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Author Topic: ac dimmer guidance  (Read 2935 times)
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I’m looking for some guidance on a circuit.
I found a circuit that would suit me down to the ground http://www.inmojo.com/store/inmojo-market/item/digital-ac-dimmer-module/. But unfortunately they are unavailable to purchase at the moment, so I (hopefully) am going to try recreate the circuit, as the schematic is supplied. See image:

Now I know working with AC is dangerous, and I will take all necessary steps to be safe.
It says that this circuit works with 120v and 240v, so that’s fine. I’m just having a hard time finding exact parts. I already have an moc3021 and the triac, so the dimmer side is sorted. I can get hold of a 4n25. It’s just the bridge rectifier i am uncertain of, if anyone can suggest an alternative, also, any ideas of what wattage resistors should be used?
Any help is greatly appreciated.
Chris
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Hi,

The bridge rectifier will have two diodes with voltage applied in the reverse direction on every cycle. The applied voltage on each diode will be the RMS line voltage times 1.414 (Sqrt 2)

If you assume 240VAC, that is 340V peak.  A 400V PIV rated diode should be OK, but 500 would be better.  So you either need to find a bridge rectifier with a 400V or higher rating, or use 4 diodes and make you own bridge..  

I have the MOC3061 and 4N25 etc. here: http://goo.gl/Cgvt7  (DISCLAIMER: Mentioned stuff from my own shop...)   I also have 1N4007 1000V @ 1 A and BT136 TRIACS (like the one in the example, but TO220 package) at a good price.   If anyone wants quantity of this stuff let me know..
« Last Edit: May 16, 2012, 06:14:03 am by terryking228 » Logged

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It's rather the parallel 47k resistors, which control the peak current through your optocoupler diode.
@230Veff they give 5mA each and thus need  >1W rating.
For zero detection an optocoupler with a 10k 3.3V output, does not need that much input current.
I guess, @230V  2 * 120k (1/2W) in parallel is fine, too.  

4* 1N4004 or any 400V rated bridge rectifier should be fine.
« Last Edit: May 16, 2012, 05:32:10 am by michael_x » Logged

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wow, thanks guys, that has cleared it up for me, spent hours googling. youv etaught me a thing or two too. If i could buy you both a beer i would!
Thanks.
Chris
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just an addition: do not use the MOC3061 as that has a zero voltage detector and that is exactly what you do not want in this circuit
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It's rather the parallel 47k resistors, which control the peak current through your optocoupler diode.

I would use two resistors in series, not in parallel, because many standard low-power resistors have too low a voltage rating for 240VAC.
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