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General Design Question - Capacitor Selection — Parallax Forums

General Design Question - Capacitor Selection

groggorygroggory Posts: 205
edited 2011-03-14 17:00 in Propeller 1
Could you guys chime in with your knowledge of what type of capacitor to use when? It seems each type of capacitor has its own strengths and weaknesses. I'll share what I know to get the ball rolling, but I think this would be very useful for MANY people who roll their own boards and do their own designs. As you guys post I'll go back and edit this post so it can useful to people in the future as an easy reference

Categories of Capacitor Usage
* Signal Level Filtering
** Mylar Film
* Mains Filtering
* DC Power Supply Filtering
** Tantalum for <= 1uF
** Electrolytic for >1uF
* Fast Bypass
** Tantalum
* Bypass Reservoir
** Electrolytic
* Super-caps / Battery Replacement
** Aerogel
* Bipolar
** Ceramic
** Bipolar Electrolytic

Specs
* Temperature Ranges
* Voltage spikes outside the cap's voltage ratings
* Bipolar vs. Polar Caps
* Low ESR vs ...

Availability in Surface Mount

Price Effective in Surface Mount

Comments

  • tonyp12tonyp12 Posts: 1,951
    edited 2011-03-13 15:09
    This post propbably should be moved to General, but anyway.
    Up to 47uF I always go with Ceramic type in X5R or X7R due to low ESR.
    Plus I don't have no worry about mounting them in reverse by mistake.
    http://www.mouser.com/ProductDetail/TDK/C3225X5R0J226K/?qs=sGAEpiMZZMvQvaS66kI3TnE1JaRpwCvuMDpKs2VXwgM%3d
  • AriAri Posts: 63
    edited 2011-03-13 16:35
    solid state where life is a concern

    monolithic ceramic where size/low value is concerned (also the lack of polarity)

    non-polarized electrolytic where polarity is a concern, but I need the benefits of an electrolytic

    polarity specific electrolytic when I have an asymmetrical hot/cold circuit, or need a large value

    any iteration of mylar/film/etc... where precise value is necessary (which is not very often)....also tantalum caps last a very very very long time
  • groggorygroggory Posts: 205
    edited 2011-03-14 00:34
    On a sidenote, I've used ceramic caps as bypass caps a few times and they've actually failed on me. I had plenty of headroom on the voltage rating and they are non polarized, so direction shouldn't matter.

    Why did my ceramic caps fail as bypass caps?
  • AriAri Posts: 63
    edited 2011-03-14 00:48
    Monolithic ceramic caps can fail from thermal runaway...as can tantalum caps

    what was the specific application you were employing the bypass caps?

    I would suggest always building a large amount of headroom into your selection....better to have too much than too little in this case....

    I personally think the best use of a ceramic is for a small value input filter

    there is a good reason for the prolific use of polarized electrolytic caps in power supplies....especially over 3 amps

    just keep in mind that a 1/2 farad polarized electrolytic will punch a hole through your ceiling if you hook it up backwards....don't ask me how I know this (I will deny that i have ever done that)
  • groggorygroggory Posts: 205
    edited 2011-03-14 05:26
    The ceramic caps were decoupling caps for a LP3853-3.3 linear regular I was using on a board. The board was being powered by 4 x AA's.
  • AriAri Posts: 63
    edited 2011-03-14 14:43
    groggory wrote: »
    The ceramic caps were decoupling caps for a LP3853-3.3 linear regular I was using on a board. The board was being powered by 4 x AA's.


    The only thing I would use a monolithic ceramic for in that regulator circuit, is an input filter.....for everything else I would use electrolytic, and if the current draw was high enough, a supercap...

    were the AA batteries lithium or alkaline....better yet 1.2-1.5 v or 3.2-3.7v?

    also how far away from the batteries is the input? I.E. how long were the leads from the battery to the Vin on the regulator?
  • groggorygroggory Posts: 205
    edited 2011-03-14 17:00
    Ari wrote: »
    The only thing I would use a monolithic ceramic for in that regulator circuit, is an input filter.....for everything else I would use electrolytic, and if the current draw was high enough, a supercap...

    were the AA batteries lithium or alkaline....better yet 1.2-1.5 v or 3.2-3.7v?

    also how far away from the batteries is the input? I.E. how long were the leads from the battery to the Vin on the regulator?
    They were AA Alkaline (~1.5V)

    There was probably 5 inches of wire and 2 inches of PCB traces between the batteries and the input of the vReg.
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