1. INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH
SECOND SEMESTER
ELECTRONICS
Module-1
PN Junction Diode

2. INSTITUTE OF APPLIED TECHNOLOGY
INTRODUCTION
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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3. INSTITUTE OF APPLIED TECHNOLOGY
Definition
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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4. INSTITUTE OF APPLIED TECHNOLOGY
Diode 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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5. INSTITUTE OF APPLIED TECHNOLOGY
Diode Symbol
The symbol of diode is shown below. K
Diode Symbol A
In the symbol, the arrow points from anode (A) to cathode (K), this is the direction of current flow.
The cathode (K) is marked with a silver color band as shown below.
Typical Diode K
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6. INSTITUTE OF APPLIED TECHNOLOGY
Types of Diode
Commonly diodes are made of Silicon (Si) or Germanium (Ge).
According to the application they are classified into:
Low power diodes.
Light Emitting Diodes (LEDs).
Zener diodes.
Rectifier diodes.
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Diode 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).
DO-5
DO-41
DO-8
Diode packing types
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8. INSTITUTE OF APPLIED TECHNOLOGY
Diode 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:
Pro-Electron System: originated and widely used in Europe.
JEDEC System: widely used in North America.
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9. Diode Identification Pro-Electron Coding System A Germanium
First Letter Specifies Semiconductor Material
Second Letter Specifies type of Diode A
Germanium
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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10. JEDEC Numbering or Coding System INSTITUTE OF APPLIED TECHNOLOGY
Diode Identification
JEDEC Numbering or Coding System
First Number
Second Letter
Subsequent numbers 1
Diode N
Semiconductor
Serial number 2
Bipolar Transistor
Example: This code “1N4001” means:
1  Diode, N  Semiconductor
4001  Serial number 3
FET
4 & 5
Photo Coupler
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Diode Operation
Forward 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 + K DC A R IF
Diode Operated in FB Direction
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12. INSTITUTE OF APPLIED TECHNOLOGY
Diode Operation
Reverse 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. + K DC A R
Diode Operated in RB Direction
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13. Testing the Diode in FB Direction
Testing 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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14. Testing the Diode in RB Direction
Testing 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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15. Testing the Diode in FB Direction
Testing 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 K A
Voltmeter
Digital
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16. Testing the Diode in RB Direction
Testing 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
Voltmeter
Digital
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Testing the Diode
When 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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18. INSTITUTE OF APPLIED TECHNOLOGY
Diode 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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19. AC Current Behavior
The AC current reverses its direction with each alteration as shown below. I
Positive half-cycle
+ve
+ve
-ve
-ve
Negative half-cycle I
Alteration of AC current between (+ve) and (-ve)
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20. Half Wave Rectifier Circuit
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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21. Operation of Half-Wave Rectifier INSTITUTE OF APPLIED TECHNOLOGY
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. IF A K +
Load
AC Input
Output
Operation of Half-Wave Rectifier
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Half 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. VS
Secondary Voltage (VS)
VRL
Voltage across the Load
Output of Half-Wave Rectifier Voltage
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23. INSTITUTE OF APPLIED TECHNOLOGY
The End
Of Module-1
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