Full-color LED display drives the function and role of IC

 

LED driver chip can be divided into general chip and special chip two kinds.

 

The so-called universal chips are not specifically designed for LEDs themselves, but logic chips that have some of the logic functions of the full-color LED display (such as string 2 and shift register).

 

The special chip refers to the driver chip designed for full color LED display according to the LED luminescence characteristics. LED is a current characteristic device, that is, on the premise of saturation conduction, its brightness changes with the change of current, rather than by adjusting the voltage at both ends. Therefore, one of the biggest characteristics of dedicated chip is to provide a constant current source. Constant current source can ensure the stable drive of LED, eliminate the flashing phenomenon of LED, is the premise of full color LED display of high quality picture. Some specialized chips have been added to meet the requirements of different industries, such as LED error detection, current gain control and current correction.

 

Driving IC evolution:

 

In the 1990s, the application of full-color LED display is dominated by single and double colors, and the constant voltage drive IC is used. In 1997, China's first full-color LED display special drive control chip 9701 appeared, from 16 levels of gray to 8192 levels of gray, to achieve video WYSIWYG. Subsequently, according to the LED luminescence characteristics, the constant current driver has become the first choice for the full color full color LED display driver, and the 16-channel driver with higher integration degree has replaced the 8-channel driver. In the late 1990s, Japanese companies such as Toshiba, American companies such as Allegro and TI launched 16-channel LED constantcurrent driver chips one after another. At the beginning of the 21st century, Chinese Taiwan-based enterprises also produced and used driver chips in mass production. Now, in order to solve the problem of PCB wiring of small spacing full color LED display, some driver IC manufacturers have introduced a highly integrated 48-channel LED constant-current driver chip.

 

Driving IC performance indicators:

 

Among the performance indicators of full-color LED display, refresh rate, gray level and image expressivity are one of the most important indicators. This requires high consistency of current between IC channels driven by full color LED display, high speed communication interface rate and constant current response speed. In the past, refresh rate, gray scale, and utilization were in a reciprocal relationship. To ensure that one or two of the indicators were superior, the remaining two indicators had to be sacrificed appropriately. For this reason, many full-color LED displays are difficult to achieve the best of both ways in practical application. Either they are not refreshed enough, and black lines are easy to appear under high-speed camera shooting, or they are not gray enough, and the color light and dark brightness are inconsistent. With the technological progress of driving IC manufacturers, there has been a breakthrough in the three high problems, has been able to solve these problems.

 

In the application of full-color full-color LED display, in order to ensure the user's comfort with the eyes for a long time, low brightness and high gray has become a particularly important standard to test the performance of driving IC.

 

The trends that drive IC:

 

1, energy saving:

 

As a green energy, energy saving is the eternal pursuit of full-color LED display, and it is also an important standard to consider the performance of driving IC. Driving IC energy saving mainly includes two aspects, one is to effectively reduce the constant current inflection point voltage, and then reduce the traditional 5V power supply to 3.8V below the operation; The second is to reduce the driving IC operating voltage and operating current by optimizing IC algorithm and design. At present, some manufacturers have introduced a constant-current drive IC with a low turning voltage of 0.2V, which can improve the LED utilization rate by more than 15%. It uses 16% lower power supply voltage than conventional products to reduce the heat, which greatly improves the energy efficiency of full-color LED display.

 

2. Integration:

 

With the rapid decline of the pixel spacing of the full-color LED display, the number of package devices to be attached per unit area increases by geometric multiples, which greatly increases the component density of the module driver surface. Taking the P1.9 small-spacing LED as an example, a 15-sweep 160*90 module requires 180 constant-current drive ICs, 45 lines, and 2 138 lines. With so many devices, the available PCB wiring space becomes extremely crowded, which increases the difficulty of circuit design. At the same time, such a crowded arrangement of components can easily cause problems such as poor welding, and also reduce the reliability of the module. Fewer driving ICs, larger PCB wiring area, demand from the application side of the drive ICs must be on the high integration of the technical route.

 

At present, the industry's mainstream driver IC suppliers have launched a high integration degree of 48-channel LED constant-current driver IC, the large-scale integration of peripheral circuits into the driver IC wafer, can reduce the complexity of the application PCB circuit board design, but also to avoid the design ability or design differences caused by the engineers of each manufacturer.