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posted by martyb on Thursday May 16 2019, @08:52PM   Printer-friendly
from the live-long-and-prosper? dept.

Phys.org:

Switching supply units used today are of light weight and compact design, but also susceptible to errors due to the incorporated electrolyte capacitors. Film capacitors would have much longer service lives. However, they need up to ten times more space. Scientists of KIT's[*] Light Technology Institute (LTI) have now developed a digital control method for use of film capacitors that need slightly more space only.

The control method runs on a microprocessor integrated in the supply unit and detects disturbing environmental impacts, such that e.g. higher voltage fluctuations can be balanced. Hence, storage capacitors of reduced capacity are sufficient. Michael Heidinger, LTI, summarizes the advantages: "Use of these film capacitors eliminates the main cause of failure of power supplies, i.e. electrolyte capacitors. Depending on the design, service life may be increased by a factor of up to three." The result is a much reduced maintenance expenditure.

This one is digital.

[*] Karlsruhe Institute of Technology.


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  • (Score: 4, Interesting) by RS3 on Thursday May 16 2019, @11:55PM (4 children)

    by RS3 (6367) on Thursday May 16 2019, @11:55PM (#844523)

    As I commented below, article does not say "capacitors have errors".

    Electrolytic caps don't do well with large RMS currents, as I'm sure you know, by the very nature of a wet electrolyte. I don't think they're advocating getting rid of all electrolytics in power supplies; in fact article talks about high-reliability / long life applications. Most low-ESR caps meant for switching supplies have 1,000 - 3,000 lifetimes (at high RMS).

    Yes, the concepts are old, but only recently do we have enough computing power in a tiny cheap package to sense, analyze, process, and control the power transistors to this level of speed and precision. The "good old way" was to throw more uF at it. This is for high-reliability applications, not the masses (yet).

    Bad electrolytic caps have been a plague. I remember blaming MS (although they deserve it anyway) for computer crashes, bluescreens, etc., years ago (late 90s - 2010 or so) when bad caps were causing the problems. Replaced them in my own motherboards and amazingly, the computers were rock-solid stable. Sorry Bill G.- I take back a few of the things I called you, but most of them are still yours to keep.

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  • (Score: 2) by RS3 on Friday May 17 2019, @12:05AM

    by RS3 (6367) on Friday May 17 2019, @12:05AM (#844532)

    Sorry, typo, meant to type: "1,000 - 3,000 hour lifetimes"...

  • (Score: 2) by Acabatag on Saturday May 25 2019, @03:05AM (2 children)

    by Acabatag (2885) on Saturday May 25 2019, @03:05AM (#847477)

    But we are talking about the capacitors in switching power supplies. They don't deal very much in 'rms currents.' I guess there's usually a big one that sees RMS current at the very front end of the switcher....

    • (Score: 2) by RS3 on Saturday May 25 2019, @05:25AM (1 child)

      by RS3 (6367) on Saturday May 25 2019, @05:25AM (#847508)

      I don't know your background or knowledge of EE stuff, so forgive me if this is elementary. "RMS" is how we refer to AC or varying currents. It involves integrating the instantaneous currents over time. In switching supplies it can be very complex due to inductance components used for energy storage.

      But we are talking about the capacitors in switching power supplies. They don't deal very much in 'rms currents.' I guess there's usually a big one that sees RMS current at the very front end of the switcher....

      In fact in switching power supplies the capacitors deal with very great RMS currents, which is why they heat up and fail.

      Electrolytic caps have high charge storage density (Farads, microfarads, nano, pico, etc.) per unit volume so they make great "filter" caps- they hold lots of electrons and give them up (supplying current to the load) while the input waveform has dropped below the needed output voltage (minus diode drop). But electrolytics have higher ESR (Equivalent Series Resistance) than other (dry) caps, like Mylar / polystyrene, paper, ceramic, etc. The current rushing in and out of the capacitor causes the capacitor's resistance component to heat up, which can be a Bad Thing.

      A good reference: https://www.ti.com/lit/an/slta055/slta055.pdf [ti.com]

      I had written more but decided not to post it. I'm happy to if anyone's interested.

      • (Score: 2) by RS3 on Saturday May 25 2019, @03:57PM

        by RS3 (6367) on Saturday May 25 2019, @03:57PM (#847631)

        I meant to write "plus diode drop", not "minus". Sorry, it was late...