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UNIVERSITI MALAYSIA PERLIS
EMT 111/4
ELECTRONIC DEVICES
EXPERIMENT 4
ZENER DIODE AND VOLTAGE REGULATION
NAME
: _____________________________________
MATRIC NO. : ______________________________________
PROGRAMME: ______________________________________
DATE
: ______________________________________
MARKS
RESULT & CALC
D
G1
C
Total
Marks
41
8
10
5
64
Electronic Devices (EMT 111) Sem 1 08/09
Laboratory Module
Exp. 4
EXPERIMENT 4
Zener Diode and Voltage Regulation
1.
OBJECTIVE
1.1
1.2
1.3
2.
To test a zener diode
Analyze zener diode characteristics
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)
(4.1)
Output voltage
Vout
Vout
= VZ
(ideal = 6.2V)
= VZ +  IZRZ (actual)
Where  IZ = IZ – IZT
RZ =
IZT =
2.2
IS – IL
(4.4)
=
Vin  Vout
RS
(4.5)
Load current
IL
2.5
=
Source current
IS
2.4
zener diode internal resistance = VZ / I Z
zener test current (20mA)
Zener diode current
IZ
2.3
(4.2)
(4.3)
=
VZ
RL
(4.6)
Zener diode power dissipation
PZ =
IZVZ
(4.7)
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Electronic Devices (EMT 111) Sem 1 08/09
2.6
Percent load regulation
%VR
=
V NL  VFL
x100%
VFL
where VNL
VFL
2.7
Laboratory Module
Exp. 4
=
=
(4.8)
no load (open circuit) output voltage
full load output voltage
Output ripple voltage
V0 (ripple)
=
 RL || RZ


Vin (ripple )
 RS  ( RL || RZ ) 
-3-
(4.9)
Electronic Devices (EMT 111) Sem 1 08/09
3.
COMPONENT AND EQUIPMENT
3.1
3.2
3.3
3.4
3.5
3.6
3.7
4.
Laboratory Module
Exp. 4
Resistors:
3.1.1 100 Ω
3.1.2 Two 220 Ω
1N753,6.2V, 400 mW or 1N4735, 1W zener diode
0-15 DC power supply
Dual trace oscilloscope
Signal generator
Two multimeters
Breadboard
PROCEDURE
4.1 Testing the zener diode:
4.1.1 Using multimeter, connect the positive lead of the multimeter to the
diode’s anode. Let the negative lead connected to the diode’s
cathode terminal.
4.1.2 Reverse the multimeter connection.
4.1.3 Record your result (which one is forward biased and reversed
biased).
4.2 Determination of zener’s current and voltage:
4.2.1 Wire the circuit shown in the schematic diagram in Figure 4.1.
Figure 4.1: Schematic diagram of zener’s current and voltage
4.2.2
4.2.3
Increase the dc supply voltage in small steps (VDC start with 1V –
6V) whiles simultaneously measuring the voltage across (VZ) and
the current through (IZ) the zener diode.
In the vicinity of the zener’s knee voltage (VZ approximately 6V),
make these steps approximately 0.05 V. (VZ = 6.05V – 6.25V)
(NOTE: Do not exceed a zener current of 40 mA )
4.2.4
4.2.5
Record your data.
Plot your results for the corresponding zener current and voltage
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Electronic Devices (EMT 111) Sem 1 08/09
Laboratory Module
Exp. 4
values on the graph provided.
(NOTE: The 1N753 diode is rated at 6.2V with a tolerance of
10%)
4.2.6
4.3
Determination of the internal resistance RZ of your 1N753 zener diode:
4.3.1 Take the change in zener voltage, VZ divided by the
4.3.2
4.3.3
4.4
Determine the voltage across the zener diode at a current of
approximately 20mA from your graph.
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.
Zener Diode Voltage Regulator (Full Load):
4.4.1 At this point, we want to measure the source current (IS), zener
current (IZ), load current (IL), and full load output voltage (VFL) :
4.4.2 Now, wire the circuit shown in the schematic diagram of Figure 4.2.
VFL
Figure 4.2: Schematic diagram of Zener Diode Voltage Regulator (Full Load)
4.4.3
4.4.4
4.4.5
4.4.6
4.4.7
4.4.8
4.5
Apply dc voltage (Vin) to the breadboard.
Measure the source current (IS).
Next, measure the zener current (IZ).
