I successfully developed produced my first AC Triac dimmer board, which works fine on resistive load like regular light bulbs. It also works fine for an AC motor the last 2 years. However, in order to use it for inductive loads (LED light bulbs and apparently motors too) I should add a snubber circuit.

Dimmer circuit

In comparison to the old circuit, I've added R10, R4 and C3. This the old circuit which is currently in use:

enter image description here

I don't fully understand how a snubber circuit works, but is this the correct implementation? Would I be able to dim dimmable LED light bulbs with this solution?

  • \$\begingroup\$ You probably need to post the unmodified cct too. It looks like you've connected the snubber in series with the LINE input which definitely won't work. \$\endgroup\$
    – user16324
    Dec 26, 2020 at 17:09
  • \$\begingroup\$ @BrianDrummond what do you mean with unmodified cct? \$\endgroup\$
    – jancoow
    Dec 26, 2020 at 18:14
  • \$\begingroup\$ before you added the snubber. \$\endgroup\$
    – user16324
    Dec 26, 2020 at 18:21
  • \$\begingroup\$ @BrianDrummond I've added the old schematics. \$\endgroup\$
    – jancoow
    Dec 26, 2020 at 18:53

1 Answer 1


I would have drawn R4 and C3 below Q1 , but yes that is a correct layout.

it probably won't work well with LED lighting, because LEDs will respond do the tiny currents that the snubber leaks through. This can be mitigated by adding a load in parallel with the LEDs, a lighting capacitor could be used here.

  • \$\begingroup\$ Yes, that's the thing I don't really understand. In my understanding, if the triac is turned off, the load is powered through the resistor and capacitor. Is this a bad thing? And what do you mean with lightning capacitor? Also, what will the snubber circuit actually do better than the original design? Will it eliminate the spikes when turning on the triac at say 50% sine? \$\endgroup\$
    – jancoow
    Dec 27, 2020 at 9:58
  • \$\begingroup\$ The snubber makes the triac able to turn off inductive loads, a lighting capacitor is a capacitor used with fluorescent lamps that have iron ballasts. it's designed for connection across he mains by electricians. an "X" capacitor is the same sort of thing but designed for use inside appliances. \$\endgroup\$ Dec 27, 2020 at 10:05
  • \$\begingroup\$ Ah, then I totally misunderstood the use of a snubber circuit. I assumed it would reduce the spiked and EMF generated by turning the triac on/off. \$\endgroup\$
    – jancoow
    Dec 27, 2020 at 10:29

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