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B Splitting Up Capacitors | Any Advantage?

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  1. Nov 1, 2018 #1
    Can someone tell me what is the advantage of using the combination instead of a single capacitor?
    capacitors-combination-adv.png

    The same total power would be dissipated?
     
  2. jcsd
  3. Nov 1, 2018 #2

    jbriggs444

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    What is the context for this question? What leads you to think that there is an advantage? And what power dissipation are we talking about?
     
  4. Nov 1, 2018 #3
    i would like to know if there is any advantage. or not?

    i thought maybe it's about the power dissipated?

    if current I flows through the single capacitor and the pd is V, power dissipated = VI

    in the combination, the current would split, but the total power dissipated would still be VI
     
  5. Nov 1, 2018 #4

    jbriggs444

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    An ideal capacitor does not dissipate power. Any energy provided to put charge in is harvested when charge comes out.

    If you want to know whether there is an advantage, ask whether there is an advantage. Don't ask what the advantage is.
     
  6. Nov 1, 2018 #5

    ZapperZ

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    What if you want a capacitor with a really large capacitance, but it doesn't exist? All you have are capacitors with smaller capacitance.

    Zz.
     
  7. Nov 1, 2018 #6
    the two gives the same overall capacitance.

    so, is there an advantage?
     
  8. Nov 1, 2018 #7

    ZapperZ

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    Isn't it an "advantage" that you can construct something with a large capacitance, without needing to actually have one large capacitor? Think of the saving in cost!

    Zz.
     
  9. Nov 1, 2018 #8

    jbriggs444

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    In what context? i.e. Why do you ask.

    As idealized circuit elements the two are identical. You know this. So you must be asking about something else. But what?
     
  10. Nov 1, 2018 #9
    if i were to choose between the 2 in a practical circuit, which one would be better? and why? or is there no difference?

    i want to know if there are changes to things like
    will the time they take to discharge be the same?
    ...
     
  11. Nov 1, 2018 #10

    jbriggs444

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    Speaking as someone with zero background in practical circuit design...

    You would be using four components instead of one. That's a win for the simple design.

    The peak voltage the element could tolerate would be doubled. That's a win for the complex design.

    You use the same standardized components in both. That's a wash.

    You can tolerate either a "fail open" or a "fail closed" event on any one capacitor in the complex design without completely compromising the element (the capacitance would change significantly, of course). That's a win for the complex design.

    Four components will tend to have a failure four times as often as one. That's a win for the simple design.
     
    Last edited: Nov 1, 2018
  12. Nov 1, 2018 #11

    ZapperZ

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    The time constant of an RC circuit depends only on R and C. If the two setups have the same capacitance, then the time constant depends on how much resistance you have in the circuit, doesn't it?

    Zz.
     
  13. Nov 1, 2018 #12

    russ_watters

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    Please stop asking this question and start recognizing that it is meaningless without context and even then will always contain an element of opinion. "Different" may or may not mean "better", depending on what you want. Learn that as a life lesson and apply it several times a day in various situations. Elevator or stairs? Chicken or steak? Drive or take the train?
    You didn't even provide values for the capacitance, but assuming equal total capacitance, the two scenarios are identical. But again: what do you want? What are your constraints? That will dictate design choices.
     
  14. Nov 1, 2018 #13

    berkeman

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    There are two scenarios that I'm familiar with for splitting up capacitors like that (beyond any power dissipation issues):

    -1- You can put two polar capacitors "back-to-back" to make a non-polar capacitor (of half the value). This is done often in audio amplifier circuits where the required value of the capacitors exceeds that of inexpensive non-polar caps. Note that most of the bias voltage appears across the correctly biased capacitor in the pair, and the other capacitor has a small forward voltage with a small overall leakage current through the pair. The leakage current and forward bias voltage are small enough that they do not hurt the "reverse biased" polar capacitor. We have used this circuit technique in a product line that has sold in the tens of millions... :smile:

    http://ecee.colorado.edu/~mathys/ecen1400/labs/lab02/acElectrolytic.png

    acElectrolytic.png

    -2- You often split up transistors, resistors and caps into multiple copies in custom analog IC design, when trying to ensure balanced operation. You might form a current mirror from 2 x 4 transistors, instead of just 2 x 1, for example. There are layout tricks when working on balanced analog designs that involve splitting up components like that, and placing them in a certain manner to help balance out any component-to-component differences. @analogdesign may have more to say about that. :smile:
     
    Last edited: Nov 1, 2018
  15. Nov 1, 2018 #14

    CWatters

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    I
    As others have said there can be advantages and disadvantages depending on context..

    Safety might be improved because you would need a double failure to cause a short circuit. Reliability might be reduced because you have more components.

    You can sometimes reduce cost by reducing the variety of different components in a design. For example if your circuit already uses a hundred 1uf capacitors but in one place you need a 2uF then using two 1uF capacitors in parallel might work out cheaper and you need fewer reels on the pick and place machine.
     
  16. Nov 1, 2018 #15

    davenn

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    agreed

    and current doesn't flow through a capacitor, it just flows in and out of each plate

    see the gaps between the plates ?

    capacitors-combination-adv-png.png

    current cannot flow across that gap
    ( caveat ... other than the tiniest bit of leakage)


    Dave
     
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