> Yes. Any fast edge will generate harmonics. Switching full cycles
> reduces or eliminates EMI. Using the trailing half of the cycle was
> practical because a DIAC (now we have SIDACs) could be used
> to delay triggering and I know of no simple way of doing otherwise
> and there's no point to it anyway.

So if I understand correctly, if there's sufficient energy present to
cause RFI at the switching point, it's irrelevant whether the triac
is turned off (if that were possible) or on. The practical difference
being that the triac "turns itself off" at the next z-c point, which
keeps switching and s/w simpler

From what I can gather, series inductors, shielding and good layout
are fairly effective at minimising RFI

Just an academic question. Is it not possible using s/w and another
device to rob the triac of through-current - at the same time both
disconnecting the load and dumping the current for the remainder
of that half-cycle into something like an inductor ?

I ask because it would be kinder to all the devices if the switching
on were to be done at low voltage rather than eg at peak to reduce
stresses caused by inrush current. To keep it simple, it seems that
something other than a triac is needed for PWM if you wish to use
the leading z-c and turn the juice off mid-wave

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