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[SOLVED] The effect of snubber on triac.

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Ogu Reginald

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Is there any implication on not using a snubber network on a TRIAC circuit? Note the gate of the TRIAC is triggered by an opto-isolated TRIAC with zero crossing capability.
 

barry

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The snubber helps diminish inductive overshoot. If you have a purely resistive load, it won't make much difference, but if your load is inductive you can get huge voltage spikes during turn-off.

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wow, same answer simultaneously!!
 

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I already experienced cases, where supply voltages waveforms with high dV/dt caused self-triggering of zero crossing detector opto-triac, even with pure resistive load. The problem could be solved by adding a snubber.
 
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Ogu Reginald

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But if I am using an inductive load and I did not add a snubber hope the circuit will work?

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What type of capacitors should be used for snubbering? The current demand of my load is 10Amps, help me with the values of resistor and capacitor that should be used and If possible please attach pictures.
 

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An opto triac with zero crossing detector has usually problems with inductive load, even with a snubber. You'll possibly observe skipping of halfwaves which might result in DC component in output current with a risk of saturating transformers or motors. You should provide a fuse with correct rating according to the load, just in case.

Inductive loads can be perfectly controlled with a non-zerocrossing opto triac and RC snubber.
 

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But if I am using an inductive load and I did not add a snubber hope the circuit will work?
Better add a snubber!

What type of capacitors should be used for snubbering? The current demand of my load is 10Amps, help me with the values of resistor and capacitor that should be used and If possible please attach pictures.
For the capacitors I'd suggest to use X- or Y-types; there are also specialized snubber types available, e.g. Snubber MKP = SNMP or Snubber FKP = SNFP types from comp. WIMA.

Attached is an application note from ON Semi about snubbers, with calculation examples and tables. Hope it's useful.
 

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Ogu Reginald

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Please is there any relationship between the power handling capacity of a resistor used for snubber and the transient to be suppressed?
 

Ogu Reginald

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But are there already made monolithic integrated circuit (IC) in the market?

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But are there already made monolithic integrated circuit (IC) in the market?

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But are there already made monolithic integrated circuit (IC) in the market?
 

erikl

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... is there any relationship between the power handling capacity of a resistor used for snubber and the transient to be suppressed?
If you can't analyze and calculate it by a simulation, I'd suggest a rather crude estimation method. Let's take this current spike for the repeating current spike through the snubber resistor (the image is the upper part of Fig. 6 of ST's application note AN437 linked to by Tahmid above).
Approximate the current waveform by a triangle, so the medium current is about 4/2A=2A. Now calculate the power consumption by N = I2*R * tspike/tperiod . For the above sample, say Rrounded-up=50Ω , length of the spike tspike=1.5ms and repetition period (50Hz full wave application) tperiod=100ms you get N = 200W * 1.5/100 = 3W . Very crude approximation, but good enough, I'd think.

However, this application note AN437 on page 13 says:
Note: For inductive load with rms current higher than 4 A, Snubberless TRIACs are recommended.
Don't know why. Perhaps somebody can explain it.
 

Ogu Reginald

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What is the difference between a snubberless Triac and ordinary Triac?

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And also what does it mean to say that a Triac is insulated.
 

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"Snubberless" triac means higher dV/dt rating. If you are using an opto-triac as trigger source, the lower dV/dt of the opto triac will often command the snubber requirements. A snubberless triac might still require a snubber for the trigger circuit. For the same reason, a popular snubber circuit (figure 6.22 in the link from post #7) primarly filters the voltage across the opto triac but also reduces overvoltage at the main triac.

Insulated triac refers to a package with insulated heatsink interface.
 

Ogu Reginald

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Does it mean that an insulated Triac does not require a heatsink.
 

Ogu Reginald

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Honestly, I must thank you all who helped in one comment/post or the other that helped finish my final year project. Thank you all.
 

erikl

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Does it mean that an insulated Triac does not require a heatsink.
No. It means that the area where the heatsink has to be connected to is insulated from the electrical terminals.
 

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