Guide to Standard Zener Diode 'Varieties'? (MMSZ vs. PDZ vs. BZT) - Page 1
Forum section: electronics / projects

author: TimNJ
author_rank: Super Contributor
timestamp: October 28, 2020, 08:09:26 pm
content: Hi everyone,I'm trying to figure out some of the key differences between different standard zener diode families. For example, the most common prefixes used across many manufacturers are MMSZ, PDZ, BZT for SOD-123 style.In my experience with "typical" circuits, with zener currents in the range of 100uA to 10mA, I have never seen much difference between zener diodes, from circuit performance perspective.Anyone know of a quick reference sheet...or know off the top of their head?Thanks,Tim

author: TimNJ
author_rank: Super Contributor
timestamp: October 28, 2020, 08:25:06 pm
content: I should add: I know that most zener diodes (at least those about >10V) will behave pretty well (Vz vs. Izt) in the range 100uA to 10mA, so no real surprises there. But, after comparing the datasheets of a few series, I still can't pull out what the notable differences are.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 28, 2020, 10:10:32 pm
content: I don't know about the various SMT families specifically. Most are similar to 1N52xx family, or the 400mW series (1Nxxx?) or whatever. Start reading datasheets.There were a few families also spec'd at low current (Vz @ Iz in the sub-mA) rather than at some nominal or near-power rating (~10s mA). As far as I know, these are essentially identical parts, binned at a different test current. But maybe they have lower noise (that would be helpful at such low currents).Some may also have TVS-like ratings? Haven't ran across any, but I have seen 1N series parts used as TVSs before, apparently to reasonable success. Speaking of, some or all of 1.5KExx is aliased to a... oh yeah, 1N62xx family? Don't know what other crosses there are.The only differentiating factors I know of are leakage (up to whatever the fundamental limit is, for a part of given breakdown voltage), pulse handling, maybe ESR, and noise. And I don't think most of those are even mentioned, in most families (like the 1N47xx or 52xx's). Fab differences relate to impurities and uniformity, as far as I know (defects spewing leakage, uneven breakdown or hotspotting, impact ionization ratio leading to excessive noise in avalanche?). Probably guard rings are also necessary in the higher voltages, or maybe also just to further optimize these parameters. (And ESR, I don't have any reason to believe a manufacturer wouldn't be using as highly doped silicon as the breakdown voltage suggests, but eh, who knows, and the die can always be some thickness or another; both factors contribute directly to ESR.)Other than that, the same gross exponential V-I curves always apply. You can do differently, but then it's not a zener/avalanche diode as such, it's some kind of snapback or punch-through diode, or a higher order active device.Tim

author: TimNJ
author_rank: Super Contributor
timestamp: October 28, 2020, 11:29:00 pm
content: Thanks. That was helpful and interesting.I think I'll put together a table of differences between a few popular varieties. My initial side-by-side comparison didn't reveal too much, as graph presentation was all over the shop, even within the same manufacturer. (Some plotted linear, some plotted log, differing minimum Iz currents on the Y-axis.)I found Diodes Inc. 'DDZ' which is specified at 50uA, as you suggested.https://www.diodes.com/assets/Datasheets/ds30410.pdfThanks!

author: floobydust
author_rank: Super Contributor
timestamp: October 29, 2020, 12:07:32 am
content: I've found are big differences. The IZT value for VZ is all over the place.i.e. for a SOT-23 "zener voltage regulator":MMBZ52xxIZT=20mA (for <12V).BZX84 NXPIZT=5mABZX84 On-Semispecs for IZT=1mA and 6mA and 20mA; best datasheet.MMBZ46xx VishayIZT is 0.25mA"350 mW high quality voltage regulator designed for low leakage, low current and low noise applications"I got burned using Diodes Inc zeners, their breakdown voltage is all over the place at lower currents like 1mA, quite a hassle in production. So I no longer use the brand there. At the "knee" there is a wide variation if you are running the zener below rated IZ it seems. But On-Semi parts were bang on, so I attributed it to low quality.

