EDN

EDN, May 26, 2011

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fluence of the product design and the requirements from the load," says Shearer. "For example, if you buy the cheapest possible dimmer, it will proba- bly have a higher holding current. Keep in mind that you've got the latching or firing current, and you've got the hold- ing current. So this cheaper dimmer will have a higher holding current of, say, 50 mA. At 50 mA, you've got 6W on a 120V line. Just to keep the TRIAC on, you're losing 6W." A more costly dimmer may have a substantially lower holding current, he adds. Another way to solve the load prob- lem is to decrease the LED light to only 10 or 20% of full intensity. If you don't go too low in light level, then the light itself still draws enough current to keep the TRIAC in a good state, Shearer explains. EDN's LED-light tear-downs show that many LED lights dim to some fraction of the light and then abruptly shut off but still draw current from the line.EDN REFERENCES 1 "Public Law 110-140, Energy Inde- pendence and Security Act of 2007," Dec 19, 2007, US Government Printing Office, http://1.usa.gov/erNM5C. 2 Conner, Margery, "LED bulbs reveal different design approaches," EDN, April 21, 2011, pg 47, http://bit.ly/ m0btRW. 3 "Black body," Wikipedia, http://bit.ly/ eFUTtv. 4 Stofka, Marian, "Finely tune the hue of blue-light sources," EDN, March 17, 2011, pg 64, http://bit.ly/hxijsC. 5 "Melatonin," Wikipedia, http://bit.ly/ eQ5N58. 6 Eskow, Cary, "Light Matters," Avnet Electronics Marketing, http://bit.ly/ e8WOUI. 7 Roberts, Seth, "Strong Light and Cancer," Seth's Blog, Oct 10, 2010, http://bit.ly/fKv8tW. 8 "50 years of history and innovation," Lutron Electronics, http://bit.ly/ ecGnFe. You can reach Technical Editor Margery Conner at 1-805-461-8242 and margery. conner@ubm.com.

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