Triac help

[Adam850]

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 VAC
Triac:
VRRM: 300V
ITRMS: 4A Max
IGT(I & III) 30 mA Max
VGT 2.5 V Max
IH 30 mA Min

How can I use this triac?
P.S.
Do I need to heat sink it?

 

[ante1]

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.pdf
I don

 

[Adam850]

Thank you. I ordered three MOC3041s. Just to be sure, the MOC3041 controls the triac, right?

View attachment 36183

 

[ante1]

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.

 

[Adam850]

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.

View attachment 36191

 

[ante1]

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.

 

[Adam850]

Thank you.

 

[Adam850]

One more thing:
I plan to use the last ciricuit above. What wattage resistors should I use, and what should Rin's value be?

 

[ante1]

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