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National Semiconductor Presents a New TRIAC Dimmer


Greetings! My name is Jordan Nicholas and I'm the technical thrust leader for National Solid State Lighting Application's Group. Today I'd like to introduce to you the LM3445 TRIAC dimmable LED driver.

Now, first I'd like to talk you a little bit about the TRIAC dimmers. TRIAC dimmers are the standard dimmer that you have probably in your house and in many commercial, industrial applications. TRIAC dimmers were meant to operate with standard incandescent or halogen based light lamps. Those lamps appear to be a resistive load to the TRIAC dimmer. Since than, we've developed many technologies that are more efficient than the incandescent and halogen, such as compact fluorescent and now LED technology. The problem is fluorescent and LED lamps don't look like a resistor to the TRIAC dimmer. So interfacing to the TRIAC dimmer is now becoming a significant challenge. The biggest problem that we had is universal dimming from a TRIAC dimmer. There are 2 main types of TRIAC dimmers: forward and reverse phase. Some lamps may only work for one type of dimmer and it can be difficult to find a product that works well with all dimmers and dimes smoothly from 100% to below 10% with all any type of flicker or orient operation.

This is the LM3445 demo. You can see on the bottom we have the boards. It's a very compact solutions. The reason that's important is because this can fit in a variety of applications; any type of bulb replacement, ballast or downlighting applications or any other application that requires TRIAC dimming. The 3445 is small enough that can fit in that type of solution.

So, here's the demo again: at the top we have 7 LEDs which are high brightest LEDs running 350Amps. The LM3445 system is capable of driving LED currents greater than 1Amp.

Now, some features that are very important: here I have a standard TRIAC dimmer and when it's off the system is driving 0 power. This is important because the energy start criteria for Solid State Lighting require 0 power in the off state. As I turn the TRIAC drimmer on, you can see a little tunnel light coming out. There is actually some light that probably can be picked up by the camera. As I move the slider up, you can see the brightness very linearly over the range until we achieve full brightness.

The kit of this system is no 120Hz flicker in the light. (***) The biggest issue 120Hz flicker is that made in cristall lifetime of the LEDs (***)

These LEDs will flicker at 120Hz if we're not using the LM3445 type of system. Other features of the system include a power factor of 0.9 or better when running of the standard line. This is also required by energy start criteria for solid state lighting. Efficiency can be as high as 90% when running from the standard from 80V AC - 270V AC.

Other features of the system include: adjustable switching frequency, thermal shutdown, small 10-pin MSOP package.

So for any application that requires interfacing to the standard TRIAC drimmers for or reverse phase, the LM3445 is the solution for you.

source: http://www.national.com/sm_video/led_driver.html

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