As a high-tech product, the led large screen has attracted people's attention. The intelligent led large screen, which is controlled by a computer and integrates light and electricity, has been used in a wide range of fields. The pixel points use LED light-emitting diodes, and many light-emitting diodes are placed in a dot matrix to form an LED array, which in turn constitutes a large LED screen. Through different LED driving methods, images with different effects can be obtained. Therefore, the quality of the LED large screen driver chip plays an important role in the display quality of the LED large screen. LED driver chips can be divided into general-purpose chips and special-purpose chips.

 General-purpose chips are generally used in low-end products with large LED screens, such as indoor single-color and dual-color screens. The most commonly used general-purpose chip is 74HC595, which has 8-bit latch, serial-to-parallel shift register and three-state output functions. Each channel can output up to 35mA of non-constant current current.

 Because the LED is a current characteristic device, that is, under the premise of saturated conduction, its brightness changes with the change of the current size, and does not change with the change of the voltage at both ends. The biggest feature of the dedicated chip is to provide a constant current source output, to ensure the stable driving of the LED, and to eliminate the flicker phenomenon of the LED. With the characteristics of large output current and constant current, it is suitable for occasions requiring high current and high image quality, such as outdoor full-color screens, indoor full-color screens, etc.

  The key goals of led large screens include:

  Maximum output current: At present, the maximum output current of the mainstream constant current source LED driver chip is about 90mA per channel. The maximum value of the constant current output for each channel is more meaningful for the display screen, because in the white balance state, each channel is required to output the constant current together. Number of constant current output channels: Constant current source output channels are available in 8-bit and 16-bit specifications. Now 16-bit occupies the main current. Its main advantage is that it reduces the chip size and facilitates the LED driver board (PCB) wiring, especially with regard to the point distance. A smaller LED driver board is more advantageous. Accurate current output: one is the current error value between channels of the same chip; the other is the output current error value between different chips. Accurate current output is a very critical parameter, which has a great impact on the uniformity of the large LED screen. The greater the error, the worse the uniformity of the display, and it is difficult to make the screen white balance. At present, the bit to bit current error of the mainstream constant current source chip is generally within ±3%, and the chip to chip current error is within ±6%. Data shift clock: It determines the transmission speed of the display data and is a key target that affects the update rate of the large LED screen. As a large-scale display device, the display refresh rate should be above 85Hz to ensure a stable picture (no scanning flicker). A higher data shift clock is the basis for a large LED screen to obtain a high refresh rate picture. At present, the shift clock frequency of the mainstream constant current source driver chip is generally above 15MHz~25MHz.