What caps in power supply?

Discussion in 'General Electronics Chat' started by RamaD, Jan 11, 2012.

  1. RamaD

    Thread Starter Senior Member

    Dec 4, 2009
    The Al Caps used in switching power supplies are rated for 2000hrs or at the max 5000hrs. I saw one switching power supply with MTBF of 100,000 hrs. I wonder what kind of caps are used to get such high life?
  2. Adjuster

    Late Member

    Dec 26, 2010
    There are several possibilities here, leaving aside the possibility that the power supply MTBF figure was simply exaggerated.

    • The capacitor lifetime rating normally applies at some elevated operating temperature. It may include wear out mechanisms that are accelerated at high temperatures, and strictly may be =Mean Time To failure (MTTF) as opposed to a constant failure rate MTBF. Whatever the definition, the capacitor lifetime will be very considerably extended if used at a lower temperature.
    • Some equipment (e.g. aerospace) may use special quality components which are not so freely available.
    • An MTBF of 100,000 hours may not necessarily mean that the unit will typically last this long. Sometimes the figure given is based on calculations using the theoretically constant failure rate applying during the design life of the product, before wear out mechanisms become significant.
    RamaD likes this.
  3. gootee

    Senior Member

    Apr 24, 2007
    Maybe they used metallized polypropylene film capacitors.

    And maybe the power supply was a switchmode type that used a very high switching frequency, requiring much lower values of capacitance than a typical linear supply, so that the mpp film capacitors did not require $20-$50 per hundred μF times some large factor.
    Last edited: Jan 13, 2012
  4. JMW

    Active Member

    Nov 21, 2011
    The answer is obvious...........flux capacitors
  5. CraigHB


    Aug 12, 2011
    Probably MLCC caps. That's what's used in some of the POL modules you can buy, like this.