Hello all gurus! I'm thinking of building a touch sensitive thingy to control my reading lights in the bedroom. I'm using a QT220 (for two lights) and have got all that figured out. My problem though lies with switching the lights them selves. Now, the design I'm working on doesn't have a whole lot of space to fit into, thus the components are fairly small and thus my PCB transformer only outputs around 19mA at 9V (that's 0.35VA) but it has dual secondary's so I suppose 38mA is possible. This goes through a 7805 to generate good clean electricity for the QT220. So here's where the problems start. First I was thinking of using simple relays for the job, but browsing through a few vendors the best ones I've found use 60mA a piece and I need two! so that's more than 3 times the power I have available. Looked through ePanorama and found semiconductor relays, but everything I saw required 12V. So, the question is; can I control 230V (max 60W) lights using either regulated 5V or (very) unregulated 9V? Thank you in advance, mikaelgu
It would be pretty much impossible to use 5v relays and not exceed your current needs, so you would defintiely have to use triacs, but they still use more current that you can source. http://www.fairchildsemi.com/pf/FK/FKPF12N80.html
Plenty or 5V relays available from all of 'em, but as I said in my first post, they exceed my available current... I think I'll just try to sqeeze a bigger transformer in there and go with the relays... Then again, doing it all in semiconductors would be more fun..
More research lead to this It's for 110V, but I suppose by changing the MOV for a 250V type and the IRF640 to a eg IRF644 should do the trick. Something in the range of this I assume would be a suitable MOV. What other properties should be considered? What puzzles me though is the "rectifying bridge". I'd imagine it to be a DC circuit, but I suppose it has something to do with the controlled AC side? Also, can't seem to find a 74C14, found several other in the 74x14 though, would they work?
maybe this is of help for you: http://www.knollep.de/Hobbyelektronik/projekte/25/index.htm it's a circuit for controlling 230V devices instead of leds. so instead of swithing a led with your original circuit you can switch 230V devices. it's in german though.
You can also try some big high-power transistors, like those used in the TVs. They work with the high voltage, and might be able to handle the big current you need to switch.
Actually the current needed to be switched isn't that big. Anyway I suppose transistors like that would use up way too much current for the switching. I think I'll go with http://www.knollep.de/Hobbyelektronik/projekte/25/index.htm but instead of the shown opto I'll use a 5mA version. That should leave me with plenty of current unused even from my only 38mA supply. Still, thank you very much for the suggestion!
What you probably want is an optocoupled power triac driver, such as a MOC3020. I'm not sure how much current their LED's consume, but it can't be much. http://us1.webpublications.com.au/static/images/articles/i1029/102979_13mg.jpg The circuit is basically like that. You can see where the 5V is going in on the left, and you've got the mains AC active in and out.
