Diodes have huge ratings without impacting performance? - Page 1
Forum section: electronics / projects

author: Chendy
author_rank: Contributor
timestamp: December 17, 2022, 05:44:07 pm
content: Hi clever people,I'm searching for diodes that can handle >500mA.The cheapest on Digikey @1k was this family.Pretty much the whole range is the same price. The S1A withVoltage - DC Reverse (Vr) (Max)of 50V costs the same as the S1M with 1000V.But, what I would like help understanding is that there doesn't seem to be any impact to any specifications of the high DC Reverse Voltage ratings?!1. Are these ratings to be believed?2. Whats the trade off with getting these super high rated diodes? I only need them to work up to ~12VJust generally seems suspicious to me, but what do I know!https://www.smc-diodes.com/propdf/S1A-S1M%20N0560%20REV.B.pdf

author: Tomorokoshi
author_rank: Super Contributor
timestamp: December 17, 2022, 08:06:34 pm
content: There are lies, damn lies, and diode datasheets.Search and look through a range of datasheets on Digi-Key.Some of the datasheets will show different parameter values at different voltage ratings, such as forward voltage drop, reverse recovery time, surge current, or even thermal resistance. Compare the overall detail of data. Do some have more graphs than others? Is the formatting precise, clear, and consistent? Do some datasheets have an odd similarity to others?With a series like that invariant values across a wide voltage range could come down to:- All the parts are actually sorted or binned into a small range and marked at the lowest ranges within the bin- Worst-case values from the whole series are published, which is easier to maintain across process variations because many parameters don't matter for most applications- It's actually the same die and is just relabeled- The manufacturer who introduced the original part set the "standard" and other manufacturers are trying to play "identical specsmanship" in order to get qualified by naive purchasing agentsIt's interesting to get a variety and actually test the parts. You could test:- Does the forward drop vary with actual reverse breakdown voltage?- Does the junction capacitance vary with actual reverse breakdown voltage?

author: bson
author_rank: Unknown
timestamp: December 17, 2022, 09:25:38 pm
content: They might very well be exactly the same diode, just different ratings and part numbers. If you need a diode with a 50V breakdown voltage you might just ignore the 1kV parts - after all they will likely cost more and be larger. Right?

author: H713
author_rank: Regular Contributor
timestamp: December 18, 2022, 06:52:10 am
content: I don't have pics, but I have tested 1N4001s, 1N4002s, 1N4003s, etc. on a curve tracer. Guess what? They were all the same thing. Seemed to be the case across multiple manufacturers.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 18, 2022, 03:50:54 pm
content: Standard silicon diodes indeed tend to come with variety of reverse voltage ratings and otherwise the same specs, and no difference in price. As said, it's even possible you get higher reverse voltage than rated. Nothing special in this, it just seemingly is easy/cheap to manufacture silicon diodes with quite high voltage ratings.You can pretty much trust the datasheet values, and the manufacturers available on distributors like Digikey. As long as you correctly understand what all the parameters mean.Price formation is much more than the numerical specifications and their superiority. It is completely normal that a part exceeding another one in every respect is a lot cheaper. Distributor markups are weird, too. If you bought 1 million parts directly from manufacturer, the price difference could turn around.As long as you understand the specifications and how to apply them, don't worry. It's ok to sort for lowest price (or best availability, these days).

author: fourfathom
author_rank: Super Contributor
timestamp: December 18, 2022, 04:39:34 pm
content: Quote from: H713 on December 18, 2022, 06:52:10 amYes, but the 1N4007s (1000V PIV) are indeed different internally. So even within a family there may be design differences -- it's not always just a factor of sorting.

author: bdunham7
author_rank: Super Contributor
timestamp: December 18, 2022, 04:48:46 pm
content: Quote from: fourfathom on December 18, 2022, 04:39:34 pmThere may have been a difference at one time (PIN for the higher voltage models) but there's nothing in the specs that would prevent you from using the 1N4007 construction and marking them 1N4001-7 as demanded by your customers. Vf, leakage, and junction capacitance might actually vary between the two constructions, but you can choose to publish specs that can be met either way. That appears to be the case with the OP's diode datasheet.

author: fourfathom
author_rank: Super Contributor
timestamp: December 18, 2022, 05:02:09 pm
content: Quote from: bdunham7 on December 18, 2022, 04:48:46 pmYou are essentially correct, but datasheets for the 4000 series vary. In the first two spec sheets I pulled up, Vishay shows identical numbers and curves for the whole 4001-4007 series, while Diodes Inc shows that the 4005/6/7 have a lower typical junction capacitance than the 4001/2/3/4. I assume this is a design factor (not a sorting one), but to be honest I don't know if Vishay and Diodes Inc are building these diodes the same way or not. And in most cases this small difference won't matter.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 18, 2022, 05:44:11 pm
content: Relevant:https://www.eevblog.com/forum/projects/diode-voltage-ratings/msg3955526/#msg3955526tl;dr diodes are rarely if ever rated the minimum they could be. Sometimes they come surprisingly low, so, it's not something you can rely on. So you still buy higher ratings when you need to. But you can often get away with a lot more than the nameplate rating would suggest.Tim

author: TheMG
author_rank: Frequent Contributor
timestamp: December 19, 2022, 06:39:06 pm
content: It's probably something only the manufacturers would know, but I wouldn't at all be surprised if several different diodes within a product range are in fact exactly the same diode, but with a different part number stamped on.These days the process of manufacturing small rectifier diodes like the 1N400x series has likely been significantly improved from when this series was first introduced many decades ago, and it's probably cheaper nowadays to make one or two diodes that exceeds the specs for several diodes in the same series than to make 7 different ones.

author: David Hess
author_rank: Super Contributor
timestamp: December 19, 2022, 07:03:13 pm
content: Higher voltage diodes in the same series and in general have slower reverse recovery, greater forward voltage drop, and maybe lower conductance. In the specifications this may be reflected by 2 or 3 "grades" of reverse recovery and forward voltage drop because of manufacturing differences.