LED light and brightness control principle

A, what is the LED?

in the semiconductor PN junction, the injection of minority carrier with majority carrier compound will release excess energy in the form of light, so as to directly convert the electric energy to light energy. PN junction to add reverse voltage, minority carrier injection, so the light. Principle of the use of injection electroluminescent diode called light-emitting diodes (leds), known as the LED. How do

2, the LED light?

the LED luminous color and associated with the production material and technology of the LED luminous efficiency, there is widespread use of red, green, blue three kinds. Because of the low voltage LED work ( Only 1. 5 - 3 v) Brightness, can take the initiative to light and to a certain extent, brightness and in voltage ( Or current) Adjust, itself and impact resistance, resistance to vibration, long life, 100000 hours) , so in the large display devices, there is no other way of display and LED display.

the red and green leds together as a single pixel of display screen called double color or color screen; The red, green, blue three kinds of LED tube together as a pixel display screen called three color or full color. Production of indoor LED screen pixel size is generally 2 - 10 mm, often using several can produce different colors of LED tube core is encapsulated into an organic whole, outdoor LED screen pixel size is 12 - more 26 mm, each pixel is made up of several kinds of monochrome leds, common product according to the pixel tube, double color pixel tube usually consists of three red 2 green, three color pixel tube in 2 red 1 green blue. Whether made of LED monochrome, double color or 3 color screen, need to display image pixels of each LED luminous brightness must be able to adjust, the adjustment of fine degree is the grey scale display. Gray level is higher, the display image is more delicate, more colorful, the corresponding display control system are more complex. General level 256 grayscale image, color transition is very soft, and gray level 16 color image, color transition boundary obviously. So, color LED current is required to make gray level 256.

3, method to control the LED brightness:

there are two ways to control the LED brightness.

1, using the human visual inertia, using pulse width modulation method to realize gray scale control, which is periodic change light pulse width ( The duty ratio) Cycle is short enough, as long as the repeated light ( The refresh rate is high enough) , the human eye is feeling less than glowing pixels in jitter. Due to the pulse width modulation is more suitable for digital control, so widely used in microcomputer to provide LED display content today, almost all the LED screen is controlled by pulse width modulation to grayscale.

2, the current through the LED change, general LED tube allows continuous working current is controlled in 20 ma, besides red leds have saturation phenomenon, other LED brightness essentially proportional to the flow of current.

the LED control system generally consists of main control box, scanning board and display control device is composed of three parts. Main box from computer display card to get a screen pixel brightness of of all kinds of data, and then reassigned to a number of scanning board, scanning each one is responsible for control of the LED screen lines ( Column) While each line ( Column) On the LED display control signal is transmitted in serial mode. There are two types of serial transmission display control signal way: one kind is centralized control each pixel gray scanning board, scanning board will come from the control box of the brightness values of all pixels decomposition ( The pulse width modulation) And then all LED to the opening of the signal pulse form ( Light is 1, not bright 0) In line with serial transmission to the corresponding LED on, control whether the light. This way using the device is less, but the serial transmission data volume is bigger, because in a repeated cycle of light, each pixel under the gray level 16 need 16 pulse, under the gray level 256 to 256 pulses, because the device operating frequency restricted, normally only the LED screen be gray level 16.

another method is to scan the board serial transmission content not every LED the brightness of the switch signal instead of an 8 bit binary value. Each LED has an own pulse width modulator to control the light time. Thus, in a repetitive cycle of light, each pixel point under the gray level 16 only need four pulse, under the gray level 256 just eight pulse, greatly reduces the frequency of serial transmission. With this kind of decentralized control LED gray-scale method can easily achieve a level 256 gray scale control.