The document discusses the use of Zener diodes as voltage regulators. It begins by describing how Zener diodes allow current to flow in the reverse direction above a certain breakdown voltage. It then discusses different types of Zener diodes categorized by voltage, current, and power ratings. The document explains that Zener diodes can regulate an unsteady input voltage to provide a steady output voltage. It provides an example circuit diagram of a Zener diode regulating a 12V supply down to a steady 8V for a 100mA load. Measurements and component selections are described to illustrate how the Zener diode maintains a constant voltage across varying loads and minor input fluctuations.

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TO,
RAVINDRA MEENA
SIR
HOD Ist YEAR
PRESENTED BY,
SANJAY(K12336), SABIHA(k12783),
ROHIT(k)
IInd Sem , 1st Year, Section A
A-3 Batch

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Introduction to Zener Diode
Types of Zener Diodes
Applications of Zener diode
Zener Diode As a Voltage Regulator
Circuit Diagram
I-V Characterstics of Zener Diode

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 Zener diodes are a special kind of diode which permits current to flow in the forward
direction.
 It is different from others diodes Zener diodes will also allow current to flow in the
reverse direction when the voltage is above a certain value.
 This breakdown voltage is known as the Zener voltage.
 Zener diodes are designed in a way where the Zener voltage is a much lower value.
 There is a controlled breakdown which does not damage the diode when a reverse
current above the Zener voltage passes through a Zener diode.

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There are many different kinds of Zener diodes :
 The most common types categorized by power dissipation, nominal working voltage,
forward (drive) current, forward voltage, packaging type and maximum reverse current.
 The parametric filters on our website can help refine your search results depending on
the required specifications.
 The most common values for nominal working voltage are 5.1 V, 5.6 V, 6.2 V, 12 V and
15 V.
 We also carry Zener diodes with nominal working voltage up to 1 kV.
 Forward (drive) current can have a range from 200 uA to 200 A, with the most
common forward (drive) current being 10 mA or 200 mA.

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Zener diodes can be found in several applications. Some of these are:
 voltage stabilizers or regulators (in shunt mode), surge suppressors for device
protection, peak clippers, switching operations, reference elements and in meter
protection applications.
 The constant reverse voltage of a Zener diode renders it a very useful component in
regulating the output voltage against variations in the load resistance or variations in the
input voltage from an unregulated power supply.
 The current through the Zener diode will change in order to keep the voltage within the
threshold limits of Zener action and the maximum power that it can dissipate.

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 ZENER DIODE
 RESISTORS
 INPUT VOLTAGE SOURCE
 REHOSTATE (VARIABLE RESISTOR)
 LOAD RESISTANCE

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Suppose we have an unstable 12 Volt supply voltage and need a stable output of 8 Volts to
power a 100mA device. 12 volts is sufficiently above 8 volts to ensure that any ripples in the
supply will not take us below our target voltage.
Than Since we need 8 Volts we can choose between a 7.5V or an 8.2V zener diode. 8.2V is close
enough to our target voltage so we choose a zener diode with an 8.2 Volt zener voltage.
Zener diodes are available in a range of difference power ratings. If a large current flows
through a small zener diode it will be destroyed, therefore we calculate the power to be lost
in the diode and select a diode rated above that value. Here the zener power rating is equal
to the zener voltage multiplied by the maximum current (Imax) calculated above which
equals 8.2 * 0.110 = 0.9 Watts. Therefore a 1.3 Watt power rated zener diode should be
perfect.

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The voltage dropped across the resistor is equal to the difference between the source voltage
and the zener voltage = 12-8 = 4 Volts, and therefore the resistance according to Ohm's Law is
the voltage drop divided by Imax = 4/0.110 = 36 Ohms so choose a 39 Ohm resisitor.
If the source voltage is likely to be much over the 12 Volts stated then the voltage dropped
across the resisitor will be larger and so a resistor with a larger resistance may be required.
The power dissipated in the resistor is equal to the voltage drop across the resistor
multiplied by Imax. Therefore in this example power = 4 * 0.110 = 0.440 Watts. Using
a 0.5 Watt resistor would be cutting it a bit fine - particularly if the source voltage is
going to fluctuate higher regularly, therefore a 1 or 2 Watt rated resisitor should be
used here despite it costing a few pennies extra.

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When the input d.c voltage across zener diode increases beyond a certain limit (i.e.
zener breakdown voltage), the current through the circuit rises sharply,causing a
sufficient increases in the voltage drop across the dropping resistor R. As a result of it,
the voltage across the zener diode remains constant and hence the output voltage
lowers back to normal value.
When the input d.c. voltage across zener diode decreases, the current through the
circuit goes down sharply causing sufficient decrease in the voltage across the dropping
resistor . As a result of it, the voltage across the zener diode remains constant and
hence the output voltage is raised to normal. Hence the output voltage remains
constant.

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R
R (load)
+ +
-
-
FLUCTUATING
D.C. INPUT VOLTAGE
CONSTANT
OUTPUT
VOLTAGE
N
P

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Hence with the help above given facts and the simulation on proteous
software correctly it is clear that above circuit for working of zener
diode as a voltage regulator is fully correct and is working properly. So
now when we noted the the reading of voltmeter which is being
connected parallel to our load resistance we got the constant reading
of voltage. So our zener diode is now truly works as a voltage
regulator.

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