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 29, 2020, 04:20:33 am
content: Quote from: T3sl4co1l on October 28, 2020, 10:10:32 pmTheVishay PLZ seriesrecommended by a coworker is a personal favorite. SOD-323F, 1/2 W, 2V to 39V, 2% tolerance, 8/20us surge rated to 70-100W (depending on voltage), package markings comprehensible to humans, good datasheet... what's not to like? Okay, they're specified at 20mA zener current rather than something lower and more useful, but you too rarely geteverythingin this job....

author: exe
author_rank: Unknown
timestamp: October 29, 2020, 08:04:13 am
content: I got good results with bzx-series. I'd expect voltages to be all over the place as zeners are hardly precise devices, but 7.5V measured 7.51V, and 16V measured 16.11V (but climbing due to self-heating). I'm no expert, but looks like a very good result to me.PS I don't know how accurate my smd twezers are, but they show sensible numbers.PPS sample size is 1 in this test, so I can't really draw conclusions about their voltage accuracy.

author: jonpaul
author_rank: Super Contributor
timestamp: October 29, 2020, 11:16:40 am
content: Bonjour a Tous, there is a very broad range of perhaps 5 or mor types and each type perhaps 1000s ...100000s of parts.A few General categories please!Small signal 250 mw..500 mw 1N52xxPower 1-25W ( MR2525)Transient absorbing Zenervoltage reference Zenernoise generator ZenerIn the 1970s some manufacturers published Zener Handbooks, perhaps, IR, RCA, Motorola?You will find them on epay or on the net!Bon chance,Jon

author: TimNJ
author_rank: Super Contributor
timestamp: October 29, 2020, 08:54:40 pm
content: Quote from: floobydust on October 29, 2020, 12:07:32 amInteresting experience. Thanks for sharing. Seems like the IZT for the rated VZ is one of the main differences. Low noise? Well, I've seen some datasheets say it, but hardly is ever quantified. Is this temperature coefficient "noise" or actual random noise.The datasheets you linked to actually have descriptive first page bullet points. Most of the ones I've opened have one bullet point that goes something like: "Yep, this is a Zener diode", and that's about it.

author: TimNJ
author_rank: Super Contributor
timestamp: October 29, 2020, 08:59:14 pm
content: Quote from: jonpaul on October 29, 2020, 11:16:40 amThanks. I had an idea that the Art of Electronics 3rd edition might have a nice updated comparison table (similar to old an databook/handbook table), but alas, nothing for zener diodes. Nice tables for common transistors, and other diodes, but hardly much mention about zeners at all. I guess I have to do the work myself.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 30, 2020, 08:56:34 am
content: The data-sheets for zener diodes are often pretty poor. In part this is because most of them handle a lot of different voltages and those diodes are quite different.Noise data are rare and often relatively high test limits. Especially the low frequency noise that can be relevant for some applications is expensive to test as it just takes time (the 0.1 - 10 Hz noise test takes at least 10 seconds, more with waiting for thermal stability - too much for a cheap part). The usual noise values given are relatively high and though often not given the frequencies are relatively high. So this would be real electric noise, not an effect of temperature fluctuations.It may be also import to note the difference between typical and tested upper limits. The acceptance limits may be much higher than typical values.The number of zener types is really confusing. Many may be different only in the case and test procedures.

author: voltsandjolts
author_rank: Unknown
timestamp: October 30, 2020, 10:08:31 am
content: Quote from: TimNJ on October 28, 2020, 11:29:00 pmThere is also the ONSEMI MMSZ4xxxT1G Series rated at Izt = 50uAhttps://www.onsemi.com/products/discretes-drivers/diodes-rectifiers/zener-diodes/mmsz4If anyone knows of simple zener diodes with rated Izt lower than 50uA I would be interested to hear about it.