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Aluminum Polymer

Polymers differ between manufacturers. The Panasonics look great. I deliberately abused a bunch of them (over voltage, reverse voltage, alternate +-) and they were fine. No failures in production gear so far.

Their leakage curve is such that series stacks are self-equalizing.

56uF, 25V Panasonics, run at -10V for a month or so:

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I tested them up to +116 volts, the limit of my old HP bench supply, with no failures.

Measured ESR was nice and low, just right for the output of a switcher.

For low voltage switchers, 3.3 or less, hi-k ceramics work fine. But they lose C fast as voltage goes up, so polymers can take over.

Tantalums can explode from excess peak current (C * dV/dT) so are dangerous across supply rails, unless greatly voltage derated.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin
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Reply to
Lasse Langwadt Christensen

Electrical failure of ceramic caps is essentially nonexistent. When speaking of ceramic failure, that's precisely what anyone else means: mechanical damage.

Some products don't sit in quiet, stable racks all their lives...

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: https://www.seventransistorlabs.com/
Reply to
Tim Williams

MLC ceramics have tiny sandwich-layer features, and manufactured-in flaws DO short them, not infrequently. By the time you see the failed unit, there's so much secondary damage that you might think that damage to be the cause (even when it isn't).

Reply to
whit3rd

Oh, no, it's certainly not extremely rare for MLCC caps to short. It's the normal failure mode when the board flexes under them. It's particularly bad for larger caps (1206, 1210, and above). We're required to use series caps, mounted at right angles to each other, when the source isn't current limited (enough to prevent smoke).

Reply to
krw

Well, we don't see them. We'd usually miss an open or a wrong value, being that most of our caps are bypasses.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

Bypass caps are the largest problem, particularly those on the power inputs. Coupling caps into power amplifiers are the other real problem (DC offsets are bad).

Your operating environment is pretty benign, obviously. It is a serious problem with ceramic caps, enough so that specialty caps with "soft (flexible) termination" are made to mitigate the problem. They're quite expensive, though.

Reply to
krw

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