Using Triacs with very small inductive loads.

Question

Hi,

I'd like to use a triac to turn on a very small (9v, 80ma) transformer. (I want to use a battery to turn it on using a triac opticoupler, then temporarily latch the triac to itself using digital logic. I don't want a transformer on-line all of the time.) I've had problems in the past with triacs not turning off. Is there an easy solution? At the time, I tried snubbers, but admit I do not understand them or know what values to use.

Any help or pointers would be much appreciated.

Thanks.

mcb1 · Answer

Why did you go from a zero-cross to a random cross MOC30xx? 
 I didn't, it was simply a circuit diagram. In our application we detected the zero volts and switched then, so a zero cross device wasn't necessary. The circuit was copied from a commercial device. I've never been brave enough to stick a scope on it, but it does result in a 0.5v drop which may help with the shutoff. I never did try to discover why it was designed in this manner. We needed to resolve the problem of partially on triacs cooking transformers, and this resolved it, and we just kept using it. Mark