I use 1W on 120V & 2W on 240. These make for nice wide gaps between the
leads, bigger than the UL ratings for spacing at line voltages. It's best to
take the min Igate from the data sheet and multiply by 5, or as much as 10
for high di/dt or low-temperatures are expected. If your 120 mA Igate is
being applied to a device with a min rating of 20mA, I'd say it'll work
well. As for the sizing, Who wants to figure out the real power for that
resistor, not I for sure. Consider that you are firing through it for how
many usec during each 8.3 msec period? add in the currrent lag time, and you
may find that after an hour or two an 1/8 W resistor works on paper, but
will make smoke 50% of the time for some of the reasons already mentioned.

  Another reality is to forget the MOC301X's. Again, smoke all too
frequently. Go with series multiples of MOC306x's (at least a pair). The
redundancy is important when you consider the failure mode, which will leave
your load full on if a single device shorts.

  Chris

   Hi all. I'm trying to build some PIC-controlled light dimmers for my
school theater. After looking at some schematics from the internet, I pieced
together the attached basic diagram. But if anyone has experience with this
kind of thing, I have a few questions. I'm very confused about how to
calculate the wattages required for the resistors. Using V=IR, and P=VI, it
seems like the 1k resistor between AC supply and the MOC triac trigger would
have to take about 15 watts. Is this correct?
  TIA,
      Eben Olson

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