The problem. as I understand it is two fold

- Tantalums fail catastrophically at a voltage slightly in excess of their
rated value.

    Energy of excess voltage spike is irrelevant

- Failure mode is a metallic short circuit

If your power bus never has voltage spikes in excess of the tantalum cap's
rating then fine.
Unfortunately, the world I live in usually can't guarantee this condition.
Mains has transients.
Car battery supplies  has transients.
External noise can induce transients in most anything else sometimes.

As a friend of mine used to say "Tantalum Caps - fastest fuse on two legs" -
really fastest crowbar on 2 legs.

As I have noted here before - with a little luck you can get noise, smell,
smoke, fire and explosion from a single tantalum failure. I have. Lots of
fun if its on the test bench. Worse if its inside some equipment.

I personally would never use a tantalum cap in a high energy circuit.
SOLID Aluminum electrolytic caps don't have this problem and are about as
good.
These are rarely seen but are available.
Philips have some.



      Russell McMahon
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-----Original Message-----
From: William Chops Westfield <billw@CISCO.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Friday, 28 April 2000 06:12
Subject: Re: [OT] From: Fire in the Hole - Tantalums


>    To re-iterate, for the sake of all those who do the same thing
>    as I too have done in the past:
>
>    "Reliability degrades when they are operated in low-impedance
>    circuits, and so they are not suitable for power supply
>    reservoir operations".
>
>    ref, p 83, "The Circuit Designer's Companion", Tim Williams,
>    1996, Newnes pub.
>
>Really?  I see them used this way constantly, even recomended (particular
>brands and values, usually) in SPS chip app notes, and advertised for this
>purpose (ie by ESR, IIRC.)  Are SOME tantalum caps specifically
(re)designed
>for such applications, or are some other specific types (perhaps no longer
>very common) the ones that are unsuitable there.
>
>(come to think of it, I don't know that I've ever seen tantalum caps widely
>used for anything BUT power bypass...)
>
>BillW
>