Best 3 Applications Involving in Zener Diode Working Functionality

Best 3 Applications Involving in Zener Diode Working Functionality

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Introduction

Zener diodes are normal PN junction diodes operating in a reverse biased condition. Working of the Zener diode is similar to a PN junction diode in forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold / breakdown voltage. These are among the basic types of diodes used frequently, apart from the normal diodes.

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Zener Diode Working







Semiconductor Diode in Reverse Bias Condition

PN junction diode is formed by a combination of a p type semiconductor material with an n type semiconductor material.

When one side of a semiconductor crystal is doped with donor impurities.

The other side with acceptor impurities, a PN junction is formed.







Unbiased Semiconductor Diode

The holes from the p side tend to diffuse to a low concentration region.

The same thing happens for electrons from n-side.

Thus the holes diffuse to the n-side and the electrons diffuse to the p-side.

This results in accumulation of charges around the junction, forming a depletion region.

An electric polarity or electric dipole is formed across the junction, causing flow of flux from n side to p side.







This results in varying negative electric field intensity, generating an electric potential across the junction.

This electric potential is actually the threshold voltage of the diode.

A normal diode is biased such that a negative voltage is applied to the n side and positive voltage to the p side.

The diode is said to be in forward biasing condition.















Applied voltage tends to decrease the potential barrier after it goes beyond the threshold voltage.

The majority carriers cross the potential barrier and the device starts conducting with flow of current through it.

When the diode is biased in reverse condition to above, the applied voltage.

It adds to the potential barrier and hinders the flow of majority carriers.

It allow the flow of minority carriers (holes in n type and electrons in p type).








As this reverse bias voltage increases, the reverse current tends to increase gradually.

At a certain point, this voltage is such that it causes breakdown of the depletion region.

Causing a massive increase in the flow of current.

This is where the zener diode working comes into play.







The Working Principle of zener diode lies in the cause of breakdown for a diode in reverse biased condition. Normally there are two types of breakdown.

Zener Breakdown

Avalanche Breakdown.

Principle Behind Zener Diode Working







Zener Breakdown

This type of breakdown occurs for a reverse bias voltage between 2 to 8V.

Even at low voltage, the electric field intensity is strong enough to exert a force.

The valence electrons of the atom such that they are separated from the nuclei.

This type of break down occurs normally for 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 the less amount of external voltage is required.

Thus zener breakdown voltage decreases with temperature.







Avalanche Breakdown

This type of breakdown occurs at the reverse bias voltage above 8V and higher.

It occurs for lightly doped diode with large breakdown voltage.

As minority charge carriers (electrons) flow across the device.

They tend to collide with the electrons in the covalent bond and cause the covalent bond to disrupt.







Avalanche Breakdown

As voltage increases, the kinetic energy (velocity) of the electrons also increases.

The covalent bonds are more easily disrupted, causing an increase in electron hole pairs.

The avalanche breakdown voltage increases with temperature.







The 3 Zener Diode Applications

1. Zener Diode as a voltage

2. Zener Diode as a voltage reference

3. Zener Diode as a voltage clamper







Zener Diode as a voltage

In a DC circuit, Zener diode can be used as a voltage regulator or to provide voltage reference.

The main use of zener diode lies in the fact that the voltage across a Zener diode remains constant for a larger change in current.

This makes it possible to use a Zener diode as a constant voltage device or a voltage regulator.

In any power supply circuit, a regulator is used to provide a constant output (load) voltage.








Irrespective of variation in input voltage or variation in load current.

The variation in input voltage is called line regulation.

The variation in load current is called load regulation.








While designing a voltage regulator using zener diode

The latter is chosen with respect to its maximum power rating.

The maximum current through the device should be:-

Imax = Power/Zener Voltage

Since the input voltage and the required output voltage is known.

It is easier to choose a zener diode with a voltage approximately equal to the load voltage, i.e. Vz ~=Vo.








The value of the series resistor is chosen to be

R =(Vin – Vz)/(Izmin + IL), where IL = Load Voltage/Load resistance.

It is advisable to use a forward biased diode in series with the Zener diode.

This is because the Zener diode at higher voltage follows the avalanche breakdown principle, having a positive temperature of coefficient.

Hence a negative temperature coefficient diode is used for compensation.







Zener Diode as a Voltage Reference

In power supplies and many other circuits, Zener diode finds its application as a constant voltage provider or a voltage reference.

The only conditions are that the input voltage should be greater than zener voltage.

The series resistor should have a minimum value such that the maximum current flows through the device.







Zener Diode as a Voltage Clamper

A Zener diode can be used in a circuit involving AC input source, different from the normal PN diode clamping circuit.

The diode can be used to limit the peak of the output voltage to zener voltage.

At one side and to about 0V at other side of the sinusoidal waveform.







From the image, during positive half cycle, once the input voltage is such that the zener diode is reverse biased.

The output voltage is constant for a certain amount of time till the voltage starts decreasing.

During the negative half cycle, the zener diode is in forward biased connection.

As the negative voltage increases till forward threshold voltage.









The diode starts conducting and the negative side of the output voltage is limited to the threshold voltage.

To get an output voltage in positive range only, use two oppositely biased Zener diodes in series.






Working Applications of Zener Diode

Another application involves use of Zener diode as a voltage regulator.

Here the AC voltage is rectified by the diode D1 and filtered by the capacitor.

This filtered DC voltage is regulated by the diode to provide a constant reference voltage of 15V.

This regulated DC voltage is used to drive the control circuit.

It used to control the switching of light, as in an automated lighting control system.

Working application of zener diode involving a Bluetooth device







Working application of zener diode involving a Bluetooth device







Zener Diode Voltage Regulation Application

Another application involves use of Zener diode as a voltage regulator.

Here the AC voltage is rectified by the diode D1 and filtered by the capacitor.

This filtered DC voltage is regulated by the diode to provide a constant reference voltage of 15V.

This regulated DC voltage is used to drive the control circuit.

It used to control the switching of light, as in an automated lighting control system.







Zener Diode Voltage Regulation Application










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Best 3 Applications Involving in Zener Diode Working Functionality