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Tantalum Capacitors in audio applications

Discussion in 'General Electronics Chat' started by 2camjohn, Mar 22, 2008.

  1. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Actually Hitachi sold HGST to Western Digital an American HDD company.
    But if beer got into the small HEPA breather filter hole, too bad but if it just got on the circuit board. good news. low residue isopropyl alcohal and 24 forced air drying time will cure the problem. Beer has a dielectric constant due to water of about 60x air, which may cause crosstalk when on signals . If no click-click -click of death sound after startup, then Spinrite will fix it if the alcohal doesn't... then if neither works, buy a bottle of good scotch and douse your tonsils with it.

    Then while waiting for it to dry. activate your spam filters on email.

    Cap distortion is all about the dependance on ESR and voltage drop on change in capacitance with bias voltage. Y type Ceramic caps are the worst. COG are the best in ceramics for this attribute.

    Old axial tanalums were high quality and many were rated for high rel quality when used in a design where the source and load impedance was greater than ESR ( such as audio applications , & filters or low current apps, but poor with ESR of cap was dominant in a high current app, meaning high ripple current and power dissipation and risk of thermal runaway.

    Although never specified, all electrolytic capacitors can safely handle 10% rated V in negative bias.
    (Note again.... "Electrolytics" includes ALL Tantalum wet or solid) common mistake to exclude them or say electolytics AND tantalum
     
    Last edited: Apr 5, 2016
  2. spec

    spec Well-Known Member Most Helpful Member

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    Yes, I did know that WD had taken over HST, but as far as I know they are still operating autonomously

    No beer got into the disk chamber and the heads are correctly parked. Also the platter spins quite freely.

    The problem is the platter does not spin up

    Thks for info. Done all that apart from trying spinrite.

    I have just received some miniature TORX drivers so I can whip the controller board off and have a look at the component side. Apparently there are two protection components that go short under fault conditions. With any luck it is just a matter of removing them.

    Scotch sounds like a good consolation.:cool:

    What do you mean by this?

    spec
     
    Last edited: Apr 6, 2016
  3. spec

    spec Well-Known Member Most Helpful Member

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    As you imply tantalum capacitors span a very wide range, all with different characteristics... and cost.

    As far as I can remember, this is a similar spec for the solid tants we used. Incidentally they are a mere £55 UK each from RS :eek: Although cheaper commercial versions are available. http://docs-europe.electrocomponents.com/webdocs/13a4/0900766b813a4bb8.pdf

    spec
     
    Last edited: Apr 6, 2016
  4. dave

    Dave New Member

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  5. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Didn't that make the sound a little rubbery? :D
     
  6. spec

    spec Well-Known Member Most Helpful Member

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    I was thinking of some other implants. :hilarious:
     
  7. AnalogKid

    AnalogKid Well-Known Member

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    A lot of the dissing of tant caps is hindsight bias. Tant caps are on so many device data sheets because many device data sheets are...old. Back in the 60's and 70's, tants were *the* part to use in power applications because aluminum electrolytics did not have the high temperature, low temperature, tolerance, or reliability ratings that they do now - 50 years later. And they still don't have the high frequency performance or high self-resonant frequency per unit capacitance/voltage/case size. In those decades we've learned that tants have more "personality issues" than first thought, but if you color inside the lines they still make outstanding decoupling caps because they are not wound or stacked.

    Like everyone else, at work we have moved away from tantalum caps, mostly to high-value SMT ceramics. Turns out that they have their own problems, the terminations. High value, high voltage ceramic caps really don't like it when a pc board flexes. A 6" x 9", 0.93" thick, 6 layer, 1 kW power supply board is not exactly flimsy, but those caps were not happy. Had to add stiffening bus bars down the long axis, but the bars improved some of the power handling so they were a net plus.

    ak
     
  8. spec

    spec Well-Known Member Most Helpful Member

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    I have always been concerned about the bigger surface mount chips, because there is no give between the pack and the board. Differential thermal expansion, board flexing, and vibration must put quite a force on the SM packs, so it is interesting to hear that you have had to stiffen PCBs to eliminate problems. Like you, we started moving over to the new high value ceramics around 2000, if I remember rightly. Electrically they seemed marvelous for decoupling on digital boards and also local switch mode power supplies and linear regulators.

    spec
     
  9. AnalogKid

    AnalogKid Well-Known Member

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    The latest gen SMT ceramic and tant caps have a bit of flex at the terminals are are way better than older parts.

    ak
     
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  10. bountyhunter

    bountyhunter Well-Known Member

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    No. The wet slug tants have enough internal impedance to limit the current to a safe value so you can connect them to an "infinite" current source and they won't blow up.

    No, they were MIL certified. The solid Tantalums simply can not be charged from an uncontrolled current source because they can blow up. It was a well known characteristic which is why they did not allow their use in designs where the current was not controlled. In other words, you could not use them on a power bus or in our case as switch caps because the start up surge current might blow them. Sprague tested a bunch and culled out the ones strong enough to handle it for us and we used those. But it was a well known failure mode due to surge current.

