Practical-10
Test characteristics of Zener diode.
A. Objective: Zener diode is mostly used as a voltage reference and as a shunt regulator
in many applications. The objective of this experiment is to examine characteristics
of a Zener diode and practical verification of its voltage regulating characteristic.
B. Expected Course Outcomes(Cos)
Identify the behavior of semiconductor and opto electronic devices.
C. Practical Outcome(PRo)
1. Select appropriate Zener diode for voltage regulating circuits..
2. Plot the practical characteristics of Zener Diode
3. Measure output voltage against variation in input voltage/load current.
D. Expected Affective domain Outcome(ADos)
1. Work as a leader/ a team member (while performing experiments).
2. Follow ethical practices.
E. Prerequisite Theory:
A PN junction diode does not conduct in reversed biased. But if reverse bias
increased at a particular voltage, it starts conducting. The rise in voltage is not
significant thereafter. The voltage is called Zener breakdown voltage. Zener diode
is always operated in reverse bias condition. i.e. its anode is connected to the
negative terminal and cathode is connected to the positive terminal of the
battery.
Zener diodes are manufactured in the voltage rating from 2.4 V to 200 V and
more and the power rating of 150 mW to 50 W.
Characteristic of Zener Diode:
The VI characteristic graph of the Zener diode is shown in the figure below. This
curve shows that the Zener diode, when connected in forwarding bias, behaves
like an ordinary diode. But when the reverse voltage applies across it and the
reverse voltage rises beyond the predetermined rating, the Zener breakdown
occurs in the diode..
At Zener breakdown voltage the current starts flowing in the reverse direction.
The graph of the Zener breakdown is not exactly vertical shown above which
shows that the Zener diode has resistance. The voltage across the Zener is
represented by the equation shown below.
V = VZ + IZRZ
Vo = Vi - I se R se .
Vo = Vi – ( I L + I Z ) R se
Consider first that the load remains constant and the input voltage rises. The
output voltage tries to increases . But the zener diode draws more current so
current through series resistance R se increases. So voltage drop I se R se increases
and the output voltage remains constant.
Similarly when the input voltage decreases the zener current decreases such that
Vo remains constant.
F. Experimental set up:
Draw Circuit Diagram Here
G. Resources/Equipment Required
Sr.No. Instrument/Equipment
Specification Quantity
/Components/Trainer kit
1 Zener diode /Zener 12 V , 1 W 1
Characteristic kit
2 DC Power Supply 0-30V, DC 1A 1
Regulated
Volt 0-20V; MC TYPE 1
3
meter/Multimeter
4 Ammeter/ Multimeter 0-100MA; MC TYPE 1
0-500µA;MC TYPE
5 Resistor 100 Ω , 2 W 1
6 Wire wound pot 1.5 K , 1 W 1
H. Safety and necessary Precautions followed
1. Do not switch ON the power supply unless you have checked the circuit
connections as per the circuit diagram.
2. Be careful to put multimeter setting in DC mode.
3. Ensure Zener diode is connected to reverse biased.
4. While performing the experiment, do not exceed the current rating of zener
diode beyond the rated value, it may lead to damaging the diode.
I. Procedure to be followed/Source code:
1. Connect the circuit as shown in circuit diagram
2. Gradually increase the supplied voltage to zener diode and take the reading of
reverse current.
3. Tabulate reading of supply voltage, zener voltage, zener current.
4. Now put load resistance on fix value and vary the i/p supply, note down the o/p
voltage
5. Put i/p supply on fix value and vary load resistance.
6. Note the range in which zener works as a voltage regulator efficiently.
7. Plot reverse characteristics VZ v/s IZ on graph paper.
J. Observations and Calculations:
Supply Zener Zener
Voltage voltage current
Sr. No.
Vs (Volt) Vz (Volt) Iz (mA)
1
K. Interpretation of Results
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L. Conclusion
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M. Practical related Questions.
1. What is the difference between p-n Junction diode and zener diode?
2. Define break down voltage.
3. State the applications of Zener diode
