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From: Phil Hobbs on 4 Jun 2010 09:47
Stupid title, but actual useful info on tantalum cap behaviour:

http://www.edn.com/article/509092-What_a_cap_astrophe_.php

Now that there's this existence proof, maybe there'll be a bit
more...perhaps someone will write them another useful article, e.g. a
compendium of all two-transistor circuits.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: John Larkin on 4 Jun 2010 10:04
On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs
<pcdhSpamMeSenseless(a)electrooptical.net> wrote:

>Stupid title, but actual useful info on tantalum cap behaviour:
>
>http://www.edn.com/article/509092-What_a_cap_astrophe_.php
>
>Now that there's this existence proof, maybe there'll be a bit
>more...perhaps someone will write them another useful article, e.g. a
>compendium of all two-transistor circuits.
>
>Cheers
>
>Phil Hobbs

Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer
and tantalum is a fuel, and only a tiny ignition source sets it off.
They are fine for current-limited applications but firebombs if used
to bypass power rails. Derate them 3:1 on voltage if you must use them
as power bypasses. Better yet use aluminums, polymer aluminums for
wide-temperature appls

John

From: Phil Hobbs on 4 Jun 2010 11:24
On 6/4/2010 10:04 AM, John Larkin wrote:
> On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs
> <pcdhSpamMeSenseless(a)electrooptical.net> wrote:
>
>> Stupid title, but actual useful info on tantalum cap behaviour:
>>
>> http://www.edn.com/article/509092-What_a_cap_astrophe_.php
>>
>> Now that there's this existence proof, maybe there'll be a bit
>> more...perhaps someone will write them another useful article, e.g. a
>> compendium of all two-transistor circuits.
>>
>> Cheers
>>
>> Phil Hobbs
>
> Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer
> and tantalum is a fuel, and only a tiny ignition source sets it off.
> They are fine for current-limited applications but firebombs if used
> to bypass power rails. Derate them 3:1 on voltage if you must use them
> as power bypasses. Better yet use aluminums, polymer aluminums for
> wide-temperature appls
>
> John
>

The interesting thing in the article is that soldering makes large tants
vulnerable to overvoltage failure well below their rating, and that they
can be reconditioned (and made much more reliable) by putting a current
limit on the power supply. That's more useful for repairs or fixing
problems with a shipping product than for new designs, admittedly.
Still, I thought it was kind of cool, and remarkable for being in EDN!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: John Larkin on 4 Jun 2010 11:45
On Fri, 04 Jun 2010 11:24:46 -0400, Phil Hobbs
<pcdhSpamMeSenseless(a)electrooptical.net> wrote:

>On 6/4/2010 10:04 AM, John Larkin wrote:
>> On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote:
>>
>>> Stupid title, but actual useful info on tantalum cap behaviour:
>>>
>>> http://www.edn.com/article/509092-What_a_cap_astrophe_.php
>>>
>>> Now that there's this existence proof, maybe there'll be a bit
>>> more...perhaps someone will write them another useful article, e.g. a
>>> compendium of all two-transistor circuits.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer
>> and tantalum is a fuel, and only a tiny ignition source sets it off.
>> They are fine for current-limited applications but firebombs if used
>> to bypass power rails. Derate them 3:1 on voltage if you must use them
>> as power bypasses. Better yet use aluminums, polymer aluminums for
>> wide-temperature appls
>>
>> John
>>
>
>The interesting thing in the article is that soldering makes large tants
>vulnerable to overvoltage failure well below their rating, and that they
>can be reconditioned (and made much more reliable) by putting a current
>limit on the power supply. That's more useful for repairs or fixing
>problems with a shipping product than for new designs, admittedly.
>Still, I thought it was kind of cool, and remarkable for being in EDN!
>
>Cheers
>
>Phil Hobbs

Serious non-commercial technical content is a good thing for EDN to do
now and then!

But tantalums are incredibly erratic, which is why different people
form different theories about their failure mechanisms. My worst
experience was with thru-hole gumdrops, hand soldered, which hadn't
been exposed to much heat. I think I still have a few thousand around
in a box somewhere.

I sometimes use tantalums as switching or linear reg output filters,
because the ESRs are often right and aluminums don't work cold. But I
try to limit dV/dT and derate about 3:1 on voltage.

The manufacturers mostly try to hide the failure mechanisms. One tant
maker recommends that they *always* be voltage derated 2:1. So why do
they call it a 25 volt cap is it's only safe to use at 12.5? Grrrrr.

ftp://jjlarkin.lmi.net/P14_reg.gif

C1 is a tantalum, and C40 limits its dV/dT.

I *have* exploded tantalums on the outputs of LM1117s.

John

From: Jim Yanik on 4 Jun 2010 11:59
Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote in
news:4C091ABE.3090007(a)electrooptical.net:

> On 6/4/2010 10:04 AM, John Larkin wrote:
>> On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote:
>>
>>> Stupid title, but actual useful info on tantalum cap behaviour:
>>>
>>> http://www.edn.com/article/509092-What_a_cap_astrophe_.php
>>>
>>> Now that there's this existence proof, maybe there'll be a bit
>>> more...perhaps someone will write them another useful article, e.g. a
>>> compendium of all two-transistor circuits.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer
>> and tantalum is a fuel, and only a tiny ignition source sets it off.
>> They are fine for current-limited applications but firebombs if used
>> to bypass power rails. Derate them 3:1 on voltage if you must use them
>> as power bypasses. Better yet use aluminums, polymer aluminums for
>> wide-temperature appls
>>
>> John
>>
>
> The interesting thing in the article is that soldering makes large tants
> vulnerable to overvoltage failure well below their rating, and that they
> can be reconditioned (and made much more reliable) by putting a current
> limit on the power supply. That's more useful for repairs or fixing
> problems with a shipping product than for new designs, admittedly.
> Still, I thought it was kind of cool, and remarkable for being in EDN!
>
> Cheers
>
> Phil Hobbs
>

TEKTRONIX used tantalums for many years in their scopes,and the failures
were not objectionably high. Usage was mostly on power rails,BTW.

--
Jim Yanik
jyanik
at
localnet
dot com
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