On Wed, 23 Sep 2015 12:47:56 -0400, krw wrote:

On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the problem
was solved. I clearly remember reading this advice in some tantalum's
datasheet or application note. As those IC's consume very little, the DC
voltage drop over the resistance was negligible, but the reduction in
current spikes through the tantalums was considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the "ESR"
of the cap(-resistor). You might just as well use an aluminum cap in
its place if ESR doesn't matter.


Look at it like this (you might switch to fixed width font).
____
+ ---|____|-----------------
small |
R |tant
---
--- -- to IC Vcc/GND
|
|
- --------------------------

It's a filter now.
Still the same (or even better) ripple suppression.
(Almost) no lowering in supply voltage for the IC.
Tantalum as near as possible to the IC in order to take account of the EMC
induced voltages also, which are caused by the HF high current switching.

joe

On Wed, 23 Sep 2015 18:35:02 +0100, John Devereux wrote:

krw writes:

On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the
problem was solved. I clearly remember reading this advice in some
tantalum's datasheet or application note. As those IC's consume very
little, the DC voltage drop over the resistance was negligible, but the
reduction in current spikes through the tantalums was considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the "ESR"
of the cap(-resistor). You might just as well use an aluminum cap in
its place if ESR doesn't matter.

No there is still a low-ESR decoupling for the IC. I do that a lot since
it isolates the IC rail from spikes on the main power rail. (Not with
tants though).

Right.
It was (at that time) even recommended.

joe

On Wed, 23 Sep 2015 14:11:36 -0400, rickman wrote:

On 9/23/2015 12:47 PM, krw wrote:
On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the
problem was solved. I clearly remember reading this advice in some
tantalum's datasheet or application note. As those IC's consume very
little, the DC voltage drop over the resistance was negligible, but
the reduction in current spikes through the tantalums was
considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the "ESR"
of the cap(-resistor). You might just as well use an aluminum cap in
its place if ESR doesn't matter.

He is talking about this...

Vcc ---/\/\/\---+-------+
| |
IC =
| |
--- ---
- -
Not this...

Vcc ----+----/\/\/\-----+
| |
IC =
| |
--- ---
- -

Correct.

joe

On Wed, 23 Sep 2015 11:58:43 -0700, Jeff Liebermann wrote:

On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin

}snip{

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.

I think you mean dI/dT which provides the heating necessary to ignite
the tantalum. That all sounds logical, but doesn't explain why a
similar amount of heating caused by normal ripple current doesn't set
fire to the capacitor. I've seen some heat darkened tantalums operating
normally without ignition. Like the bulging electrolytics and burning
LiIon batteries, I suspect there's been some changes in production
methods (like skipping important steps to save pennies).

Are you sure? I understood that the I=C.dV/dt was responsible for the
damage. The higher dV/dt, the higher I. And the longer the dV/dt
continues, the hotter the C gets.

}snip{

joe

On Wed, 23 Sep 2015 11:16:35 -0700, Jeff Liebermann wrote:

On 23 Sep 2015 04:18:36 GMT, joe hey wrote:

Tantalums have such a low HF resistance that it is sometimes recommended
to put a current limiting resistor in series if there is a serious
ripple voltage around.

Really?

Yes

}sorry for snipping, but I hate scrolling a lot{

Your "current limiting resistor" sounds like something that would raise
the ESR of the device by the resistor value. Much depends on the ripple
current, which presumably in a switching power supply filter cap, is
quite high.

If you read the post carefully, you'd see that between power supply and C
there is a small R, which gives a tiny reduction of voltage to the IC,
and then there is the C // Vcc-GND. So the IC sees the same (or even
smaller) ripple from the power supply, EMC suppression is still the same
(or even better due to more damping of the ringing) and everything went
fine from then on.

When playing with ESR's of less than 1 ohm, minor variables such as PCB
plating thickness and trace width/length become significant. When the
lowest ESR is at the series self resonant frequency of the capacitor,
the selection of type, value, voltage, package, etc also become
important.

