Light Emitting Diode (LED)

presentation..

1. Initialized by Almas Akram

2. OPTOELECRONIC A light emitting diode (LED) is essentially a PN junction opto -semiconductor that emits a monochromatic (single color) light when operated in a forward biased direction . LEDs converrt electrical energy into light energy. They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not

3. HOW DOES A LED WORK? When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions . In the p region there are many more positive than negative charges . When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region

4. How does LED work?

5. How Does A LED Work? Each time an electron recombine swith a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a 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(usually a combination of the chemical elements gallium, arsenic and phosphorus .

6. How Much Energy Does an LED Emit? The energy (E ) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression : E = qv Joules . Finding the Energy from the Voltage Suppose you measured the voltage across the leads of an LED , and you wished to find the corresponding energy required to light the LED . Let us say that you have a red LED, and the voltage measured between the leads of is 1.71 Volts. So the Energy required to light the LED is E = qv or E = -1.6 x 10-9

7. Finding the Energy from the Voltage Voltage Suppose you measured the voltage across the leads of an LED, and you wished to find the corresponding energy required to light the LED. Let us say that you have a red LED, and the voltage measured between the leads of is 1.71 Volts. So the Energy required to light the LED is E = qV or E = -1.6 x 10-19(1.71) Joule, since a Coulomb-Volt is a Joule. Multiplication of these numbers then gives E = 2.74 x 10-19Joule.

8. NEXT proceeded by MUBEEN TALHA.

9. LED VOLTAGE AND CURRENT To prevent from destruction of LED we use a resistor There are two voltages Source voltage and Diode voltage.  

10. LED Brightness the brightness of an LED depends on the current When Vs is much greater than Vd the brightness of LED is approximately constant. If Vs is only slightly more than Vd , the LED brightness will vary noticeably. To keep the brightness of LED constant the source current must be constant .

11. Colours of LEDs LEDs are available in red, orange, amber, yellow, green, blue and white . Blue and white LEDs are much more expensive than the other colours . The colour of an LED is determined by the semiconductor material , not by the colouring of the package (the plastic body ). LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color. Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels.

12. BREAKDOWN VOLTAGE LED have very low breakdown voltage , typically between 3V and 5V LED destroyed if the too much voltage applied. It works only in farward biased

13. NEXT proceeded by AQSA

14. Seven-Segment Display It contains seven rectangular LEDs ( A through G ) Each LED is called a segment. External series resistors are included to limit the current to safe levels. Using seven segment we can form any digit from 1 to 9 . It can also display the capital letters(A,C,E,F) . In seven-segment indicator all anodes are connected together. It is also in common cathode type in which all cathodes are connected together

15. Seven segment Display

16. NEXT proceeded by Zoya

17. Photodiode What is photodiode ? Photodiode is a reverse of led In photodiode input is light and the output is voltage It works in reverse biased. When the covalent bond break electrons emit and it moves from lower to higher orbit and gain energy. When it come back to lower energy level it emits radiation in form of voltage .

18. photodiode - Principle of photodiode When light energy bombarded a pn junction ,it dislodge valance electrons More the light strike the pn -junction more is the reverse current produce Incoming light produces free electrons and holes The stronger the light the larger the minority carriers and greater the reverse current As the light become brighter , the reverse current increases.

19. NEXT proceeded by Muneeba Nisar

20. optocoupler Optocoupler combines led and the photodiode -led convert voltage into light and work as a input -photodiode convert light into a voltage and work as a output. When the input voltage is varying ,the amount of light is fluctuating

21. optocoupler Advantage of optocoupler Easily availaible No gas , No pollutant produce Less area required for installation D isadvantage of optocoupler Not always produce constant electricity Due to temperature variation after some time decrease the efficiency

22. Laser diode In a led free electrons radiate light when falling high energy level to lower one A laser diode is different , it produce the coherent light A laser diode produce a narrow beam of light which is very intense ,focused and pure. These are also known as semi-conductor laser, it can produce visible and invisible lights.

23. NEXT proceeded by M . ABDULLAH HASHMI (GROUP leader )

24. Applications Sensor Application Mobile Applications Sign Applications Automobile Applications LED Signals Indicators

25. Sensor Applications Color Bar Code Readers Medical Instrumentation (blood group detection using fiber optics) M oney sensors Optical switches Fiber optical cummunication

26. Mobile Applications General Backlighting Lap Tops Digital Cameras PDAs Mobile Phone

27. Sign Applications Transportation Passenger Information Traffic Monochrome Message Board Full color video

28. Automobile Applications Interior Lighting - Instrument Panels& switches,courtesy lighting Exterior lighting,rear stop/turn/tail Truck/bus lighting ,new turn/tail/marker lights

29. Signal Appications Runway Tower Lights Aviation Rail Traffic Emergency/Police Vehicle Lighting LEDs offer enormous benefits Lights Energy savings (up to 85 % less power than incandescent) Reduction in maintenance costs Increased visibility in daylight and adverse weather conditions

30. Indication VCR / DVD/ Stereo and other audio and video devices Household appliances Security Equipment Instrumentation Toys/Games Switches

31. Some type of LEDs

32. THE END THANKS FOR LISTENING ANY QUESTION ?? 