capacitor voltage!

Discussion in 'Wireless & RF Design' started by aj_silverthunder, Nov 9, 2009.

  1. aj_silverthunder

    Thread Starter Active Member

    Jun 6, 2009
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    guys in a amplifier circuit a 2.2μF(3v) capacitor is used to input the signal to the amplifier,but i have a 2.2μF(16v) capacitor!can i use that 16V capacitor,will there be any minor problems!please help me guys!
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It is always better to use a higher voltage rating capacitor as the supply voltage.
    So I would say NO PROBLEM.

    Greetings,
    Bertus
     
  3. aj_silverthunder

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    Jun 6, 2009
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  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    If you are using an 18 volt supply you would be wise to increase the voltage rating of C4 to 15 volts.

    The schematic shows C1 as a polarised capacitor. Your 16 volt one will not work well in this position as I doubt the correct polarising voltage is available. In fact you would be better served obtaining a non polarised capacitor for this position as I doubt even 3 polarising volts are available at the input to this amp. These are readily and cheaply obtainable these days.
     
  5. aj_silverthunder

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    Jun 6, 2009
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    will the amplifier take the input from the capacitor c1(2.2μF,16V),but 2.2μF,3V is not available!
     
  6. studiot

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    Nov 9, 2007
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    You are misunderstanding the meaning of the voltage rating of capacitors.

    In general the voltage rating is the working voltage rating.

    This will be the max Alternating voltage you can pass through the cap. You can also use any lower alternating voltage safely.

    This parameter has the same meaning for all types of capacitor.

    The DC voltage rating is the maximum direct voltage the capacitor can safely block.

    Again this is the same for all types of capacitor, and may be different from the AC rating.

    However in the case of polarised capacitors (electrolytics), the capacitor is designed to be polarised or biased with the rated working DC voltage. They do not work well at lower polarising voltages ( of course not higher either).

    So a 16 volt cap will not work well in a position that does not supply a polarising voltage.

    There are two ways round this.

    1) Use a non polarised capacitor, as I suggested.

    2) Use a capacitor with a very low polarising voltage ( and hope) as the designer of your circuit has done with his 3 v cap.
     
  7. aj_silverthunder

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    Jun 6, 2009
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    what if i dont use the capacitor C1 in the circuit
     
  8. aj_silverthunder

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    Jun 6, 2009
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    what if i dont use the C1 in the amplifier circuit,what will be the result
     
  9. studiot

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    Well it all depends upon what you are driving your amp with.

    It's true you may not actually need one at all.
     
  10. aj_silverthunder

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    Jun 6, 2009
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    majority of them say i can use 2.2μF (16v) capacitor for C1,they say there will be no problem,what do u say about it!
     
  11. studiot

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    Have you tried to understand my explanations?

    It would be safe to use a 16 volt or 160 volt cap but you might not like the audio result.
     
  12. aj_silverthunder

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    Jun 6, 2009
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    if i use 16v cap,will result be the same as the 3volt cap!
     
  13. wr8y

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    Sep 16, 2008
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    I have never read or heard this one before. It was my understanding that if you are using a polarized capacitor, you never want to apply anything to it that causes a "reverse polarity" condition to occur across the cap.

    THAT IS TO SAY
    , that if you have a 16 volt cap, and you bias it with 5 volts, you should not apply a sine wave greater than 5 volts peak to peak as this would cause the cap to see reverse polarity.

    And, of course, you dont' want to apply any signal voltage that would exceed the 16 volt rating, either.

    You have me wondering about my facts. Gonna go do some reading now.... ! :confused:
     
  14. studiot

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    Nov 9, 2007
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    This is true and not inconsistent with what I said.

    If you think about it why would there be 3V, 16V, ....150V...1500V electrolytics?
    Why not simply use 1500V caps for everything?
    Because 1500V caps are designed to be run with a DC potential (or bias or voltage) of 1500 volts across them.
    We also have 3V etc caps because 1500V caps do not perform well at lower voltages.

    And if you don't bias it at all as in the OP/s circuit it will soon fail.
     
    Last edited: Nov 15, 2009
  15. aj_silverthunder

    Thread Starter Active Member

    Jun 6, 2009
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    majority of them say i can use 2.2μF (16v) capacitor for C1,they say there will be no problem,what do u say about it!
     
  16. aj_silverthunder

    Thread Starter Active Member

    Jun 6, 2009
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    what do u say will i use 16 v cap or 3v cap
     
  17. studiot

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    @silverthunder

    Why do you expect me to answer your questions, if you don't answer mine?

    I have no idea what you will be connecting this thing to, as you won't tell me, or what supply you are proposing.

    The TDA2003 was primarily designed for use in automobiles and the questions you ask and others are dealt with in the manufacturer's data sheet

    http://www.st.com/stonline/books/pdf/docs/1449.pdf

    The circuit you show is straight out of this sheet (although much copied by others).
     
  18. wr8y

    Active Member

    Sep 16, 2008
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    Ok, you have lost me totally here. First you say:

    I then questioned this by saying:

    Then you said:

    First you said that polarized caps must be operated with a bias voltage that equals their rated voltage. I then questioned this, offering the example of operating one at much less than it's rated voltage. You then agreed, then in the same post disagreed with "why would there be 3V, 16V, ... 150V ... 1500V electrolytics".

    My answer for that last question: there are different ratings for capacitors because a higher volt cap is both larger and more expensive than a lower voltage cap.

    I have been taught to use a capacitor rated high enough that I never exceed it's voltage rating. I have never been taught that using a polarized capacitor below it's rated voltage presents any problem. Nor have I seen any problem - I have often replaced caps with ones of a higher voltage rating and not noticed any problem.

    Not sure where we disagee, or even IF we disagree.
     
    Last edited: Nov 15, 2009
  19. studiot

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    Don't forget we are talking about electrolytics here.
    You can always use a higher voltage rating non polarised cap without problem.

    Higher voltage caps are not necessarily more expensive, only the very highly rated ones.
    I think you will find 3V ones harder and costlier to come by than 16v ones as has the OP.

    In fact it is much more costly on a production line to source, stock and install several ratings of caps than using a single rating in all situations.

    But this is not done. Why do you think this is?

    If you use a significantly higher voltage polarised capacitor the electrolytic action will not operate properly and the full capacity will not be developed. In time the elctrolyte may separate and the capacitor fail prematurely. Finally in audio applications the distortion levels will be magnified.

    Try it with a sig gen and a scope under running some electrolytics. You can observe some horrendous waveforms.
     
  20. hgmjr

    Moderator

    Jan 28, 2005
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    It is my understand ing that the justification for the availablity of capacitors with a variety of low dc voltage ratings is that a capacitor's physical size is directly proportional to the product of V times C. Most capacitor voltage ratings in a given design are chosen to be around 2 times the dc voltage it is used to filter. Real estate on PC boards is almost always at a premium so a cap is selected to keep it as mechanical small as possible

    hgmjr
     
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