Yes. And all those factors are uncertain to a high degree.
Therefore it could be advisable to just add a resistor of a known value,
if your design permits it.

Much of the RF circuitry involved in a radio requires
broadband bypassing. That rapidly becomes an exercise in capacitor
selection based on series resonant frequencies and lowest overall ESR.
It was not unusual to have 3 different bypass caps in parallel at key
locations, such as the corners of PCB's to chassis ground points.
Adding a series resistor to the tantalum cap would not have worked for
obtaining the lowest possible ESR.

Indeed, not in that case. But where we had the problem, it worked well.

I've witnessed a lot of IGBT's being blown up because those resistors
were failing. The voltage feeding the tantalums had such a large HF
ripple due to the switching of the IGBT's that it blew the tantalums out
of the control board, after which the IGBT's also went to pieces.

Indeed.

Did the ripple voltage on the power supply line increase with the added
series resistance?

After finding out the problem, we (finally) read up to the specs and
recommendations, found the suggestion to add small R's, did it, and the
problem was gone. We did not measure ripple voltage. I guess that would
have been useless because the problem was caused by EMC, and the
measuring probe would probably have suffered the same problem and not
given the right picture.

joe

On Wed, 23 Sep 2015 18:35:02 +0100, John Devereux
wrote:

krw writes:

On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the problem
was solved. I clearly remember reading this advice in some tantalum's
datasheet or application note. As those IC's consume very little, the DC
voltage drop over the resistance was negligible, but the reduction in
current spikes through the tantalums was considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the
"ESR" of the cap(-resistor). You might just as well use an aluminum
cap in its place if ESR doesn't matter.

No there is still a low-ESR decoupling for the IC. I do that a lot since
it isolates the IC rail from spikes on the main power rail. (Not with
tants though).


No, the point is that there is no reason to use a tantalum cap if
you're going to blow its ESR with a resistor. Just use an aluminum.

On 23 Sep 2015 23:14:46 GMT, joe hey wrote:

On Wed, 23 Sep 2015 14:11:36 -0400, rickman wrote:

On 9/23/2015 12:47 PM, krw wrote:
On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the
problem was solved. I clearly remember reading this advice in some
tantalum's datasheet or application note. As those IC's consume very
little, the DC voltage drop over the resistance was negligible, but
the reduction in current spikes through the tantalums was
considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the "ESR"
of the cap(-resistor). You might just as well use an aluminum cap in
its place if ESR doesn't matter.

He is talking about this...

Vcc ---/\/\/\---+-------+
| |
IC =
| |
--- ---
- -
Not this...

Vcc ----+----/\/\/\-----+
| |
IC =
| |
--- ---
- -

Correct.

Nevermind!

I sit corrected. ;-)

"krw" wrote in message
No, the point is that there is no reason to use a tantalum cap if
you're going to blow its ESR with a resistor. Just use an aluminum.

I was thinking one reason to use the tantalum was because it could pack more
capacitance in a smaller space.

On Wed, 23 Sep 2015 22:17:58 +0100 piglet wrote
in Message id: :

On 23/09/2015 21:56, John Larkin wrote:
On Wed, 23 Sep 2015 21:34:38 +0100, piglet
wrote:

On 23/09/2015 15:24, John Larkin wrote:
Most tantalum caps are solids, with the MnO2 electrolyte. Less common
are liquid types and polymers.


There is even solid aluminum, now only made by Vishay (I think) and cost
more than equivalent tantalum. The ones I use are resin dipped through
hole parts and look like a big resin dipped tantalum bead. Nice caps,
very low ESR and supposedly very reliable, claim "no-known wear-out
mechanism".

piglet

Do you mean polymer aluminums? Those are great, super low ESR. We use
United Chem-Com and Nichicon. 47 cents for 180 uF 6.3 volts, about 2x
tha price of a regular aluminum cap.



