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electrolytic caps VS. tantalum caps

Discussion in 'General Electronics Chat' started by hardcore misery, Jan 2, 2007.

  1. hardcore misery

    hardcore misery New Member

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    which is better in high frequency operation?
    or in high-gain pedals like BOSS metalzone
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I wouldn't recommend tantalums for anything, they are far too unreliable!.
     
  3. gramo

    gramo New Member

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    Not sure about that, esp when high frequencies are concerned, heres an extract from http://www.engineersedge.com/instrumentation/tantalum_capacitors.htm

     
  4. dave

    Dave New Member

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  5. dknguyen

    dknguyen Well-Known Member

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    Tantalums are better than electrolytics for high frequency, but electrolytics are cheaper and can come in much larger sizes.
     
  6. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    They were only ever used for a small number of years in domestic electronics, their huge failure rate caused all manufacturers to stop fitting them. Personally the only place I'd consider using one is as the timing capacitor on a 555 - where their lower leakage is a great advantage.
     
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  7. eng1

    eng1 New Member

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    In fact they don't tolerate voltage peeks and may explode if their ratings are exceeded. On the other hand, they are more precise, stable and suitable for higher frequencies. I've recently used tantalum capacitors after LDO regulators because of their low ESR.
     
  8. Oznog

    Oznog Active Member

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    I'm not sure what you're saying. Tantalums have been the capacitor of choice for many years and are used almost exclusively in many consumer electronics products. Their size is the primary advantage, like the description says, not only is a cap in a similar voltage and capacitance much smaller, but due to the lower ESR the tantalum can often be of a much smaller capacitance. MP3 players are almost all tant. Hard drives, tants.

    In fact a big issue is that tantalum only comes from one part of the world, a somewhat unstable part at that, and most electronics depend so heavily on tant caps that it's become a real concern. Awhile back I saw they were working hard to develop vanadium caps as a substitute for tantalum primarily due to supply issues.
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Just checked six different TV's, from a brand new LCD one to one 12 years old - can't see a single tantalum capacitor in any of them. In fact I've not seen any since the late 70's early 80's when they were dropped because of their poor reliability. Also just checked a digital satellite receiver, a DVD player, a 40Gb HDD, and a PC motherboard - none in those either.

    I've not seen them used for over 20 years!.
     
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  10. Oznog

    Oznog Active Member

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    Generally don't show up as often in non-space-critical items like a TV, they're a bit more expensive. I have several recent hard drives I just had in front of me and most had tants. Are you sure you even know what they look like now?

    Also tants fit in SMD pkgs better. Electrolytics are still generally cans which is sort of an awkward to turn into an SMD as well as being a tall profile. Tants are usually a flat construction and fit into some common sizes of rectangular SMD pkgs.

    Now remember what you saw 20 yrs ago is not a permanent state of tech. Come on, you know this. Don't be the grampa who talks about how color TV picture tubes go out too soon because he saw them do that in the early days. Tech doesn't work like that. A product can easily be unreliable or impractical for a few years and then totally change.

    Fact is tants are actively being used in LOTS of stuff. They've been the hot component that is essential for miniaturization and the industry has successfully embraced it for many years! There are no really problematic "gotchas" to them, at least not for the past 5 years. Can't say why you're not seeing them in the items you have picked up, but you gotta look around- they're used, and they're used in lots of stuff!
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Hard to tell with SM components, but the only ones I've had occasion to check are listed as SM Electrolytics - NOT as Tantalum. However, perhaps they are tantalum, and listed wrongly in the manufacturers literature? - it would certainly explain why they fail and require changing! :D

    Agreed, but the manufacturers don't seem to want to get bitten again, as I say, I don't really see any.
     
  12. chemelec

    chemelec Well-Known Member

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    I use Thousands of tantalums in my projects and have Never had one fail. (Unless Connected in Backwards by Mistake)

    But Most important is to know "Where" and "Where-Not" to use them.

    They were never ment to be a Blocking Capacitor for AC Signals.

    As Bypass Caps on "Voltage Requlators", they are the BEST.

    But they are NOT the Only cap you should use here as they are Not ment for Brute Force Filtering.
    (Generally speaking they should be placed Directly across the input and Output of the actual regulator IC, Thus Complimenting the supply of the additional Electrolytic filter caps.)

    They also work very well for Bypassing IC Supplies, Directly across the IC's Supply Pins.
     
  13. Oznog

    Oznog Active Member

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    Actually electrolytics themselves bit mfgs about 5 yrs back. One of the big Asian mfgs of components supposedly stole a formula for electrolytics but only got part of the formula. Bad caps saturated the industry and nobody knew. Those caps went into most of the motherboards for quite a while. Then they all started to go out, caps leaking crap all over. I have a prime example.

