What I'm trying to do is use a triac to switch an assortment of loads on/off using a low voltage control via an opto-diac. The problem is that once the unit has been running and is then switched off - the triac keeps firing but not at full duty-cycle! The triac switch works fine with just a transformer load (wall wart adapter) but when combined with loads that include a switching PSU, I think the SMPSU pulses cause high Dv/Dt transients across the triac.
What I think is needed is a snubber network to limit the Dv/Dt, but I do not know how to calculate the values of the capacitor & resistor. Having tried a couple of searches for triac application notes, I'm coming up a little thin on articles about how to handle the math for this - so I'm obviously not wording the search string well enough!