As a high-tech product, LED display has attracted great attention. Intelligent full-color display which integrates light and electricity by computer control has been applied in a wide range of fields. The pixels of LED light-emitting diodes are arranged in dot array to form an LED array, and then form an LED screen. Different effect images can be obtained by different LED driving modes. Therefore, the advantages and disadvantages of LED driver chip play an important role in the display quality of LED display screen. LED driver chip can be divided into general chip and special chip.
Universal chips are generally used in low-end products of LED display screen, such as monochrome and bichrome screens in the house. The most commonly used general purpose chip is 74HC595, which has 8-bit latch, serial-parallel shift register and three-state output function. The maximum output current is 35 mA.
Because LED is a current characteristic device, that is to say, under the premise of saturated conduction, its brightness changes with the change of current size, not with the change of voltage at both ends. The most important feature of the special chip is to provide constant current source output, ensure the stable driving of the LED, and eliminate the flashing phenomenon of the LED. It has the characteristics of high output current and constant current. It is suitable for occasions requiring high current and high picture quality, such as outdoor full-color screen and indoor full-color screen.
SMT5026. SMT5026, a series of LED driver chips for LED display, has built-in CMOS shift register and latch function, which can convert serial input data into parallel output data format.
The second part: the system structure of LED display screen
(1) Display unit
This is the main part of the LED display screen, which is composed of luminous materials and driving circuit. The indoor screen is the unit display board of various specifications, while the outdoor screen is the unit box.
(2) Main Controller
The function is to buffer the input RGB digital video signal, transform the gray level, reorganize, and generate various control signals.
(3) Switching power supply
The purpose is to convert 220V AC into various DC currents and supply them to various circuits.
(4) Transmission cable
The display data and various control signals generated by the main controller are transmitted to the screen body by twisted pair cable.
(5) Scanning Controller
The function of the circuit board is to buffer data, generate various scanning signals and gray control signal of duty cycle.
(6) Special Display Card and Multimedia Card (Video Card)
In addition to the basic functions of the computer display card, the special display card for full-color LED screen also outputs digital RGB signals, line, field and blanking signals to the main controller. In addition to the above functions, the multimedia card can also convert the input analog Video signal into digital RGB signal (that is, video acquisition).
(7) Other signal sources and their external devices
Including computers, TV sets, Blu-ray, DVD, VCD, video cameras and so on.