[volt-nuts] Some questions to zeners (1N823-1N829)

WarrenS warrensjmail-one at yahoo.com
Sat Jan 26 15:48:46 EST 2013


If you want to make something in volume which is just pretty good, I would 
not recommend this method for a new design.
On the other hand, if this is a nuts thing to make the very best, this is 
one of only a very few possible solutions.

Here are some general answers, most of my experience with these parts is 
pretty dated, (i.e long ago).
As when pushing the performance limit of any reference, there is a  lot of 
variation between parts and even more so between manufactures.
Solution is, select, Age, select, test, grade, select.

As far as my experience with 1N823, performance depends on the run and what 
is left after the manufacture has selected out the others.
With 1N823's, Yield can often go to zero. With 1N825's a typical yield I've 
seen is around 25-50% (from the right manufacture and batch)

Yes the main difference is the zero TC current, with some parts there is no 
zero TC current.
So yes you are more likely to get a lower current TC such as 5 ma from a 
1N823 or 1N825 than a 1N829, but it could of course be > than 7.5 ma.
I don't use anything that does not have a zero TC between ~ 4 and 10 ma
I found TC to be very much a Batch thing, with up to 50% of the majority of 
a batch, tending to be similar.
>From a given batch, any that are considerable different, I don't use because 
they may have something else wrong going on.

Another thing that needs to be selected for in high end references, and will 
vary by manufacturer, is 1/F noise.  The random jumps in the voltage.

For me, hysteresis has not been a issue over room temperature changes for 
the most part, but something that has to be checked.
Some Manufactures are better than others, and hysteresis can and will be 
effected by assembly, layout, or anything that puts any stress on the part.
Don't just solder the parts down on a PCB without a stress relieve loop in 
the leads.

The zero TC current can be set so that the voltage at most any two 
temperatures will be the same. (<< 1PPM)
If the voltage change in-between those two temperatures is too much, lots of 
ways to add an additional second order temperature compensation.

For the best TC performance, consider the mini-oven idea with the zener, 
heater resistor, and thermistor all  heat shrunk together.
With a lot of outer insulation, it could be done low power by adding an 
addition 0 to 5 ma to the heater resistor.

Everything has it's trade offs.
The trade off using these zeners is time and complexity.
For these parts, 5ma is about as low as you are going to get.
For low power, there are many things Much better.
The trade off you make to get low power is "Noise" & stability.
The trade off you make for the good TC of LM399 is long term stability, PPM 
noise, and the high cost of selection fall outs.

The best solution will depend on many things including the desired 
performance, how many you want to make, the cost you place on selection 
and if you can still find the 1N825's at a reasonable price like they where 
in the 70s & 80s. (&  $0.10 in 2000s)

For a xfer standard, the Most important criteria is 1/f random noise. Most 
everything else can be compensated out.
For that, it is hard to build anything better than using a 1N825 selected 
device.  Plot attached.


> Date: Sat, 26 Jan 2013 16:30:34 +0100
> From: "Andreas Jahn" <Andreas_-_Jahn at t-online.de>
> Subject: [volt-nuts] Some questions to zeners (1N823-1N829)
> Hello all,
> Hello Warren,
> after having experimented a lot with 5V monolithic zener references
> and still not found the ideal solution I want to try a 1N82x based 
> solution.
> For me a extended room temperature range of
> 25 degrees centigrade +/- 7 degrees (64-90 ?F)  is of interest.
> Since I plan to have battery supplied instruments a lower supply current 
> would be of interest.
> For the zeners a zero TC current is stated.
> Over which temperature range the TC is nearly zero.
> How large is the voltage deviation in the above mentioned range?
> Does it play a role for the absolute temperature deviation if a 1N823 or a 
> 1N829 is used?
> Or is the behaviour equally when the individual zero TC current is used?
> Is the only difference between the selections that the zero TC current is 
> more near the 7.5mA value on the 1N829?
> So is it more likely to get a low zero TC current of 4 mA on a 1N823 
> device than on the 1N829?
> Or should I go for the 1N829A for the lowest absolute TC?
> How large is the hysteresis on the zeners in a temperature range of 10-40 
> degrees celsius (50-104?F).
> On monolithic unheated reference voltages with hermetic case I have up to 
> around 2 ppm hysteresis difference
> on temperature cycling. (see attached picture with 10-45 degrees celsius 
> on X-Axis for an ADC with a 5V reference
> measuring a LM399 heated reference over a 2:1 precision voltage divider. 
> The ADC with the 5V reference is temperature cycled).
> I blame the temperature hysteresis on the die attach to the lead frame 
> which seems to be usually a silver filled epoxy compound.
> I hope that the hysteresis on a discrete zener is much lower.
> With best regards
> Andreas
> Name: AD586_05_Hyst_20130120.PNG
> URL: 
> <http://www.febo.com/pipermail/volt-nuts/attachments/20130126/4a3abca5/attachment.png>
> ------------------------------
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