EKT 102 / Basic Electronic Engineering
EXPERIMENT 4
Zener Diode and Voltage Regulation
1.
2.
OBJECTIVES
1.
To test a zener diode and analyze their characteristics
2.
Zener diode as a simple voltage regulator
INTRODUCTION
Operation wise, zener diodes are normally reverse biased. They maintain a constant
voltage across their terminals over a specified range of current. A zener diode can be
modeled by a constant dc voltage source in series with a resistor. As a regulator, the
zener diode maintains a dc output voltage that is essentially constant level regardless
of the fluctuations in load current.
2.1
Maximum limiting series resistance
RS (max)
=
Vin (min)  Vout
I L (max)
(1)
=
VZ
(2)
Output voltage
Vout
RZ
2.2
=
Where  IZ
=
IZT
zener diode internal resistance = V Z / I Z
=
zener test current (20mA)
(3)
Zener diode current
IS – IL
(4)
=
Vin  Vout
RS
(5)
=
VZ
RL
(6)
=
Source current
IS
2.4
VZ +  IZRZ (actual)
=
IZ – IZT
Vout
IZ
2.3
(ideal = 6.2V)
Load current
IL
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EKT 102 / Basic Electronic Engineering
2.5
Zener diode power dissipation
PZ
2.6
=
IZVZ
(7)
Percent load regulation
%VR =
where VNL =
V NL  VFL
x100%
VFL
no load (open circuit) output voltage
VFL =
full load output voltage
2
(8)
EKT 102 / Basic Electronic Engineering
3.
COMPONENT AND EQUIPMENT
1
2
3
4
5
6
7
4.
Resistors:
100 Ω &220 Ω(2)
1N753,6.2V
0-15 DC power supply
Dual trace oscilloscope
Signal generator
Multimeter
Breadboard
PROCEDURE.
A.
Determination of Zener’s current and voltage:
1. Construct a circuit as shown in Figure 1.
Figure 1: Schematic diagram of zener’s current and voltage
2. Increase the dc supply voltage as in Table 1 whiles simultaneously measuring the
voltage across (VZ) and the current through (IZ) the Zener diode.
(NOTE: Do not exceed a Zener current of 40 mA )
3. Record your data and plot a graph zener current versus voltage
(NOTE: The 1N753 diode is rated at 6.2V with a tolerance of
10%)
4. Determine the voltage across the zener diode at a current of approximately
Id = 20mA from your graph.
i.
Determination of the internal resistance RZ of your 1N753 zener
diode:
 Take the change in zener
voltage,
V Z divided by the
corresponding change in current, I Z from the plotted graph.
 Do this calculation only on the straight line breakdown region of
your diode curve that you plotted.
 Record your result for the internal zener resistance.
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EKT 102 / Basic Electronic Engineering
B.
Zener Diode Voltage Regulator (Full Load):
1. Wire the circuit shown in the schematic diagram of Figure 2.
VFL
Figure 2: Schematic diagram of Zener Diode Voltage Regulator (Full Load)
2. Apply dc voltage (Vin) and measure the source current (IS), zener current (IZ), load
current (IL), and full load output voltage (VFL, RL = 220 Ω).
Record all values.
3. Now, compare the measured output voltage with the expected value (Equation 3)
using the zener voltage (@20 mA) and the internal zener resistance calculated.
C.
Zener Diode Voltage Regulator (No Load):
1. At this point, disconnect the 220 Ω load resistor (RL). Measure the source current (IS),
zener current (IZ), and output voltage with no load (VNL).
2. Record your values.
3. Then, determine the percent load regulation, and record your result.
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EKT 102 / Basic Electronic Engineering
Lab Assignment 3
Zener Diode and Voltage Regulation
Name
:___________________________________
Matrix Number
:___________________________________
Programme
:___________________________________
Date
:___________________________________
Total marks:
5
EKT 102 / Basic Electronic Engineering
A.
Determination of Zener’s current and voltage:
1. Table 1
Supply
Voltage(015V)(Volt)
1
Zener Voltage
(Vz) (Volt)
Zener Current
(Iz)(Ampere)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
2. Plot Graph
From graph :i. Voltage across Zener Diode when Id=20mA
____________________
ii. Internal Resistance of Zener Diode
____________________
**Note: Please submit your graph with a complete label
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EKT 102 / Basic Electronic Engineering
B. Zener Diode Voltage Regulator (Full Load)
1. Measured Value:Source Current, Is = __________________
Zener current , Iz
Load Current 𝐼𝐿
= __________________
= __________________
Full Load Output Voltage 𝑉𝐹𝐿 = _______________________
2.
Calculated Value :-
**Show your calculation
Output Voltage = ________________
Internal Resistance = _______________
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EKT 102 / Basic Electronic Engineering
C. Zener Diode Voltage Regulator (No Load)
Source Current, Is = __________________
Zener current , Iz
= __________________
No Load Output Voltage 𝑉𝑁𝐿 = _______________________
Calculate Voltage Regulation
**Show your calculation
VR = ___________________________
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