May 13, 2014, 08:17 PM Thermite + ice = Big boom. Canada, ON, Ottawa Joined Apr 2009 2,247 Posts Discussion Variable triac? I got an email from STmicro about this : http://www.st.com/st-web-ui/static/a...DM00084356.pdf I had never heard of triacs before and I was thinking about using one for my hot wire cutter. Is it possible to use these to vary/ limit the current or voltage?
 May 13, 2014, 08:40 PM Registered User Joined Jun 2013 362 Posts i don't think to Driver it easy. i often see it in circuits high volt AC .
 May 13, 2014, 09:29 PM Thermite + ice = Big boom. Canada, ON, Ottawa Joined Apr 2009 2,247 Posts So it's basically just a relay? The only thing I'm thinking is possibly a PWM driver, but that would increase complexity beyond what could be obtained by other methods.
 May 14, 2014, 02:20 AM Registered User Staffs, UK Joined Nov 2003 10,258 Posts Triacs have been used in AC dimmers for many years. But they are indeed switches not linear devices if that's what you're asking. So some form of PWM is needed. Steve
May 14, 2014, 06:07 PM
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Hastings, New Zealand
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Foam Cutting Power Supply
Quote:
 The circuit is a simple AC Triac voltage control circuit similar to the ones used to control house lamps. The transformer provides the electrical isolation the makes this item safe to operate.

# Images

 May 14, 2014, 07:56 PM Thermite + ice = Big boom. Canada, ON, Ottawa Joined Apr 2009 2,247 Posts Interesting, I didn't think triacs took an analog voltage. Is that a junction between C1 R2 and R3?
May 14, 2014, 08:47 PM
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Hastings, New Zealand
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Quote:
 Originally Posted by boaterguy Is that a junction between C1 R2 and R3?
Yes.

The Triac triggers when its gate voltage goes over about 1.1~1.4V. The purpose of the capacitor and pot are to delay triggering of the Triac until later in each half of the mains cycle. Varying the pot's resistance changes how fast the capacitor is charged up, providing a varying conduction angle which controls the rms output voltage.
 May 14, 2014, 09:48 PM Thermite + ice = Big boom. Canada, ON, Ottawa Joined Apr 2009 2,247 Posts I never would have come up with that. Thanks a ton!