Capacitor symbol confusion

Discussion in 'General Electronics Chat' started by Involute, May 25, 2011.

  1. Involute

    Thread Starter Active Member

    Mar 23, 2008
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    In the attached brief schematic, why use different symbols for the 10 uf and 100 nf capacitors? I assume the 10 ufs are polarized (the straight line being the + end, or does the + have to be there to indicate polarization?), and the 100 nfs aren't, but why bother using polarized caps in one area and non-polarized ones elsewhere? Does one symbol represent a specific technology (e.g. electrolytic)? A brief look around the net uncovered conflicting data. Thanks.
     
  2. magnet18

    Senior Member

    Dec 22, 2010
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    Yes, that capacitor is polarized. It's because it's big enough that any capacitor that size is probably electrolytic unless you go with an mkp or mylar, which are somewhat expensive.
     
  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Polarized capacitors can have different shapes in the schematics:
    Capacitors

    This is due to the region and time.

    Bertus
     
  4. Involute

    Thread Starter Active Member

    Mar 23, 2008
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  5. Wendy

    Moderator

    Mar 24, 2008
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    Yes, as long as you don't exceed the voltage rating. But a word to the wise, many of the capacitors in that series are still polarized. It makes for smaller sized caps with larger capacitances. I see a lot of that style in my current job.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Those caps have a X5R dielectric and are not polarized.

    Electrolytic caps, or tantalum for that matter do have a polarity. I don't know why offhand, something in the physics of construction.

    As a general rule, try to choose a cap with TWICE the voltage rating as it will ever see. They just last longer that way.
     
  7. Jotto

    Member

    Apr 1, 2011
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    There are also electrolytic capacitors that don't observe the polarity. I find these mostly in high voltage circuit, not used often.

    Ceramic caps always have two straight lines, electrolytic always have one straight and one curved. Ceramic caps have no polarity, electrolytic and tantalum you most observe polarity.

    Bertus, I am confused on the region and time you posted. I have always seen caps posted how I listed above. I even get drawings from other countries and I have never seen it listed different.
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    With tme I mean old or new schematic symbols.
    With region I mean whre the symbols are most used.
    I have made a little remark in the drawing to ilustrate it.

    [​IMG]

    Bertus
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    <sigh> Again, they can be polarized. They don't have to be. Like I said, I see them all the time at work. I've been doing this a while. Microelectronic circuits use that size exclusively.

    The picture the OP had wasn't, but it is all a matter of what you purchase.

    Another way to make electrolytics non-polarized is to put them back to back.

    [​IMG]

    Electrolytics have lousy high frequency response, but can have really large capacitance's in a small place. They are OK for audio and filtering.
     
    Last edited: May 25, 2011
  10. magnet18

    Senior Member

    Dec 22, 2010
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    They have a thin layer of aluminum oxide in them that acts as one "plate", it's also a semiconductor, exceed the reverse voltage (or forward, I guess) and the current shorts out. This explains it better than I can- http://teravolt.org/capboom.htm
     
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