Re: Low ESR Tantalum Failure due to Power On- Design Fix?


Eeyore wrote:
Mateo EE wrote:

I am having problems with the caps failing and shorting input power. I
have found a lot of pages on Tantalum Capacitor failures, but very
little satisfactory fixes.

Here is set up: I have an 18.5 volt (7.2 amp) linear regulated power
supply. It is connected to a DC to DC power supply board with a number
of linear and switching power supplies. This power supply board is
connected to another electronic board. The overall electronics draw
about .5 amps at 18.5 volts. The caps that fail are on the input of the
DC to DC power supply board. I am using 47 uF 35 volt Tantalum Low ESR
capacitors. Actually, I have three of these caps in parallel and two
more in parallel individually shielded by a ferrite bead. All fail
over time.

How is the problem occurring?

It's usually dV/dt creating a high I. I've seen the problem, albeit less so,
with ceramic MLCs and even mylar types used for decoupling. Heavily derating the
rated voltage seems to work empiricially

Graham

Graham,

I will look into using various other caps to see if they would work in
this situation.

I would agree that a larger rating on the cap would help solve issues
with over-voltage spikes. But one source (see
http://www.kyocera.co.jp/prdct/electro/pdf/technical/dipptant.pdf under
"Experience from Promotion Screening") seems to suggest that for
issues of dv/dt just the opposite: "...the results showed a slight
increase in failure rate with increased capacitor size and voltage
rating..." Thus increasing the rated voltage would actual cause more
failures due to surge currents!

Thanks,
Matthew

.

Relevant Pages

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  • Re: Low ESR Tantalum Failure due to Power On- Design Fix?
    ... It is connected to a DC to DC power supply board with a number ... I am using 47 uF 35 volt Tantalum Low ESR ... I have three of these caps in parallel and two ... 18% equipment failures). ...
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