BASIC ELECTRONICS LAB (PHY 212L)
DATE: EXPERIMENT NO:
Forward & Reverse Bias Characteristics of
p-n Junction Diode
Objective:
To study and verify the functionality of p-n junction diode in forward bias and reverse
bias and to
1. Plot Current-Voltage, Forward Bias Characteristics of p-n junction diode.
2. Plot Current-Voltage, Reverse Bias Characteristics of p-n junction diode.
3. Find out cut-in voltage for p-n junction diode.
4. Find out static and dynamic resistances in both forward and reverse biased
conditions.
5. Draw load line for p-n junction diode.
Components:
S.No. Name Quantity
1 Diode (1N4007) 1(One) No.
2 Resistor (1K ) 1(One) No.
3 Bread board 1(One) No.
Equipment:
S.No. Name Quantity
1 Dual DC Regulated Power supply (0 - 15 V) 1(One) No.
2 Digital Ammeters ( 0 - 200 mA, 0 - 200 µA) 1(One) No. Each
3 Digital Voltmeter (0 - 20V) 1(One) No.
4 Connecting wires 5-10
pg. 1 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Theory:
A p-n junction diode is formed when a single crystal of semiconductor doped with
trivalent impurities [ Boron(B), Gallium(G), Indium(In), etc.] on one side and pentavalent
impurities [ Phosphorus(P), Arsenic(As), Antimony(Sb), etc.] on 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 p-n junction diode:
Applying external DC voltage to any electronic device is called biasing. There is no
current in the unbiased p-n junction at equilibrium.
Depending upon the polarity of the DC 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 positive
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.
pg. 2 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Load line:
A load line is used in graphical analysis of nonlinear electronic circuits, representing the
constraint other parts of the circuit place on a non-linear device, like a diode or transistor.
It is usually drawn on a graph of the current vs the voltage in the nonlinear device, called
the device's characteristic curve.
The load line represents the relationship between current and voltage in the linear part of
the circuit.
Diode current equation:
The volt-ampere characteristics of a diode explained by the following equations
V
ηV T
I =I 0 (e −1)
Where,
I = current flowing in the diode,
I 0 = reverse saturation current
V = Voltage applied to the diode
kT
V T = volt- equivalent of temperature = = T/ 11,600 = 26mV (@ room temp)
q
η=1 (for Ge) and 2 (for Si)
Here, k=Boltzmann’s constant=1.3807 ×10−23 J / K∨m2 kg s−2 K −1
q=charge of electron¿ 1.60217662× 10−19 Coulombs
It is observed that Ge diodes has smaller cut-in-voltage ( V cut −¿ ≈ 0.3V ) when compared to
Si diode (V cut −¿ ≈ 0.7 V ). The reverse saturation current in Ge diode is larger in magnitude
when compared to silicon diode.
pg. 3 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Circuit Diagram:
Fig. (1) - Forward Bias Condition:
Fig. (2) –Reverse Bias Condition:
pg. 4 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Fig (3): Basic electronics
lab trainer.
Fig (4): Forward bias of diode(Current,
I DF =0.1 mA=100 μA , Voltage acroos diode V DF =0.505 V ¿
pg. 5 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Fig. (5): Reverse bias of diode(Current, I DR =2 μA ,Voltage acroos diode V DR=2.09 V ¿
Fig. (6) – Load line
VS
R
Vs
pg. 6 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Procedure:
Forward Bias Condition:
1. Connect the circuit as shown in figure (1) using p-n Junction diode.
2. Initially vary Regulated Power Supply (RPS) voltage V s in steps of 0.1 V. Once the
current starts increasing vary V s from 1V to 15V in steps of 1V and note down the
corresponding readings V DFand I DF .
3. Tabulate different forward currents obtained for different forward voltages.
Reverse Bias Condition:
1. Connect the circuit as shown in figure (2) using p-n Junction diode.
2. Vary V s in the Regulated Power Supply (RPS) gradually in steps
of 1V from 0V to 15V and note down the corresponding readings V DRand I DR .
