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'How to switch a SCR? , Please some ideas...'
1998\11\28@141724 by Ricardo Ponte G

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       Hi people, How are you:

       Here I«m trying to switch two SCR in some Hybrid module.  The AC soruc
e is
220 Vrms and I got to do the job with a PIC.  Of course need to isolated de
TTL reference from the Hybrid Module reference (GND) with optos.


       Any one out there have some good advice to me ???

       I want to thank you., bye and good luck.

1998\11\28@182309 by Eric Borcherding

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rniniver

In an AC application usually a TRIAC is used, in this case a DIAC into the
TRIAC control from an OPTO output will do the trick.   You have control dwon
to a zero crossing at 60Hz.  If you want to USE an SCR this will require phase
control
and opposing above and below rectified wall these require a signal to PIC on
+/-
peaks or Zero crossing if you a running asymmetricly.   In the SCR case a
direct drive "pulse" from a OPTO thru a resistor will fire the SCR into self
sustaining
conduction until a zero crossing occurs at which point the SCR has no
conduction path and will shutoff.   You can look up simple ideas in the
DIGIKEY catalog
that show some of these...

Eric Borcherding

1998\11\28@225414 by Russell McMahon

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Ricardo,

Using an opto coupler made for this application makes the job very
straight forward.

The MOC3041 from Motorola is one such device. This switches at the AC
zero crossing point which may be an advantage or a disaster depending
on your application. I don't know where you live but RS (who are in
many countries) have them as part number  301-628.


regards

   Russell McMahon

{Original Message removed}

1998\11\29@180456 by mkeitz

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On Sun, 29 Nov 1998 05:46:13 EST spam_OUTSpk41qTakeThisOuTspamAOL.COM writes:

>Two comments, MOC3041 stand for 400V. If you want to use in europeen
>community, use MOC3061 for 600V for your protection.
>I do not have MOC datasheet near me, but I think (may I wrong?), that
>this
>product was design for triacs and not for scr.

It should work for SCRs by placing a diode in series with the MOC output
stage so it doesn't try to apply negative pulses to the gate of a
reverse-biased SCR (though would this mess up the zero-crossing logic?).
For inverse-parallel SCRs you'd need two MOC30X1's.

I think a pulse transformer would do better in circuits for high voltage
and current, especially if you're using a PIC that is smart enough to
drive the transformer with the necessary pulses instead of DC.  The
MOC30X1's seem to be a lot more fragile than the triacs they control.



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