No, I don't think these are polymer, may even predate polymer
electrolyte. Uses Mn02 I think like solid Ta. See Vishay SAL 122 series.
Temp range -55 to +175 C.

piglet

Couldn't find anything on them. Do you mean SAL 128?
http://www.vishay.com/docs/28354/128salrpm.pdf
End of Life. Last Available Purchase Date is 30-December-2015

Must be too reliable.

On 24/09/2015 14:46, JW wrote:
On Wed, 23 Sep 2015 22:17:58 +0100 piglet wrote
in Message id: :

On 23/09/2015 21:56, John Larkin wrote:
On Wed, 23 Sep 2015 21:34:38 +0100, piglet
wrote:

On 23/09/2015 15:24, John Larkin wrote:
Most tantalum caps are solids, with the MnO2 electrolyte. Less common
are liquid types and polymers.


There is even solid aluminum, now only made by Vishay (I think) and cost
more than equivalent tantalum. The ones I use are resin dipped through
hole parts and look like a big resin dipped tantalum bead. Nice caps,
very low ESR and supposedly very reliable, claim "no-known wear-out
mechanism".

piglet

Do you mean polymer aluminums? Those are great, super low ESR. We use
United Chem-Com and Nichicon. 47 cents for 180 uF 6.3 volts, about 2x
tha price of a regular aluminum cap.



No, I don't think these are polymer, may even predate polymer
electrolyte. Uses Mn02 I think like solid Ta. See Vishay SAL 122 series.
Temp range -55 to +175 C.

piglet

Couldn't find anything on them. Do you mean SAL 128?
http://www.vishay.com/docs/28354/128salrpm.pdf
End of Life. Last Available Purchase Date is 30-December-2015

Must be too reliable.


Yes SAL128 are miniature, just a bit smaller than the 122 range. Shame
about the EOL - they are great parts and should have been much more
popular. The axial part (SAL123) is rated from -80 to +200 deg C.

Polymer can't match that temp range (yet).

piglet

On Thu, 24 Sep 2015 15:15:22 +0100, piglet
wrote:

On 24/09/2015 14:46, JW wrote:
On Wed, 23 Sep 2015 22:17:58 +0100 piglet wrote
in Message id: :

On 23/09/2015 21:56, John Larkin wrote:
On Wed, 23 Sep 2015 21:34:38 +0100, piglet
wrote:

On 23/09/2015 15:24, John Larkin wrote:
Most tantalum caps are solids, with the MnO2 electrolyte. Less common
are liquid types and polymers.


There is even solid aluminum, now only made by Vishay (I think) and cost
more than equivalent tantalum. The ones I use are resin dipped through
hole parts and look like a big resin dipped tantalum bead. Nice caps,
very low ESR and supposedly very reliable, claim "no-known wear-out
mechanism".

piglet

Do you mean polymer aluminums? Those are great, super low ESR. We use
United Chem-Com and Nichicon. 47 cents for 180 uF 6.3 volts, about 2x
tha price of a regular aluminum cap.



No, I don't think these are polymer, may even predate polymer
electrolyte. Uses Mn02 I think like solid Ta. See Vishay SAL 122 series.
Temp range -55 to +175 C.

piglet

Couldn't find anything on them. Do you mean SAL 128?
http://www.vishay.com/docs/28354/128salrpm.pdf
End of Life. Last Available Purchase Date is 30-December-2015

Must be too reliable.


Yes SAL128 are miniature, just a bit smaller than the 122 range. Shame
about the EOL - they are great parts and should have been much more
popular. The axial part (SAL123) is rated from -80 to +200 deg C.

Polymer can't match that temp range (yet).

piglet

Polymers are great cold, below 0C when wet aluminums freeze and ESR
skyrockets. I suppose the polymers melt at high temp.

The UCC parts are rated for -55 to 105C.

https://dl.dropboxusercontent.com/u/...olymer_ESR.JPG

On 24/09/2015 10:26, krw wrote:
On Wed, 23 Sep 2015 18:35:02 +0100, John Devereux
wrote:

krw writes:

On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the problem
was solved. I clearly remember reading this advice in some tantalum's
datasheet or application note. As those IC's consume very little, the DC
voltage drop over the resistance was negligible, but the reduction in
current spikes through the tantalums was considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the
"ESR" of the cap(-resistor). You might just as well use an aluminum
cap in its place if ESR doesn't matter.

