Dan Michaels wrote:
>
> Robert Wuest wrote:
> ......
> >Tantalum caps are notorious for exploding due to inrush, or surge
> >current.  Some parts are tested for surge and may be purchased as such.
> >
> >The methodology of the test is to inject a high surge current into and
> >discharge the DUTs several cycles (usually 3).  Limit the "parts
> .....
> >If you buy leaded Kemet parts that are surge tested, they were run one
> >of several testers I designed and built.  Surface mount parts was some
> ....
>
> Ok, for the testing part, but what would you recommend as far as use
> of tantalums in practical circuits?

Most applications of Ta caps that I have seen are OK.  Most power supply
circuits cannot provide the high amp surges required for this to be a
really significant issue and most Ta caps don't blow up :)

> Use as P/S reservoir filters would seem to be a problem. Yes?

Same thing.  What kind of currents can the supply provide?  Some
applications may require protection for the caps.

> And in use as Vcc bypass caps, they'd still be right on the main
> power bus in general. Yes?
>
> Would you have to put a small series R in the power bus to the
> chips where they are used for bypassing?

If the power supply can provide mucho current, you should place some
sort of inrush current limiting (like an NTC device) in series.  On a
linear supply, put it before the regulator. Also, you can use a higher
voltage rated part because they can take more inrush.

Actually performance specs are hard to get, but 1 ohm source impedance
can blow parts.  So for a 5 Volt supply that provides 5 amps max (and
say a 6 volt cap), you're on thin ice.  2 ohms is safer.  Or use a 10
volt cap.

--
Robert Wuest, PE
Sirius Engineering Company