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Name & Surname:
Bahçeşehir University
Engineering Faculty
ID:
Electrical-Electronics Department
Date:
EXPERIMENT 4
Light-Emitting and Zener Diodes
Objective
To calculate, draw, and measure the currents and voltages of light-emitting diodes
(LEDs) and Zener diodes.
Tools and Equipments Required
DMM (Digital Multi Meter)
DC Power Supply
100 Ω or 120 Ω
220 Ω
Silicon Diode
LED
Zener
x1
x1
x1
x1
x1
Theory And Descriptions
The light-emitting diode (LED) is a diode that will give off visible light when
threshold voltage is given. In LED material gallium arsenide phosphide (GaAsP) or gallium
phosphide(GaP) used to create light, which is called electroluminescence. For every LED
there is a distinct forward voltage and current that will give bright, clear light.
The Zener diode is a p-n junction device designed to take full advantage of the Zener
breakdown region. Once the reverse-bias potential reaches the Zener region, the ideal Zener
diode is assumed to have fixed terminal voltage and zero internal resistance. All practical
diodes some internal resistance which is limited to 5 to 20 Ω.
The experimental procedure will show the variation in terminal voltage for different
loads and currents. The following procedures are used to determine the state of Zener diode.
For most configurations, the state of Zener can be determined by replacing it with an open
circuit. If the open-circuit voltage equal or exceeds Zener potential, Zener diode is “on” and
Zener diode can replace with a DC power supply.
<-- Reverse biased operation for Zener diode.
EEE 2116 Electronics I Lab. Page 1 of 5
Bahçeşehir University
Engineering Faculty
Electrical-Electronics Department
PROCEDURE
PART 1. LED Characteristics
a) Record the measured value of resistor R and construct the circuit in fig.4.1. Initially,
set the supply voltage to 0V.
Figure 4.1
R (measured) =
b) Increase the supply voltage E until “first light” is noticed. Record the VD and VR using
DMM. Calculate ID using ID = VR / R.
VD (measured) =
VR (measured) =
ID (measured) =
c) Continue to increase the supply voltage E until “good brightness” is first established.
DO NOT OVERLOAD the circuit. Record the VD and VR using DMM. Calculate ID
using ID = VR / R.
VD (measured) =
VR (measured) =
ID (measured) =
d) Set DC supply E to corresponding values on the table 4.1 and measure the values VD
and VR and calculate the current ID and fill the table.
Table 4.1
E(V)
0
1
2
3
4
5
VD(V)
VR(V)
IDVR/R(mA)
EEE 2116 Electronics I Lab. Page 2 of 5
Bahçeşehir University
Engineering Faculty
Electrical-Electronics Department
e) Using the table 4.1 sketch the curve ID vs. VD on the graph fig.4.2.
Point the ID and VD of “good brightness” from the Part1.(c) and draw a vertical line
from this intersection point. Area on right of line is “good brightness”
Figure 4.2
f) Record the measured value of resistance and construct the circuit of fig.4.3. be sure
that both diodes are connected properly.
R (measured) =
Figure 4.3
EEE 2116 Electronics I Lab. Page 3 of 5
Bahçeşehir University
Engineering Faculty
Electrical-Electronics Department
g) Do you expect the LED to burn brightly? Why? What if the silicon
diode is reversed?
h) Energize the circuit for both conditions of silicon diode. (as shown in fig.4.3 and
reversed). If the LED is “on” with “good brightness”, measure VD and VR and
calculate ID. compare with the area “good brightness” on graph of fig.4.2.
PART 2. Zener Diode Characteristics
a) Record the measured value of resistance R. Construct the circuit of fig.4.4. Initially set
DC supply to 0 V.
figure 4.4
R ( measured) =
b) Set the DC supply E to the values on table 4.2 and measure both VZ and VR. Calculate
the Zener current IZ in mA
Table 4.2
E(V)
0
1
2
3
4
5
6
7
8
VZ(V)
VR(V)
IZ=VR/Rmeas(mA)
EEE 2116 Electronics I Lab. Page 4 of 5
Bahçeşehir University
Engineering Faculty
Electrical-Electronics Department
c) Since the Zener region is I the third quadrant of a complete diode
characteristic curve, place a minus sign in front of each IZ and VZ value. Plot the curve
IZ vs. VZ
Figure 4.5
d) For the range of measurable current IZ in the linear region, what is the average value
of VZ? Estimate the average resistance of Zener diode in the linear region using ravg =
ΔVZ / ΔIZ. choose an interval for ΔVZ at least 2 V.
VZ (approximated) =
RZ (calculated) =
Conclusion
Write in 2-3 sentences at maximum, that what you learn about all diodes.
EEE 2116 Electronics I Lab. Page 5 of 5