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Question about power supply filter capacitors — Parallax Forums

Question about power supply filter capacitors

RDL2004RDL2004 Posts: 2,554
edited 2012-10-20 05:17 in General Discussion
I'm thinking about building a new power supply and I ran across this new Panasonic EEU-FR series at Mouser. I'm wondering if there's any good reason to not use low ESR electrolytics for the filter capacitors?

Comments

  • davejamesdavejames Posts: 4,047
    edited 2012-10-18 08:32
    With low ESR caps, I'd be curious/watchful of the inrush current when in the charging cycle - and that translates to higher current capacity rectifier diodes.

    Does the Panasonic data sheet for said beasties discuss anything of the sort?
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-10-18 09:47
    Well, they don't specify too many applications directly. Switch mode power supplies is one, LCD backlights, home appliances and LED "systems" are also listed. I was mainly looking at the very long rated life at 105C, which is pretty good. I didn't think ESR would have much effect on inrush current, seems like the caps are going to have to charge up no matter what. Like most stuff I build for myself, the rectifier diodes will probably be way over spec anyway. I guess I don't really understand ESR that well, I thought it was kind of like AC only resistance. I'm going to have to do more research on the subject.
  • davejamesdavejames Posts: 4,047
    edited 2012-10-18 10:31
    RD - here's some info that may help:

    http://www.illinoiscapacitor.com/pdf/Papers/low_ESR_fact_or_fiction.pdf
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2012-10-18 10:44
    Hi RDL2004;

    Generally, low ESR capacitors are better quality than regular capacitors.
    In power supply applications low ESR caps tends to exhibit less ripple voltage.

    The thing about needing larger rectifier diodes is not true.
    Yes, the peak charging current can be higher but for a shorter period of time.
    Rectifier diodes can take much higher surge currents than their steady state
    current rating.
    You will not notice any difference using low ESR capacitors.
    Further, the peak charging current is probably limited by other resistances
    in the power source and not by the low ESR in the capacitor.

    If you want to use low ESR capacitors they will directly replace
    standard ESR capacitors in power supply circuits.

    Duane J
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-10-18 11:05
    If the filter caps are used post-regulator, you need to check the regulator specs to make sure it will be stable with those caps. Not all regulators are, but some may even require low-ESR caps. The datasheet is your friend here and may even have a graph showing the ESR zones of stability over output current.

    -Phil
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-10-18 14:38
    My bad Phil, I was indeed referring to the big caps on the input to the regulator. From what I have been reading, it seems like like the low ESR caps are probably not a problem. Apparently, heat is one of the main causes of electrolytic capacitor failure. High ESR causes more heat, which in turn leads to more ESR, which causes more heat ...and so on. A vicious circle is started.


    (thanks to Dave for that useful link and to Duane for the good information)
  • davejamesdavejames Posts: 4,047
    edited 2012-10-18 18:57
    RD - it really comes down to using good quality product in line with regulator specs.

    ...and, you're welcome! Happy to help.
  • SRLMSRLM Posts: 5,045
    edited 2012-10-20 05:17
    Ceramic caps (the traditional low ESR and low capacity caps ) are susceptible to microphonics, which could be an issue in certain circuits: http://en.wikipedia.org/wiki/Microphonics
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