LED display driver chip and its function
As a high-tech product, LED display has attracted people’s attention. The large-screen intelligent LED display that integrates light and electricity with computer control has been used to a large extent. The LED outdoor large screen manufacturer will explain to you the driver chip of the LED display.
The pixels of the LED display screen are LED light-emitting diodes, and many light-emitting diodes are arranged in a dot matrix method to form an LED array, which in turn constitutes an LED display screen. With different LED driving methods, images with different results can be obtained. Therefore, the quality of the driver chip plays a very important role in the display quality of the LED display.
LED driver chips can be divided into general-purpose chips and special-purpose chips.
1. General-purpose chips are generally used in low-end products of LED displays, such as indoor single-color and double-color LED displays. The most commonly used general-purpose chip is the 74HC595, which has an 8-bit latch, a serial-parallel shift register, and a three-state output function. Each channel can output a maximum current of 35 mA (not constant current). General IC manufacturers can produce such chips.
2. The special chip used for full-color display screen, because LED is a current characteristic device, that is, under the premise of saturated conduction, its brightness changes with the change of the current size, not with the change of the voltage at both ends of the LED. . Therefore, one of the biggest features of the special-purpose chip is to supply a constant current source. The constant current source can ensure the stable driving of the LED and eliminate the flashing phenomenon of the LED.
Important parameters of the special chip for LED display:
The special chip for LED display has basic features such as large output current and constant current, and is suitable for places with high current and high image quality, such as outdoor full-color screens, indoor full-color screens, etc.
The key performance parameters of the special chip for LED display are the maximum output current, the current output error (bit to bit, chip to chip), the constant current source output duration and the data shift clock.
Maximum output current:
At present, the maximum output current of mainstream constant current source chips is mostly defined as the maximum output current of a single channel, generally about 90 mA. Constant current is the basic feature of special-purpose chips, and it is also the basis for obtaining high image quality. The maximum value of the constant current output by each channel at the same time (that is, the maximum constant output current) is more meaningful to the display screen, because under the condition of white balance, each channel is required to output constant current at the same time. Generally, the maximum constant current output current is less than the allowable maximum output current.
Current output error:
There are two types of current output errors, one is the inter-bit current error, that is, the error between each output of the same chip; the other is the inter-chip current error, that is, the output current error between different chips. The current output error is a very critical parameter, which has a great influence on the uniformity of the display screen. The larger the error, the worse the uniformity of the display screen, and it is difficult to make the screen body reach the white balance.
At present, the current error between bits (bit to bit) of mainstream constant current source chips is generally within +60%, and the current error between chips (chip to chip) is within ±15%.
Constant current source output number:
There are 8-bit (8-channel constant source) and 16-bit (16-channel constant source) output specifications for the constant current source. Now 16-bit source is the mainstream. Its important advantage is that the chip size is reduced, which is convenient for LED driver board (PCB). ) wiring, especially for LED driver boards with smaller dot pitch.
Data shift clock:
The data shift clock 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 sparkle). A higher data shift clock is the basis for the display to obtain a high refresh rate picture. At present, the shift clock frequency of mainstream constant current source driver chips is generally above 15 MHz.
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