more questions on triacs

[djacobow]

I've been experimenting with triac dimming circuits. I've built a few and they work, but I am seeing some complexity I do not fully understand.

Let's take a look at the typical "hobbyist" dimmer circuit you'll find on the interwebz. It looks like this:



This one was even kind enough to provide a snubber for managing the spike from inductive loads.

But I've taken apart some real commercial wall dimmers and found that they don't look quite like this. In particular, they usually have a snubber, but just cap and no resistor, and they have an inductor in series, like this:




(I stole this drawing from here: http://www.irf.com/technical-info/appnotes/an-1153.pdf)

I guess the inductor is acting as a filter to keep all the EMI out of the AC system.

So my questions are:

 - is the inductor just a low-grade EMI filter? My projects are actually boxed and a bit more complex than just a triac dimmer (multiple channels, uC control, blah blah) and actually have an IEC input with a mains filter. Can I go without the extra inductor then?
 - Why do the hobbyist circuits all leave it out?
 - What are the implications of the snubber without the resistor? Especially without the R to dampen things? The freq would be ~3/4 MHz.

Anyway, taking apart commercial products has been instructive. They are /incredibly/ cheaply made, single sided boards, through hole, shoddy soldering. The triacs never have part numbers I can match to commercial parts. I can't seem to find inductors like the ones they use, either. I have a feeling they are custom.


PS -- Bonus question! I've noticed that if I include a snubber circuit, say, with a 100 nF and 200 ohm  resistor, then small loads, like phone chargers and even an aquarium air pump, will actually stay partially "on" even when the triac is off. The impedance of the RC network at 60 Hz is low enough that for a high impedance load, it continues to see a reasonably high voltage. This is interesting because in one of my projects I want to make a smart power strip that can control a bunch of arbitrary loads (no dimming). It seems like for this app, I can't make one circuit that would work for everything, at least not with a triac. I'm thinking of leaving out the snubber, since the triac won't be constantly hammered like in a dimmer, only very occasionally when it switches. But that seems 1/2 baked. Any ideas?