According to forecasts, the global high-brightness LED market in 2015 reached 14.52 billion US dollars, but the annual growth rate was only 2%. It is expected that in the next five years, the annual compound growth rate of the LED industry will be difficult to reproduce the growth rate of the past 10% or more, and the industry growth will slow down. As the use of AC direct drives continues to rise, one problem is the higher flicker index of LEDs, which is less important in outdoor lighting applications, but in the office, retail, and other commercial lighting environments, the scintillation index Below a certain level is very important.
It can be seen that the lamp flashes because the LED loses excitation energy whenever the AC input voltage passes its zero crossing, and Fairchild uses a scintillation index of less than 0.1 and is a solution that does not degrade PF and THD performance. To this end, the reporter interviewed Dr. Hong Yongwei, director of Fairchild's new business development, for the direct-drive LED solution.
Dr. Hong Yongxi, Director of New Business Development at Fairchild, said that by adding an energy storage network to each string of LEDs and working with many of China's top lighting manufacturers, the AC direct drive solution is designed to power from 12 W to 120 W. A variety of commercial and industrial lighting applications.
Currently LED drivers are divided into two main types: switching power supplies and AC direct drive solutions. According to Hong Yongxi, director of new business development at Fairchild, switching power supplies are more complex in design, the total cost of the solution is higher, and the number of BOMs is larger, including magnetic components and electrolytic capacitors, which may result in reduced system reliability and reduced system life. The AC direct drive method is simpler in design, the cost of the solution is lower, the BOM is also less, and no magnetic components and electrolytic capacitors are required.
Of course, these two methods will coexist. Hong Yongqi added that the switching power supply solution is suitable for applications where the end user may be exposed to the risk of LEDs, and the magnetic components provide isolation to prevent electric shock. In most commercial and industrial applications, such as downlights, slot lighting, patio lights and street lights, there is no direct contact with LEDs, so AC direct drive solutions are very attractive because of their simple design and cost-effective BOM. The number is also small. In these applications, AC direct drive solutions are the best choice.
LED brightness and flicker are two technical difficulties
In AC direct drive solutions, the LED string lights up in sequence as the AC voltage rises, with enough voltage to forward bias the next string of LEDs, which means that some LEDs are turned on during the AC voltage cycle. Shorter.
Hong Yongxi pointed out that in order to offset this effect and maintain the brightness of the target luminaire, AC direct drives require more LEDs than switching power supplies. Since LEDs can be continuously energized with the help of electrolytic capacitors, switching power supply drivers have 100% LED usage, and the increase in the number of LEDs offsets the cost savings from switching power supplies to AC direct drives because it is cost throughout the lighting system. Still occupy a large part.
However, LED costs have recently been found to be significantly reduced. As production methods become more mature, demand and capacity continue to increase, and LED usage becomes less and less problematic. In fact, Hong Yongyu said that Fairchild's AC direct solution can save 10% total BOM cost at 20W and 30% at 100W compared to switching power solutions.
In addition, it is flashing. Hong Yongxi pointed out that Fairchild's solution has now been resolved. Many suppliers currently offer AC direct drive LED solutions. However, there are still some problems with existing solutions, such as the inability to scale to higher power, poor flicker performance, high BOM cost, and incompatibility of intelligent lighting, which are important reasons for the low usage rate of this technology.
LED AC direct drive solution highlights
In the superior performance of the program. According to Hong Yongyu, Fairchild AC direct-drive LED solutions accelerate time-to-market and differentiated features by providing smart LED lighting products for commercial and industrial lighting manufacturers. For example, by paralleling products to support applications up to 120 W, the number of different ICs that manufacturers need to reserve is reduced.
While addressing the flicker problem, it also maintains high PF and lower THD performance, which can be achieved with Fairchild's proprietary system-level solution. According to Hong Yongyu, this system-level solution provides the current needed to keep the LEDs energized while maintaining the sinusoidal waveform of the input current, without interfering with PF and THD performance, providing the important dimming capabilities required for smart lighting products, including Phase cut dimming, analog dimming, and PWM dimming. For example, the FL779xx family of LED drivers, eliminating electrolytic capacitors eliminates the most common points of failure in LED lighting solutions, increasing reliability and extending system life to match the life of the LED itself.
In general, current AC direct drive LEDs are more attractive to lighting manufacturers than some switching metrics in terms of drive metrics such as drive size, cost and design simplicity. Hong Yongying stressed that AC directly drives LEDs. In addition to adding more features and functions to smart LED lighting, the drive topology and system structure are simplified through innovation, reducing BOM and end-user acquisition costs and accelerating market utilization. , gradually recognized by users.
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