michael brown wrote:

>What is the difference between the MOC30xx's?  I've noticed that some
>have zero-crossing circuitry built in, and some don't.  Since the
>zero-crossing circuitry doesn't appear to connect to any of the external
>pins of the MOC30xx chips, what purpose does it serve.  I've looked at
>the datasheets, but I don't see the purpose of the zero cross circuitry.
>
>Is it so that when I tell the MOC to turn on, it waits until the next
>zero-cross before actually turning on it's internal TRIAC, or is there
>some other reason?
>

The zero-cross versions (3041 etc) are for when you only want
on/off control. You've guessed exactly how it works already!
Switching on at the zero-cross point greatly reduces EMI.

>I was poking around on the net and thinking that building some type of
>light dimmer might be fun and educational.  I'm far from being expert
>with analog devices, but I think I have a basic understanding of a
>TRIAC.  Since the circuits I've seen already use a TRIAC (in combination
>with a MOC30xx) to switch the high voltage, why would the MOC need to
>know anything about zero-crossing?
>

The "normal" (3021 etc) versions are for phase/angle control. (dimming)
Switch the LED on earlier to the zero-cross for higher brightness.
The Motorola datasheet should have a few example circuits for you.
David...

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