1N829A temperature coefficient of only 0.0005%/K , non stress free mounting ? - Page 1
Forum section: electronics / general

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 14, 2025, 12:27:32 pm
content: Hello1N829A is quite cheap fron Mouser , and in use in some classic multimeters as Solartron the diode just soldered as all the other passive components , no holes in the PCB , no stress free setup , even no shield to protect the diode of air flowMy question is why , over a oven use which is another concern , why a sensible component as 1N859A is not mounted stress free ??RegardsOS

author: EC8010
author_rank: Frequent Contributor
timestamp: October 14, 2025, 12:49:16 pm
content: Sadly, I can't remember where I bought them from (whether Farnell or Mouser), but a year ago I measured a 1N829A and it wasn't very good. It should have had zero tempco at 7.5mA. Before people get excitable about ovens and stress-free mounting, they'd better check that the device is genuine...

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 14, 2025, 01:06:26 pm
content: Quote from: EC8010 on October 14, 2025, 12:49:16 pmHellloI agree on non over quality system regarding mounting but as another side If I shall purchase a batch of them up to several batches that start to be a bit costly project.what ever first step is to built a bomb proof 7.5mA current source . PCB can be designed step by step this old suject is interestinghttps://www.eevblog.com/forum/metrology/old-fashioned-zener-10v-reference/RegardsOS

author: MiDi
author_rank: Frequent Contributor
timestamp: October 14, 2025, 03:56:19 pm
content: E.g. in Solartron 7071/81 it is mounted in stress reduced manner - stress free only exists theoretically.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: October 14, 2025, 06:44:16 pm
content: possible to hook on spring, that would be stress independent from base support .0.0005% - 50PPM ... like TL431

author: gamalot
author_rank: Super Contributor
timestamp: October 14, 2025, 07:19:40 pm
content: Quote from: GigaJoe on October 14, 2025, 06:44:16 pm5ppm

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 14, 2025, 08:01:58 pm
content: Quote from: MiDi on October 14, 2025, 03:56:19 pmHelloI have more skills in mechanical design than in electronic , free free is perhaps a common way to describe the purpose but a very limited stress mount is possible , Zener 1N8XX are glass body , small with quite thick wire so even a small stress can generate trouble1N829 is quite cheap and interesting for DIY purpose , just need to avoid design mistakesRegardsOS

author: branadic
author_rank: Super Contributor
timestamp: October 14, 2025, 08:54:42 pm
content: Keep in mind that zeners in glass body are prone to ambient light, unless the glass body is black. Apart from fundamental learning how to deal with raw zeners and how to apply a proper oven to them, I don't see the huge benefit of a t.c. compensated, but temperature-unstabilized zener reference. The benefit of using an ADR1399 is way larger and still, there is a lot to do to make a proper voltage reference of it.-branadic-

author: EC8010
author_rank: Frequent Contributor
timestamp: October 14, 2025, 09:52:08 pm
content: Good point; all semiconductors are photosensitive (actually, almost everything is), and a bit of black paint isn't enough. Stopping photons requires a metal; I had to work hard to allow photomultipliers to detect single photon events.I'd be interested to hear your thoughts on how to best use an ADR1399.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 14, 2025, 11:17:21 pm
content: Quote from: Overspeed on October 14, 2025, 01:06:26 pmI'm not sure a laser focus on 7.500mA is needed.They seem to simply bin the zeners in bands, by nominal TC, so as #1 shows, manual adjust of actual zener operating point wil give best TC null.See examples of bands for 'TC Zeners' here - the curves are all typical band means, adjacent bands give a better indication of expected variations.https://www.lcsc.com/datasheet/C3737677.pdfI've been thinking some about best packages for stable zeners, andlowest thermal resistanceand small has appeal.Relatively new is the SOD323HE package (from ROHM and Panjit and Diodes inc)ROHM give nice curves on their parts, but they identify a TC null only on lower voltage parts, and then at high impedance parts of the curve.It seems smarter to target stable parts of the curves with low Zc, and then use OP amp gain to fine tune the temperature coefficient differences.Looks like a single opamp can do both gain to 10.00V and TC gain correction along these lines :

author: David Hess
author_rank: Super Contributor
timestamp: October 14, 2025, 11:24:54 pm
content: A couple years ago, I did a survey of desirable references and temperature compensated zeners were almost comparable in price to integrated references in the same performance class, but the later are much easier to apply. At the time, 1N829s were $8 each, and so were LT1021s and LT1236s roughly. I have since added the LTC6655s, ADR45xx, and LT6654s bandgap references, which are half, quarter, or even a fifth of the cost.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 14, 2025, 11:34:30 pm
content: Quote from: David Hess on October 14, 2025, 11:24:54 pmAnother point of difference is integrated references usually have far better tolerances, Zener TC parts have quite poor tolerance bands, and are close to obsolete.The 'Zero TC' detail was mostly tested in, making them very expensive (and as #1 also shows, of dubious quality).Hence my focus on other ways to get TC nulls, using tight thermal coupling on high volume modern Zeners.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 15, 2025, 12:34:35 am
content: Quote from: EC8010 on October 14, 2025, 12:49:16 pmThat was improving with higher currents, I wonder what current would have given zero TC ?The binning of other TC zeners suggest these have bands, for the others I linked they are appx 2:1, so maybe the 1N829A is allowed a wide variation in Iz ?

