Mymensingh Engineering College
Department of Electrical & Electronic Engineering
Lab Report-02
Lab Report On: V-I Characteristics of a PN Junction Diode
Course Name: Electronic Circuit Simulation Laboratory
Course Code: EEE 302
SUBMITTED BY SUBMITTED TO
Md. Monirul Islam Milon Md. Khalid Saifullah
Roll:1101 Lecturer,
Group: A Department of EEE
Batch:11th Mymensingh Engineering College
Dept. of Electrical & Electronic Engineering
Session: 2018-19
Date of Experiment: 01/09/2020
Submisssion Date: 08/01/2020
Signature
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2.1: Experiment No: 02
2.2.Experiment Name: V-I Characteristics of a PN Junction Diode
2.3.Objectives: (i) To know about the Voltage and Current in a junction diode
(ii) To verify V-I characteristics both practically and theoretically
2.4.Theory: I-V Characteristic Curve: In order to understand how a diode functions, it is useful
to look at a plot of the voltage across the diode vs. the current through the diode. We call this
type of curve and i-v characteristic curve. If we were to create an i-v curve of a resistor, where
the current is directly proportional to the voltage (V=IR), we would see a straight line with a
constant slope or R-1. When we plot the characteristic curve of an ideal diode (that switches
on when the voltage across it goes above zero), we see zero current when VD is negative and
infinite current as soon as VD tries to go positive. This is shown in figure2.2. Note that, when
and ideal diode turns on, it is a short circuit and, therefore, the voltage across the ideal diode
when it is on is always zero
iD
VD
Fig. 2.1.V-I Characteristics of a real diode
I-V Curve of a Diode: Figure 2.1 shows typical characteristics of a real diode
Ideally, a diode is a device that allows current to flow in one direction only. In practice, diodes
allow large amounts of forward current to flow when the positive voltage across them reaches
a small threshold. They also have a small “saturation” current and a “breakdown” region in
which a large amount of current will flow in the opposite direction when a large negative
voltage is applied. In small signal diodes, the forward current will typically be up to a few tens
of mA at a forward voltage of about 1 V. The reverse-breakdown voltage might be about 100
V, and the saturation current Is may be of the order of 1 nA. Power diodes may allow forward
currents up to many amps at forward voltage drops of 0.6 to 1.5 V or so, depending on the type
of diode. The reverse-breakdown voltage of power diodes may range from as low as 50 V up
to 1000 V or even much more.
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Fig.2.2.V-I Characteristics Curve of ideal diode
2.5.Tools/Software: OrCAD Capture CIS Lite 16.6
2.6.Working Procedure:
Fig. 2.3.V-I Characteristics Circuit of forward bias
• Modifying our OrCAD schematic by adding R1 with D1, a D1N4148 diode, as shown
in figure 2.3. We will find this diode in the parts list. It is in the EVALAA library
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Fig. 2.4. Simulation profile of V-I characteristics of a diode
• Running a simulation and creating the i-v characteristic curve
o Setting up a DC sweep from 0 to +15 volts in increments of 0.1 volt.
o We Select "Add Trace" to plot the current through resistor D1, I(D1).
o Changing the x-axis of our plot as follows (same as with resistor):
1. We click on the right of the plot and choose "Settings"
2. Then we click on the X-axis Tab.
3. Clicking on the "Axis Variable" button at the bottom.
4. Entering V(D1:AN)-V(D1:CAT) as the new X axis variable. This sets our x-axis to the voltage
across the diode.
5. Rotating the diode by 180o in the circuit it can be possible to take the diode in reverse bias a
shown in figure.2.5.Then we will find v-i characteristics of a diode of reverse biasing.
Fig.2.5. V-I Characteristics Circuit of reverse bias
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2.7.Calculation & Result: The plot produced will show the i-v characteristic curve for
diode D1. It should look like the i-v curve for a real diode as shown in figure 2.5
Fig.2.6. V-I Characteristics Curve in Forward bias
Fig.2.7. V-I Characteristics Curve in reverse bias
2.8.Discussion: A diode is a device that allows current to flow in only one direction. An
ideal diode looks like a short circuit when the current is flowing and an open circuit when
the current is not flowing. A real diode has a small voltage across it when it is on, a small
negative current through it when it is off, a region in which it switches from on to off, and
a breakdown region where it stops blocking the current entirely. As long as the voltages we
use do not reach the voltage of the breakdown region, the diode will work close to ideally.
