Different Cap sizes in parallel??

Discussion in 'General Electronics Chat' started by rasosina, May 12, 2011.

  1. rasosina

    Thread Starter Member

    Jun 30, 2010
    25
    0
    Hello,

    I just had a quick question. I've seen several different places people put two caps of different sizes in parallel to ground. like a 0.1uF and a 10uF. why is that?? why not just put one? is it to block a certain range of frequencies?

    here's an example:
    http://electroschematics.com/wp-content/uploads/2009/01/cell-phone-jammer-schematic.gif

    in that circuit there are several places where they have 2 caps in parallel to ground.

    thanks
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You are close, different caps have different frequency responses. A small ceramic cap generally is viable much higher in the spectrum than an electolytic, while the much larger electrolytic can provide a stable voltage for a longer duration.

    Bypass caps don't block frequencies, they shunt them to ground. A wall blocks, a pipe redirects (shunts).
     
  3. nbw

    Member

    May 8, 2011
    36
    10
    You'll often see pairs like this, like on the output side of a voltage regulator. My ASCII art skills are atrocious, but a schematic involving the ubiquitous 7805 should help :)
     
  4. radiohead

    Active Member

    May 28, 2009
    474
    31
    Sometimes specific values are needed.

    Capacitors in parallel: Ct = C1 + C2 + C3 + C4 etc...
    Three or more Capacitors in series: Ct = 1/(1/C1)+(1/C2)+(1/C3)
    Two capacitors in series: Ct = C1 x C2 / C1 + C2
     
  5. rasosina

    Thread Starter Member

    Jun 30, 2010
    25
    0
    great. thanks for all the input.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
  7. rasosina

    Thread Starter Member

    Jun 30, 2010
    25
    0
    Gotta love this forum. everyone's knowledgeable and respond quickly to questions.

    thanks again for all the inputs.
     
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