Which type of non electrolytic capacitors should I use?

Discussion in 'General Electronics Chat' started by dansteely, Feb 26, 2017.

  1. dansteely

    Thread Starter Member

    Feb 26, 2017
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    Hi All,

    I’ve been assembling some small amplifier circuits based upon the TBA820M, LM386N, TDA2822M devices and as a starting point have used the test circuits in the datasheets. My question is regarding the capacitors in the circuits and am unclear on the difference of the non polarised capacitors.

    With that regard which type of capacitors should be used in these type of circuits? E.g. can a 0.22uF can be a metalized polyester, a ceramic, a tantalum or even a non polarised electrolytic?

    I am building up a stock of components including capacitors and am fine with electrolytic's but it’s the other types i’m confused about. I seem to have quite a few ceramics & less metalized polyester but that’s about it.

    When not stated on circuit diagram how do know what flavour of non electrolytic's to use?

    Another question: Why are polystyrene capacitors significantly more expensive than other sorts, what are they required for and do I need to add some to my stock?

    And how about the little box shaped polyester capacitors with the very short legs - do I need them?

    BTW: Apart from small amplifiers I'm doing some experimentation with 555's, logic and Arduino.

    Sorry for the rambling. Any thoughts and comments would be most welcome. (If there is an online guide to this subject, a pointer would be appreciated)

    Sincere thanks
     
  2. dl324

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  3. dansteely

    Thread Starter Member

    Feb 26, 2017
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    Hi Dennis, Both sites are great. I may be back for further clarification...

    Many thanks.
     
  4. ian field

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    Don't use a tantalum on the C/R damper on the output - they are *VERY* intolerant of *ANY* reverse voltage.

    Multilayer ceramic chip capacitors have impressive size/capacitance ratio and very low ESR, I've seen brochures offering up to 180uF. Might take some effort to find leaded resin dipped parts. They're excellent for things like supply decoupling, but most audiophools will hit the roof at the suggestion of putting them in the signal path.

    Most metallised foil capacitors are suitable generally around the amplifier circuit.

    Polystyrene tend to be used for low RF and some precision applications - their tempco is complementary to ferrite pot cores.
     
  5. #12

    Expert

    Nov 30, 2010
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    When I decided to get down with capacitor types I think I spent about 12 hours reading spec sheets and learning about frequency limitations, self-healing, dissipation factor, etc. I'm not going to spend 12 hours typing them in and explaining them to you. You have to, "do your homework" by reading what dl324 provided, and then come back with the parts that didn't become clear.
     
  6. ian field

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    You go to *THAT* much effort for an audio amplifier?!!!

    Maybe for a high end discrete component design - but for integrated in the realms of TBA820. LM386 and TDA2822 that the TS is talking about; not so much.

    The LM386 has been dubbed; "the cockroach of audio amplifiers".
     
  7. OBW0549

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  8. MrChips

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    As others have said, don't use tantalum or aluminum except for power supply filtering (above 1μF).
    For power supply decoupling use ceramic disc.
    For temperature stability, timing and filter circuits use mica or poly.
     
  9. ian field

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    Tantalum are rare in audio - it may be an audiophool thing, but they will go leaky if used for coupling AC signals.

    They're pretty good for supply decoupling where they only ever see right way round DC, but tantalum beads have been known to go off like match heads.

    With aluminium supply decoupling, a few ceramic caps in parallel are a good idea - its a matter of preference and most people can't hear the difference.
     
  10. dansteely

    Thread Starter Member

    Feb 26, 2017
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    Many thanks chaps for all the information and pointers. I'ts starting to make sense!
     
  11. #12

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    No, I went to that much trouble for my entire career in electronics.
    I didn't go to "electronics school" so I had to teach myself.
    Do B.S.E.E. courses spend less than 12 hours on capacitors?
    I wouldn't be surprised if the answer is, "yes".:(
     
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  12. MrSoftware

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  13. OBW0549

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    In my case, the answer is definitely "yes." My BSEE was almost 40 years ago and things may be different now; but in our courses ZERO time was spent discussing the characteristics of real-world, "non-ideal" components like capacitors, inductors and resistors. Such things as dielectric absorption and the effects of parasitic resistance and inductance were not mentioned, as best I can recall.

    That "grubby, non-theoretical stuff" was relegated to OJT.
     
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  14. bertus

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    Hello,

    Have a look at the attached PDF's.

    Bertus
     
  15. #12

    Expert

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    What an attitude! No wonder some engineers think they are God. "No sense learning real world limitations. Our capacitors and op-amps are made by angels.":)

    Then they hire people like me to fix their designs.;)
    I had so much fun correcting the BSEE's.:p
    Can you say, "14 circuits that won't work, on one page"?:D
    Not complaining. That was the stuff that made the light bulb in my head go on.
    I wooda never got good at any of this if I hadn't followed "real" engineers around, fixing their mistakes.
     
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  16. KeepItSimpleStupid

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    Just a few comments. Polystyrene is primarily reserved for precision. Electrolytic' s for higher capacitance and sloppy tolerances.

    Bypass capacitor selection is generally an art. In general use what the manufacture recommends. It might not be right for the application. In SOME cases multiple capacitors are paralleled such as a ceramic, tantalum and metalized polyester all in parallel.
     
  17. OBW0549

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    At the time I got my degree, I had already worked as a technician for 13 years and had been a hobbyist another 8 before that, so I already had a fair amount of practical experience in "what works, what doesn't." I'm not sure how well I'd have fared as a design engineer without it.
     
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  18. #12

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    That's exactly my point.
    All the "book learning" in the world won't make you an effective designer if the book learning specifically excludes real limitations in the physical world.

    Structural engineering is all about physical limitations of real materials. In electronics, we are way past the LM741, but capacitors just aren't on the same improvement curve with IC's. (Thank Dog we don't have to use paper and beeswax capacitors now.) Thin film technology has done amazing things with the size of a real capacitor in the last 40 years, but you can't just etch in more transistors to make a capacitor better.

    A couple of months ago I replaced two metal can capacitors that amounted to about 14 cubic inches, with 3 capacitors the size of grapes. I'm happy about that, but they were still aluminum electrolytics and they will still go bad in 10 or 20 years.:(
     
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  19. ian field

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    The real art is knowing what type of amplifier chip, the TS mentioned the LM386 among others, its been dubbed; "the cockroach of audio amplifier chips" - hardly worth the kind of decoupling you'd put on a board that combines, say; RF and digital.

    Single ended like the 386 is more dependent on the reservoir function of the bypass caps, BTL types can get away with less reservoir capacitance, but they disturb the rail more around the zero crossing region. Adding a parallel say; 0.22uF ceramic is pretty much required.
     
  20. Sinus23

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    Sep 7, 2013
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    I found this video to be useful.
     
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