LED screen by use of the environment is divided into indoor and outdoor LED display screen LED screen; LED screen by the display color is divided into single-color LED screen, LED screen dual-color and full-color LED screen; LED screen can be divided into 16 in grayscale , 32 , 64 , 128 , 256 grayscale LED screens ; LED screens are divided into text LED screens, graphic LED screens, synchronous video LED screens, TV video LED screens, etc. according to display performance .
　　 LED display system composition
The display unit: This is the main part of the LED display screen, and a light emitting material composed of a drive circuit. The indoor screen is a unit display panel of various specifications, and the outdoor screen is a unit cabinet.
Main controller: The function is to buffer the input RGB digital video signal, grayscale transform, reorganize, and generate various control signals.
Switching power supply: The purpose is to convert 220V AC into various DC power to provide various circuits.
Transmission cable: The display data generated by the main controller and various control signals are transmitted to the screen body by the twisted pair cable.
Scan controller: The function of this board is data buffering, which generates various scan signals and duty cycle gray control signals.
Dedicated display card and multimedia card ( video card ) : LED full color screen dedicated display card not only has the basic functions of computer display card, but also outputs digital RGB signal and line, field, blanking and other signals to the main controller. In addition to the above functions, the multimedia card can also convert the input analog video signal into a digital RGB signal ( ie, video capture ) .
Other sources and their external devices: including computers, televisions, Blu-ray, DVD , VCD , camcorders, etc.
　　 LED display LED driving Products
　　 As a high-tech product, LED display has attracted people's attention. The intelligent full-color display that integrates light and electricity with computer control has been applied in a wide range of fields. The pixel points adopt LED light-emitting diodes, and many light-emitting diodes are arranged in a dot matrix to form an LED array, thereby forming an LED screen. Different effect images can be obtained by different LED driving methods. Therefore , the advantages and disadvantages of the LED driver chip play an important role in the display quality of the LED display . LED driver chips can be divided into general-purpose chips and dedicated chips.
General-purpose chips are generally used for low-end products of LED displays , such as single and dual-color screens in indoors. The most commonly used general-purpose chip is the 74HC595 , which has an 8 -bit latch, a serial-to-parallel shift register, and a three-state output function. Each channel can output a maximum of 35mA non-constant current.
Since the LED is a current characteristic device, that is, under the premise of saturation conduction, its brightness changes with the magnitude of the current, and does not change with the voltage across it. ASIC most important feature is to provide a constant current source output to ensure stable driving of the LED, the LED flicker elimination. It has the characteristics of large output current and constant current, and is suitable for occasions requiring high current and high image quality, such as outdoor full color screen and indoor full color screen.
Key indicators for LEDs include:
Maximum output current: The current mainstream constant current source LED driver chip maximum output current is about 90mA per channel . The maximum value of the constant current output per channel simultaneously makes more sense for the display, because in the white balance state, it is required to simultaneously output a constant current per channel.
Number of constant current output channels: Constant current source output channels are available in 8 -bit and 16 -bit formats. Now 16 -bit is dominant. Its main advantage is to reduce chip size and facilitate LED driver board (PCB) wiring, especially for dot pitch. A smaller LED driver board is more advantageous.
Accurate current output: one is the current error value between the same chip channel ; the other is the output current error value between different chips. Accurate current output is a critical parameter that has a large impact on the display uniformity of the LED display . The larger the error, the worse the display uniformity is, and it is difficult to achieve white balance of the screen. At present , the bittobit current error of the mainstream constant current source chip is generally within ±3% , and the chiptochip current error is within ±6% .
Data Shift Clock: This determines the transmission speed of the display data and is a key indicator that affects the update rate of the display. As a large-size display device, the display refresh rate should be above 85 Hz to ensure a stable picture ( no scanning flicker ) . A higher data shift clock is the basis for the display to obtain a high refresh rate picture. At present, the mainstream constant current source driver chip shift clock frequency is generally above 15MHz~25MHz .
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