## Triac Control Circuit

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Gregg
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Joined: Wed Dec 05, 2001 1:01 am
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### Triac Control Circuit

Hi everyone. I am looking for some advice on the contruction of a circuit to control a load, using a triac, using a 0-10v dc source. The load is a theatrical type light and requires full dimming capabilities. The triac to load circuit is not the problem, its the circuit to allow max firing angle and power to the load. Thanks for any help.<p>[ June 17, 2002: Message edited by: Gregg ]</p>

Michael Vickers
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Joined: Tue May 21, 2002 1:01 am
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### Re: Triac Control Circuit

Back in college we had to construct a similar circuit. We were given a circuit diagram, but if we could design our own we were given bonus marks. My circuit ended up taking about half the bread board real estate as the circuit our instructor gave us, and it seemed to be more reliable.<p>I don't have the schematic anymore for the control circuit, but it went something like this (modified slightly). <p>On the front end use a step down transformer. Feed the stepped down signal into an op-amp comparator circuit (single supplied at 5-6V), so that you get a 60 Hz 5V(p-p) square wave. <p>Feed the square wave into the clock of a dual non-retriggerable monostable multivibrator (one-shot). I used a 74LS221. Set the first one shot up so that it provides the delay time (contolled with a pot), and set the second one up to give your first pulse. I believe the delay time eq'n is <p>t=ln(2)*R*C<p>Also, you'll need to tap off the output of the "delay time" stage to clock a second 74LS221. Set this one up so its delay time stage is permanently 8.333ms (half a cycle behind the first pulse). Use this to clock the second stage of the second chip, which is set up to provide the second quick pulse (which is exactly 180 deg behind the first.<p>Put a blocking diode at the output of each stage, and feed these signals into your pulse transformers. You may want to include a driver transistor stage before the pulse transformers to
provide some extra ooomph.<p>Email if you have questions.

Edd
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### Re: Triac Control Circuit

Gregg:
If you're not requiring multi KW light control using "hockey puck" SCR's; All the works have
been available for years in premanufactured small
Triac driver circuits. A far cry from those great shades of TTL design days! Since a picture is worth 999 words..?; why not see the write up at this site for reference....being in lighting you might even get a kick out of the circuitry for that particular application. All you're basically interested in is the bottom rt corner of the schema and all you would need is a res
voltage/ divider pair to scale down ur 0-10v to 0-5v for the ISOLATED DC drive input(to an internal LED) at the left side of the IC. The last device option listed is particularly desirable if U want a clean RFI environment,as it uses 0 crossing referencing for turn on of the triac's drive signal. And the site is: <p>http://www.phantasmechanics.com/alf.html <p>73's de Edd
[email protected] (Interstellar Warp Speed)