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Taiwan-based LED chip maker Epistar says it expects to be “the first company in the world to ship AC-LED chips in volume,” starting in the second quarter of 2009.
The company has been developing AC-LED chips since 2004 and has filed more than 10 patent applications in related fields. Last year, the company obtained a patent license from ITRI, the Taiwan-based Industrial Technology Research Institute (see below).
The company will join a small number of suppliers that have been at the forefront of AC-LED development, notably Lynk Labs, which build AC-driven modules and light engines, and Seoul Semiconductor, which sells power LEDs that can be connected directly to an AC source.
Epistar says that it is aware of the lighting industry’s desire for a “two wire solution” i.e. a light engine without complicated electronics. The AC-LED concept simplifies system design by making the AC-DC converter redundant. For a conventional DC-driven LED design, the AC-DC converter introduces a conversion loss typically in the range of 15% to 30%. Any reliability issues with the converter are also eliminated.
Epistar acknowledges that the luminous efficacy of an AC-LED is lower than that of a DC-LED at the same chip size. However, based on the cost saving from eliminating the AC-DC converter, Epistar is working with a larger chip size, currently 55 mil per side, equivalent to approx. 1.4 mm. Many “one watt class” DC-driven LEDs measure 1 mm (40 mil) per side.
Epistar says that its AC-LED chip, when driven at 1 W, has an efficacy of up to 70 lm/W at a color temperature of 5700K. This is equivalent to a DC-driven LED with 85 lm/W efficacy and a converter with 15% conversion loss, claims Epistar.
The company believes that both AC-LED and DC-LED technologies have their own unique characteristics, and each will be suitable for different applications; AC-LED is best suited for LED spot lights with less than 10 W power, such as MR16 or AR111 replacements. Meanwhile, says Epistar, DC-LEDs are suitable for high-brightness applications such as street lamps or automotive headlights.
ITRI and Seoul Semiocnductor
ITRI has established a patent portfolio related to AC-LEDs, which includes design, processing, packaging and applications. On October 3rd, 2008, ITRI assembled 19 companies in Taiwan, including Lite-On and Epistar, to create an AC LED Application Research Alliance. ITRI says the goals of the alliance are “to expedite new product development and promote this burgeoning market all together.”
The AC LED technology developed by ITRI and Epistar appears to be superficially similar to that used by Seoul Semiconductor in its Acriche AC LED products. The chip is divided into a number of “micro-diodes”, which are connected into two parallel strings. Current flowing in one direction illuminates the micro-diodes in one of the strings. When the current changes direction, the other string is illuminated.
Seoul Semiconductor has a large number of patents in the field of AC LED technology, and may act to prevent other LED makers from entering the market. When Nichia and Seoul reached a cross-licensing agreement earlier this year (see News), a Seoul spokesperson told LEDs Magazine that the deal would allow Seoul greater freedom to pursue other infringing companies, since its resources were no longer being diverted by its battle with Nichia.
As we wrote in the News article, “we might expect to see a crackdown against companies that supply AC-driven LEDs similar to Seoul's Acriche product; Seoul has more than 200 products in this area, according to the spokesperson.”