On 4/11/20 8:22 PM, Ben Bradley wrote: =
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
reading the data sheet and ap notes very carefully is important. A lot of times, the ratings are for a situation which actually doesn't occur in the application. That is, you have some current, which leads to some heating, which puts the internal temperature at some number other than 25C, at which the rating is specified.
When it comes to pulse capacitors with polypropylene dielectric, the ratings go as V^7.5 - that is, doubling the voltage reduces the life by a factor of 181.
tungsten filaments go as something like the 12th power. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
