I have a Triac that I want to use to control low voltage (~16 V) AC. The data sheet is found here. It specifies that the peak gate voltage is 5 V with a peak current rating of 2 A (which seems quite high to me). The datasheet also lists out the Gate trigger voltage as 0.7 V (typical).

I'll be using this opto-isolator to drive the triac gate, which doesn't seem to have much play in my question (but I could be wrong).

UPDATE: After some additional research it turns out that I was wrong here. The opto-isolator's max current is the determining factor for the gate resistor value. The iosolator used here has a max detector current of 1A. 16VAC has a RMS voltage value of 22.62VAC which leads to a minimum resistor value of 22.6 / 1 = ~22 ohms.

My question is which of these values should I consider when choosing a resistor to place before the triac's gate/opto isolator? I understand how a Triac and it's associated driver works but I just need a little assistance with reading the datasheet and which of the values I should be considering.

Also, are there any good resources for learning how to read datasheets or is this something that just comes with experience?

  • 1
    \$\begingroup\$ I am sorry, but I can't see how you plan to use a triac and, basically, PWM driving, without having a proper idea about the circuit you want to use, the devices themselves or simply reading a datasheet. Maybe it's best to either call a friend or wait until you are certain about these things. I am sorry if this sounds harsh, but there is a reason for it. \$\endgroup\$
    – Vlad
    Commented Nov 14, 2012 at 7:20
  • \$\begingroup\$ @Vlad I'm not sure I get your perspective or what you comment is trying to accomplish. Maybe I didn't ask the question well. I'm just trying to determine which of the values in the datasheet I should use or a nudge in the right direction for learning. It would be great if I could call someone, but then no one else would benefit from my experience. In any case, Felice was kind enough to answer the question for me. \$\endgroup\$
    – Matt Ruwe
    Commented Nov 14, 2012 at 12:02
  • \$\begingroup\$ My intention was not to put you down or to put myself above, I hope this isn't what came out. To me, after reading your post, it seemed that not only you can't read a datasheet (don't know which one to consider, max gate voltage or threshold), that you have pieces but no schematic or can't think about one ("opto-isolator...which doesn't seem to have much play..."), and that you're not familiar with electronics in general ("...good resources for how to read datasheets or...?"). All these made me say that, but I apologize if my answer made you feel bad -- such was my conclusion then. \$\endgroup\$
    – Vlad
    Commented Nov 14, 2012 at 13:11
  • \$\begingroup\$ I try to keep my questions short and specific because this typically leads to the best answers (like Felice's below). The focus of my question was around the datasheet (as indicated in the title). I didn't want answers to focus on the parts or the schematic, just the datasheet. I certainly could learn some things about reading datasheets, but when I said that opto-isolator didn't "have much play" I was referring to the fact that it didn't have any effect on the choosing of a resistor value. \$\endgroup\$
    – Matt Ruwe
    Commented Nov 14, 2012 at 13:42

1 Answer 1


I think you have to design in term of current, that must be >= to the Gate Trigger current in order to have the device ON. You can use the Gate trigger voltage as a voltage drop when you measure the current flowing in the gate in order to switch the TRIAC.


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