No there is still a low-ESR decoupling for the IC. I do that a lot since
it isolates the IC rail from spikes on the main power rail. (Not with
tants though).


No, the point is that there is no reason to use a tantalum cap if
you're going to blow its ESR with a resistor. Just use an aluminum.


I suspect you need to see a diagram of the circuit because you are
thinking of a resistor directly in series with the capacitor whereas Joe
and John were thinking of placing the capacitor directly across the load
(chip) and a resistor between the regulator and the supply pin of the
load (chip), (with its capacitor).

The ESR would be high if measured from the location of the regulator,
because there would be a resistor between the regulator and the
capacitor. The ESR would appear low if measured from the location of the
chip which is the load (chip), because the capacitor is directly in
parallel with the load (chip). The disadvantage of this arrangement is
that the average (DC) load current flows through the resistor which
might cause an annoying reduction in the supply voltage at the load.

On 24/09/2015 10:26, krw wrote:
On Wed, 23 Sep 2015 18:35:02 +0100, John Devereux
wrote:

krw writes:

On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

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!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the problem
was solved. I clearly remember reading this advice in some tantalum's
datasheet or application note. As those IC's consume very little, the DC
voltage drop over the resistance was negligible, but the reduction in
current spikes through the tantalums was considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the
"ESR" of the cap(-resistor). You might just as well use an aluminum
cap in its place if ESR doesn't matter.

No there is still a low-ESR decoupling for the IC. I do that a lot since
it isolates the IC rail from spikes on the main power rail. (Not with
tants though).


No, the point is that there is no reason to use a tantalum cap if
you're going to blow its ESR with a resistor. Just use an aluminum.



Nevermind, others have already said what I tried to say.

bitrex wrote:

So I'm working on repairing a Korg MS2000B synthesizer for a friend with
a dead power supply. Here's the service manual:

http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf

The first thing I notice when looking inside is that the small SMT 100uF
10V tantalum capacitor C109 has completely vacated - it appears to be
gone, blown right off the board. There are some little fragments
rattling around in the case.

I have little experience with tantalum capacitors. Any suggestions for
a more reliable replacement?
One other option is Niobium Oxide caps, sold under the brand oxi-caps.
Digi-Key has them. I have used several thousand of them on some gear that
some users run in hard vacuum, so aluminum electrolytics were out of the
question. I have mis-connected a few of the oxi-caps, and can verify they
will char a bit, but not burst into flame.

Jon

"bitrex" wrote in message
...
So I'm working on repairing a Korg MS2000B synthesizer for a friend with a
dead power supply. Here's the service manual:

http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf

The first thing I notice when looking inside is that the small SMT 100uF
10V tantalum capacitor C109 has completely vacated - it appears to be
gone, blown right off the board. There are some little fragments rattling
around in the case.

I have little experience with tantalum capacitors. Any suggestions for a
more reliable replacement?


You can get MLCC capacitors as big as 180uF - but it won't fit in the
original space.

They're mostly advertised as SMD, but that certainly won't fit - a few
suppliers offer resin dipped leaded versions that you could form the leads
to meet the pads.

Aluminium electrolytics of any kind are a no no! - there was much chatter
about organic semiconductor electrolytics a decade or so ago, that were
claimed to be as good as tantalum, but it lately seems to have gone very
quiet on that front.

Tantalum electrolytics are *VERY* intolerant of reverse voltage, even just a
little bit makes them go leaky. When the normal supply comes back - if it
can shift much current; the tantalum goes off like a match head!

