What is the Destructive Failure Voltage of a  40-V Schottky 1A Diode? - Page 1
Forum section: electronics / projects

author: SuzyC
author_rank: Frequent Contributor
timestamp: April 17, 2023, 02:40:02 pm
content: Spec Question:Attached are the Specsheet and a specific graph of aSB-140 Schottky barrier diode. The graph shows capacitancetests at 100V, yet thediode has a Peak Reverse Voltage rating of 40V.This leads me to believe that I can get away(at least at room temps) with using this diode in alow-current gate drivebootsrap circuit for a power N MOSFET in a Buck Converter that would expose this diode to ~45V peaks when the MOSFET is being switched on/off.There isno absolute max breakdown voltage shown in the attached data sheet.Can I use this diode in my circuitwith switching transients of reverse volts > ~45V ?

author: RoGeorge
author_rank: Super Contributor
timestamp: April 17, 2023, 02:53:58 pm
content: From the datasheet,https://www.vishay.com/docs/88715/sb110.pdf, 40V is the "Maximum repetitive peak reverse voltage, VRRM" which means the diode is not guaranteed to withstand repeatedly at more than 40V reverse. At 40V it will last "forever", if used in the conditions specified in the datasheet.However, the diode won't suddenly break at 41V. Might withstand at higher voltages, just that the behavior and lifespan of the diode is not guaranteed when working at more than 40V reverse voltage.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 17, 2023, 02:58:04 pm
content: Vishay datasheet of equivalent part,https://www.vishay.com/docs/88715/sb110.pdf,Fig. 5, only shows up to rated voltage. I don't know why and how Diodes Inc have characterized the capacitance over the rated reverse voltage.QuoteWhat do you mean? Page 2, maximum ratings, first item. 40V. What difference would you expect with wording "breakdown voltage" instead of "peak reverse voltage"?QuoteNo.Maximum peak reversemeans exactly that. Besides, if you are scoping 45V on a switcher, there will be larger spikes you miss due to limited scope BW or just operating conditions not being worst case when you test (things like output current, duty cycle, temperature, unit-to-unit variations of parts, manufacturing tolerances in parasitics - everything has an effect). As a rough rule of thumb, add at least 20%.

author: SuzyC
author_rank: Frequent Contributor
timestamp: April 17, 2023, 03:01:49 pm
content: Thanks, but quite obvious the 1-A 40V rectifier use specifies safe use at 40V, with high forward surge currents, yet the capacitance graph shows a 100V test.There is a maximum voltage clearly shown, butno ABSOLUTE Max V.Seems to me that the graph shows there must be some short-circuiting bricking voltage >100V. some value of voltage high enough to cause punch-through and certain destruction that is at least >100V?What is that voltage?For a BJT, the absolute max voltage exceeded causes secondary breakdown C-E short circuit. But a barrier diode is not a BJT.Who knows from experience at what voltage does a certain failure or degradation of a barrier Schottky is?

author: Siwastaja
author_rank: Super Contributor
timestamp: April 17, 2023, 03:04:55 pm
content: Don't overthink it - datasheets are full of weird stuff like that. Possibilities run from Diodes Inc. just drawing random curves out of their asses, to them characterizing the parts at two-three points within the voltage rating and inter/extrapolating the curves from those (and forgetting to clip out the excess), to the parts actually not breaking down at the test voltages.Destruction when absolute maximum ratings are exceeded is still very likely, just don't do it.

author: SuzyC
author_rank: Frequent Contributor
timestamp: April 17, 2023, 03:25:04 pm
content: Vishay clearly also show test at 100% of rated voltage.At room temp, very little leakage!Is this diode at all stressed at its 40V rating? That so, what's the chance of smoke at 50V?Thanks Siwastaja,prudent advice. Operating this diode out of spec is not good design practice and not for critical life-support circuitry!My question is, what is known about real-life voltage breakdown characteristics of Schottky barrier diodes versus specs?I know from experience with other specs likepower MOSFET Gate-Drain Absolute Max Vratings that to exceed this breakdown voltage by several volts ~20% is deadly.

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 17, 2023, 04:58:38 pm
content: Quote from: SuzyC on April 17, 2023, 03:25:04 pmNothing is for sure, you’d have to test for each manufacturer/part #. And this is one of the beauties of electronics, Chatpgt also won’t know about it!But who cares, just don’t exceed that value.