# Diac / Diode Confusion ?

Discussion in 'Electronic Basics' started by Robert Monsen, Jan 19, 2005.

1. ### Robert MonsenGuest

A 1N4148 is a diode. A diac is not a diode.

http://www.americanmicrosemi.com/tutorials/diac.htm

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Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

2. ### TrudeauGuest

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. 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.

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? Does the
Diode also limt voltage eg. a 5v Diode limits voltage to well .. 5V.

Regards

3. ### Graham KnottGuest

A diac the same physical size as a 1N4148

and say 100 to 200 mW dissipation and about 2V across the
See above.

Please bear with me as I'm a
True but it is reversable (symettrical, unlike a diode)

I Get that.
Have a look at Zener diodes.

4. ### John FieldsGuest

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No. Notice they were referring to a 1N4148 _sized_ diode. That is, a
Diac in the same size package as a 1N4148.
---
---
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
---
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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.
---
---
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 sheet 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,

5. ### TrudeauGuest

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

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