinary diodes. For silicon this is about 0.6 volts.

Zener diode voltage-current characteristic
Zener diode voltage-current characteristic

In the reverse direction, the operation of a Zener diode is quite different to an ordinary diode. For low voltages the diodes do not conduct as would be expected. However, once a certain voltage is reached the diode "breaks down" and current flows. Looking at the curves for a Zener diode, it can be seen that the voltage is almost constant regardless of the current carried. This means that a Zener diode provides a stable and known reference voltage.

Zener diode circuit symbol

There are many styles of package for a Zener diode. Some are used for high levels of power dissipation and others are contained within surface mount formats. For home construction, the most common type is contained within a small glass encapsulation. It has a band around one end and this marks the cathode.

It can be seen that the band around the package corresponds to the line on the diode circuit symbol and this can be an easy way of remembering which end is which. For a Zener diode operating in its reverse bias condition the band is the more positive terminal in the circuit.

Zener diode markings, symbol and package outlines
Zener diode markings, symbol and package outlines

Zener diode overview

A Zener diode is a particularly useful component for the design of electronics circuits. As a result many millions of Zener diodes are used each year in the construction of electronics equipment both as discrete components as well as components contained within large integrated circuits. Although voltage reference integrated circuits are available that provide very high degrees of accuracy and temperature stability, for most uses a straightforward Zener diode of more than satisfactory and will provide a much cheaper solution. Accordingly it helps to know what is a Zener diode, how one works, and the basics of a Zener diode circuit.

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