LED driver chips can be divided into general-purpose chips and special-purpose chips.
The so-called general-purpose chip, the chip itself is not designed specifically for LEDs, but some logic chips (such as string 2 and shift registers) with some logic functions of the LED display.
The dedicated chip refers to a driver chip specially designed for LED display screen according to the LED light-emitting characteristics. The LED is a current-characteristic device, that is, under the premise of saturation conduction, its brightness changes with the change of current, rather than by adjusting the voltage across it. Therefore, one of the biggest features of the dedicated chip is to provide a constant current source. The constant current source can ensure the stable driving of the LED and eliminate the flickering phenomenon of the LED, which is the premise that the LED display screen displays a high quality picture. Some dedicated chips also add special features for different industry requirements, such as LED error detection, current gain control and current correction.
Evolution of driver ICs:
In the 1990s, LED display applications were dominated by single and dual colors, using a constant voltage driver IC. In 1997, China's first LED display driver control chip 9701 appeared, which spanned from 16 gray levels to 8192 gray levels, realizing the WYSIWYG of video. Subsequently, for LED lighting characteristics, constant current drive became the first choice for full-color LED display drive, while the more integrated 16-channel drive replaced the 8-channel drive. In the late 1990s, companies such as Toshiba of Japan, Allegro and Ti of the United States successively launched 16-channel LED constant current driver chips. In the early 21st century, the driver chips of Chinese Taiwanese companies were also mass-produced and used. Nowadays, in order to solve the problem of PCB layout of small-pitch LED display, some driver IC manufacturers have introduced a highly integrated 48-channel LED constant current driver chip.
Performance indicators of the driver IC:
Among the performance indicators of LED displays, refresh rate and gray level and image expressiveness are among the most important indicators. This requires high consistency of current between the LED display driver IC channels, high-speed communication interface rate, and constant current response speed. In the past, the refresh rate, grayscale and utilization rate are a trade-off relationship. To ensure that one or two of the indicators can be superior, it is necessary to sacrifice the remaining two indicators. For this reason, many LED displays are difficult to achieve the best of both worlds in practical applications, or they are not refreshed enough. High-speed camera equipment is prone to black lines when shooting, or grayscale is not enough, and the brightness of the color is inconsistent. With the advancement of the technology of the driver IC manufacturers, there have been breakthroughs in the three high issues, and these problems have been solved.
In the application of LED full-color display, in order to ensure the user's long-term use of eye comfort, low-light and high-ash is a particularly important criterion for testing the performance of the driver IC.
Driving IC trends:
1. Energy saving:
As a green energy source, energy saving is the eternal pursuit of LED display, and it is also an important criterion to consider the performance of driving IC. The energy saving of the driver IC mainly includes two aspects. One is to effectively reduce the constant current inflection point voltage, and then reduce the traditional 5V power supply to below 3.8V operation; the second is to reduce the operating voltage and operating current of the driving IC by optimizing the IC algorithm and design. At present, manufacturers have introduced a constant current driver IC with a low turning voltage of 0.2V and an LED utilization rate of up to 15%. The power supply voltage is reduced by 16% compared with conventional products, and the heat output of the LED display is greatly improved. .
As the pixel pitch of the LED display decreases rapidly, the packaged device to be mounted per unit area grows geometrically, which greatly increases the component density of the module driving surface. Taking the P1.9 small-pitch LED as an example, the 16-scan 160*90 module requires 180 constant-current drive ICs, 45 row tubes, and 2 138 tubes. With so many devices, the wiring space available for the PCB becomes extremely crowded, which increases the difficulty of circuit design. At the same time, the arrangement of such crowded components can easily cause problems such as poor soldering and also reduce the reliability of the module. The smaller amount of driver IC, the larger wiring area of â€‹â€‹the PCB, and the demand from the application end drive the IC must embark on a highly integrated technology route.
At present, the mainstream driver IC suppliers in the industry have successively introduced a highly integrated 48-channel LED constant current driver IC, which integrates large-scale peripheral circuits into the wafer of the driver IC, which can reduce the complexity of the application PCB board design. It also avoids the problems caused by the design capabilities or design differences of engineers in various manufacturers.
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