BANGABANDHU SHEIKH MUJIBUR RAHMAN
AVIATION AND AEROSPACE UNIVERSITY
Department of Avionics Engineering (AVE)
Program: Bachelor of Science in Aeronautical Engineering (Avionics)
Course Code: AVE 4302
Course Title: Electronics Circuit I Sessional
Course Credit: 1.5
Experiment No 01: Study of I-V characteristics of a PN junction diode
Objectives:
To study and verify the functionality of PN junction diode in forward bias and
reverse bias and to
1. Plot Volt-Ampere Characteristics of P-N Diode.
2. Plot Volt-Ampere Characteristics of P-N Diode in XY mode.
3. Find cut-in voltage for P-N Junction diode.
Theory:
A PN junction diode is formed when a single crystal of semiconductor is doped with
acceptors impurities (Penta-valent) on one side and donor impurities (Trivalent) on the
other side. It has two terminals called electrodes, one each from P-region and N-
region. Due to two electrodes it is called (i.e., Di-electrode) Diode.
Biasing of PN junction Diode
Applying external D.C. voltage to any electronic device is called biasing. There is no
current in the unbiased PN junction at equilibrium. Depending upon the polarity of the
D.C. voltage externally applied to diode, the biasing is classified as forward biasing
and Reverse biasing.
Forward bias operation
The P-N junction supports uni-directional current flow. If +ve terminal of the input
supply is connected to anode (P-side) and –ve terminal of the input supply is
connected the cathode. Then diode is said to be forward biased. In this condition the
height of the potential barrier at the junction is lowered by an amount equal to given
forward biasing voltage. Both the holes
from p-side and electrons from n-side cross the junction simultaneously and constitute
a forward current from n-side cross the junction simultaneously and constitute a
forward current (injected minority current – due to holes crossing the junction and
entering P- side of the diode). Assuming current flowing through the diode to be very
large, the diode can be approximated as short- circuited switch.
Reverse bias operation
If negative terminal of the input supply is connected to anode (p-side) and –ve terminal
of the input supply is connected to cathode (n-side) then the diode is said to be reverse
biased. In this condition an amount equal to reverse biasing voltage increases the
height of the potential barrier at the junction. Both the holes on P-side and electrons
on N-side tend to move away from the junction there by increasing the depleted region.
However, the process cannot continue indefinitely, thus a small current called reverse
saturation current continues to flow in the diode. This current is negligible; the diode
can be approximated as an open circuited switch.
Diode current equation
The volt-ampere characteristics of a diode explained by the following equations:
I = current flowing in the diode, I0 = reverse saturation current
V = Voltage applied to the diode
VT = volt- equivalent of temperature = k T/q = T/ 11,600 = 26mV (@ room temp)
=1 (for Ge) and 2 (for Si)
It is observed that Ge diodes has smaller cut-in-voltage when compared to Si diode.
The reverse saturation current in Ge diode is larger in magnitude when compared to
silicon diode.
List of equipment:
1. Breadboard
2. Diode(1n4007)
3. Resistor
4. Connecting wires
5. DC Power supply
6. Multi-meter
Practical Circuit diagram:
Fig. (1) - Forward Bias Condition:
Fig. (2) - Reverse Bias Condition:
Working Procedure:
Forward Bias Condition:
1. Connect the circuit as shown in figure (1) using PN Junction diode.
2. Initially vary Regulated Power Supply (RPS) voltage Vs in steps of 0.1 V. Once
the current starts increasing vary Vs from 1V to 12V in steps of 1V and note
down the corresponding readings Vf and If.
3. Tabulate different forward currents obtained for different forward voltages.
Reverse Bias Condition:
1. Connect the circuit as shown in figure (2) using PN Junction diode.
2. Vary Vs in the Regulated Power Supply (RPS) gradually in steps of 1V from
0V to12V and note down the corresponding readings Vr and Ir.
3. Tabulate different reverse currents obtained for different reverse voltages.
4. To get the graph in reverse region (theoretically), remove voltmeter and with
reference to the supply voltage note down the reverse current readings in
Ammeter because current always selects low reactance path. (Diode have infinite
resistance in reverse bias ideally). To get the graph in reverse region
(theoretically), replace voltmeter with nano ammeter. Voltmeter has less load
resistance when compared to diode. Current conducts in low resistance path.
Table:
Forword:
Power supply VF IR
0.1
0.2
0.3
0.5
12
Reverse:
Power supply VR IR
1
2
12
Graph:
