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We Need Cheap LED Drivers

On our sister site All LED Lighting, my colleague Keith Dawson (or K-Dawg as we affectionately call him) often talks about different versions of line-powered LED lighting. There is a lot of work being done on various types of LED light “bulbs” and fixtures — architectural, down-lighting, display case… I'm most interested in residential, incandescent bulb replacement lamps (the big market item). And I am specifically interested in whether anyone can make a dimmable LED lamp inexpensively.

There are several large companies manufacturing LED devices intended to replace the standard A19 incandescent bulb. Cree and Philips are probably the leaders. Prices are dropping, but for my money, they still have a ways to go. At the present prices, the ROI (cost of LED + cost of electricity vs. cost of incandescent) is still too steep.

Let's take a closer look at the problems being faced. To get a lamp that has the proper color temperature and properly renders surrounding objects' colors is tricky. Add to that the requirement that it must work properly on a triac or phase-cut dimmer… well, it ain't easy. If the cost of the drive electronics could be sufficiently reduced, the manufacturers might be able to hit the Planet Analog price sweet-spot. With sufficiently low-cost drive electronics, it would be easy to build lamps with a tri-color LED array. That way, you could get whatever color you wanted.

Let's look at the drive electronics. Based on the applications notes I've seen, some suggested circuits use a flyback topology switch-mode power supply. Some (though not all) of the suggested circuits use two or three ICs, a power FET, and the flyback transformer. Additionally, there are easily one to two dozen passive components.

If we could do this with a buck switcher instead, we'd only need an inductor instead of a flyback transformer. It would require two FETs if it's done as a synchronous switcher, although efficiency might be just fine if done as a non-synchronous switcher.

The real way to take the cost out is to push all this circuitry onto one IC. Can this be done? Note that besides being triac dimmable, the IC must tolerate line voltage. Assume that it's intended for “universal” input, so that means 240VAC, 340VDC nominal, or around 400V with a suitable margin (more if you want lots of margin). The output should be constant current, so there should be a way to monitor the output current. If that can be done without putting a resistor in series with the LED string and monitoring the IR drop, all the better.

This is a lot to ask for, but if someone can do it, the market is huge. Even at a slim margin, the multiple millions of units that would be sold will make for high sales dollars. Let us know your thoughts on this.

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