News and New Products

Power-converter IC targets dimmable LEDs, needs no optoisolator

By Margery Conner, Technical Editor -- EDN, 11/12/2009

The large installed base of dimmable-lighting switches dictates that most new lighting technologies, including LED lights, should support dimming, and the myriad disparate specifications for dimming switches requires these lights to meet a wide range of characteristics. Meeting both of those requirements, iWatt’s new iW3610 ac/dc digital-power controller for dimmable LEDs includes intelligent wall-dimmer detection for both leading- and trailing-edge dimmers. It also detects an unsupported dimmer and turns off the light rather than self-destructing. The IC supports dimming from 2 to 100% and has an optimized dimming frequency of 900 Hz, so there is no visible flickering over the entire range.

LED lighting that gets its power directly from ac-line voltage requires some form of isolation from the ac mains. An optoisolator typically performs this task, especially in low-cost, high-volume products. However, LED lights place a high premium on long life, and, because optoisolators can degrade with time, they can become a failure point in devices that must operate for 10 or more years. The 3610 tackles this problem by using primary-side regulation, eliminating the need for an optocoupler and sense resistor, reducing bill-of-material costs, and improving reliability for dimmable LED lights of 40W or lower wattage. Another version, the iW3620, is similar to the 3610, but does not support dimming.

The devices’ ac/dc-power-control ICs use digital topology that’s transparent to designers and requires no programming or GUI (graphical-user-interface) development. The iW3610’s switching frequency as high as 200 kHz means that designers can use smaller capacitors and transformers, and the devices comply with EMI (electromagnetic-interference) standard EN55015B. The 3620 supports an internal switching frequency of 130 kHz and sells for 38 cents (1000); the 3610 sells for 98 cents (1000).