LIGHT EMITTING DIODE

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LED Light Emitting Diode MANISH BHELOTKAR BY

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Synopsis:- Introduction Basic structure of LED. Type of LED. Manufacturing of LED. Application of LED. Conclusion.

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1 . Introduction:- A P-N junction diode, which emits light when forward biased, is know as a LIGHT EMITTING DIODE. The emits light may be visible or invisible. The amount of light output is directly proportional to the forward current. Thus higher the forward current, higher is the light output. when we increased the forward current, increase the brightness of light. We know that the LED is not ordinary diode, because ordinary diode make with hate production semiconductor material. Fig-A

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2. Basic construction of LED:- The schematic symbol of a LIGHT EMITTING DIODE show in fig-A, the arrow pointing away from the diode symbol represent light, which is being transmitted away from the junction and fig-B show’s the basic structure of a LIGHT EMITTING DIODE . Here, an N-type layer is grow on a P-type substrate by a diffusion process. Then a thin P-type layer is grow on the N-type layer. The metal connection make anode and cathode terminal’s as indicate . The light energy is released at the junction, when the recombination of electron’s with holes take place. After passing through the P-region, the light is emitted through the window provided at the top of the surface. Fig-A

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Fig- B When the LED is forward biased, the electron’s and hole’s move towards the junction and recombination take place. After recombination, the electron’s laying in the conduction bands of N-region, full into the hole’s laying in the valence band of a P-region. The difference of energy between the conduction band and valance band is radiated in the from of light. In ordinary diodes, this energy is radiated in the from of heat.

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3. Types of LED:- There are two types of LED. Single color LED. Multi color LED. Single color LED:- A LED have only one P-N junction diode in forward biased, which emits only single color light is called single color LED.

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ii. Multi color LED:- The LED which emits one color of light, when forward biased and another when reverse biased, are called multi color LED. Multi color LED is actually contain two P-N junction that are connected in reverse biased. They are parallel with the anode of one being connected to the cathode of the other. Multi color LED’s are typically red when biased in one direction and green when biased in the other direction. Incidentally if a multi color LED is switched fast, the LED will produce a yellow light. One commonly used symbol for a multi color LED is shown in figure- Fig-A

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4 . Making led by semiconductor :- The semiconductor material used for manufacture light emitting diode’s are Gallium Phosphate and Gallium Arsenide Phosphate. The silicon and germanium is not used for manufacturing LED because these are heat producing materials moreover, these materials are very poor in emitting light radiation. The LED radiate light in different color’s such as red, green, yellow etc. Some LED’s emits infrared light, depends upon the types of the semiconductor used. Some types of semiconductor emits either one color or other, depends the wavelength of the semiconuctor . We can understand from this table, which semiconductor Emits emits which types of light radiation.

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Color Wavelength{nm} Semiconductor Infrared > 760 Gallium arsenide (GaAs) Aluminum gallium arsenide (AIGaAs) Red 610< <760 Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphite (AlGaInP) Gallium(III) phosphide (GaP) Orange 590<<610 Gallium arsenide phosphide ( GaAsP ) Aluminium gallium indium phosphide ( AlGaInP ) Gallium(III) phosphide ( GaP ) Yellow 570<<590 Gallium arsenide phosphide ( GaAsP ) Aluminium gallium indium phosphide ( AlGaInP ) Gallium(III) Phosphide ( GaP ) Green 500<<570 Indium gallium nitride ( InGaN ) Gallium(III) phosphide ( GaP ) Aluminium gallium indium phosphide ( AlGaInP ) Aliuminium galliim phosphide ( AlGaP ) Blue 450<500 Zinc selenide ( ZnSe ) Indium gallium nitride ( InGaN ) Silicon carbide ( SiC ) as substrate Table of different types of semiconductors:-

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Application of LED:- The LED’s operate at low voltage’s l.c. form 1.5v to 2.5v they have a long life of about 10000 hour’s and can be switched ‘ON’ and ‘OFF’ at a very fast speed. These feature’s make LED’s very important electronic device. Following are important application’s of the LED’s For indicating ON/OFF conditions, power level indicator’s or stereo amplifier. In optical switching application. For solid state video displays, which are rapidly replacing cathode ray tubes. In the field of optical communication. For image sensing circuit’s in picture phone. In 7-segment display’s. In the remote control of electronic device's. widely used for traffic signal management.

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6. Conclusion:-

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THANK YOU