Triac misbehaving?

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Chupa
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Posted by Chupa: Sat. Oct 9, 2010 - 03:40 AM
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I'm using the Littelfuse Q4008LH4 (alternistor triac) and the Q2008L4 (standard triac) for digital dimming control of a standard incandescent bulb. Both should operate the same way for this application.
http://www.littelfuse.com/data/e... ... x08xHx.pdf

I'm having troubles making the Triacs behave as they should. When they have no load the AC sine wave is clipped as it should, however once I turn on the lamp it stops behaving as it should, and just seems like its full on. Any idea whats causing this behavior? I feel like Ive done the exact same circuit before and didn't have any issues, but this time around I am.

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Learning and Information, General Electronics
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Kartman
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Location: Melbourne,Australia
Posted by Kartman: Sat. Oct 9, 2010 - 11:25 AM
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You need to turn off the triac about 500us before zero crossing. The opto and the triac are a bit slow. Also turn on the triac about 500us or greater after zero crossing so the current through the triac is enough to hold it on.

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