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Snubber for a TRIAC controlled by phototriac

Associate II


I'm designing an AC switch with a TRIAC. This TRIAC is controlled by a phototriac.

The following connexnio is used :

0690X00000895JNQAY.pngR1 and C1 is a snubber to protect the phototriac.


Is this case, is it necessary to add a second snubber (see below) to protect TRIAC with inductive load ?

Best regards

Associate II

I read this application note but there is any information about impact of phototriac snubber.

Not applicable


Page 10:

[Opto-TRIAC Examples Single Snubber, Time Constant Design]
Figure 22 illustrates the use of the RC time constant design method. The optocoupler sees only the voltage across the snubber capacitor. The resistor R1 supplies the trigger current of the power TRIAC. A worst case design procedure assumes that the voltage across the power TRIAC changes instantly. The capacitor voltage rises to 63% of the maximum in one time constant. 
The optocoupler conducts current only long enough to trigger the power device. When it turns on, the voltage between MT2 and the gate drops below the forward threshold voltage of the opto-TRIAC causing turn-off. The optocoupler sees (dV/dt)s when the power TRIAC turns off later in the conduction cycle at zero current crossing.
Therefore, it is not necessary to design for the lower optocoupler (dV/dt)c rating. In this example, a single snubber designed for the optocoupler protects both devices.