Re: Diac / Diode Confusion ?

From: Trudeau (Trudeau_at_123.com)
Date: 01/19/05 

Date: Wed, 19 Jan 2005 15:40:35 -0600

"John Fields" <jfields@austininstruments.com> wrote in message
news:brdtu092eg0edakv09v0gja52mpt10di3l@4ax.com...
> On Wed, 19 Jan 2005 13:51:49 -0600, "Trudeau" <Trudeau@123.com> wrote:
>
> >On the following link it says in part the following....
> >
> >Most diacs are used for pulse generation, probably in the order of amps,
and
> >are designed as such. I think the published ratings for static (DC) use
are
> >a bit on the consevative side, take a 1N4148 sized diac and say 100 to
200
> >mW dissipation and about 2V across the diac we are left with 50 to 100
mA,
> >more than enough!
> >
> >http://www.hut.fi/Misc/Electronics/circuits/tele_privacy.html
> >
> >My question is, Is this web site confused.
>
> ---
> No. Notice they were referring to a 1N4148 _sized_ diode. That is, a
> Diac in the same size package as a 1N4148.
> ---
>
> >When I looking up a 1N4148 it is
> >NOT a Diac, it is a Diode. Please bear with me as I'm a novice.
> >A Diac goes in one direction and will start conducting electricity
> >at a certain voltage. I Get that.
>
> ---
> No, you don't. Not quite, anyway. A Diac is bidirectional.
>
>
http://www.littelfuse.com/cgi-bin/r.cgi/prod_series.html?LFSESSION=Stkas7zMnz&SeriesID=605
> ---
>
> >A diode works in one direction also but from that point I'm a little
unsure
> >what the difference is. Can anyone explain this in simple terms?
>
> ---
> A diac is a full-wave or bidirectional thyristor. Whenever the
> amplitude of applied voltage exceeds the breakover voltage rating of
> the diac, it switches from blocking- to conducting-state.
> ---
>
> >Does the Diode also limt voltage eg. a 5v Diode limits voltage to well ..
5V.
>
> ---
> A reverse-biased Zener diode forced into conduction will cause the
> voltage across its junction to be limited to the value specified in
> the data *** for that diode with the specified current flowing
> through the diode. Forced to conduct in the forward direction, the
> voltage across the diode, and most silicon junction diodes, will be
> substantially less than one volt,
>
> --
> John Fields

Thanks, Yes I missed the "sized diac".
I also think I was a little confused because a diac diagram is like two
diodes in oposite direction.
Previous to my post I read
http://www.ibiblio.org/obp/electricCircuits/Semi/SEMI_7.html
and the concept of hysteresis my head was swimming a bit.

Thanks