Full-color led display drives the functions and functions of IC
Time:2018-10-24
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In the work of full-color led display screen, the role of driving IC is to receive display data conforming to the protocol (from information sources such as receiving card or video processor), produce PWM and current time changes internally, and output PWM current related to brightness and gray refresh to lighten the led.Drive IC, logic IC and MOS switch to form the peripheral IC, and jointly act on the display function of full-color led display and determine the display effect.
LED drive chip can be divided into general chip and special chip.
The so-called universal chip itself is not specially designed for LED, but some logic chips (such as string 2 and shift register) with partial logic function of full-color LED display.
The special chip refers to the drive chip specially designed for full color LED display screen according to LED luminescence characteristics.LED is a current characteristic device, that is, under the condition of saturation conduction, its brightness changes with the change of current, instead of changing by adjusting the voltage at both ends.Therefore, one of the biggest characteristics of dedicated chip is to provide constant current source.Constant current source can guarantee the stable drive of LED and eliminate LED flicker, which is the premise of full-color LED display to display high-quality pictures.Some special chips are also designed for different industries, such as LED error detection, current gain control and current correction.
Driving the evolution of IC:
In the 1990s, full-color led displays were mainly used in single and double colors, with constant pressure driving IC.In 1997, the first full-color led display dedicated drive control chip 9701 appeared in China, which jumped from 16 levels of gray to 8192 levels of gray, realizing what video saw and obtained.Subsequently, constant current drive has become the first choice for full-color and full-color LED display driver, and the 16-channel driver with higher integration has replaced the 8-channel driver.In the late 1990s, companies such as Japan‘s Toshiba, American Allegro and Ti successively introduced 16-channel LED constant current drive chips, and in the early 21st century, the drive chips of Chinese Taiwan enterprises were also mass produced and used.Now, in order to solve the problem of small spacing and full-color led display PCB wiring, some drive IC manufacturers have introduced a highly integrated 48-channel led constant current drive chip.
Performance index of driving IC:
Among the performance indexes of full-color led display, refresh rate, gray level and image expression are the most important.This requires full-color led display to drive the current between IC channels with high consistency, high-speed communication interface speed and constant flow response speed.In the past, the three aspects of refresh rate, grey level and utilization ratio were in a reciprocal relationship. To ensure that one or two of the indicators could be better, the remaining two indicators should be sacrificed appropriately.For this reason, many full-color led displays are hard to get the best of both worlds in practical application, either the refresh is not enough, black lines are easy to appear under high-speed camera equipment, or the gray level is not enough and the color brightness is inconsistent.With the development of technology driving IC manufacturers, there has been a breakthrough in the high three problems, which have been able to solve these problems.
In the application of full-color led display, low light and high ash become a particularly important standard to test the performance of driving IC in order to ensure the comfort of the user‘s eyes for a long time.
Trends driving the IC:
1. Energy saving:
As a green energy, energy saving is the eternal pursuit of full-color led display, and also an important standard to consider driving IC performance.The energy saving of driving IC mainly includes two aspects. First, it can effectively reduce the constant current inflexion point voltage, thus reducing the traditional 5V power supply to below 3.8v.The second is to optimize IC algorithm and design drive IC operating voltage and operating current.At present, some manufacturers have introduced the constant current drive IC with 0.2v low turning voltage and improved LED utilization rate of over 15%. The power supply voltage of 16% lower than that of conventional products is used to reduce heat output, which greatly improves the energy efficiency of full-color LED display.
2. Integration:
With the rapid decrease of pixel spacing in full-color led display screen, the number of encapsulated components to be pasted on unit area increases exponentially, which greatly increases the density of components on module drive surface.Taking P1.9 small-spacing LED as an example, the 15swept 160*90 module needs 180 constant current drive IC, 45 line tubes, and 2 138.With so many devices, the space available for routing PCB becomes extremely crowded, making circuit design more difficult.At the same time, such crowded arrangement of components can easily cause welding defects and reduce the reliability of module.Driving IC with less consumption, PCB with larger wiring area, and the demand from the application end forced the driving IC to go on the high integration technology route.
At present, the mainstream drive IC suppliers in the industry have successively introduced the highly integrated 48-channel LED constant current drive IC, which integrates the large-scale peripheral circuits into the drive IC‘s wafer, which can reduce the complexity of the PCB circuit board design at the application end, and avoid the problems caused by the design ability or design differences of various manufacturers.
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