Description of zener diode. Know about the equivalent circuits. Know about zener diode and how it works as voltage stabilizer. see its advantages and also its disadvantages Thanks in advance.

1. Z E N E R D I O D E

2. WHAT IS ZENER DIODE???
A zener diode is a type of diode that permits current not only in the forward direction like a
normal diode , but also in the reverse direction if the voltage is larger than the breakdown
voltage known as “Zener KneeVoltage” or “ ZenerVoltage”.
Zener diode basics:
• Made of silicon p-n junction.
• Heavily and properly doped crystal diode for reducing the breakdown voltage.
• Symbol of a zener diode:
• Used for operation in the reverse breakdown region.
Applications:
• Voltage regulator :-The output voltage remains the same while changing the input voltage
• Signal limiter.

3. KEY POINTS/NOTABLE POINTS
• A zener diode is like an ordinary diode except that it is properly doped so as
to have a sharp breakdown voltage.
• A zener diode is always reverse connected i.e. it is always reverse biased.
• A zener diode has sharp breakdown voltage, called zener voltageVZ.
• When forward biased, its characteristics are just those of ordinary diode.
• The zener diode is not immediately burnt just because it has entered the
*breakdown region.

4. EQUIVALENT CIRCUITS
ON STATE
OFF STATE

5. Ei = InputVoltage
Eo = OutputVoltage
R = Resistor
RL = Load Resistor
IL = Load Current
Iz = Zener Current
I = Source current / Total current = Iz + IL

6. ZENER DIODE AS VOLTAGE STABILIZER
A Zener diode is one of the specially designed diodes that predominately works
in reverse biased conditions. They are more heavily doped than ordinary diodes,
due to which they have narrow depletion region. While regular diodes get
damaged when the voltage across them exceeds the reverse breakdown voltage,
Zener diodes work exclusively in this region. The depletion region in Zener
diode goes back to its normal state when the reverse voltage gets removed. This
particular property of Zener diodes makes it useful as a voltage regulator.
In short, a zener diode can be used as a voltage regulator to provide a constant
voltage from a source whose voltage may vary over sufficient range.
Let us see how this happens…

7. Suppose the input voltage increases.
Since the zener is in the breakdown
region, the zener diode is equivalent
to a batteryVZ as shown in Fig. 2 (ii).
It is clear that output voltage remains
constant atVZ (= E0).The excess
voltage is dropped across the series
resistance R.This will cause an
increase in the value of total current
I.The zener will conduct the increase
of current in I while the load current
remains constant. Hence, output
voltage E0 remains constant
irrespective of the changes in the
input voltage Ei.
When the circuit is properly designed, the load voltage E0 remains
essentially constant (equal toVZ) even though the input voltage Ei and
load resistance RL may vary over a wide range.

8. Now suppose that input voltage is
constant but the load resistance RL
decreases.This will cause an increase
in load current.The extra current
cannot come from the source
because drop in R (and hence source
current I) will not change as the
zener is within its regulating range.
The additional load current will
come from a decrease in zener
current IZ. Consequently, the output
voltage stays at constant value.

9. ADVANTAGES
• The Zener diode is less expensive than another diode
• This diode can be used in regulate and stabilize the voltage in a circuit
• These diodes have a high-performance standard
• Control the flowing current
• Compatibility and obtainability
• It can be used in a smaller circuit that would not work with any larger form of the current
regulation.
• They are compatible with the most system due to their lower cost and greater control
DISADVANTAGES
• Zener diode cancels out voltage by applying an even larger voltage in the reverse direction
wasting electricity in the process.
• A Zener diode has a relatively poor regulation ratio and is generally not as good as the
transistor.

10. THANK YOU
M D. A N I S U R R A H M A N
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