Roines, you can get transformers that will step sufficiently in either
direction in smd packaging that is no more than a 1cm^2.

Here's a site of such a company producing these transformers:
http://www.tmpco.com.tw
or
http://www.tmpco.com.tw/kmportal-deluxe/front/bin/ptlist.phtml?Category=100038



Shawn Wilton
Junior in CpE
MicroBiologist

Phone: (503) 881-2707
Email: shawn@black9.net

http://black9.net


roines reenig wrote:
> Hi,
>
> I think we have drifted a little bit from what I attempted to describe initially. I drew up some diagrams to explain the original question better.
>
> http://www.geocities.com/roinesreenig/picture1.JPG
>
> If you look at picture 1, above, it's just a picture of how a normal house light switch is wired.
>
> http://www.geocities.com/roinesreenig/picture2.JPG
>
> Picture 2, above is what this board that we're all trying to guess at is. I've replaced what used to be a simple switch with this control device. On this board, the control device was a samsung 8 bit CPU with either RF or an IR interface for remote control. So basically, you click on a remote control, and this control device dimms up/down and/or turns on/off your load. The load could be anything, typically, it'd be a set of lamps or fluorescent tubes. That part I think is typical, what's atypical is how it's powering itself from just the one-wire mains live wire.
>
> http://www.geocities.com/roinesreenig/picture3.JPG
>
> Picture 3, above is my interpretation of what Shawn Wilton described, ie: step down and a bridge rectifier to power a micro that controls the load. David Duffy pointed out the fact that things are more complicated and mentioned the LS7631 (discussed as picture 4). Now, Shawn's circuit could work, I think, except there's that question mark above the load. The question-mark-box, QMB would need to somehow turn fully on when we want the load to be on and turn somewhat off but still allow for dropping a sufficient current to power the CPU. Then as Russell McMahon pointed out, it's possible that this QMB, under the control of the CPU, or maybe without, could be switching on and off with respect to the input mains at a sufficient frequency. Thus, the QMB would prevent the load from appearing to be turned on, (for example, a flourescent light should not be flickering) but it would be able to charge up a capacitor enough to provide a reasonably clean 5 Volt DC to the CPU. That's wh
ere I
>  thought they might be using something like a VB409. Link to that datasheet below. But the problem is that the VB409 still needs a return neutral or at least a sufficient potential difference across itself, so it's not clear if that's feasible without a return neutral or earth.
>
> http://www.st.com/stonline/books/pdf/docs/6941.pdf
>
> Issue 2 with what Shawn described is the mechanical design. The board/package I saw was somewhat "thin". Coudn't have been more than an inch and a half in height. Maybe about 2 inches on both sides in terms of area. So if it was using transformers in there, which is possible, they were definitely small. A mains to around 5V step down would be pretty big woudn't it? I don't know how many turns it would have but a ratio of (120/5=24) 1:24 or 1:48 if 240V supply.
>
> Basically, the key piece of information is that you don't have access to a neutral return and/or earth but you still need to generate 5 Volts of potential difference in order to power a controller/cpu. I think Russell's answer listed the right needs except he left figuring out the details as a challenge to the reader with the "not too hard to engineer" :-). I certainly don't know how to do it. Anybody else?
>
> http://www.geocities.com/roinesreenig/picture4.JPG
>
> Picture 4, is extracted from the LS7631 datasheet that David Duffy mentioned.
>
>  http://www.lsicsi.com/pdfs/LS7631_LS7632.pdf
>
> I drew it up, hoping that I could understand how it worked. But I don't. I can see that the Zener would allow a potential to develop when the mains was moving up to and down from the 5.6V mark, this would charge up C5 (flowing through D1 and charging C2 as well) which could then power the control device during the negative part of the cycle. But it's not clear to how C1, R1, C2 and D1 participate. Further, this circuit would have to use the LS7631 since it's LS7631 that would modulate the power to control the load. Maybe the LS7631 in conjuction with a PIC controlling it's external input would be the answer? I think that this board isn't a typical design and does appear to have something unique about it's power supply mechanism.
>
> Thanks,
>
> Roines
>
> ps: nope Shawn, I don't think I can get access to the board again. A sales guy brought it in to show it and I started taking it apart at which point it was taken back. I saw it work so I know it somehow works. It had a bicolor LED with which it reflected the state of it's load (in the demo, a regular light bulb), so if the load was on, it was green, load was off, it was amber.
>
>
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