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Tantalum follow-up

Discussion in 'Electronic Design' started by [email protected], May 16, 2005.

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  1. Guest

    My thanks to all who responded to my 'Tantalum failures' thread.

    Having looked at all the options, I intend to replace the tants with
    Multi Layer Ceramic Caps - probably TDK's 10uF/50V part, (always
    assuming of course that we can get them in the UK to the requisite
    spec.).

    The ripple voltage with the tantalums was dominated by the I*esr
    product, (by a factor of around 5:1 over dV/dt), so we can get away
    with sigificantly less capacitance and I calculate that 100uF will be
    more than enough, in terms of ripple voltage and ripple current
    requirements.

    I accept that these parts can fail quite spectacularly, due to
    mishandling during assembly, but we already have an array of 14 470nF
    surface-mount ceramics in parallel with the tantalums on the present
    design and have had just two failures out of around 2800 capacitors, so
    we can happily live with that level of reliability.

    My thanks again for all the contributions.

    Ted
     
  2. Joerg

    Joerg Guest

    Hello Edward,
    It depends on how much time these systems have clocked under load so
    far. Sometimes the caps take the ripple hit for a while and then after x
    number of hours you might see the failure rate run up.

    Regards, Joerg
     
  3. budgie

    budgie Guest

    Ted, as a fly on the wall during that interesting thread, can you keep this
    community updated on how things pan out with the changed caps?

    Thanks
     
  4. Guest

    Hello

    Since posting this follow-up, things have moved on and it would appear
    that there are significant reliability problems with MLCCs that will
    probably preclude their use in our application.

    At the moment, the most likely contender looks to be solid polymer
    aluminium, although I've yet to confirm that we can get these in a
    suitable voltage rating for our application. There's also MLPs to
    consider, as suggested by Mike Monett.

    I'm having all sorts of problems with net access at the moment, so I've
    not been able to check a lot of the details on the various parts that
    have been suggested.

    Anyway, it's Friday afternoon, my head's suffering from capacitor
    overload, and I'll be going home shortly and will tackle things afresh
    on Monday.

    Once things are sorted, I will put an update on here. (By the way, if
    you check the original thread, you will see there have been several
    further posts since I posted this follow-up).

    Regards

    Ted
     
  5. Mike Monett

    Mike Monett Guest

    wrote:

    [...]
    Ted, it seems quite a few people are interested in what you decide to use
    and why, so have a good weekend and we hope to see you again Monday.

    Personally, I'd like to see if you can confirm that drilling a hole in a
    MLP and driving a nail through it won't affect it very much. For a
    warplane with shrapnel flying around, that has to be a positive
    attribute:)

    Mike Monett
     
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