This document discusses light emitting diodes (LEDs). It begins by stating the objectives of understanding how LEDs work, including being able to identify terminals, select materials, understand characteristics, and list applications. It then provides an introduction to LEDs as semiconductor devices that emit light when activated between 2-8V. The working principle is explained, that electrons recombine with holes in the P and N regions, releasing energy as light. Key materials used to produce different colors are also outlined, along with common applications such as sensors, mobile devices, traffic signals and illumination.

1. Er. Swapnil V. Kaware
B.E.(Electronics), M.E.(Electronics & Tele.)
svkaware@yahoo.co.in
www.slideshare.net/svkaware
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“Light Emitting Diode”

2. CONTENTS:-
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 OBJECTIVES
 PRE-REQUISITES/ENTRY LEVEL SKILLS
 INTRODUCTION
 WORKING
 CHARACTERISTICS
 APPLICATIONS
 REFERENCES
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3. OBJECTIVES:-
 Able to identify terminals of LED.
 Able to select appropriate materials for LED.
 Able to know working of LED.
 Able to plot characteristics of LED.
 Able to state applications of LED
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After completing the session you will be…..

4. INTRODUCTION:-
 A semiconductor device with two terminals.
 The terminals are anode (+) and cathode (-).
 It is works between voltage level 2V to 8V.
 It emits light when activated .
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5. WORKING:-
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Fig:- (a)
Fig:- (c)
Fig:- (b)

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WORKING:-
Fig:- (d)
Fig:- (e)
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7.  When LED is forward biased, then the electrons from N
region will combine with holes present in P region.
 But due to heavily doped P region majority of free
electrons will reside in conduction band.
 Hence this free electrons goes into high energy state (i.e.
at conduction band) & holes goes into lower energy state
(i.e. at valence band).
 But after the recombination, this electrons return back to
the valence band i.e. at lower energy state.
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8.  Hence by this way, when electrons come from
higher state to lower energy state they generates
excess amount of energy in the form of light or
radiaton.
 This process of LED is also known as
‘Electroluminescence’.
 Hence on this principle LED’s generates light.
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9. CHARACTERISTICS:-
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10. MATERIALS USED:-
 Gallium phosphide (GaP) for generating green
light.
 Gallium arsenide (GaAs) for generating red light.
 Silicon carbide(SiC) for generating yellow light.
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LED’s are made up of…..

11. APPLICATIONS:-
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 Sensor Applications
 Mobile Applications
 Security Applications
 Traffic Signals
 Illuminations
 Indicators
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12. SUMMARY:-
 Identify terminals of LED.
 Select appropriate materials for LED.
 Know working of LED.
 Plot characteristics of LED.
 State applications of LED
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After completing the session it becomes easier to…..
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13. Have a nice day ahead!!!!
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