"John Larkin" wrote in
message ...
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
wrote:


snip

Wet-slug tants are expensive (do they still have silver cases?) but
don't blow up like the dry ones. The dry slugs coat the sintered
tantalum (fuel) with MnO2 (oxidizer).

Boy are they ever. I have some surplus ones, but they have cases that are
more of a silver-gray than that nice yellowish-white look you get from
silver-plated connectors. These are special parts, but if you want a
generally high-performance cap in a (relatively) small package they're hard
to beat.

I worked for a while on a project to make a power-wire networking device.
During testing I accidentally dragged a scope ground across a circuit that
was referenced to the 115V power line, thereby exceeding the tantalum cap's
voltage rating -- er -- "slightly". Little pieces of flaming capacitors
bounced around the lab. After that all of my digital logic (3.3V and lower)
coworkers _never_ messed with my bench.

The problems with tantalum are their fragility (we've had exploding caps
on
our boards, with one manufacturer's part being fine and another being
horrid), cost, and the relative scarcity of tantalum.

This is really erratic. One spool of tants will be bombs, another
can't be made to fail by deliberate abuse.

Interesting. I'll have to remember that. Thanks. In any case when
designing with _any_ electrolytic capacitor it's best to use specify a cap
for 20-50% higher voltage than what you think it's ever going to see,
particularly because many voltage regulators overshoot on power up and the
output cap sees more voltage than you think.

John