snubering a triack

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chava
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snubering a triack

Post by chava » Thu Feb 12, 2004 7:06 am

Hello
I have an application in which a programmable chip has to drive a triack, depending on the phase.
I want to give a short ( 300 usec) pulse to an opto-triack , so that the opto-triack will ligth anther triack.
the problem is that i think I have a snuber which doesnt work.
can anyone suggest me a draw?
As I understood, I need two snabers - one for each triack OR one snuber for both triacks.
Help.....
Jukin Chava<p>E.Dove Israel
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bridgen
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Re: snubering a triack

Post by bridgen » Thu Feb 12, 2004 7:15 am

I don't think the optical triac will need a snubber as it will only be switching the gate current to the other one. <p>However the one which is switching the light ought to have one. They normally consist of 100ohms in series with 0.1uF.

L. Daniel Rosa
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Re: snubering a triack

Post by L. Daniel Rosa » Thu Feb 12, 2004 7:43 pm

A lot of optotriacs that I've seen have a zero crossing detector that keeps them from switching when more than a few volts are accross the terminals. If the driving signal isn't there when the zero crossing occurs, the triac won't fire.

Bernius1
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Re: snubering a triack

Post by Bernius1 » Fri Feb 13, 2004 4:37 am

Triacs can run without a snubber. But noise, residual charge, and voltage spikes can keep it 'latched' thru the zero crossing, into the next 1/4 phase. A snubber unloads the gate to prevent this. (Like a reverse diode across a transistor which drives a motor) If the capacitor is too large for your ckt., it may be absorbing all the current that's supposed to turn the triac ON. In this case I would check the low-level opto-triac, like David said. But if .1uf works at line level, and your opto-triac is only providing 1/10th of load current, then I would try a .01uf, & work up & down until the results match the theory. With a touch lamp, the snubber and drive cap's matter, because if wrong, the 'lo-med-hi' levels will be all too low, or all at 'full ON'; which is something you might not 'see' in a motor control ckt.
Can't we end all posts with a comical quip?

Chris Foley
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Re: snubering a triack

Post by Chris Foley » Fri Feb 13, 2004 6:01 pm

If you're using anything like the MOC3010 opto-triac to drive another triac, you can use the solid-state relay circuit shown on page 5 of this Fairchild app note -- this exact circuit has worked for me on several occasions, if you're not driving a *very* inductive load (if you're driving 120 VAC load, use a 600 V min triac):<p>http://www.fairchildsemi.com/an/AN/AN-3003.pdf#page=1<p>Good luck
Chris

chava
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Re: snubering a triack

Post by chava » Sun Feb 15, 2004 1:36 am

thanks you all
Jukin Chava<p>E.Dove Israel
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