Am 12.04.20 um 05:22 schrieb Ben Bradley:
More recently, I saw this Kemet presentation on Digikey about tantalum capacitors. Certainly for aluminum electrolytic capacitors, the rated voltage is "the rated voltage" and as long as the capacitor never goes ABOVE that voltage (and has no overcurrent that would heat it up, etc.), the cap is good for its combination of temperature and lifetime rating. I (and as far as I know, everone I've known) assumed this was the same for tantalums, but it appears that's not the case (this presentation mentions several failure causes and shows how they are multiplicative). As you go from 1/2 rated voltage to full rated voltage, the chances of a tantalum failing goes up substantially. The implied rule seems to be for maximum reliability, don't operate a tantalum above HALF the rated voltage. I'd heard a lot of anecdotal things about tantalums suddenly shorting out for this or that reason, but hadn't heard of this, and here it is straight from the manufacturer. https://www.digikey.com/en/ptm/k/kemet/derating-guidelines-for-surface-mount-tantalum-capacitors/tutorial
For a space project, I was surprised that ESA required derating of tantalum working voltage only to 50%, where I was used to derate down to 1/3 as was proposed in a NEC data sheet from 30 years ago. But then, the only allowed Ta caps had 6 times the volume of commercial ones, so the first round of derating probably was already built-in. Those fat capacitors did really hurt, esp. when the proposed SEU mitigation of the regulators consisted of providing large enough load capacitance so that the regulators could go Berserk for a millisecond or two without blowing up the FPGA. cheers, Gerhard _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
