What does it means _real_ Schottky diode? - Page 1
Forum section: electronics / beginners

author: RoGeorge
author_rank: Super Contributor
timestamp: October 26, 2020, 11:07:34 am
content: "Is the lowest forward voltage drop ofrealSchottky diodes always the best choice?" (https://www.ixys.com/Documents/AppNotes/IXAN0042.pdf)Both in the title and text of the application note, the word 'real' is never missing before the name 'Schottky diode'.What does it means? Are there other kinds of 'not real' Schottky diodes?

author: exe
author_rank: Unknown
timestamp: October 26, 2020, 11:35:43 am
content: Looks like a translation/wording issue to me. I think "real" in the context of article means "not simulated". My best guess they say thatrealdiodes have additional losses due to, e.g., reverse current or something.In my opinion, the text reads a bit like German English. I had three or four books from Wurth Electronics and I think I can recognize some similarity. Any comments from German-speaking audience?PS disclaimer: I've read only a small portion of the paper you shared.

author: LaryPant
author_rank: Contributor
timestamp: October 26, 2020, 11:45:52 am
content: Quote from: exe on October 26, 2020, 11:35:43 amYou are correct, the text seems to be based of an original German version.The axis titles on the graphs from the second page are in German. Somebody probably forgot to translate the entire paper and not just the actual text. Although the graph on page three is correct.I am not qualified to comment on the properties of Schottky diodes, but as I am a native German speaker I agree with @exe, this is most likely an error in translation and by "real" they mean a simulation of a real Schottky diode, meaning a simulation which is pretty close to the real world.LaryPS: Although my language flag indicates that I am Danish, I do speak native German.

author: harerod
author_rank: Frequent Contributor
timestamp: February 26, 2021, 04:52:20 pm
content: This document has been around for a while. It provides a well defined checklist for designers.The author's point is that in his experience many designers fail to understand germane properties of real world components. For instance, designers of switched mode power supplies look for low forward voltage only and fail to understand other properties exhibited by real world components. Depending on the actual application environment, secondary effects, like recovery time, barrier charge, reverse current may become dominant. Therefore a real world Schottky diode may be a poor choice, in comparison to other diodes, with higher forward voltage.On a side note: I regret that I never met Walter Schottky, he is buried not far from were I live.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 26, 2021, 05:21:03 pm
content: Quote from: harerod on February 26, 2021, 04:52:20 pmYes; in my experience, schottky can perform worse, in applications where the higher capacitance hurts worse than reverse recovery does; or in pulsed application, where the internal resistance is just too high, with results ranging from simply poor operation, to destruction.So, snubbers may be contra-indicated, and perhaps some nonresonant converters.That said, I've also had good results with a couple of snubbers using SiC schottky; they happened to have modest peak currents, and the added capacitance wasn't too troublesome.I don't have much to comment on the article; I will note that, although it makes light of the foward/reverse tradeoff, I haven't seen many diodes, or applications, where reverse power dissipation was objectionable, or actually dominant.At nominal maximum design temperature.Leakage goes up exponentially with temperature -- it can very quickly run away. This is the sneaky part that can be easy to miss. And it's more about thermal design, always a challenge to solve reliably.Also interesting to note that, what passes for modern schottky, can be quite strange indeed -- in the high voltage range where innovation is still going on. Namely, 150-300V Si types. Some of these actually have reverse recovery, they are just much better behaved than PN types (short t_rr, low I_rr, little dependence on forward-bias duration* or temperature).*Maybe not well known, another quirk of PN diodes: when forward biased briefly (forward-bias pulse widths t_p comparable to t_rr, say), charge storage in the junction is nonuniform, and this is reflected in turn by the high transient Vf (forward recovery), and the shorter, uneven, and potentiallyextremely sharp,recovery.QuoteWell, if you can get the plot beside him, perhaps you can always make it a buried junction.Or wait, I suppose that joke works better for his wife (er, if he was married--?).Tim

author: Terry Bites
author_rank: Super Contributor
timestamp: February 26, 2021, 05:25:21 pm
content: Shottkys are great in LV systems but as you go up in voltage losses from Vf become less of an issue. Shottkys can have awfull reverse leakage. On the other hand they are fast. Horses for courses.

author: TimFox
author_rank: Super Contributor
timestamp: February 26, 2021, 05:38:26 pm
content: Dr W H Schottky lived for 90 years and made great contributions to physics, vacuum-tube electronics, and his now well-known eponymous diode. Seehttps://en.wikipedia.org/wiki/Walter_H._SchottkyA few examples:1. The derivation of "image charge" interaction between a point charge and a conductive surface.2. Invention of the ribbon microphone.3. Early development of the superheterodyne receiver, independent of Armstrong's work.4. Invention of the tetrode vacuum tube (also independent of several others).

author: harerod
author_rank: Frequent Contributor
timestamp: February 26, 2021, 07:59:28 pm
content: Quote from: T3sl4co1l onTodayat 06:21:03 pm>Quote from: harerod onTodayat 05:52:20 pm. . .QuoteWell, if you can get the plot beside him, perhaps you can always make it a buried junction.Or wait, I suppose that joke works better for his wife (er, if he was married--?).Tim. . .I have no intention of buying a farm anytime soon.And yes, it is a family site.