Capacitor substitution

Discussion in 'General Electronics Chat' started by ke5nnt, Oct 28, 2009.

  1. ke5nnt

    Thread Starter Active Member

    Mar 1, 2009
    384
    15
    Is there a different kind of capacitor other than an Aluminum Electrolytic that you can use for General Purpose Filtering, Bypassing, and Power Supply Decoupling? I have 12V going into a Linear Regulator (LM7809) and the 12V continues through a 35V 220uF electrolytic cap to ground.

    Problem is, surface mount and standard through-hole electrolytic capacitors are pretty much the same size, and too darn big for my tastes in my specific application. Can I use something else? Like a ceramic disk SMT cap?

    Capacitors have been a stitch in my side ever since I got into electronics, just can't seem to figure out what kind is good for what. Plus I know certain elements like temperature, stability and all that makes a difference.
     
  2. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    surface mount tantalum perhaps?
     
  3. Thav

    Member

    Oct 13, 2009
    82
    0
    Tantalum can be kind of expensive (I'm not sure why, exactly). Maybe SMT polyester/polypropylene (sometimes just called plastic) film caps.

    You can't beat electrolytics for capacitance/$ though. Any film cap will likely be ~3x an electrolytic as the same capacity and voltage rating.

    If the electrolytics are too big for your application, take a look around for lower voltage rated ones if you haven't already, they can be smaller for the same capacity.
     
  4. MaxSmoke

    Active Member

    Oct 29, 2009
    35
    0
    As an aside, another capacitor to be aware of is the relatively new low ESR ceramic capacitors, these are in dielectric types X5R and X7R. As they are low ESR, you can consider using a lower value than you would have used for an electrolytic. The tolerance is as tight or better too, normally +/- 20% some +/- 10%. Where as electrolytic caps can be +20% to -80%, although often better these days.

    Most of the higher values of X5R, greater than 100uF, are not rated above 16V and I would want more margin than this when working on a 12V supply, at least 25V. But they are worth bearing in mind.
     
  5. ke5nnt

    Thread Starter Active Member

    Mar 1, 2009
    384
    15
    Thanks Max, I will look them up and bear them in mind. size is killing me, i want something small.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    The size pretty much defines the best choice for cap type. For 220uF/35V, aluminums are the only practical choice.
     
  7. ke5nnt

    Thread Starter Active Member

    Mar 1, 2009
    384
    15
    Yeah pretty much figured that out. SMT electrolytic it is!
     
  8. peranders

    Well-Known Member

    May 21, 2007
    87
    0
    How big cap are you looking for? What size?
     
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