On Wed, Oct 3, 2012, at 05:44 PM, IVP wrote:
> Are MT1 and MT2 of a triac interchangeable ?

No, because gate is referenced to MT1. Required gate current is
different depending on polarity, both absolute and relative, but is
lowest when gate polarity is the same as MT2.

Best regards,

Bob


>=20
> I see circuits with either MT1 or (more often) MT2 to phase. I
> don't use triacs a lot, but do recall making a heater control (an
> immersion element) that didn't work with MT1 to phase but did
> with MT2 to phase. Gate control was DC from a CMOS gate,
> a 4017 I think. Are the positions of MT1 and MT2 less important
> if gate control is AC, through a diac for example ?
>=20
> When I've used low-power optotriacs like MOC302x to drive
> triacs, I've never had a diac. Gate current is AC via a resistor
> from phase through the opto's triac
>=20
> In this document
>=20
> Thyristors & Triacs - Ten Golden Rules for Success In Your Application
>=20
> www.nxp.com/documents/application.../AN_GOLDEN_RULES.pdf
>=20
> MT2 is to phase, as it is here
>=20
> http://en.wikipedia.org/wiki/TRIAC
>=20
> with note that filters should be referrred to MT1, likening it to the
> 'cathode' of an SCR, implying that MT1 is to neutral
>=20
> In the previous version of his dimmer
>=20
> http://www.circuitstoday.com/simple-lamp-dimmer-fan-regulator
>=20
> the author has MT2 to phase, but in the revision of my original
> post MT1 and MT2 are not identified
>=20
> I'm asking for general knowledge and so that I can make a
> small controller PCB
>=20
> TIA
>=20
> Joe

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