Low-voltage diac?

range?

conditions

typical

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.

"Neil Preston" wrote in news:3IKAd.7273$ snipped-for-privacy@newssvr30.news.prodigy.com:

How about an MBS4992 (Motorola) ? M

Neil Preston schrieb:

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

HTH

Reinhard

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.

"breakover"-voltage

It won't?? Try this.

Or scroll down to the third one here

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 !

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

Thomas

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

Gerard Bok schrieb:

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

Greetinx

Reinhard

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 snipped-for-privacy@eskimo.com Washington State resident

UJT inside a bridge?

Ah, what the heck. Use a PIC.

-- Nicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. Remove spaces etc. to reply: n o lindan at net com dot com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

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

range?

conditions

typical

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

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. M

"Neil Preston" wrote in news:%BVCd.7280$ snipped-for-privacy@newssvr12.news.prodigy.com:

Have you Googled for "lambda diode"?

Mark L. Fergerson

An image seach cleared out the crud.

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

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

range?

conditions

typical

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,