Which way do non-polarized film capacitors go? There is an answer.

orienting-non-polarized-film-caps

If you, like us, thought that capacitor orientation only matters for polarized varieties like electrolytic capacitors you should read through this article. [Bruce Trump] looks at why some film capacitors have a stripe printed on one end and why their orientation can matter.

He has an image rolled into his post showing both axial and dipped capacitors with a black stripe printed on one end of the package. This is an indicator of what is going on inside of the component. The end with the line has a conductive foil layer which acts as a shield. But it seems that this shield will do its job better if you do a better job of designing for the capacitor.

The diagram above shows two op-amp circuits, both using a non-polarized capacitor that will affect the circuit if it receives external interference. [Bruce] discusses various aspects of this phenomenon, mentioning that although these careful layouts can be tested in your designs to prove which has more benefits, simulated applications (using SPICE) will perform exactly the same.

Comments

  1. adcurtin says:

    That cap is “not polarized” in the same way most mosfets aren’t polarized. I.e. it is polarized‚Ķ

  2. Orienteerer says:

    Informative posts like this are one of the reasons I frequent Hackaday.

  3. The same sometimes is an issue with unshielded inductors: if you can hook it up so the outermost coils go to ground, rather than to a wildly switching node, you can often quiet a layout.

  4. mjrippe says:

    I did know this, but never thought about why it was important. Good info to have!

  5. echodelta says:

    This is old hat. In the tube days in a rats nest of a chassis, this mattered. Sometimes it would carry the label “outside foil” at one end. It’s not a shield, just the lesser of two evils.

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