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ESR in caps

Discussion in 'Electronic Design' started by [email protected], Feb 26, 2007.

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  1. Guest

    Is a lower ESR always a better thing without qualification? That is to
    say, no thinking has to be done, just change the caps.We are changing
    some bulk decoupling caps to a part with 50% lower ESR. 150uF 16V
    tant. Doesn't this change the inrush current when turning on the
    device on empty caps?
     
  2. Mook Johnson

    Mook Johnson Guest

    ESR can be a good thing sometimes.

    If your circuit has high inductance traces teh ESR can damp the resonant
    tank circuit and reduce ringing. Also ESR may be required by some switching
    regulators for stability.

    So a sort answer, lower ESR is not ALWAYS better but it often is.
     
  3. Eeyore

    Eeyore Guest

    That depends on the source resistance.

    Graham
     
  4. Joerg

    Joerg Guest

    And in LDO regulators. Where they don't always tell you how critical the
    lower limit is because the marketeers might think that wouldn't look good.

    Tantalums? I've had my fair share of kaboom experiences with them and
    its back to electrolytics here.
     
  5. John F

    John F Guest

    I once got hit by a piece... It punched through my skin and had to be
    removed in a tiny surgery. Weird.
     
  6. John  Larkin

    John Larkin Guest

    What's the operating voltage?

    Tantalums have a bad habit of detonating when used as supply bypasses.
    Inrush current heats up tiny asperites, then the tantalum becomes fuel
    and the MnO2 is the oxidizer. Boom. A change in vendor, plus lower
    esr, may introduce problems that you haven't seen before. Our rule is:
    no tantalums on supply rails.

    Some voltage regulators, both linear and switchers, get unstable with
    low esr-loads.

    John
     
  7. Eeyore

    Eeyore Guest

    Have you looked at the 'solid aluminium' types ?

    Graham
     
  8. John  Larkin

    John Larkin Guest

    I've been meaning to research polymer tantalums and polymer aluminums,
    both of which are claimed to have very low esr and to be
    detonation-proof. Haven't got around to it. For now, we just use
    regular aluminums.

    John
     
  9. Eeyore

    Eeyore Guest

    Motherboard manufacturer Gigabyte has moved to using them FWIW.

    Graham
     
  10. Fred Bartoli

    Fred Bartoli Guest

    John F a écrit :
    Then you are Robocap, aren't you?
     
  11. Fred Bartoli

    Fred Bartoli Guest

    John Larkin a écrit :
    Check some Sanyo Oscons.
     
  12. Guest

    Seasonic power supplies use aluminum electrolytics. Looking at the
    gigabyte mobos, I believe you are correct.
     
  13. John F

    John F Guest

    LOL
    That one was good!

    Another one: My girlfriend read over a page of my books that i had
    left open on my desk. All over the day she was very silent and then
    during dinner she asled: "Why do you read all that stuff about
    Tantra-Capacitors? And that it brings a high capacity but is
    dangerous? What are you preparing for?"

    I spent a whole night showing her what the difference between Tantal-
    and Tantra- was... Rather on the Tantal- side (to stay OT here) :)
     
  14. mg

    mg Guest

    Low ESR (and ESL) capacitors should be used whenever you need a fast
    surge or frequency response like in most low-voltage (3.3V and lower)
    circuits, for instance.

    When using electrolytics, by the way, one should pay attention to load
    life and temperature ratings if you care about reliability and
    longevity.
     
  15. Mike

    Mike Guest

    Very strange - I use tantalums on almost 100% of my boards, and have
    only destroyed one. That happened when a 12V battery lead got shorted
    to the 3.3V supply regulated supply which had a tantalum on it. I
    think the tantalum was rated for about 6V. It just smoked and got a
    crack in it. A part next to it was more interesting, however. I can't
    remember the part number, but I had a TI CAN 3.3V transceiver in a
    SOIC-8 package nearby - and about half of the package blew out,
    leaving a gigantic hole in the chip. (and lots of magic smoke in my
    lab). That was exciting.

    But anyways - under normal usage - I have never, ever had a tantalum
    explode, crack, or have any other problems.

    -Mike
     
  16. John F

    John F Guest

    :) Great luck there was not 'nuf dI/dt in that...
    Had that with a BC548 once. It kept on glowing in the crater :)
    Don't try to use it in SMPS. Never ... <looking around suspiciously>
    .... ever.
     
  17. Guest

    Thanks to all that replied. It turned out that the LDO would be
    unstable with a low ESR cap on its output. As a kind of manager, I
    really had to put the brakes on the "lower ESR is always better"
    idea....
     
  18. Alex

    Alex Guest

    My thoughts
    It must allways be best with low ESR .
    Remember that the ESR will disipate heat in the capacitor, and this
    heat is damaging the cap in short time.. If there is no heat ,then a
    electronic circuit can live forever.
    Heat is also a waist of power, and we always try to design to the
    lowest power-use.
    If a circuit will be unstable ,if the caps is changed with better
    caps, then the design is bad.. if resistors was needed ,then you put a
    resistor, and do not use the ESD resistor.

    Alex in Denmark
    I'm new to this group, so I introduce myself here as an engineer
    working in the electronic field..( in most countries , think my degree
    would be like BSC ), I have 30 Y experience in repair of electronics,
    and 2Y experience with taking care of a electronic lab at university..
    I live in Sonderborg Denmark..
     
  19. mg

    mg Guest

    With power supplies, the first and most difficult problem is to
    determine the characteristics of the load, i.e., the surge current or
    frequency response required. Once that's done, it's just a matter of
    going shopping for the correct regulator and then following the
    vendor's application notes in regard to what capacitors to use, and
    how many, to insure that the regulator is stable while at the same
    time providing a fast frequency response.
     
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