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DEPARTMENT OF ELECTRICAL ENGINEERING
Electronics I Laboratory
(AEEE238)
Exercise 1:
V-I Characteristics of Si Diode
Name:
Reg. No.:
Semester:
Date:
Instructor:
Stathis Efstathiou
2222
Fall 16
04/11/2016
Dr. Michael Komodromos
Exercise 1
Diode Characteristics
Objective:
The objective of this experiment is to make measurements in order to determine
the V-I characteristics of a silicon diode. Biasing voltage and dynamic resistance is extracted
from the plot and their importance in design is demonstrated.
Equipment:
1.
2.
3.
4.
5.
6.
1x 1N4001 Si Diode
1x 0.5W 100Ω Resistor
1x 0.5W 470Ω Resistor
IDL-600 Trainer with DC PSU
GW-394 DMM
Wires
Theoretical Backround
A silicon PN junction (or diode) is a two-terminal device that “ideally” conducts only in one
direction and has zero resistance to the flow of current, while it acts as open switch in the
other. The diode examined in this experiment is a silicon diode, which practically conducts –
or is forward biased- when the potential difference between anode and cathode is more
then 0.7volts.
An Ideal Diode it conducts perfectly (no resistance) when is forward biased and the voltage
drop between anode and cathode is 0v. A Practical Diode is the model used in design.
Although it acts as a perfect conductor when forward biased, a constant voltage drop of 0.7
volts occurs at the terminals and when is reversed biased it acts as an insulator.
Figure 1.1.: Ideal and Practical Diode V-I Characteristics
In Real Diode on the other hand, there are more characteristics to consider. When Reversed
biased, a leakage current is occurred because the semiconductor depletion region has very
large resistance. The same happens for positive but not high enough biasing voltage, but
when barring voltage is exceeded current gradually (and almost linearly) increases.
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Stathis Efstathiou
Exercise 1
Diode Characteristics
Figure 1.2.: V-I Characteristics of Ideal Diode
During this experiment the following circuit was built and measurements were made.
Figure 1.3.: Diode biasing circuit
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Stathis Efstathiou
Exercise 1
Diode Characteristics
Procedure
Part one
1. On the breadboard, the 100 Ω resistor was connected in series with an 1N4001
diode. Then the circuit was supplied through an adjustable positive power
supply.
2. The source voltage was set to 0.2volts (0volts measurement was omitted).
3. Using a DMM, VRs and VD was measured with the polarity shown in Figure 1.3.
The results were recorded in Table 1.1 in Results section.
4. By gradually increasing VS, step 3 measurements were repeated. Accuracy on the
source adjustment was trivial, so Kirchhoff’s Voltage law might not but exactly
true when comparing data.
5. Current ID was calculated using Ohm’s Law i.e
𝐼𝐷 =
𝑉𝑅𝑠
100
6. A plot of VD versus ID was constructed to display the data as shown in Figure 1.4.
7. Using the results in Table 1.1, barrier voltage, dynamic and static resistance was
calculated.
Part two
1. The resistor in the circuit was replaced with a 470 Ω while the voltage was
adjusted to 12v.
2. The current was measured using a DMM.
3. By using Rd from Part one, the current on the resistor was calculated. (30.31mA)
Page 4 of 6
Stathis Efstathiou
Exercise 1
Diode Characteristics
Results & Calculations
Part One
7VS
(v)
0.0
VRs
(V)
VD
(V)
ID
(mA)
0
0
0
0.2
0
0.18
0
0.4
0.0002
0.478
0.002
0.6
0.0048
0.633
0.048
0.7
0.02
0.664
0.2
0.8
0.109
0.743
1.09
1.0
0.238
0.768
2.38
1.5
0.72
0.796
7.2
2.0
1.23
0.811
12.3
3.0
2.25
0.825
22.5
4.0
3.31
0.837
33.1
6.0
4.27
0.844
42.7
8.0
7.29
0.857
72.9
10.0
9.12
0.858
91.2
12.0
11.23
0.869
112.3
Table 1.1
120
100
80
Id
Linear (Rd)
60
40
20
0
0
0.2
0.4
0.6
0.8
1
-20
Figure 1.4: V-I Characteristics of the 1N4001 diode
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Stathis Efstathiou
Exercise 1
Diode Characteristics
Dynamic Resistance:
𝑉𝑏 = 0.796 𝑣
𝑅𝑑 =
𝛥𝑉
𝛥𝐼
=
0.869−0.796
112.3−7.2
= 0.69 Ω
Part Two
𝐼𝑑 =
𝑉𝑠 − 𝑉𝑏 12 − 0.796
=
= 30.63𝑚𝐴
𝑅𝑠 + 𝑅𝑑 463 + 0.69
%𝑑(𝐼𝑑 ) =
30.31 − 30.63
100 = 1.04%
30.63
Conclusions
The measurements on the diode biasing circuit proved the forward biased operation of the
junction. It can be seen that the actual biasing voltage of the diode differs slightly from 0.7v.
The leakage current on small biasing voltages as well as the linear response near the
operating point is also shown in the graph.
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Stathis Efstathiou