Then, measure the load current (IL), and full load output voltage
(VFL, RL = 220 Ω).
Record all values.
Now, compare the measured output voltage with the expected value
(Equation 4 .3) using the zener voltage (@20 mA) and the internal
zener resistance calculated.
Zener Diode Voltage Regulator (No Load):
4.5.1 At this point, disconnect the 220 Ω load resistor (RL).
4.5.2 Measure the source current (IS).
4.5.3 Then, measure the zener current (IZ), and output voltage with no
load (VNL).
4.5.4 Record your values.
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Electronic Devices (EMT 111) Sem 1 08/09
4.5.5
4.6
Laboratory Module
Exp. 4
Then, determine the percent load regulation, and record your result.
Determination of input and output voltage using oscilloscope:
4.6.1 Now, add a function generator in series with the dc voltage source,
as shown in Figure 4.3.
Figure 4.3: Schematic diagram of input and output voltage.
4.6.2
4.6.3
4.6.4
4.6.5
Adjust the output of the function generator at 0.5V peak to peak.
Set a frequency of 1 kHz.
Set on dc coupling.
Then, with setting your oscilloscope at point A, observe both the dc
and the ac voltage levels. (Observed Vin(DC) and Vin(AC))
(NOTE: You should see a 0.5 V peak to peak sine wave superimposed
on a 15 V dc level above ground.)
4.6.6
4.6.7
Next, set your oscilloscope at point B, measure the dc output
voltage of the zener diode regulator,
Record your value. (Observed Vout(DC))
(NOTE: At this point you should see virtually no ripple voltage on the
regulator’s output signal.)
4.6.8
Then, set your oscilloscope to ac coupling. Increase your
oscilloscope sensitivity to 5 mV/division.
(NOTE: You should observe a sine wave ripple signal, but it is now
peak to peak ripple voltage.)
4.6.9
Records your result. (Observed Vout(AC))
(NOTE: The zener diode regulator provides a relatively constant
output voltage as long as the input voltage is greater than the zener’s
knee voltage. If there is any voltage variation or ripple on the input
voltage signal, the output remains essentially constant)
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Electronic Devices (EMT 111) Sem 1 08/09
Name
Laboratory Module
Exp. 4
: ______________________________
Matrix No.:______________________________
5.
Date: ______________
Course: ______________
RESULT & CALCULATIONS
4.1 Testing the zener diode
(4m)
4.2 Determination of zener’s current IZ (mA) and voltage VZ (V)
(15m)
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Electronic Devices (EMT 111) Sem 1 08/09
Name
Laboratory Module
Exp. 4
: ______________________________
Matrix No.:______________________________
Date: ______________
Course: ______________
4.3 Determination of the voltage across zener diode @ 20mA and internal
resistance Rz from the plotted graph.
(4m)
4.4 Zener Diode Voltage Regulator Full Load (measured and expected value of
IS, IZ, IL and VFL)
(9m)
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Electronic Devices (EMT 111) Sem 1 08/09
Name
Laboratory Module
Exp. 4
: ______________________________
Matrix No.:______________________________
Date: ______________
Course: ______________
4.5 Zener Diode Voltage Regulator No Load (measured and expected value of
IS, IZ, VNL)
(7m)
4.6 Determination of percent load regulation (%VR)
(2m)
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Electronic Devices (EMT 111) Sem 1 08/09
Laboratory Module
Exp. 4
4.7 Determination of input and output voltage using oscilloscope (Vin(DC), Vin(AC),
Vout(DC) and Vout(AC)).
(4m)
4.8 Determination of output ripples voltage.
(2m)
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Electronic Devices (EMT 111) Sem 1 08/09
Name
Laboratory Module
Exp. 4
: ______________________________
Matrix No.:______________________________
Date: ______________
Course: ______________
6. DISCUSSION
1.
Analyze the characteristic (V-I) curve of a zener diode.
2.
A certain voltage regulator has a 12V output when there is no load (I L = 0).
When there is a full load current of 10mA,the output voltage is 11.9V.
Express the voltage regulation as a percentage change from no load to full
load and also as a percentage change for each mA change in load.
(8m)
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Electronic Devices (EMT 111) Sem 1 08/09
Name
Laboratory Module
Exp. 4
: ______________________________
Matrix No.:______________________________
8.
Date: ______________
Course: ______________
CONCLUSION
Explain in your own word about zener diode and voltage regulation, and its
differences (your answer should be in simple note).
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(5m)