1A. ALIA. ALI
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FUJAIRAHFUJAIRAHINSTITUTE OF APPLIED TECHNOLOGYINSTITUTE OF APPLIED TECHNOLOGY
FUJAIRAHFUJAIRAHG-11G-11
SECOND SEMESTERSECOND SEMESTER
ELECTRONICSELECTRONICS
G-11G-11
SECOND SEMESTERSECOND SEMESTER
ELECTRONICSELECTRONICS
Module-1Module-1PN Junction PN Junction
DiodeDiode
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INTRODUCTIONINTRODUCTION
Semiconductor devices, made electronics physically
very small, for example:
Computers.
certain types of medical diagnostic and treatment
equipment.
popular telecommunication devices.
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DefinitionDefinition
Define the term Diode.
Diode is a PN junction semiconductor device that
allows current to flow in only one direction.
How does the current flow in the Diode?
The current flows when the Anode (A) is made positive
with respect to the Cathode (K).
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Diode ConstructionDiode Construction Diode is created by doping a single piece of pure semiconductor
so that half is N-type and the other half is P-type as shown below.
It has two electrodes and hence the name diode.
(di two and ode electrode).
The electrode connected to the P-type is called Anode “A” and
that connected to N-type is called Cathode “K”
Anode (A)
Cathode (K)
N-TYPE
Electrons
+
Diode Structure
P-TYPE
Holes
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Diode SymbolDiode Symbol The symbol of diode is shown below.
The cathode (K) is marked with a silver color band as
shown below.
K
Diode Symbol
A
Typical Diode
K
In the symbol, the arrow points from anode (A) to
cathode (K), this is the direction of current flow.
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Types of DiodeTypes of Diode Commonly diodes are made of Silicon (Si) or Germanium (Ge).
According to the application they are classified into:
a) Low power diodes.
b) Light Emitting Diodes (LEDs).
c) Zener diodes.
d) Rectifier diodes.
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Diode PackingDiode Packing Diode is generally mounted in one of the three basic
packages as shown below.
The function of the package is to protect the diode
from mechanical stress and environment
The size of the package indicates the current rating
(larger size means higher current rating).
Diode packing types
DO-41
DO-5
DO-8
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Diode IdentificationDiode Identification In order to distinguish between diodes, each type is
given a unique code so that it can be identified.
There are two main semiconductor numbering
systems in use:
a) Pro-Electron System: originated and widely used in
Europe.
b) JEDEC System: widely used in North America.
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Diode IdentificationDiode Identification
Pro-Electron Coding System
First Letter Specifies
Semiconductor Material
Second Letter Specifies type
of Diode
A Germanium A Low power or signal
B Silicon P Light detector
EXAMPLE: BZY74-C6V3
B = Si, Z = Zener diode, Y74 =
Commercial or Industrial use,
C = 5% of rating voltage.
6V3 = 6.3 Volt (Rating Voltage)
Q (LED)
Y Rectifier
Z Zener (V- reference)
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Diode IdentificationDiode Identification
JEDEC Numbering or Coding System
First Number Second LetterSubsequent
numbers
1 Diode N Semiconductor Serial number
2Bipolar Transistor Example: This code “1N4001”
means:
1 Diode, N Semiconductor
4001 Serial number
3 FET
4 & 5Photo Coupler
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Diode OperationDiode OperationForward Biased:
The diode is forward biased (FB) when the (A) is
positive with respect to the (K).
The diode in FB allows the current to flow from A to K
as shown below
Diode Operated in FB Direction
+
K
DCA
RIFIF
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Diode OperationDiode OperationReverse Bias:
The diode is reverse biased (RB) when the (A) is
negative with respect to the (K).
The diode in RB does not allow the current to flow as
shown below.
Diode Operated in RB Direction
+KDC
A
R
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Testing the DiodeTesting the DiodeTesting in Forward Direction with an Ohmmeter:
Connect the Red-lead to the (A) and connect the
Black-lead to the (K) as shown below.
A good diode must display low resistance
(typically < 10) in FB.
Testing the Diode in FB Direction
IN 4001
K
Ohmmeter
A
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Testing the DiodeTesting the DiodeTesting in Reverse Direction with an Ohmmeter:
Connect the Red-lead to the (K) and connect the
Black-lead to the (A) as shown below.
A good diode must display a very high resistance
(> 1000 M) in RB.
Testing the Diode in RB Direction
IN 4001
K
Ohmmeter
A
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Testing the DiodeTesting the DiodeTesting in Forward Direction with a Digital Voltmeter:
Connect the Red-lead to the (A) and connect the
Black-lead to the (K) as shown below.
For a diode in a good condition the reading will be in
the range of 0.3V for Ge and 0.7V for Si.
Testing the Diode in FB Direction
IN 4001
KA
DigitalVoltmeter
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Testing the DiodeTesting the DiodeTesting in Reverse Direction with a Digital Voltmeter:
Connect the Red-lead to the (K) and connect the
Black-lead to the (A) as shown below.
For a diode in a good condition the reading will be
1.5V for both Ge and Si (in some cases it shows OL).
Testing the Diode in RB Direction
IN 4001
K A
DigitalVoltmeter
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Testing the DiodeTesting the DiodeWhen Testing with Analogue Voltmeter:
If both bias conditions show low resistance, then the
diode is shorted.
If both bias conditions show very high resistance, then
the diode is open circuit.
When Testing with Digital Voltmeter:
If in both cases the reading is 0V, then the PN junction
is shorted, and if it is 1.5V then the PN junction is
open.
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Diode ApplicationDiode Application The diode offers very little resistance to the
current flow in the FB direction.
It offers very high resistance to the current flow in
RB.
For this reason, the diodes are used in
rectification.
What is Rectification?
It is the process of converting ac to pulsating dc.
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AC Current BehaviorAC Current Behavior The AC current reverses its direction with each
alteration as shown below.
Alteration of AC current between (+ve) and (-ve)
I
I
-ve
+ve +ve
-ve Negative half-cycle
Positive half-cycle
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Half Wave RectifierHalf Wave Rectifier The half-wave rectifier circuit is constructed simply by
connecting a diode between the secondary of a
transformer and the load as shown below.
Load
Half Wave Rectifier Circuit
IF
AC Input
A K
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Half Wave RectifierHalf Wave Rectifier During the positive half-cycle, the diode turns ON and
connects the positive half-cycle across the load (RL).
During the negative half-cycle, the diode turns OFF (RB)
as shown below. The lamp is ON during the +ve half
cycle only.
AC Input Output
Operation of Half-Wave Rectifier
IF
A K
+
Load
+
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Half Wave RectifierHalf Wave Rectifier Output Voltage
Only positive half-cycles of the AC input appear across
the load, providing a pulsating DC voltage at the output
as shown below.
Secondary Voltage (VS)
Voltage across the Load
Output of Half-Wave Rectifier Voltage
VRL
VS
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The End
Of Module-1