On Wed, 30 Sep 2015 19:42:56 +0100, "Ian Field"
wrote:


"bitrex" wrote in message
. ..
So I'm working on repairing a Korg MS2000B synthesizer for a friend with a
dead power supply. Here's the service manual:

http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf

The first thing I notice when looking inside is that the small SMT 100uF
10V tantalum capacitor C109 has completely vacated - it appears to be
gone, blown right off the board. There are some little fragments rattling
around in the case.

I have little experience with tantalum capacitors. Any suggestions for a
more reliable replacement?


You can get MLCC capacitors as big as 180uF - but it won't fit in the
original space.

They're mostly advertised as SMD, but that certainly won't fit - a few
suppliers offer resin dipped leaded versions that you could form the leads
to meet the pads.

Aluminium electrolytics of any kind are a no no! - there was much chatter
about organic semiconductor electrolytics a decade or so ago, that were
claimed to be as good as tantalum, but it lately seems to have gone very
quiet on that front.

The polymer aluminums are really good. Low leakage, low ESR, don't dry
out.

"John Larkin" wrote in message
...
On Wed, 30 Sep 2015 19:42:56 +0100, "Ian Field"
wrote:


"bitrex" wrote in message
.. .
So I'm working on repairing a Korg MS2000B synthesizer for a friend with
a
dead power supply. Here's the service manual:

http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf

The first thing I notice when looking inside is that the small SMT 100uF
10V tantalum capacitor C109 has completely vacated - it appears to be
gone, blown right off the board. There are some little fragments
rattling
around in the case.

I have little experience with tantalum capacitors. Any suggestions for
a
more reliable replacement?


You can get MLCC capacitors as big as 180uF - but it won't fit in the
original space.

They're mostly advertised as SMD, but that certainly won't fit - a few
suppliers offer resin dipped leaded versions that you could form the leads
to meet the pads.

Aluminium electrolytics of any kind are a no no! - there was much chatter
about organic semiconductor electrolytics a decade or so ago, that were
claimed to be as good as tantalum, but it lately seems to have gone very
quiet on that front.

The polymer aluminums are really good. Low leakage, low ESR, don't dry
out.

Saw an article about those a while ago - did they ever take off?

The organic semiconductor variety were supposed to be the "dog's nuts" - but
all the hoo ha seemed to mysteriously fade away.

John Larkin wrote:

The polymer aluminums are really good. Low leakage, low ESR, don't dry
out.

Do they exist in the upper mF range (4700+uF) for, say, 35V?

Best regards, Piotr

On Sat, 3 Oct 2015 21:31:00 +0200, Piotr Wyderski
wrote:

John Larkin wrote:

The polymer aluminums are really good. Low leakage, low ESR, don't dry
out.

Do they exist in the upper mF range (4700+uF) for, say, 35V?

Best regards, Piotr

Check the distribs, but I think not. The CV products seem low, like
4700 at 2.5v. Don't know why.

On 10/03/2015 04:02 PM, John Larkin wrote:
On Sat, 3 Oct 2015 21:31:00 +0200, Piotr Wyderski
wrote:

John Larkin wrote:

The polymer aluminums are really good. Low leakage, low ESR, don't dry
out.

Do they exist in the upper mF range (4700+uF) for, say, 35V?

Best regards, Piotr

Check the distribs, but I think not. The CV products seem low, like
4700 at 2.5v. Don't know why.

Well, in LV SMPSes you really really care about ESR.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

John Larkin wrote:


Al polys can make voltage regulators oscillate. Tantalums have a nice
middle-of-the-road ESR that makes 7800s happy.

My favorite cheap "MDO" regulator, the LM1117, loves a 10 uF tantalum
on its output.
I've had excellent results using two 22uF aluminum electrolytics, one on the
input, one on the output, of ZLDO1117 regulators. I've built several
hundred devices with that setup, to produce 1.2 to 3.3 V supplies for FPGAs.

Jon

rickman wrote:



Is it about clearing damage or just to show the added resistance
prevented the failure? I found the story a bit hard to follow.

I believe he set up the production line to ramp up the supply voltage with
current limiting on EVERY board as it comes out of the reflow oven.

Jon