Timeline for Ceramic capacitors shorting on power up
Current License: CC BY-SA 4.0
33 events
| when toggle format | what | by | license | comment | |
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| Sep 15, 2021 at 3:00 | history | tweeted | twitter.com/StackElectronix/status/1437974634624864262 | ||
| Sep 14, 2021 at 9:23 | comment | added | Edin Fifić | @Jake I haven't seen any updates or responses from you to my inquiries. Can you please post a scope shot of voltage surges across those caps during normal operation, and let us know if you have tried my suggestions and what has worked for you? Thank you. | |
| Sep 12, 2021 at 11:07 | answer | added | Russell McMahon♦ | timeline score: 1 | |
| Sep 11, 2021 at 11:38 | comment | added | Edin Fifić | @RussellMcMahon Thank you. I understand. I find this site as a useful outlet for finding answers and explanations or solutions to some of my circuit problems. Often, while answering a question, I get more insight into the issue as well, so I basically help myself while helping others. In this question here, I can see multiple reasons and approaches to the problem and the ways of solving it, and I can barely wait to hear what was the real reason and what has worked. I feel like being in a room with technicians, engineers and scientists, all suggesting a solution until the problem is solved. | |
| Sep 11, 2021 at 11:30 | comment | added | Russell McMahon♦ | @EdinFifić ... || I assume the question you refer to was your MOSFET selection question - in my opinion it was quite likely to be useful to enough people for long enough to be worth leaving open BUT it was definitely against site rules. I had no part in closing it but understand the motives of those who did. | |
| Sep 11, 2021 at 11:29 | comment | added | Russell McMahon♦ | @EdinFifić I'm a moderator. I see all sorts of views and interpretations and try to accommodate as many as I reasonably can. Many of those who are active in voting to close are competent sight members and the majority probably have a genuine desire to keep the site close to what the rules suggest. I personally feel that the rules tend to be less permissive than I feel is useful BUT I don't set the rules and usually "go with the flow". ... | |
| Sep 11, 2021 at 11:15 | comment | added | Edin Fifić | @RussellMcMahon It seems to me that some people have nothing better to do, and want to feel useful and powerful at the same time, voting to close a post just because they can, not because there is a good reason for it. This question here is thought-provocative and helps get an insight into unexpected circuit problems. My question was closed as well, reasons that were cited were not to be found in my post, such as "promoting specific product, manufacturer or distributor"; it was as generic as it could get. | |
| Sep 11, 2021 at 11:08 | comment | added | Russell McMahon♦ | *** CLOSE VOTERS *** - would you please tell me WHY you voted to close. Everyone is entitled to their opinion but itwould be useful to know what people found wrong here. | |
| Sep 10, 2021 at 14:21 | comment | added | marcelm | That spike at powerup look suspect; there's clearly significant ringing. You need to inspect it at a much smaller timescale; currently you're at 100ms/div. Zoom in by a factor 10,000 or so. | |
| Sep 10, 2021 at 12:30 | comment | added | Edin Fifić | Can you include a scope capture of the voltage across those caps while the circuit is running (before changing the circuit)? | |
| Sep 10, 2021 at 10:53 | history | edited | Jake | CC BY-SA 4.0 |
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| Sep 10, 2021 at 8:52 | history | edited | Jake | CC BY-SA 4.0 |
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| Sep 10, 2021 at 8:29 | comment | added | Russell McMahon♦ | Some ceramic capacitors will produce a substantial voltage spike far above the supplied voltage when hit with a sharp voltage transient. These spikes can destroy connected semiconductors so presumably also other caps when multiple parallel caps are used. IF this is the cause then turn in and maybe off management may help confirm this cause. Note that worst case inductor input is zero crossing point and Vinmax for caps. Large value of C206 suggests turn off spike more likely. | |
