I already asked this question Triac BT 136 getting shorted when load is given to T1.

When I referred this link, I understood rate effect is the root cause for our problem. To avoid this either we could use RC snubber or high power triac. Such as BTA316B-800E and BTA316B-800B.

Now I got confused which one to select from these.

My application is to dimmer control incandescent bulb or fan.

Switching ON/OFF LED lamps(all appliances with 240V/50Hz) or any other alternative step I could make in the circuit.


You have an MCU of some type that you are using to control those inputs to the opto-isolators. I suggest that you get rid of the one problem with the switches by instead wiring in low voltage switches directly into the microcontroller and let the software resident in the microcontroller provide for the override function.

Rate control (dV/dT) problems with triacs can still exist for cases when the AC power is interrupted or applied.

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  • \$\begingroup\$ These options-isolators are preventing my DC circuit. Are you suggesting to remove them and controlled via MCU? \$\endgroup\$ – abab Feb 4 '19 at 12:54
  • \$\begingroup\$ It is opto-isolator not options-isolator. I am NOT suggesting to remove them. You want the isolators for the safety to keeping AC voltage circuits from coming to the MCU and other low voltage circuits. \$\endgroup\$ – Michael Karas Feb 4 '19 at 15:37
  • \$\begingroup\$ Sorry for that typo mistake. I need to overcome the rate effect. For that could you suggest any other options in the given circuit? \$\endgroup\$ – abab Feb 4 '19 at 15:44
  • \$\begingroup\$ Use clamps for high voltage spikes like MOV or TVS. Then add snubber circuits to change the rate of dV/dT at the triacs, \$\endgroup\$ – Michael Karas Feb 4 '19 at 15:47

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