'600V' Diode in a 3.3mm Square Package? - Page 1
Forum section: electronics / projects

author: ShaunAndFRED
author_rank: Contributor
timestamp: October 03, 2014, 06:59:46 am
content: So I'm a little confused, I'm looking for a zero reverse recovery diode for a bootstrap circuit which could see up to 600 Volts. If the creepage distance for 600 Volts is on the order of 7mm, why wouldn't this just arc under the part between the .5mm pad space or just around the tiny component?Specifically I'm looking at C3D1P7060Q at Digikeyhttp://www.digikey.com/product-detail/en/C3D1P7060Q/C3D1P7060QCT-ND/3586865Am I missing something here?

author: penfold
author_rank: Frequent Contributor
timestamp: October 03, 2014, 11:56:44 am
content: You might want to check your values of creepage. Its heavily dependent on pollution degree etc. Assuming (hoping) that you're not using the diode to protect somebody against electrical shock then you can be flexible on the exact values.You are right that the 600 V over a 0.5 mm pad separation is a touch over the dielectric breakdown for air at STP. Except, the exact clearance distances are different when you have the gap sandwiched between PCB substrate with solder mask and the component. And, 600 V will be the absolute maximum rating, so you'll be expecting to operate a bit below this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 04, 2014, 12:40:41 am
content: UL508 might be okayish up around there, for coated conductors (UL compliant solder mask). But that won't be true once soldered, not without underfill.Wouldn't be surprised if it's rated as such, but never intended to be used that high -- since, SiC diodes don't really get lower than 600V (there's no point, Si SJ/TrenchMOS schottky go up to 300V, which however isn't really enough for e.g. PFC applications).Tim

author: ovnr
author_rank: Frequent Contributor
timestamp: October 04, 2014, 02:14:14 am
content: Hah, that's kind of silly.So isthis- 3.3 kV rated diode in a SMB package (2.75mm clearance between pads).I imagine these things would work better if you potted the whole thing. I'd still not go feeding 3 kV into a tiny SMD package, though...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 04, 2014, 05:41:33 am
content: About the most expensive SMB I've ever seen... if I need that much voltage at high frequency, I'll gladly pay the cost of heating aone of these. Half the sticker price!Tim

author: wraper
author_rank: Unknown
timestamp: October 04, 2014, 12:14:18 pm
content: Quote from: AcHmed99 on October 04, 2014, 11:26:10 am15kV is not the voltage that will be present on them. Breakdown voltage is only a few volts.

author: coppice
author_rank: Super Contributor
timestamp: October 04, 2014, 12:18:57 pm
content: Quote from: AcHmed99 on October 04, 2014, 11:26:10 amDon't you think the massive arcing across the pins might spoil performance at 15kV?Dry air breaks down at about 3kV/mm. That should tell you something is wrong about how you are looking at that device.

author: ShaunAndFRED
author_rank: Contributor
timestamp: October 04, 2014, 09:33:14 pm
content: Quote from: penfold on October 03, 2014, 11:56:44 amYea, the whole system is galvaniclly isolated, and failure of this device would just pop the control electronics. Three of these diodes would be acting as a bootstrap for each of the high-side IGBTs of a 300-380 V thee phase VFD.Quote from: T3sl4co1l on October 04, 2014, 12:40:41 amWhoa, this underfill stuff is crazy. I just read the datasheet on Loctite 3593, with a breakdown of 29 kv/mm, and self wicking under the component this may be the way to go. Could be interesting to flow under some of the BGA packages on the board as well. Cool stuff, another vial for the solder fridge.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 04, 2014, 09:40:37 pm
content: Beware of monolithic gate drivers in that voltage range. You have to control ground bounce extremely tightly to use them safely. Personally, my cutoff is around 400VDC: anything above (say 380VAC+ applications) gets fully isolated drivers. You have some leeway if the current is low, but over a few kW, you're back to trouble.Tim

author: ShaunAndFRED
author_rank: Contributor
timestamp: October 04, 2014, 10:08:28 pm
content: This is definitely an experiment to see how these little Fairchild SPM blocks stack up. It's going to be operating in the sub kilowatt regime, even below 300w on some channels so I'm not too stressed. I'll post up some scope traces when I start testing it.