LED-light emitting diode

presentation

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? E xpression 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