The document discusses light emitting diodes (LEDs). It describes how LEDs work, including that they emit light when electrons recombine across the PN junction semiconductor. It also covers LED characteristics like color, types of LEDs including bi-color and tri-color LEDs, and applications such as in electronics, transportation displays, and as replacements for incandescent lights due to their energy efficiency.

1. GROUP MEMBERS
BEEF16E037
BEEF15E037
BEEF16E039
Electronic Devices and Circuits

2. Light Emitting Diode (LED)

3. ABOUT LEDS
 Nick Holonyak Jr. developed first LED in 1962
 Symbol of LED is
 A light emitting diode (LED) is essentially a PN
junction semiconductor and emits light.

4.  The most important part semi-conductor
chip.
 The chip has two regions separated by
junction.
 The junction acts as a barrier to the flow of
electrons between the P and N regions.

5. P AND N TYPE REGIONS

6. BAND GAP IN LED
 Semiconductor conduct electricity because of
small band gap between the valence and
conduction bands, which allow electrons to
move throughout the material with a
moderate input of energy.
conduction band
Band gap
valence band

7. DIRECT BAND GAP INDIRECT BAND GAP
 In indirect band gap highest
energy of valence band is
lower to energy of
conduction band which
mean they are at different
momentum.
Conduction band
Valence band
 In direct band gap highest
energy of valence band is
equal to the lowest energy
of conduction band which
means they are at same
momentum.
Conduction band
Valence band

8. HOW DOES LED WORK?
 When sufficient voltage is applied to the chip
across the leads of the LED and current start to
flow then electrons can move easily in one direction
across the junction between the P and N regions.

9.  For each recombination of negative and a positive
charge, a quantum of electromagnetic energy is
emitted in the form of a photon of light with a
frequency characteristic of the semi-conductor
material.

10. CHARACTERISTIC CURVES
.

11. TESTING OF LEDS

12. HOW MUCH ENERGY DOES LED EMIT?
 Expression of light emitted by an LED is
E=hc/λ joules.
 The constant h=6.626176 x 10-34

13. COLORS OF LEDS
 LEDs are made from Gallium-based crystals
that contain one or more additional materials
such as phosphorus to produce a distinct
color.

14. BI COLOR LEDS
 A bi-color LED has two LEDs wired in inverse
parallel combined in one package with two leads.
 Only one of the LEDs can be glow
at one time.

15. TRI-COLOR LEDS
 The most popular type of tri-color LED has a
red and a green LED combined in one
package with three leads.
 There are different lengths of the three leads.

16. TYPES OF LEDS
 Bargraph
 7-segment
 Starburst
 Dot matrix

17. APPLICATIONS
 Bar code reader
 Color and money sensors
 Mobile phones
 Lap tops
 Digital cameras
 Transportation-Passenger Information

18. ADVANTAGES
 Save up to 90% energy
 No heat up
 100% brightness immediately
 No IR and UV radiations produces

19. Thanks