    Some other types also have surge current specs not to exceed: I remember the metal poly caps had a "dV/dt" rating which translated to inrush current (I/C) rating. They also have very low internal impedance.
     
  11. bountyhunter

    bountyhunter Well-Known Member

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    Exactly. The ones I was referring to were the early 80's vintage.

    We used a lot of surface mount tantalums on our switcher designs at Nat Semi in the 90's and they were reliable enough. Really had no choice because there were no small size low ESR aluminum electrolytics available at that time and the large value ceramics had not yet been developed. Once they came out with the high value (low voltage) ceramics, we went with those for most applications.
     
  12. The Electrician

    The Electrician Active Member

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    What do you mean by "safely handle"?

    Are you saying that a 250V rated electrolytic can be used with a steady 20 volts reverse bias? Or do you mean that it would be ok to allow 20 volt reverse voltage peaks, say at a 120 Hz rate?
     
  13. bountyhunter

    bountyhunter Well-Known Member

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    That's not my understanding. I thought it was more like a "zener breakdown" type of condition where you had to limit the reverse current to a very small amount. I think if you actually force 10% of rated voltage in reverse (like from a power supply output) it damages the cap.
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    Thks for explaining that so clearly. I get what you mean now and what Tony meant with his reference to the MIL handbook.

    I can also see the logic of it, but am intrigued because I can't remember such a severe problem with solid tants and have never experienced it either. Out of interest, you don't have a document link describing the limitation? I don't have access to MIL specs anymore.

    Quite a few components have dv/dt limitations which often get ignored.:arghh:

    spec
     
    Last edited: Apr 6, 2016
  15. spec

    spec Well-Known Member Most Helpful Member

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    My understanding from the Vishay documentation is that solid tants will take a maximum of 100mV reverse without damage and with normal performance.

    spec
     
  16. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I also bricked a laptop with a beer spill thru the top keyboard.
    I tried fixing twice. 2nd fix worked. My secret was eliminate all residue trapped under IC's where solvent is trapped and air flow is poor.
    So copeous amounts of isoprop. solvent and forced air with heat drying time.

    re: beer induced faults
    Having worked as Test Eng / Mgr in HDD industry for 11 years, I am familiar with most failure modes. Look for a SMT picofuse around <1A and perhaps an unmarked black 3mm square SMT near power jack. Spindle motor drivers draw more current when wet from square wave frequency and hi-K factor of beer. Hopefully you never turned the spindle in reverse which may damage the heads. in other words, beer makes a good capacitor but may draw unexpected current from large high RPM square waves with contaminants.

    spec, I thought you got daily viagra emails so I suggest hardening your email spam filter settings instead.

    cheers... Tony

    addendum
    - its hard to be accurate and generalize but in general, means there may be exceptions
    - capacitor failures can be prevented with design care and a good test plan for qualifying suppliers for each part series
    - surge protectors can protect old tantalum caps. in good designs
    - PU sub-floor adhesive for large ceramic MLCC from piezo-electric effects.
    - bad layout using large SMD ceramic near PCB edges are big risk of fracture from depanelization stress,
    - redundancy is necessary for coupling and decoupling cap design for improved reliability.
    - peak current margin to spec is another MTBF failure rate accelerator.
    - most component failures are design related by user or process of Mfg.
    - rookies would learn much from Japanese reliability reports on root causes
     
    Last edited: Apr 6, 2016
  17. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  18. spec

    spec Well-Known Member Most Helpful Member

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    A Vishay FAQ document does say that a short duration reverse voltage is tolerable: (page 5 lower/page 6 upper) http://www.vishay.com/docs/40110/faq.pdf.
    'Solid tantalum capacitors are capable of withstanding short duration peak voltages in the reverse direction limited to 5 % of the DC rating at +25 °C'

    It also describes the connection of solid tants back to back to handle bipolar signals- this topic was discussed in the original part of this thread.

    spec
     
  19. bountyhunter

    bountyhunter Well-Known Member

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    That's about what I remember as well. Very small reverse voltage tolerance before damage.
     
  20. bountyhunter

    bountyhunter Well-Known Member

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    Interesting. Maybe the new ones are more robust than the old ones. I never tried reversing the voltage... at least, never intentionally.
     
  21. bountyhunter

    bountyhunter Well-Known Member

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    I don't recall what MIL STD had what in it, they kept changing.

    Found this, sounds like they knew about the problem:

    http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080039306.pdf

    Effect of Surge Current Testing on Reliability of Solid Tantalum Capacitors


    https://www.researchgate.net/public...g_on_Reliability_of_Solid_Tantalum_Capacitors

    "A specific feature of tantalum capacitors is so
    -called surge current or turn-on failures when
    the board is first powered up. The mechan
    ism of surge current failures has not been
    understood completely yet, and different hypoth
    eses were discussed in relevant literature.
    These include a sustained scintillation breakdown model [1-3]; electrical oscillations in
    circuits with a relatively high inductance [4-6]; local overheating of the cathode [5, 7, 8];
    mechanical damage to tantalum pentoxide dielectric caused by the impact of MnO crystals
    [1, 9, 10]; or stress-induced-generation of electron traps caused by electromagnetic forces
    developed during current spikes [11]."
     
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