Low-voltage diac?

[Neil Preston]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

I wish to make a sensitive triac trigger to detect certain fault conditions
on an AC signal, and I need the negative resistance characteristics typical
of a diac, but at much lower threshhold voltage. It must also be
bidirectional.

Thanks,
Neil

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

I wish to make a sensitive triac trigger to detect certain fault conditions
on an AC signal, and I need the negative resistance characteristics typical
of a diac, but at much lower threshhold voltage. It must also be
bidirectional.

Thanks,
Neil

Some DIACs are rated for 30V, but that's not as low as what you asked
for.

Maybe you should use a more complicated circuit like a PUT.

 

[Mike Diack]

Is there available a DIAC with breakover voltage ratings in the 5-15V
range? Or an equivalent device?

All I've seen so far are in the 50-60v range.

I wish to make a sensitive triac trigger to detect certain fault
conditions on an AC signal, and I need the negative resistance
characteristics typical of a diac, but at much lower threshhold
voltage. It must also be bidirectional.

Thanks,
Neil

How about an MBS4992 (Motorola) ?
M

 

[Reinhard Zwirner]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

Maybe 2 zeners connected "back-to-back" could work; "breakover"-voltage
would be [Uz + 0.7] V.

HTH

Reinhard

 

[Gerard Bok]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

Maybe 2 zeners connected "back-to-back" could work; "breakover"-voltage
would be [Uz + 0.7] V.

The original message read "... and I need the negative resistance
characteristics ..."

Your solution will mimic a low voltage diac but won't provide the
negative resistance characteristics.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

Maybe 2 zeners connected "back-to-back" could work; "breakover"-voltage
would be [Uz + 0.7] V.

The original message read "... and I need the negative resistance
characteristics ..."

Your solution will mimic a low voltage diac but won't provide the
negative resistance characteristics.

It won't?? Try this.
http://www.freeinfosociety.com/electronics/schematics/zeneroscillator.ht
ml

Or scroll down to the third one here
http://www.geocities.com/CapeCanaveral/Lab/5185/circuit.html

Now I've tried it, and was unsuccsssful, but I've read that other people
have been able to get it to work. I've also hear that it helps to heat
the zener up with a soldering iron to roast it and make it change its
characteristics.

 

[Gerard Bok]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

Maybe 2 zeners connected "back-to-back" could work; "breakover"-voltage
would be [Uz + 0.7] V.

The original message read "... and I need the negative resistance
characteristics ..."

Your solution will mimic a low voltage diac but won't provide the
negative resistance characteristics.

It won't?? Try this.
http://www.freeinfosociety.com/electronics/schematics/zeneroscillator.ht
ml

Or scroll down to the third one here
http://www.geocities.com/CapeCanaveral/Lab/5185/circuit.html

Now I've tried it, and was unsuccsssful, but I've read that other people
have been able to get it to work. I've also hear that it helps to heat
the zener up with a soldering iron to roast it and make it change its
characteristics.

The instructions basically say: fry the part beyond being a zener
diode.
The question is, if this circuit --if operating at all-- is using
a zener diode to operate or is exploiting idiosyncratic behaviour
of overstressed part. And still: I'd like to see the negative
resistance display in the graph.

But either way: it's not a diac. (Rememer, the nice tiny device
that fires reliably, even in the absence of a soldering iron

Happy New Year !

 

[Zak]

But either way: it's not a diac. (Rememer, the nice tiny device
that fires reliably, even in the absence of a soldering iron

What about two zeners and a triac? That could be a nice diac



Thomas

 

[Gerard Bok]

What about two zeners and a triac? That could be a nice diac

Could well be. Provided that you get the triac fired on 12..15
volts.

 

[Reinhard Zwirner]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

Maybe 2 zeners connected "back-to-back" could work; "breakover"-voltage
would be [Uz + 0.7] V.

The original message read "... and I need the negative resistance
characteristics ..."

Your solution will mimic a low voltage diac but won't provide the
negative resistance characteristics.

You're right; I've just read the first part of Neil's message <sigh>.
On the other hand I successfully built a low voltage dimmer with such
a "diac" a few years ago.

Greetinx

Reinhard

 

[Mark Zenier]

Could well be. Provided that you get the triac fired on 12..15
volts.

Sure, they usually have a max gate voltage of a volt or two. It looks
like a anti-parallel pair of diodes from gate to "cathode".

But, you'd have to use an SCR and a zener inside of a full wave bridge
because triacs are too slow and don't come unstuck at frequencies that
are too high. (Over a couple of hundred Hz, as I understand it).

Mark Zenier [email protected] Washington State resident

 

[Nicholas O. Lindan]

[What it says in the title]

UJT inside a bridge?

Ah, what the heck. Use a PIC.

 

[Neil Preston]

Thanks for the ideas, guys.

I had tried the zeners. Didn't do what I needed because the current couldn't
'pulse' to fire the triac being driven. The idea is to monitor the voltage
across a capacitor, and if it rises to a positve or negative value it should
fire the triac. For this I need the diac.

I had also considered the PUT inside a bridge. I was hoping to keep it
simpler than that.

I'll look into the MBS4992.

Happy New Year!

Neil

 

[Neil Preston]

The MBS4992 looks like it would be perfect for my app. Unfortunately, it
appears to be no longer manufactured. Any suggestions for sources? (10-15
pcs.)


Neil

 

[Mike Diack]

A bit of quick googling shows that the brokers (touts and shysters) are
sitting on mountains of them, but the regular supply lines are indeed
dry. I'm sort of amazed that these useful little widgets have gone on
the endangered species list. On semi still list them and Crown Audio are
still using them (in their CE series pro amps) so they gotta be out
there. Otherwise you could get creative with a bridge wrapped around a
little SCR (5060) and a couple of resistors. <sigh>
M

 

[Mark Fergerson]

Is there available a DIAC with breakover voltage ratings in the 5-15V range?
Or an equivalent device?

All I've seen so far are in the 50-60v range.

I wish to make a sensitive triac trigger to detect certain fault conditions
on an AC signal, and I need the negative resistance characteristics typical
of a diac, but at much lower threshhold voltage. It must also be
bidirectional.

Have you Googled for "lambda diode"?

Mark L. Fergerson

 

[JeffM]

DIAC with breakover voltage ratings in the 5-15V range?

Have you Googled for "lambda diode"?
Mark L. Fergerson

An image seach cleared out the crud.
http://images.google.com/images?q=lambda-diode

 

[Neil Preston]

That was exactly the piece of information I needed. I'm a Crown authorized
servicer, and believe it or not, I have 3 in stock. They are marked with a
different number, and are not identified by part number on the parts list,
but the schematic labels them as an MBS4993, with an 8v breakover rating.
It's perfect!

Thanks Much!

Neil

 

[Neil Preston]

Thanks, guys.... interesting item.

I knew that an e-b junction would zener at about 6V, but hadn't thought
about the breakover characteristic E-C.

Neil

 

[Winfield Hill]

Neil Preston wrote...

The MBS4992 looks like it would be perfect for my app. Unfortunately,
it appears to be no longer manufactured. Any suggestions for sources?
(10-15 pcs.)

The MBS4992 was Motorola's version of GE's original 2n4992 SBS,
or Silicon-Bilateral Switch, which was widely second sourced.
Lot's of surplus places carry them, such as ampslab.com,
http://www.ampslab.com/trans_2n4992.htm