Zener Diode - Electrical C & V


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20 February 2020

Zener Diode

What is Zener Diode?

A Zener diode is a diode that not only allows current to pass from its anode to the cathode but also allows the current to flow in the reverse direction when the voltage reaches the Zener voltage.
It is a silicon semiconductor device. It is named after the clarence zener that discovered the zener effect.

What is Zener Diode

The p-n junction of Zener Diode is highly dope. Normal diodes breakdown at reverse voltage and are not designed to operate in the breakdown area. But Zener diodes operate strongly in the breakdown area.

Zener reverse breakdown is caused by electron quantum tunnelling, which is caused by an electric field with more power. Zener diodes rely more on avalanche breakdowns.

Zener diodes use both the zener effect and avalanche breakdowns. The zener effect occurs at low voltage and avalanche breakdown occurs at high voltage. Zener diodes are widely used in all types of electronic devices.

The zener diode is a common block of electronic circuits. Zener diodes are used for stable power supply. And they are used to protect the circuits from overvoltage.

Working of Zener Diode

A normal diode allows some current to flow when the reverse bias occurs above the reverse breakdown voltage. When the reverse bias breakdown voltage increases then the diode allows more current to flow due to avalanche breakdown. Because of this diode overheating can be ruined forever. Zener diodes also have the same properties as normal diodes, but are designed to have a lower breakdown voltage, called a Zener voltage.

A reverse bias zener diode exhibits controlled breakdown compared to a normal diode and the current (current) is what keeps the voltage close to the Zener breakdown voltage across the Zener diode.

For example, if a Zener Diode whose Zener breakdown voltage is 3.7V, its voltage drop also remains around 3.7V. So therefore Zener diode can be used as a voltage stabilizer.

Construction of Zener Diode

The mechanism of Zener diode depends on the excessive doping of its pn junction. The depletion field in the diode is very thin and the electric field is quite strong. The electric field is too high even for the reverse bias voltage of 5V due to which electrons move from the valence band of the p type material to the conduction band of the n type material.

The breakdown voltage for commonly available zener diode can vary from 1.2V to 200V. In diodes that are less doped, avalanche breakdown is greater than Zener breakdown. Due to which the breakdown voltage in such devices is high.

Effect of Zener Diode

The zener effect is a type of breakdown that occurs in a reverse biased PN junction.


Due to the high amount of dope of p and n substances, they become good conductors and the depletion layer also becomes thin, the electric field across the depletion layer becomes very strong. Due to which the holes and electrones which are present at low voltage cross the depletion layer and are added which causes the reverse current. This effect occurs mostly in Zener diodes which have low reverse breakdown voltage.

What is Avalanche Breakdown?

The breakdown voltage of Zener Diode which is wide depletion layer is also high. In those diodes,the current increases in breakdown voltage very fast, which reduces the reverse resistance of the diode.

A reverse leakage current flows below the reverse breakdown voltage. Because of which electrons and holes (holes) go into the depletion layer. Now the voltage is equal to the reverse breakdown voltage. In the depletion layer, the existing electrons and holes fall under a strong electric field, which is rapidly accelerated.

These electrons and holes collide with other atoms and eject electrons from their atomic bonds, this is called impact ionisation. Thus more electron / hole pairs are formed which are greatly accelerated by electric field. These electron holes in turn ionize the other atom, which causes a very sharp increase in the reverse current of the diode. This process is called avalanche breakdown.

Uses of Zener Diode

1: - It is used for voltage reference and shunt regulator, and for controlling voltage in short circuits.

2: - Zener Diode is used in surge protector to limit the transient voltage spikes.

3: -The noise of the generator diode, which is caused by avalanche breakdown, is used in the random number generator.

4: - waveform clipper-Zener diode is used to clip the waveform. When the two Zener diodes are placed in front of each other in the range, it clips both the semicircles of the input signal. The use of waveform clippers is not only to resize the signal but also to voltage spike such circuits

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