Triac

Lightfoot

I am trying to control a positive or negative DC voltage with an SX pin. I am planning on using a triac to accomplish this. The load on the triac is a 12 volt DC motor that draws up to 3 amps (I think). What is the best way to drive a triac for this purpose, or is a triac the best way?

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Well well, I'm seeing things, three of them.

-Stanley Blystone

PJAllen

What's the BIG picture, what're you really trying to do?

Post Edited (PJ Allen) : 6/5/2006 12:07:23 AM GMT

Lightfoot

I'm making a fan controller with two outputs. One is a fixed direction and the other is bidirectional (where triac comes in). They both need solid state control. What controls them is a thermometer circuit I constructed with an SX that causes an output to go high if the temp goes above a certain point. Sorry for not being specific before.

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Well well, I'm seeing things, three of them.

-Stanley Blystone

Nate

First -determine the actual load of the motor - 12VDC @ 3A "I think" is a good way to spend some money toasting components.

Second - Properly sized (see above) H-Bridge - Home-built with discrete components or a assembled unit such as SN754410.

Bruce Bates

Stanley -

For what I suspect you're trying to do, Nate is right on the money. Here is an H-Bridge project which should meet your voltage and current needs. It's complete with images for making the traces on a PCB as well, for a nice professional job:
http://www.bobblick.com/techref/projects/hbridge/hbridge.html

If you'd prefer a canned solution, but don't mind constructing a small kit, this should meet your needs as well:
http://www.hobbyengineering.com/H1918.html

Regards,

Bruce Bates

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RGuyser

another question has to be if you want set speed control, or variable.

if you want a varialbe control, i think it makes everything far more confusing, otherwise a tip120\tip125 h-bridge would probably work... for the 1-direction circuit you can use a half h-bridge... if your application was more intensive than a fan, you would be well advised to try a h-bridge chip, but i think a simple fan controller can be built easily enough with some transistors.

a triac or SCR would be helpfull if you were dealing with AC, i believe...

Manuel

Im trying to use a triac to activate an ac circuit. i have seen the datasheet and they are designed for ac. the problem I have is that i can get the triac on, but not off. also im using a moc3011 to get optic isolation and I have the same problem, turning it off.

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Best Regards

Manuel C. Reinhard