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I am working with this circuit:

triac ckt

I am using a snubberless triac (BTA216X) and hence I am getting rid of snubber circuit (39 ohm res and 0.01 uF cap circled in red). Am I right in doing so?

Besides this, can I get rid of 330 ohm resistor circled in blue? As per my understanding, it works like a pull down resistor but I have seen some comparable circuits not using this resistor.

How critical is this component and what problems might occur if I don't use it?

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    \$\begingroup\$ What is the load? Using a 'snubberless' TRIAC doesn't always mean a snubber circuit isn't needed. Comments on the role and design of the gate resistor are here electronics.stackexchange.com/questions/248743/… \$\endgroup\$
    – user133493
    Jun 27 '18 at 8:36
  • \$\begingroup\$ Thanks for the link. It helped a lot. For my use case, the loads can be either capacitive, resistive or inductive. For ex - incandescent bulbs (Resistive), LEDs with their ac to DC converters (capacitive) and ceiling fans (inductive). \$\endgroup\$ Jun 27 '18 at 9:01
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You have to analyze whether the triac in the optocoupler can be triggered by the dv/dt, not just the power triac, before you can draw conclusions about the snubber.

The 330 ohm resistor prevents leakage in the optocoupler from triggering the triac. Snubberless triacs tend to be fairly insensitive so you may not need that, but you can analyze the minimum trigger current vs. maximum leakage (probably at maximum temperature). You should try to keep the opto cool for lifetime reasons, but usually it ends up being mounted near the triac. In this case your triac is guaranteed not to trigger with 2mA gate current at 25°C Tj, and from Fig 7 we can assume that <1mA will not trigger it even when hot. The optotriac leakage appears to be <100uA at 100°C so I think you're fine without the resistor.

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Ans: Rs = 33 Ohms, Cs = 10nF (Approx) for 250VAC. You can use a 250VAC MOV with this snubber circuit You can use 360 Ohms resistor for MOC3021. Don't use 330 Ohms resistor because MOC3021 is destroyed for high current. Maximum Surge current of this MOC3021 is 1AMP. Supply Voltage 220VAC +/- 20%. So, you can use maximum 250VAC for 250V MOV. R=(1.4142 x 250VAC)/Surge Current of MOC3021 =353.55VDC/1AMP = 354 Ohms >= 360 Ohms. (Accroding to R=V/I.)

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    \$\begingroup\$ Welcome to EE.SE. (1) Your "I am Rajib ..." belongs in your user profile, not in an answer to a question. (2) There is no Rs in the OP's schematic. (3) What is "this Snu"? (4) Can you explain why (and where) a 330 ohm resistor would destroy a triac while 360 ohm would not? (5) Which triac would be destroyed? The FKPF or the opto-triac? You can edit your answer to improve it. \$\endgroup\$
    – Transistor
    Oct 29 '20 at 17:49
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    \$\begingroup\$ Some improvements with your edit. (1) not fixed. (2) not explained. Is Rs the snubber resistor? Why would 33 Ω be better than 39 Ω? (3) fixed. (4) The OP isn't using an MOC. S/he is using an FOD. In any case, the main triac will turn on causing the voltage across the opto-triac and the 330 Ω resistor to collapse to near zero. It won't see anything near 1 A. \$\endgroup\$
    – Transistor
    Oct 29 '20 at 18:08
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    \$\begingroup\$ RAJIB DAS - Welcome :-) I have removed your introduction (as highlighted by Transistor) in accordance with this site rule. I recommend you read the tour and help center to learn more about the site rules. Thanks. \$\endgroup\$
    – SamGibson
    Oct 29 '20 at 18:23
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enter image description here

In case of snubber, 39 Ohms resistor is used > 400VDC and 33 Ohms resistor is used for 352VDC. From Rajib Das

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