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From: email@example.com (carltons)
Subject: Re: 1.6V zener diodes?
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sat, 19 Oct 2002 11:49:52 GMT
Date: Sat, 19 Oct 2002 11:49:52 GMT
In article <firstname.lastname@example.org>, email@example.com
(Tom Bruhns) wrote:
> firstname.lastname@example.org (carltons) wrote in message
> > In article , Winfield Hill
> > wrote:
> > >
> > > You're right Steve, the use of zener (field-emission breakdown)
> > > is not recommended for low-voltage design. But don't trash zener diodes
> > > for all the "high-voltage" (over 5 volts) folks. High-voltage zeners
> > > (avalanche technology) work very well in a wide variety of tasks, often
> > > much better or at least more efficiently than the alternates.
> > I appreciate what you're trying to say, however most of the "Zeners" above
> > have a lot of IC circuitry around them and loads of gain and feedback
> > along with heaters, etc to make them acceptable. My term "Zener" is a
> > single diode with nothing in the package but the diode and its wire
> > bonds. The LTZ1000 and LM399 both have great TC, but at the expense ($
> > and Isupply) of on-board heaters. The zeners that I refer to a have
> > designations such as 1Nxxx etc. and they don't have schematics on their
> > spec sheet to show what's inside. You already know that there is just a
> > diode with two leads and some plastic on the outside.
> > Good trick is to get the same specs for a 1.6v "zener" with a supply of
> > 2.0v (end of life for two "AA" or "AAA" cells) at less than 1 mA of total
> > drain.
> So...the really good references (short of NIST Josephson junctions ;-)
> appear, still, to use a zener at their heart.
> But what I was thinking of was, just as you say, those little two-lead
> (or SOT-23) parts that just have a single junction in there doing the
> work. Given that I'm dealing with volumes that don't warrant a custom
> IC design, how else can I very simply get less than 1uA between two
> nodes up to within a volt or closer of the knee (at 10 volts), and
> with not very many millivolts change have the current go from the uA
> region to the mA region? The ability to do that with such a simple
> part is sometimes quite valuable. In the application I'm thinking of,
> I don't have to introduce any power supplies to accomplish the task.
> Both nodes can be high impedance and there's no problem. When below
> its knee voltage, it's pretty darned quiet. Unlike with the 6AL5, I
> don't have to provide any heater current... I'd be much less likely
> to use zeners in low-voltage circuits, but they're quite handy,
> sometimes, in things that run from +/-15V or more.
Boy! In a world with infinite power supply voltages and don't worry about
current levels, life is great. Be that as it may, try getting a 1.6 v
zener. I would be willing to bet that you would end up with a tunnel
diode instead or at least a good percentage of the time. Look up a 1N3712
and see what the sheet says about Vf. Further note the dynamic impedance
and the fact that it is negative and not positive. The difference is the
amount of doping of the silicon. They now use ion implantation and this
may cure this problem, but the present day market is not hugh for discrete
Bottom line: know the limitations of zeners and the fact that they are
used in some IC's means diddly. They don't work worth a hill of beans in
the zener levels and must be augmented with loads of circuitry to make
them acceptable as references. This includes the kind of heating you get
in a 6AL5, although at a lower level in a solid medium and not in a
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