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GROUP 1 PRESENTS

GROUP 1 PRESENTS

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GROUP 1 PRESENTS

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  1. GROUP 1 PRESENTS NASEEB ALI 2011-EE-502 YASOON ASLAM 2011-EE-504 PIRZADA ZAIN-UL-ABIDIN SHAH 2011-EE-507 ALI ZIA 2011-EE-508 SHAWAIZ ALI MALIK 2011-EE-511 ROHAAN BUTT 2011-EE-513 SAJJAD ASLAM 2011-EE-514

  2. LIGHT EMITTING DIODE (LED) SCHEMATIC SYMBOL

  3. CONTENTS • INTRODUCTION • CONSTRUCTION • WORKING PRINCIPLE • TYPES OF LED • PHYSICAL PARAMETERS • SPECIFICATION • V-I CHARACTERISTIC CURVE • MULTI-COLOURED LED • TESTING OF LED • APPLICATIONS

  4. INTRODUCTION

  5. 1957 - LED invented by Radio Corporation of America (RCA) • 1968 – First economically mass produced LEDs made by Monsanto Corp & Litronix • 1972 - HP introduces the HP35 calculator using an LED display • 1993 - Nichia Corp produces the first high brightness LED using phosphor conversion to create white light • 2009 - European Union bans most incandescent light bulbs IEEE Library

  6. CONSTRUCTION

  7. LED has two leads- cathode and anode • We can identify from either points: • Either Cathode lead is of lesser length • OR Cathode is of broader filament. • Different LEDs are made from different compounds like GaAs, GaAsP, etc. IEEE Library

  8. WORKING PRINCIPLE

  9. When diode is forward biased, electrons of n-region cross p-n junction and combine with holes in p-region. As a result of this, large amount of energy is released in the form of heat and light. The photons of light fall in visible region. This process is known as electroluminescence. ELECTRONIC DEVICES AND CIRCUITS BY BOGART

  10. Excitation E Electron (excited by the biased forward voltage) is in the conduction band k Normally the recombination takes place between transition of electrons between the bottom of the conduction band and the top of the valance band (band exterma). The emission of light is therefore; hc/ = Ec-Ev = Eg(only direct band gap allows radiative transition) Hole is in valance band

  11. Electrical Contacts P-n junction How does it work? A typical LED needs a p-n junction There are a lot of electrons and holes at the junction due to excitations Electrons from n need to be injected to p to promote recombination Recombination produces light!! Junction is biased to produce even more e-h and to inject electrons from n to p for recombination to happen

  12. TYPES OF LED

  13. LEDs are classified with respect to following types : • W.r.t Size. • W.r.t Colour. • W.r.t Shape. LAB MANUAL BY ENGR USMAN ASLAM

  14. Types w.r.t Size • most familiar LED size is T 1 ¾ (where “T” refers to the bullet shape) whose approximate diameter is 1/8ths of an inch often listed as 5 mm (millimeters). • the smaller T 1 size is more modern looking and uses up less space • Surface mount LEDs are smaller still LED sizes: surface-mount (1.5 mm), small - T 1 (3 mm), standard - T 1 ¾ (5 mm), and jumbo - T 3 ¼ (10 mm) LAB MANUAL BY ENGR USMAN ASLAM

  15. Types w.r.t Shape • LEDs also differ due to their shapes: • Some are curved bullet shaped (commonly used in labs). • While many others are found in multiple varieties. LAB MANUAL BY ENGR USMAN ASLAM

  16. Types w.r.t Colour WIKIPEDIA

  17. PHYSICAL PARAMETERS

  18. Forward operating voltage is b/w 1.4 to 3.6 volts. • its current rating is 20mA. • Max reverse voltage b/w -3V and -10V. • life time is 2 lakh hours. • 75% of power converted to heat. • Operating Temperature For indoor is 25C & for outdoor 15C. IEEE Library

  19. SPECIFICATIONS http://www.hebeiltd.com.cn/led

  20. V-I CHARACTERISTIC CURVE

  21. http://www.hebeiltd.com.cn/led

  22. MULTI-COLOURED LED

  23. Some LEDs give different colour when forward biased and other when reversed biased, if their changing frequency is increased then a third colour will also be seen, hence that LED will be known as Multi-Colour LED. IEEE Library

  24. TESTING OF LED

  25. 1. On the multimeter, the black lead should be connected to the COM terminal. 2. The red lead is usually connected to terminal. 3. Turn the multimeter dial to the diode symbol, which looks like an arrow crashing into a wall. This indicates a component that allows electricity to flow in one direction (the arrow) but not the other direction (the wall). The diode setting is appropriate for LEDs, because the “D” in “LED” stands for diode. 4. Power up the meter and note what the display indicates. 5. Select an ordinary red LED. The color is important for this test. 5. Find the cathode lead of the LED. Usually that’s the shorter of the two wires and connect the red probe to the LED’s anode (+) 6. If the LED is faulty then the beep will be heard otherwise a forward biased voltage in mV will be displayed on the screen showing that the LED is working properly. LAB MANUAL BY ENGR USMAN ASLAM

  26. APPLICATIONSOF LED • LEDs are being used in wide range nowadays in many electronic components. • Some of their applications are: • Traffic lights and signals. • Motorcycle and Bicycle lights.  • Toys and recreational sporting goods, such as the Flashlight.  • Railroad crossing signals . http://www.doubulb.com/LED-applications.

  27. LED Flashlights • ARC introduced the first LED flashlight in 2001 • LED’s are more efficient than ordinary light bulbs. • LED flashlights, in some cases have a battery life of hundreds of hours. • LED’s can survive shock that often break conventional light bulbs. • LED flashlights are electronically regulated to maintain constant light output independent of battery voltage. • Incandescent flashlights becomes progressively dimmer as the battery voltage drops IEEE Library

  28. Why LED’s Now? • Global Warming • Exponential consumption of electricity • Fossil Fuel / Peak Oil • Government Mandates • European ban on Incandescent bulbs • Mercury in Florescent bulb, now a hazardous material. Against the law in California to put in your trash IEEE Library