How about using an IGBT to turn off at peak?

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Denny Esterline
> Sent: Saturday, June 15, 2013 12:46 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Favorite photo-voltaic opto-isolators?
>=20
> > 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)
> >
>=20
> Perhaps I'm missing something... How are you turning _off_ a triac
_during_
> the phase? Does not a Thyristor continue to conduct until the zero
crossing?
> Did you by-chance fall into the same automatic brain substitution I did?
>=20
>=20
>=20
> > 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 cycle 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.
>=20
> -Denny
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