LED display structure and drive analysis
LED screen according to the use of the environment is divided into indoor led large screen and outdoor LED screen; LED screen according to the display color is divided into single-color LED screen, dual-color LED screen and full-color LED screen; LED screen grayscale can be divided into 16 , 32,64,128,256 gray LED screen, etc .; LED screen display performance is divided into text LED screen, graphic LED screen, synchronous video LED screen, TV video LED screen.
led display system composition of the system
Display unit: This is the main part of the led display screen, composed of luminescent materials and drive circuit. Indoor screen is a variety of unit display panel, outdoor screen is the unit box.
The main controller: the role is to enter the RGB digital video signal buffer, grayscale transformation, reorganization, and produce a variety of control signals.
Switching power supply: use is 220V AC power into a variety of DC power to provide a variety of circuits.
Transmission cable: the display device generated by the control device and a variety of control signals from the twisted pair cable transmission to the screen body.
Scan controller: The function of the circuit board is data buffer, generate a variety of scanning signals and duty cycle gray control signal.
Dedicated display card and multimedia card (video card): LED full color display card In addition to the computer graphics card with the basic functions, but also output digital RGB signals and lines, fields, blanking and other signals to the master. Multimedia card in addition to the above functions can also enter the analog video signal into a digital RGB signal (ie video capture).
Other sources and their external devices: including computers, televisions, Blu-ray, DVD, VCD, video recorders and so on.
led display with LED driver products
Led display as a high-tech products caused a high degree of attention, the use of computer control, light, electricity, integrated smart full-color display has been widely used in the field. The pixels using LED light-emitting diodes, many light-emitting diodes arranged in dot matrix, constitute the LED array, and then constitute the LED screen. Through different LED drive mode, you can get different effects of the image. So the advantages and disadvantages of LED driver chip, led display display quality plays an important role. LED driver chip can be divided into general-purpose chips and special chips.
General chip is generally used for low-end led display products, such as indoor single, two-color screen. The most commonly used general-purpose chip is the 74HC595, with 8-bit latch, serial and shift registers and tri-state output. Each channel can output up to 35mA non-constant current current.
As the LED is the current characteristics of the device, that is, under the premise of saturation conduction, its brightness changes with the size of the current changes, not with the voltage changes at both ends of the change. The biggest feature of the dedicated chip is to provide constant current source output, to ensure the stability of the LED drive to eliminate the LED flashing phenomenon. With the output current, constant current and other characteristics, suitable for demanding high-current, high-quality occasions, such as outdoor full color, indoor full color and so on.
Key indicators of LED include:
Maximum output current: the current mainstream constant current source LED driver chip maximum output current of about 90mA per channel. The maximum value of the constant current output per channel is also more meaningful for the display, since the constant current is required for each channel in the white balance state.
Constant current output channels: constant current source output channels are 8-bit and 16-bit two specifications, now 16-bit mainstream, the main advantage is to reduce the chip size, easy to LED driver board (PCB) wiring, especially for point spacing The smaller LED driver board is more advantageous.
Accurate current output: one is the same chip channel current error value; the other is different chip output current error value. Accurate current output is a very critical parameter, the display display uniformity of a great impact. The greater the error, the worse the display uniformity, it is difficult to make the screen to white balance. At present, the current constant current source chip bit to bit current error is generally within ± 3%, chip (chip to chip) current error within ± 6%.
Data shift clock: it determines the transmission speed of the display data, which is the key indicator of the update rate of the display screen. As a large-size display device, display refresh rate should be above 85Hz, in order to ensure a stable picture (no scan flashing sense). The higher data shift clock is the basis for the display to get a high refresh rate picture. At present the mainstream constant current source driver chip shift clock frequency is generally above 15MHz ~ 25MHz.