author: Kleinstein
author_rank: Super Contributor
timestamp: October 15, 2025, 09:53:03 am
content: The 1N829 has the zero TC relatively close to the nominal 7.5 mA. This is what allows the low TC. The other grades like 1N827, 825, 823, 821 have higher tollerace and the zero TC point can be further away. E.g. I have found around 3 mA for some 1N825. Chances are other units could be even lower or also higher like 10 or 15 mA.Another point is that there is also a 2nd order TC. Ideally one would still have a stable temperature, but no need for a very stable temperature as the linear TC can be low.

author: miro123
author_rank: Frequent Contributor
timestamp: October 15, 2025, 05:05:32 pm
content: [I cannot find from datasheet which discrete zenners are buried and which are planar/bulk.LF , pop-corn noise and long term stability depends on it.Personally - with this prices I wil go with adr1399 or even ebay LM399 that buy those disrete zenners with unknown spec

author: Gyro
author_rank: Super Contributor
timestamp: October 15, 2025, 05:57:33 pm
content: The iN82x are planar [actuall bulk] Zeners, actually Zener die stacked with a diode die to provide temperature compensation. Over the years, they have been used as high stability references in DMMs and even in standards labs (in batches and closely compared with batches of standard cells) but they need careful selection and care - relatively stress free mounting (eg. forming loops in the leads when PCB mounting) and particularly, isothermal conditions on the leads. You can also expect a voltage shift if thermally or power cycled.Yes, the performance between samples is variable, needing individual current setting and having quite a wide output voltage tolerance (as the LM399 does). DMM manufacturers like Solartron and Datron used long term burn-in and thermal cycling to weed out noisy or drifty excessive TC examples (or rather, identify the best ones). Datron actually used to buy large quantities of 1N827s, rather than buying the expensive 1N829A, and perform their own burn-in and characterization rather than relying on the manufacturers', necessarily time and condition limited, batch selection.To achieve the most stable (both popcorn and long term) result you need to be prepared to buy multiple samples and characterize them, even with buried Zeners.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 15, 2025, 06:04:03 pm
content: AFAIK the 1N82x are not burries zeners. They are usually still low noise. It likely needs some selection for low popcorn noise. Different from the LM399 where the current is set internal, the popcorn noise may depend on the current and one may have a 2nd / 3rd chance to find a low noise / low noise operating point. A lower voltage often helps with noise (but often comes with high differential resistance). In addition the reference current is much higher than with the LM399 / ADR1399, which also helps with low noise.The somewhat unknown is the longer time drift and aging. The LM399/ADR1399 run at a rather high oven temperature and can age faster from this.Some old circuits used a reduced stress mounting with long wires bend to a 3/4 loop.

author: Gyro
author_rank: Super Contributor
timestamp: October 15, 2025, 06:06:38 pm
content: Yes, I incorrectly used planar to distinguish against buried. I guess the correct term would be bulk?

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 15, 2025, 06:16:17 pm
content: Quote from: Kleinstein on October 15, 2025, 06:04:03 pmHelloSome thing like that ?RegardsOS

author: Gyro
author_rank: Super Contributor
timestamp: October 15, 2025, 06:33:40 pm
content: Quote from: Overspeed on October 15, 2025, 06:16:17 pmLike this (Datron 1072)...(Note the selection paint blobs).

author: iMo
author_rank: Super Contributor
timestamp: October 15, 2025, 07:27:58 pm
content: FYI

author: David Hess
author_rank: Super Contributor
timestamp: October 15, 2025, 09:06:58 pm
content: In the past I made loops in the leads, and when I laid out the circuit boards, I left extra room for the part, like 0.7" or 0.9" instead of the standard 0.5" spacing.

author: guenthert
author_rank: Frequent Contributor
timestamp: October 16, 2025, 03:40:19 pm
content: Quote from: branadic on October 14, 2025, 08:54:42 pmThe 1N829 I got might be in a glass body, but it's (opaque) orange. I'd think the 1N829A will be the same.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 06:23:20 pm
content: Quote from: guenthert on October 16, 2025, 03:40:19 pmHelloUnder the orange paint that glassRegardsOS

author: Gyro
author_rank: Super Contributor
timestamp: October 16, 2025, 06:49:43 pm
content: Quote from: guenthert on October 16, 2025, 03:40:19 pmI wouldn't trust the Orange coating to be completely opaque. Colour (or none) varies with manufacturer. My 1N82x collection..

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 16, 2025, 07:23:05 pm
content: HelloNice pics onhttps://www.richis-lab.de/REF22.htmRegardsOS

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 16, 2025, 10:11:24 pm
content: Quote from: Overspeed on October 16, 2025, 07:23:05 pmInteresting, looks like they process both sides of the wafer, (identically?) to get something they can then fit onto a glass package. Also explains the price and rarity.Identical processing would allow them to select the direction that worked best, when finally marking the part.