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LED Driver Offers Full-Range, Flicker-Free Dimming
Enables LEDs to replace incandescent or halogen lights
Charles J. Murray, Senior Technical Editor -- Design News, February 18, 2009
National Semiconductor this week rolled out a light-emitting diode (LED) controller that eliminates flicker during full-range dimming of LED lights.
Known as the LM3445, the new product enables users to replace halogen or incandescent lights with LEDs in homes, restaurants and architectural applications. The device could be significant because it solves a flicker problem that commonly occurs when users with TRIAC (triode for alternating current) dimmers install LED lighting.
"With the introduction of LEDs, a lot of customers want to replace halogen or incandescent bulbs with LED bulbs," says Kristen Elserougi, technical marketing engineer for National Semiconductor. "But there's a problem with that. Today's LED driver solutions often don't provide full dimming range, or they don't allow for uniform dimming of LEDs without flicker."
National Semiconductor engineers say the core of the problem lies in the fact that today's TRIAC dimmers are designed to interface with resistive loads, such as incandescent or halogen light bulbs. The company's engineers say they've solved the problem by enabling their new LED driver to emulate that resistive load.
"The 3445 will translate the chopped waveform from the TRIAC dimmer to a signal for the LEDs," Elserougi says. By doing so, it eliminates the 120-Hz flicker that would otherwise be present and enables a full 100:1 dimming range.
National Semiconductor engineers say a system including the LM3445 and as many as 60 LEDs in serial or parallel strings can be created using the company's Webench LED Designer suite of tools. "With Webench, a mechanical engineer can do this as easily as an electrical engineer," Elserougi says. "Everything is spelled out for them."
