| Electronics > Projects, Designs, and Technical Stuff |
| "MLCCs ... do not require any voltage derating" |
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| thm_w:
--- Quote from: 741 on May 15, 2020, 11:22:49 am ---Here is TDK's paper https://product.tdk.com/en/contact/faq/20_mlcc_voltage_strength.pdf That seems useful information, I think 6.3V is therefore fine for 5V, and that makes some cost difference for 10uF units. --- End quote --- Interesting, can be quite useful. Specifically for a boost converter I was looking at, it had a short high voltage spike which dissipates quickly. I could never get any ceramic capacitors to fail on my ~60v power supply, now I know why, its not even close. |
| Someone:
--- Quote from: Siwastaja on May 15, 2020, 05:28:46 pm ---* Rated voltage at least your bus voltage, but no extra margin needed. You should include higher ratings, though! You may find a better deal by "derating" voltage, but contrary to common misbelief, this always isn't the case. --- End quote --- I've seen enough volume production to conclude that derating does improve product reliability/lifetime. The policies in place at large companies come to similar figures from their production histories. Voltage x2 is a good starting point for most capacitors, if lifespan is a concern. --- Quote from: T3sl4co1l on May 15, 2020, 06:54:53 pm ---You'll also often see families of parts, where it seems to be the absolutely identical component, just bearing different voltage ratings. Presumably you are paying a little premium for quality -- hopefully, they were tested to that voltage, but yeah as far as I know they may very well be utterly identical parts. No difference in C(V), obviously -- might as well get the cheaper (lower voltage) option that still suits the application (C at V and V rated >= V needed). --- End quote --- Many ceramic capacitors are guaranteed for a 2x/2.5x/3x voltage withstand, not sure if it is 100% tested but a single short constant current test would quickly bin them for capacitance and voltage rating. |
| Someone:
--- Quote from: thm_w on May 15, 2020, 10:21:21 pm ---I could never get any ceramic capacitors to fail on my ~60v power supply, now I know why, its not even close. --- End quote --- When they do fail it can be spectacular. Lots of energy in a tiny volume = explosion and/or flames. |
| T3sl4co1l:
AFAIK, ceramic failures are more commonly due to cracking, which can be poor soldering profile, improper handling, strong vibration, etc. One product (I work on from time to time), the customer has had consistent problems with a few large capacitors around the edge of the board; probably they're getting stressed during assembly? (Fortunately, they just announced a re-design campaign! I can get my hands all over this finally, instead of the small maintenance fixes I've done over the years.) It's often standard in automotive to use caps in series, so that your 12V, 30A+ circuit doesn't unload through a puny cracked capacitor. There are also types with floating electrode design (effectively two caps in series, in one part), longer terminations (so the crack propagating from the solder joint tends not to cross the electrode stack), and soft terminations (so the crack propagates through the metallization, avoiding the chip). --- Quote from: Someone on May 15, 2020, 11:17:03 pm --- --- Quote from: thm_w on May 15, 2020, 10:21:21 pm ---I could never get any ceramic capacitors to fail on my ~60v power supply, now I know why, its not even close. --- End quote --- When they do fail it can be spectacular. Lots of energy in a tiny volume = explosion and/or flames. --- End quote --- Yeah, the capacitor itself discharging can deliver enough energy to locally melt things, leaving a conductive path; even if not, a mere crack at the kinds of distances scales we're talking here (microns) can break down easily. And if you've got any kind of DC or AC power behind it, well... Tim |
| wraper:
--- Quote from: Someone on May 15, 2020, 11:17:03 pm --- --- Quote from: thm_w on May 15, 2020, 10:21:21 pm ---I could never get any ceramic capacitors to fail on my ~60v power supply, now I know why, its not even close. --- End quote --- When they do fail it can be spectacular. Lots of energy in a tiny volume = explosion and/or flames. --- End quote --- More like dead short and nothing spectacular happens. As it's dead short, not a lot of power to dissipate. And ceramic does not burn. If something will burn spectacularly due to this short, it will probably be something else. |
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