| Sep 10, 2021 at 8:24 | history | edited | SamGibson♦ | CC BY-SA 4.0 |
appended answer 586147 as supplemental
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| Sep 10, 2021 at 4:18 | comment | added | user57037 | Input voltage overshoot seems the most likely explanation. Check application note 88 (AN88). analog.com/media/en/technical-documentation/application-notes/… | |
| Sep 10, 2021 at 2:12 | answer | added | Edin Fifić | timeline score: 4 | |
| Sep 10, 2021 at 1:30 | answer | added | DrMoishe Pippik | timeline score: 0 | |
| Sep 9, 2021 at 16:51 | comment | added | qrk | Tagging on to @Neil_UK posit on resonance, I have found that circuits such as yours with the 12uH inductor and capacitors on the right side of the inductor will ring with current spikes. You can have ring voltages that may grossly exceed the voltage rating of your capacitors. My solution was to de-Q the inductor by placing a 10 ohm resistor across the inductor. | |
| Sep 9, 2021 at 13:04 | comment | added | Neil_UK | Those are huge values for ceramics, obviously very high K ceramic. I notice they're all different values, following the 'decouple all frequencies' philosophy that I find very dubious. I wonder if the LM25011 is drawing a current frequency that puts one of them into series resonance? They will all have different SRFs, and the large ones will go inductive, and a high Q resonance could kill them. With its 45 V abs max, the LM25011 may not blow as a result. You would need a 'scope to see, OR, put a 1 ohm resistor in series with each to reduce the Q as an experiment (not as a permanent fix) | |
| Sep 9, 2021 at 12:59 | comment | added | Simon Fitch | It strikes me that a discharged capacitor is supposed to be a dead short intially, that's what capacitance is. Could you please explain how your "shorts" differ from this natural behaviour? | |
| Sep 9, 2021 at 11:14 | history | edited | JRE | CC BY-SA 4.0 |
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| Sep 9, 2021 at 10:30 | comment | added | thisjt | Not sure what you mean by "short." Are the caps blowing up? I don't see any issues with your schematic that will mess up these capacitors, assuming of course that you are using nonpolarized caps. | |
| Sep 9, 2021 at 9:55 | comment | added | Dirk Bruere | Have you looked on a scope to see what the voltage waveform is like on power-up? Note that under EMI rules spikes on mains up to 4kV should be tolerated. | |
| Sep 9, 2021 at 9:10 | comment | added | Ferrybig | Do you have a scope capable of measuring the voltage on caps? It could be that during the inrush, the inductor gives big spike as the capacitors charge, higher then their maxium voltage | |
| Sep 9, 2021 at 9:00 | comment | added | Jake | Not that we now. The caps are placed beside the transformer, at least 10mm from pcb edge. There are other caps in the same area that never fails so it should not be pcb stress that causes this. | |
| Sep 9, 2021 at 8:42 | review | Close votes | |||
| Sep 15, 2021 at 3:02 | |||||
| Sep 9, 2021 at 8:36 | comment | added | Kartman | Have the capacitors been physically stressed? Too close to edge of the pcb? | |
| Sep 9, 2021 at 8:33 | comment | added | Jake | didnt find a good way to post schematic. added dropbox link to pdf | |
| Sep 9, 2021 at 8:32 | history | edited | Jake | CC BY-SA 4.0 |
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| Sep 9, 2021 at 8:23 | comment | added | Andy aka | And make your component IDs and names bigger. | |
| Sep 9, 2021 at 7:47 | comment | added | Neil_UK | What's the half component on the left of the picture? What's the AC voltage across pins 2/3 of D201? How does the 230 V mains get to C218? The attached png, while a lot better than nothing, is still mostly illegible at that scale, and incomplete. You're having trouble with mains switch-on killing C218? Show the entire path, legibly, from mains to C218. | |
| S Sep 9, 2021 at 7:41 | review | First questions | |||
| Sep 9, 2021 at 17:34 | |||||
| S Sep 9, 2021 at 7:41 | history | asked | Jake | CC BY-SA 4.0 |