3. Tabulate different reverse currents obtained for different reverse voltages.
pg. 7 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Observations:
Forward Bias Condition: Table (1)
Voltage across Regulated Forward current through Forward Voltage across
power supplyV s (V ) the diode I DF (mA) the diode V DF (V )
0 0 0
0.1 0 0.1
0.2 0 0.196
0.3 0 0.297
0.4 0 0.393
0.5 0.1 0.484
1 0.4 0.564
2 1.4 0.617
3 2.4 0.642
4 3.4 0.658
5 4.4 0.670
6 5.4 0.679
7 6.4 0.687
8 7.4 0.693
9 8.4 0.699
10 9.4 0.704
11 10.4 0.709
12 11.5 0.713
13 12.5 0.717
14 13.5 0.720
15 14.5 0.723
pg. 8 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Reverse Bias Condition: Table (2)
Voltage across the Regulated Reverse Current through Reverse Voltage across
power supply V s (V ) the diode I DR ( mA) the diodeV DR (V )
0 0 0
1 0.9 1.01
2 1.9 2.02
3 2.9 3.03
4 3.9 4.03
5 4.9 5.05
6 5.9 6.07
7 6.9 7.06
8 7.9 8.09
9 8.9 9.09
10 9.9 10.08
11 10.9 11.08
12 11.9 12.14
13 12.9 13.12
14 13.9 14.13
15 14.9 15.14
pg. 9 Department of physics SRM University Andra Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Load Line: Table (3): Applied voltage, V s (10V)
S.No. Resistance R(KΩ) VS Forward Forward
(mA )
R Current across Voltage
diode I DF (mA ) across
diode
V DF (V )
1 0.470 21.276 19.4 0.740
2 1 10 9.4 0.708
3 2.2 4.545 4.3 0.672
4 4.7 2.127 2.0 0.637
5 8.2 1.219 1.1 0.611
6 10 1 0.9 0.602
7 22 0.454 0.4 0.565
8 47 0.212 0.2 0.531
9 100 0.1 0.1 0.499
Load Line: Table (4): Applied voltage, V s (13V)
S.No Resistance R(KΩ) VS Forward Forward
(mA )
. R Current across Voltage across
diode( I DF ¿ mA diode(V DF )V
1 0.470 27.66 26.0 0.753
2 1 13 12.3 0.718
3 2.2 5.91 5.7 0.683
4 4.7 2.766 2.7 0.648
5 8.2 1.585 1.5 0.622
6 10 1.3 1.3 0.613
7 22 0.590 0.6 0.575
8 47 0.276 0.2 0.541
9 100 0.13 0.1 0.508
pg. 10 Department of physics SRM University Andra
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BASIC ELECTRONICS LAB (PHY 212L)
Graph
1. Now mark +ve X-axis as V DF ,+ve Y-axis as I DF ,for forward bias condition.(Fig-7)
2. And mark +ve X-axis as V DR, +ve Y-axis as I DR for reverse bias condition. (Fig-8)
3. Mark +ve X-axis as V s , +ve Y-axis as I DF , for forward bias condition. (Fig-9)
4. Mark +ve X-axis as V s , +ve Y-axis as I DR , for reverse bias condition. (Fig-10)
I- V
Forward bias I-V characteristics of given p-n junction diode.Fig(7)
16
14
12
10
Current, IDF (mA)
0
0 5 10 15 20 25 30
Voltage across diode, VDF (V)
Characteristics of p-n Junction Diode under Forward & Reverse Bias Conditions
pg. 11 Department of physics SRM University Andra
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BASIC ELECTRONICS LAB (PHY 212L)
Reverse bias I-V Characteristics of given p-n junction diode Fig(8).
16
14
12
10
Current ,IDR (µA)
0
0 2 4 6 8 10 12 14 16 18
Voltage across diode, VDR (V)
pg. 12 Department of physics SRM University Andra
Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Forward I-V Characteristics
Reverse bias of given
I-V Characteristics p-n junction
of given diodediode Fig(10).
p-n junction Fig(9).
16
16
14
14
12
( mA)
12
10
, IDR (µA)
10
Current,IDF
8
8
6
Current
6
4
4
2
2
0
0 2 4 6 8 10 12 14 16
0
0 2 4 across
Voltage 6 Dc regulated
8 10
power 12
supply,Vs14
(V) 16 18
Voltage across Dc regulated power supply,Vs (V)
Load lines of given p-n junction diode applied voltage is (10V). From Table(3)
8
.Fig(11)
7
5
Current, IDF (mA)
0
0 1 13 2
pg. 3 4 5Department
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of 8 9 10 SRM
11University
12 13
Andra 14
Pradesh. Voltage across diode, VDF (V)
BASIC ELECTRONICS LAB (PHY 212L)
Load lines of given p-n junction diode applied voltage is (13V) From Table(4).Fig(12)
8
5
Current, IDF (mA)
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Voltage across diode, VDF (V)
pg. 14 Department of physics SRM University Andra
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BASIC ELECTRONICS LAB (PHY 212L)
Calculations from Graph:
Cut in Voltage , V cut −¿=¿
V DF
Static forward Resistance, Rdc = KΩ
I DF
ΔV DF
Dynamic Forward Resistance, Rac = KΩ
Δ I DF
V DR
Static Reverse Resistance , Rdc = MΩ
I DR
ΔV DR
Dynamic Reverse Resistance , Rac = MΩ
Δ I DR
Precautions:
1. While doing the experiment do not exceed the bias voltage above 15V. This may
lead to damaging of the diode.
2. Connect voltmeter and ammeter in correct polarities as shown in the circuit
diagram. Do not switch ON the power supply unless you have checked the circuit
connections as per the circuit diagram.
pg. 15 Department of physics SRM University Andra
Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
Result:
Current-Voltage Characteristics of p-n junction Diode are studied and load line is
determined.
a) Forward Bias of p-n Junction Diode:
1. The Cut- in Voltage or Knee Voltage ¿) of 1N4007 is 0.5 Volts.
2. The Static Forward resistance of 1N4007 is,
V DF 0.693 V
= =0.0936 K Ω . From Fig (7)
I DF 7.4 mA
3. The Dynamic Forward resistance of 1N4007 is,
ΔV DF ( 0.687−0.617) V
= =0.014 K Ω . From Fig (7)
Δ I DF (6.4−1.4)mA
b) Reverse Bias of p-n Junction Diode:
1. The Static Reverse resistance of 1N4007 is,
V DR 8.09 V
= =1.024MΩ. From Fig (8)
I DR 7.9 μA
2. The Dynamic Reverse resistance of 1N4007 is,
ΔV DR (10.08−4.03)V
= =1.0083 M Ω. From Fig (8)
Δ I DR (9.9−3.9) μA
Reference book: Robert L. Boylestad and Louis Nashelsky(Electronics devices and circuit theory)
pg. 16 Department of physics SRM University Andra
Pradesh.
BASIC ELECTRONICS LAB (PHY 212L)
pg. 17 Department of physics SRM University Andra
Pradesh.
