Tài liệu LED and LCD

Hanoi University of Science and Technology LED and LCD Presented by:Nguyen Thanh BinhNguyen Van TuPhi Ngoc TuInstructor: Dr. Pham Nguyen Thanh Loan.1ContentsLCDLEDComparision between LED TV and LCD TV2What is LCD?Liquid Crystal Display3LCD BacklightLCD BacklightLED(RGB LEDs or WLEDs) CCFL(Cold-Cathode Fluorescent Lamp )4What is LED?Light-emitting diode.5LED ApplicationsTraffic lights and signals6LED ApplicationsArchitectural lighting7LED ApplicationsBacklighting for LCD televisions and displays8LED ApplicationsLight sources for machine vision systems9How does it work?10LED ColorsGreen LEDs: 1958Red LEDs :1960s  RGB LEDsBlue LEDs: 197111LED ColorsHow to create White Light LEDs (WLEDS)?Mix three primary colors: red, green, and blue  Ultraviolet (or Blue) LEDs + phosphor  WLEDs12How to “drive” a LED?Use a LED driver: to regulates the power to an LED 13What is a LED driver?Example: LED driver as ‘Cruise Control’ (like in a car) for the LED : Temperature increasesdriver LED decreases power and reverse. Without the driver?the LED may become too hot and unstable poor performance or complete failure.14Characteristic curves R VS LED15LED WITH CURRENT LIMITING RESISTORExample: Vin=5vVF= 2.1V, IF=25mAVR=5-2.1 = 2.9VR= V/I = 120ΩPower dissipationP= I^2*R = 0.075 W16Another Method to Driver LEDIt can handle higher power The current is stable regardless of the voltage supply17Another Method to Driver LED18AdvantagesSmall size:smaller than 2 mm2Power consumption: save energyCool light: radiate very little heatDimming: easily be dimmed either by pulse-width modulation or lowering the forward current.On/Off time: switch very quicklyDurability: last virtually forever19Is LED better than CCFL?20LED Backlight vs CCFL Backlight1. Screen sizeCCFL Backlight:	Images start to break down and colors look noticeably muted, blacks are grey, and the contrast is so-so.21LED is better than CCFL?22LED Backlight vs CCFL Backlight2. ThicknessLED Backlight: Thin LED edge-lighting system (a long LED module of tiny white diodes along the outside edges of the screen)23LED is better than CCFL?24LED Backlight vs CCFL Backlight3. Color GamutLED Backlight : use RGB LED arrays a color gamut about twice that of a conventional CCFL LCD.An RGB backlight(Credit: Samsung)25LED Backlight vs CCFL Backlight3. Picture ContrastLEDs can be switched on and off faster than CCFLs offer very high contrast ratios (produce deep blacks (LEDs off) and high brightness (LEDs on)).vivid colors, truer blacks, and deeper contrast.26LED Backlight vs CCFL Backlight5. Power ConsumptionLED LCD is thinnerLighting by LEDs saves a lot of energyLED BacklightCCFL (Cold Cathode Fluorescent Lamp)Power consumption(watts per square inch)0.072Sony KDL-46EX7000.155Sony KDL-46W410027References You!Questions?29How does a LCD work?A sandwich-like structure of LCD30TN PanelLight can’t go through second polarizer31TN PanelLight can go through second polarizer.32Different Kind of PanelTN panel has high raterefresh up to 120Hz, and fast responseIPS panel has wide view angle, true color33