@Danny...Yeah I missed something,....true, triac control works by turning
'ON" after a delay following ZC detect, Dwayne wants to turn 'OFF' at a
particular point in the phase.
The application was not explained in any detail...why would such a
switching point be required?
Perhaps a more detailed elucidation as to what exactly the purpose of this
circuitry might be would help us to render some more constructive
suggestions.

Power MOSFETs..would work....one would still have to determine the ZC point
and invoke a delay to cut off at the required point within the ensuing 50
millisecond phase.

What degree of precision is required?

Perhaps the application requires not time but level dependency....in which
case the solution would be quite different..,,,dunno, not enough info


On Sat, Jun 15, 2013 at 9:45 PM, Denny Esterline <desterline@gmail.com>wrot=
e:

> > To accomplish this, the zero crossing point need be precisely derived, =
as
> > this is the reference from which the phase switching is determined.
> > The actual switching is handled with a triac (BT139 to BTA 25/26
> depending
> > upon the load requirements) which in turn is driven by a random phase
> > opto-coupler with triac output (MOC3020)
> >
>
> Perhaps I'm missing something... How are you turning _off_ a triac _durin=
g_
> the phase? Does not a Thyristor continue to conduct until the zero
> crossing? Did you by-chance fall into the same automatic brain substituti=
on
> I did?
>
>
>
> > A good, simple DIY zero crossing circuit I have applied in the past can
> be
> > found here:
> >
> > http://www.dextrel.net/diyzerocrosser.htm
> >
> >
> Hmmm... this seems... needlessly complex. My preferred solution has been
> simply a PS2502 optocoupler (AC input/ two reverse parallel LEDs) with th=
e
> necessary current limiting resistors directly across the line. The
> resulting waveforms are exactly the same shape, though the exact timings
> have some dependency on the resistors chosen and exactly when in the cycl=
e
> enough forward current is present to turn the output on. In practice a
> micro is constantly timing the overall width of the ZC pulse and deriving
> the true zero mathematically.
>
> -Denny
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>



--=20
Perry Curling-Hope

Research and Development
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.