    Look on Digikey, the ratio of hits for electrolytics to tants is about 2:1. Note that tants cover a more limited range- there are no high voltage or super-high capacity tants, so fewer types are expected. But you gotta see that 7400+ types available doesn't indicate a product line that failed years ago!

    You'll also find in many spec sheets (for a regulator for example) they specify "low ESR electrolyic or tantalum type". Sometimes they say if you don't use a tantalum you may need a ceramic in parallel with an electrolytic to meet both the ESR and capacitance spec. That's sort of half-assed when you think about it. The ceramic has a low ESR but only a capacity of like 0.1uF at best which only counters high freq ripple. A tant has low impedance for all of its capacitance.

    I've used plenty of tants in my projects. They do work well and I've only had one fail because it was in backwards. I greatly prefer them for their small size and low ESR.

    I have heard not to use a tant for a continuous voltage of more than like half the peak voltage rating. I am unsure how universal that recommendation is. I mean that may or may not have been true for one mfg, but is it true for all the technology? I don't see this in cap spec sheets. I do see 16v as a popular voltage, yet I have to note that there are few 8v circuits out there that would justify its popularity. And that's too far off to be intended for regulated 5v circuits. It suggests people might be using these for a regulated 12v line to me.
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    That's where they used to fail, most of them were used as supply decouplers on large PCB's, scattered all over the board. They invariably failed S/C, making the faulty one VERY difficult to find.
     
  15. Oznog

    Oznog Active Member

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    Oh hey I found this neat formula that estimates tant reliability:
    [FONT=Times New Roman,Times,Times NewRoman]LT=LR*(ER/EO)^3*2^(deltaT/10)[/FONT]​
    [FONT=Times New Roman,Times,Times NewRoman][SIZE=-1]Where:
    LT = failure rate under stated temperature and voltage
    LR = the failure rate at rated limits
    ER = rated voltage limit
    E O = operating voltage
    deltaT = difference between rated operating temperature and actual capacitor temperature in C[/SIZE][/FONT]
     
  16. eng1

    eng1 New Member

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    You may see some SMD tantalum capacitors on PC soundcards, for example.


    That formula might be good only at DC? It doesn't consider frequency. And the maximum voltage of a capacitor is specified at DC.
     
    Last edited: Jan 2, 2007
  17. hjames

    hjames New Member

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    You're pretty much guaranteed to see tantalum capacitors in use in any height/space constrained device. They come in thicknesses from 1.2mm to ~6mm, while "cans" start at ~8mm for the smallest capacitances. There are some high capacitance ceramic parts, but they come with their own baggage.

    Niobium capacitors are the new tantalum alternatives. They have lower capacities, but also don't go up in flames when stressed. Keep in mind that standard tant's may be "stressed" if the voltage isn't derated by 100%! (A tantalum on a 12V line wants to be rated at 25V, etc.)

    There are also "organic polymer" versions of aluminum and tantalum capacitors which offer much lower impedance and better reliability for a higher price - although the only applications which really benefit are high density power supplies.

    Thing is: I don't think tantalums are really recommend for use in the audio signal path:
    http://www.electro-tech-online.com/custompdfs/2007/01/AN3171.pdf
    If they're for bypassing the power supply, that's all well and good, but they typically aren't used anywhere you want an "ideal" capacitor....
     
  18. Optikon

    Optikon New Member

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    I've found that with sufficient voltage derating (someone mentioned 100%) but I've used as low as 50% _AND_ derating in the ripple current spec, they can be very reliable.

    If the physical space is available, I would not risk using a tantalum.

    Also to be proper, a tantalum capacitor is an electrolytic. The electrolyte is tantalum. A clear way to distinguish is "Aluminum electrolytic" versus "tantalum electrolytic."
     
  19. Dr.EM

    Dr.EM New Member

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    Interesting. I have 2 tantalums in my whole collection, both 16v 10uf :D. I bought them for some mic's that reccomended them. I then read about unreliability both here and on Rod Elliot's site and have never actually installed them. I currently have one across an ADC's power supply (currently on breadboard). I am hoping to not need it on the "real" version which has a 100uf low impedence electrolytic (suitable for SMPS type) nearby. I also read the tantalum comes from a Gorilla habitat and that it is damaging that habitat by us taking it?
     
  20. Hero999

    Hero999 Banned

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    It also depends on whether you're talking about the SMT or TH blob style packages, I've heard that some of the older TH designs can have reliablility issues.
     
  21. chemelec

    chemelec Well-Known Member

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    Actually I use a Lot of them this way. No Problems.

    ** Maybe there using Poor Quality one.

    But on the other hand, I bought 7,500, 1uf @ 35 volt rating at a Surplus place for less than 1 cent each.
    Never had one fail yet and I'm down to my last 2,500 piece roll.

    Definately One of my Better Buys.

    As to Voltage ratings Verses the Supply voltages, Most often my caps are rated at Double the Supply. I can't say if this makes a difference, But Possibly it does.
     

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