On 23 Sep 2015 11:06:49 GMT, joe hey wrote:

On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote:

On 9/23/2015 12:20 AM, joe hey wrote:
On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote:

On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann
wrote:

On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin
wrote:

Dry-slug tantalums across power rails are bad news. High dV/dT
literally ignites them; MnO2 is the oxidizer and tantalum is the
fuel.

That's what I've read everywhere. Yet, I spent 10 years shipping
marine radios that were literally crammed with dipped and molded
tantalum caps on power supply rails with never a problem. The only
ones I've ever seen go up in smoke were reverse polarized (which
produced an impressive red glowing piece of slag and plenty of white
smog). Mostly, these caps were 25V caps on the 12V (nominal) power
supply lines and 16V caps on the 8 and 10V regulated lines. There
were also a bunch used in audio circuits.

The tantalum thing is very erratic. Some batches blow up, some are
fine.



However, we never used tantalums on the output of a switcher, where I
would expect problems. I guess using a tantalum in this 3.3V
switcher would qualify. However, at the time (1970's) the literature
declared that high voltage spikes were the culprit, not voltage slew
rate. Since these often appear together, I can see where there might
be some confusion.

I know for sure that tantalums sometimes blow up at below their rated
voltages, with no overshoot spikes. It's dV/dT, namely peak current,
that can ignite tiny particles of tantalum, which then burn in the
solid MnO2 electrolyte.


That's why in those cases a series resistor might be recommended in
order to limit the current spikes.

Add series resistance to a tantalum cap and you have just created an
electrolytic replacement.

Sorry, I forgot to mention to put the resistance in between the power
line and the tantalum.


But than it doesn't bypass the power rail!