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I'm planning on building some dimmable lighting controller for Christmas lights, but with LEDs being all the rage nowadays, I was thinking that instead of using triacs and dimming at 60/120 Hz, rectify the AC to DC and use MOSFETs to reduce the strobing that is more evident in LEDs. This might allow the controller to be smaller and/or cheaper.

This would depend on how the LED strings are actually wired up. I don't currently have any to look at, and I could imagine a few different ways they might be connected, such as diodes that only conduct for half the cycle, which would axe the DC idea if true.

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I think you need to dissect one, in order to find out what it is doing... – Johan Nov 11 '10 at 19:47
In the past a lot of the technology behind different Christmas light displays has had patents to how they translate different independence from failure and lifetime/safety features. I know this may not be the case with most simple designs, but just dropping a warning from what I have seen. – Kortuk♦ Nov 11 '10 at 21:53

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LED Christmas lights are wired in series to "gobble" up the 110V applied to them. A great site to read up on this is here.

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Nice read. Was very surprised about the breakdown rate though! – Vincent Van Den Berghe Nov 17 '10 at 13:35
So an antiparallel pair of LED strings--guess powering them off rectified AC won't work that well; only half will ever be on. – Nick T Nov 17 '10 at 18:25
@Nick T: Over the last couple years, I've seen "color-changing" LED lights which have anti-parallel LED strings in different colors. The supply selects one or other polarity to light a particular string. I've been thinking it would be fun to have some processor-controlled TRIAC outputs so I could nicely sequence the lights in different colors, but I don't know of any off-the-shelf controllers that would allow one to dim the hot-positive and hot-negative phases separately. – supercat Mar 11 '11 at 18:15

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