Best 3 Applications Involving in Zener Diode Working Functionality

Best 3 Applications Involving
in Zener Diode Working
Functionality

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Best 3 Applications Involving in Zener
Diode Working Functionality
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.

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

Diode
Working application of zener diode involving a Bluetooth device

Diode
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.

Diode
Zener Diode Voltage Regulation Application

Best 3 Applications Involving in Zener Diode Working Functionality

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