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Ripple current (how to measure)

Discussion in 'Electronic Design' started by joble, Mar 1, 2004.

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  1. joble

    joble Guest

    Hi,

    I'm working at an SMPS and since the capacitors are the most critical
    components for the life time, i'd like to calculate the lifetime of
    those components.

    If i look at the datasheets the ambient temperature and the ripple
    current are the parameters to calculate the lifetime. It's no problem
    to measure the temperature, but the ripple current is not as easy to
    measure.

    How can i do this?

    With the currentprobe and a scope i measure a 100Hz ripple (i'm in
    europe) with 130kHz added to it (= Switching frequency of the smps).
    So what is the max ripple current i should take, the one at 100 Hz and
    100kHz.


    Can somebody explain me some about ripple currents and lifetime of
    cap's.

    Thanks
     
  2. The manufacturer have plenty of Appnotes about that subject.
    I'd think both values are to be compared.

    Rene
     
  3. R.Legg

    R.Legg Guest

    to measure the temperature, but the ripple current is not as easy to
    The current probe will give an accurate measurement of ripple current.
    This can be read on an RMS-reading scope or by plugging the current
    probe into an RMS meter.

    As the two component frequencies of the ripple current are widely
    spaced, they could be separated by fairly simple filters, before
    measurement. Depending on your topology and the capacitor location,
    one is likely to dominate over the other.

    Some topology capacitor stresses are fairly well documented in the
    literature, allowing an indirect calculation, but you'd have to
    indicate where and how this part is used before a specific reference
    can be cited.
    This is better done by the capacitor manufacturer:

    http://www.cde.com/tech/appguide.pdf

    RL
     
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