Jason,


The circuit is a little confusing. It seems that MT1 and MT2 should be
swapped.
Indeed the circuit seems to be simply wrong. MT1 is the reference pin
and it is kept always more than 10 V above or below the GATE.

TRIACs can be fired in all four quadrants, that is, the polarity of the
current on MT2 or GATE respective to MT1 can be any combination, BUT it
is more sensitive in quadrants I and III, and much less sensitive in
quadrant IV.

For simple AC circuits, the TRIAC is usually fired in quadrants I and
III, but for digital circuits the circuit would be too complicated, and=20
to avoid firing it in quadrant IV, it is usually fired in quadrants II
and III.

It seems that the original intention of the author was to fire it in
quadrants II and III.


Isaac




Em 01/01/2016 21:56, Jason White escreveu:
> Hello,
>
> I am a student, I saw this low voltage TRIAC driving circuit on the
> internet and am puzzled as to why it uses a negative voltage rail?
>
> As far as I know, TRIACS are not sensitive to the polarity of the signal
> applied to the gate (with respect to MT1). Could this configuration work
> with a positive supply (with respect to neutral) in all four quadrants?
>
>
>

--=20
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