Adam850 Posted November 7, 2004 Report Share Posted November 7, 2004 I am trying to use a triac to replace a broken relay in a circuit I made. A 555 is setup to flash on and off about every second. The positive pulses go to a relay, which controls a 60W 120VAC light bulb. I have bought a triac to replace the relay, but I don't exactly know how to use it. Relay: Coil: SPST 12 volt, 20mA, 250 ohm Contacts 0.5A @ 125 VACTriac: VRRM: 300VITRMS: 4A MaxIGT(I & III) 30 mA MaxVGT 2.5 V MaxIH 30 mA MinHow can I use this triac?P.S.Do I need to heat sink it? Quote Link to comment Share on other sites More sharing options...
ante Posted November 8, 2004 Report Share Posted November 8, 2004 Hi Adam,You need an optoisolator to safely use the triac here. Something like the MOC3041 : http://www.web-ee.com/Electronic-Projects/data/moc3041.pdfI don Quote Link to comment Share on other sites More sharing options...
Adam850 Posted November 9, 2004 Author Report Share Posted November 9, 2004 Thank you. I ordered three MOC3041s. Just to be sure, the MOC3041 controls the triac, right? Quote Link to comment Share on other sites More sharing options...
ante Posted November 9, 2004 Report Share Posted November 9, 2004 Adam,Not so fast! If you look at the datasheet you see that you need a few more parts to make it work. First a series resistor for the input (or you blow the led inside). And also a snubber circuit to help the triac get the correct gate current and such you can see an example of this on page 4. Quote Link to comment Share on other sites More sharing options...
Adam850 Posted November 10, 2004 Author Report Share Posted November 10, 2004 Like so?This will work without much problem, running a lightbulb? The tungsten filiment is coiled, does that make it an inductive load?Thank you for pointing me to this solution, though. Quote Link to comment Share on other sites More sharing options...
ante Posted November 10, 2004 Report Share Posted November 10, 2004 Adam,The filament is not very inductive, consider it as an resistive load. You can omit the extra gate at pin 2 just connect pin 2 to neg on your timer circuit. The capacitor should be rated 250VAC. I understand why your relay is broken, a one second on off time will kill any relay quite fast. This new circuit will not be worn out. Quote Link to comment Share on other sites More sharing options...
Adam850 Posted November 10, 2004 Author Report Share Posted November 10, 2004 Thank you. Quote Link to comment Share on other sites More sharing options...
Adam850 Posted November 13, 2004 Author Report Share Posted November 13, 2004 One more thing:I plan to use the last ciricuit above. What wattage resistors should I use, and what should Rin's value be? Quote Link to comment Share on other sites More sharing options...
ante Posted November 13, 2004 Report Share Posted November 13, 2004 Adam,The Rin resistor is the series resistor for the LED inside the opto. If you have 12 Volts input (vcc) a 390ohm 0.25W resistor will work. For the rest of the resistors use 0.5W or higher.Always be careful with mains, don Quote Link to comment Share on other sites More sharing options...
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