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Caps caps caps...

Discussion in 'Electronic Design' started by Fred Bartoli, Dec 16, 2012.

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  1. Fred Bartoli

    Fred Bartoli Guest

    You've guessed, I need a cap... (or maybe several if one is impossible)

    No Esr spec (ultra low power)
    Low cost, as much as possible (by the 10^6 truck load)
    Low voltage Vmax=4V
    Cap = 220/330/470uF (may I dream 1000?)
    Temp range 0-70°C

    So far, so good.

    Now, I want it ultra low leakage, possibly below the 1µA level over the
    temp range...
    No wear out mechanism and ultra low FIT: product life = 20 years, 24/24,
    no possible service,...

    And the customer will want dual source, yeah...

    Any thought?
  2. Fred Bartoli

    Fred Bartoli Guest

    Fred Bartoli a écrit :
    Should have said :
    No wear out mechanism and _ultra low FIT_ : product life = 20 years,
    24/24 operation, expected installed base = 10M, no possible service,...
  3. Guest

    Sounds like a ceramic cap.

    That's a lot of uF for a uW supply though. 100uA = 1V/S from a 100uF
    cap., which is only 1mV ripple if you switch at 1kHz.

    Frequent, short pulses into a smaller filter cap might be worth

    I've designed discrete microwatt boost converters. That's probably
    easier cap-wise, 0.5 x CV**2 and all.
  4. Fred Bartoli

    Fred Bartoli Guest

  5. Fred Bartoli

    Fred Bartoli Guest

    Phil Hobbs a écrit :
    At the qty level I guess it's a no-no, but I'll have to check what the
    customer say...
    Thanks for the hint. I didn't look because I thought the 100uF were only
    of the Y5V-Z5U ilk...

    I'll have to check what they're worth though. On a previous design I've
    found some 1uF/10V 0402 X7R loose their capacitance with voltage rather
    quickly, almost like the Y5V :-(

    A bit nervous with chip cracks too... (but the board is smallish)
  6. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    Oh, I'm way higher in power, at the mW level :)
    Switching at 100kHz, but it's not a bypass cap, rather a reservoir cap
    here. Sorry can't say too much...
    Indeed, but I'm bucking it down later and efficiency is a real big
  7. Fred Bartoli

    Fred Bartoli Guest

    Phil Hobbs a écrit :
    Excellent idea! Thanks.
  8. Guest

    mW? Monster!
    Naturally. Who uses 330uF bypass caps?
    Oh yeah, 'twas a current source, right? So that's current ripple.
    I used discrete components expressly for high efficiency. (All the
    commercial controller chips would've drawn several times the intended
    load power--no one made efficient controllers for a 20uW supply.)

    I'd think a good CMOS totempole would be an awfully good head-start on
    a synchronous mW buck, but I haven't actually tried.
  9. Guest

    The loss of C with V goes with volume--bigger caps used at a fraction
    of rated voltage are far less affected. Still, I'm surprised to hear
    that of X7R--I've not seen that. But then I've not personally seen a
    1uF/10V 0402 either.
  10. Joerg

    Joerg Guest

    Oh no, this is an application where there are electrons and those can go
    berserk. So you need one of these:
  11. Joerg

    Joerg Guest

    But be careful. This can also cause a cantilever vibration at the end of
    a fall, and hair-crack the ceramic.
  12. Guest

    Lots of switches, lots of switches to drive. But that might work,
    since he's really making a current source.

    As an alternate, he might be able to dispense current 'packets' via a
    cap[*], and smooth the doses with an inductor. That would be very

    [*] like V-to-F's and A/D's.
  13. legg

    legg Guest

    If it's a reservoir you're looking for, you might try storing at a
    higher voltage, and only use the part and energy stored, when needed.
    The storage could be performed over the long term, not drawing
    significantly on power consumption, and not effecting efficiency, once

    Switch into buck reg when needed.....

  14. Guest

    Not to answer your question, but I do have some thoughts.......
    (at least on the days when I'm not in senile mode).

    My thought today is to change all circuit boards. In the old days,
    tubes had sockets because they failed often. These says the caps are so
    lousy, that they need to be replaced often. Therefore, all caps should
    have sockets, rather than being soldered in. Then the corner drug store
    should have a cap tester where you take your caps to be tested, and buy
    new replacements for those that check out bad.

  15. Sounds to me like Cap' Atrick needs a tester ran on him.
  16. Fred Bartoli

    Fred Bartoli Guest

    Jan Panteltje a écrit :

    (roasted bollocks, of course)
  17. Don't remember those. I do remember octal-base mercury relays that
    looked like tubes.
  18. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    Just did the measurement again as I couldn't find it back...

    That one:

    I misremembered and it was rather one 1uF/16V-X5R-0402 that I measured

    Measurements done @10kHz
    DC bias Value
    0V 808nF
    2V 705nF
    4V 475nF
    6V 320nF
    8V 230nF
    10V 180nF
    15V 110nF
    20V 80nF

    It also show a pretty high dependency on frequency:

    Freq @0V DC bias @6V DC bias
    10K 803n 310n
    20K 765n 295n
    40K 735n 284n
    100K 700n 275n
    200K 680n 270n
    400K 670n 268n

    I can't measure at the 1kHz specified frequency right now, but IIRC the
    value was spot on at that frequency...

    Also, at 3 to 7ohm depending on conditions, ESR surely is not something
    to brag about.

    I finally resorted to use 470nF caps which behaved better at the wanted
    working voltage...

    Time to order some and see how the 100uF ones behave...
    Maybe not so bright a solution as it first seemed :-(
  19. Guest

    I have some very old tube power amplifiers that have them. Back in the
    70's I needed replacements and found an old electronics store that still
    had some on the shelf. I bought all of them he had. I have not fired
    up those amps in years, but still got them.
  20. Guest

    I have fond memories of going to the corner drug store with my dad and
    testing tubes. I was very young, and dad would ahve them all in a bag,
    and it was my job to read the numbers to him so he could look them up on
    the chart. (usually a wheel turned to expose the rolled up list).

    That's sort of what got me started in electronics as a hobby and an old
    tube tester was one of the first instruments I bought. I still have
    thatr old tester too.

    These days that closeness of family doing things together is lost.
    Everything involves calling in some specialist or dropping the tv off as
    some place where you never see the repair guy, just a salesman with a
    repair book and later a bill.
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