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I have a T1635H-T triac, that i would like to control with MOC3041. I use typical circuit from the optocoupler datasheet:

enter image description here The only difference is that i'm using 330Ohm resistor instead of 360Ohm. As a test load i use 40W incandescent bulb.

For some reason, when i enable the optocoupler by closing led-side circuit, triac burns almost immediately with clearly visible clearly visible traces of damage on the gate pin.

What i'm doing wrong?

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    \$\begingroup\$ Pics or it didn't happen ... \$\endgroup\$
    – brhans
    Commented Oct 7, 2017 at 22:26
  • \$\begingroup\$ If the main triac is burning out it sounds as though you are short-circuiting the mains. Are you sure that your load is connected? Again, add a photo of your setup. \$\endgroup\$
    – Transistor
    Commented Oct 7, 2017 at 23:21
  • \$\begingroup\$ Thre datasheet says that I_GT(MAX) is just 35 mA. I suspect that you're dumping way too much current into the gate. \$\endgroup\$
    – Dave Tweed
    Commented Oct 8, 2017 at 1:04
  • \$\begingroup\$ If you have let the magic smoke out then it probably won't work any more... \$\endgroup\$
    – Solar Mike
    Commented Oct 8, 2017 at 4:10
  • \$\begingroup\$ @DaveTweed probably yo are right. I expected MOC3041 to limit current here :) But now i checked optocoupler datasheet and clearly see, that tat was my misunderstanding. What is the best way to limit current on a gate then? Straightforward approach with current limiting resistor will give me a couple of watts and that's a lot \$\endgroup\$
    – akashihi
    Commented Oct 8, 2017 at 10:18

1 Answer 1

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What you say is pretty surprising as this triac is pretty much overkill for a simple 40W resistive load.

The figure in the MOC3041 datasheet shows a very standard circuit for controlling a triac in particular,using a 300 ohm resistor instead of 360 Ohm is perfectly okay for a 240V AC main.

The most likely cause of the death of your triac is that the capacitor discharges too fast in the triac when the latter is turned ON. Using a higher capacitor value than 0.01µF could induce a high current spike that can kill the triac.

My recommendations:

  1. Please check that you used the right scheme: are you using a 110V AC main or a 240V AC main?
  2. Please check the rating of your capacitor ; it must be less than or equal to 0.01µF.
  3. If all you want to control is a resistive load, you can also completely remove the snubber. The snubber is only useful in case of noisy environment or highly inductive loads; on top of that the T1635H seem to have pretty solid snubberless performances that could probably allow you to remove the snubber all together.
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  • \$\begingroup\$ I use 40W load only for prototyping. Actual load will be 2kW heating element, but it is easier to debug with 40w bulb. Snubber was the first thing i suspected and removed it at my first try with no effect. Mains are 240VAC, definitely. @DaveTweed pointed to possible gate over current, so i replaced pin 6 resistor with 100k 1w resistor, but without any success. \$\endgroup\$
    – akashihi
    Commented Oct 9, 2017 at 14:33
  • \$\begingroup\$ * 100k is too low I thik. You'd better keep it at 300/1W. * Gate over current is unlikely at 40W, as it represents only 0.2A in the whole system, way under the 1A maximum current in allowed for the gate. * Are you sure that you keep the IGT ABOVE 35mA? \$\endgroup\$
    – ARB
    Commented Oct 10, 2017 at 14:48
  • \$\begingroup\$ One more question: have you re-measured your 300 Ohm resistor after the failure? \$\endgroup\$
    – ARB
    Commented Oct 10, 2017 at 14:52

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