Ok guys, this has been driving me crazy and I would love an absolute universal answer (even though I know there are disputes)...

Which symbol should I use for a polarized capacitor? At school they taught us to use the "two straight lines with a + indicator", however, online I mostly come across the "one straight and one curved line", sometimes with a + indicator. And then there is the unholiest of all that is unholy, the "white box for positive and black box for negative" approach.

I googled PSU schematics to try and get a good picture of which once were most used, but out of the top three schematics, they used all of the above mentioned conventions.

So, to sum up: Which symbol should I use from now on?

  • \$\begingroup\$ Whichever floats your boat? \$\endgroup\$ – ThreePhaseEel Sep 10 '16 at 16:58
  • \$\begingroup\$ You might find your employers or customers have a preference. \$\endgroup\$ – gbulmer Sep 10 '16 at 17:04
  • \$\begingroup\$ As @ThreePhaseEel says "Whichever floats your boat?", just be consistent! \$\endgroup\$ – StainlessSteelRat Sep 10 '16 at 18:24
  • \$\begingroup\$ Ah - you mean a polarised condenser. Circuit symbols (and components) have been around a long time and have been subject to change by various national and international engineering bodies. Learn to appreciate the beauty and elegant simplicity of a circuit diagram and its many foibles. \$\endgroup\$ – JIm Dearden Sep 10 '16 at 18:55
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    \$\begingroup\$ My understanding was that the open and full rectangles were the current preference. The curved one I have seen mostly in rather old circuit diagrams and the one with the "+" symbon could cause confusion in a dense schematic. However it is up to you though best to conform to the guy who is paying the bills. \$\endgroup\$ – KalleMP Sep 10 '16 at 19:21

All of these are listed in assorted "standards", and so are correct. But different symbols are more prevalent depending on your geographical location.

The American standard is IEEE 315 and the European is IEC 60617. There is enough crossover, however, that people are accustomed to seeing both types of symbols.

In the USA, I almost always see

enter image description here

for non-polarized caps, and

enter image description here

with or without the plus sign for polarized caps. That is, the curve generally denotes polarization. I seldom (almost never) see the curved line used for non-polarized caps.

These IEEE symbols are also common on non-USA schematics. On sheets with European-style symbols, I usually only see these:

enter image description here

Sometimes the + side of the polarized cap has a white box, but black or white, the + sign always seems to be there.

As people are saying in the comments, choose either:

  1. Whatever you like, or
  2. Whatever your company (or customer) likes.
  • 2
    \$\begingroup\$ As an IC designer, I would like to add, that we often use the curved line to indicate the "bottom plate" of the capacitor, which is the one closer to the substrate. However, this really only matters for IC design. \$\endgroup\$ – Mario Sep 10 '16 at 21:34
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    \$\begingroup\$ @Mario It actually matters for precision analog design too-- you usually want the outer part of a film cap to be sitting on and connected to a ground plane or other low impedance node. \$\endgroup\$ – Spehro Pefhany Sep 10 '16 at 21:49
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    \$\begingroup\$ The curved line also represented the "outside" foil of a typical rolled foil/dielectric capacitor. In some cases, you can make a circuit (particularly audio) quieter by connecting the "outside" pole to the lower-impedance side of the interconnection. \$\endgroup\$ – Richard Crowley Sep 10 '16 at 21:49
  • \$\begingroup\$ @Spehro Pefhany and Richard Crowley very interesting indeed. I also do discrete design from time to time but I didn't know that. \$\endgroup\$ – Mario Sep 10 '16 at 21:58

There are several "standards". As in many cases there are "European" (DIN or EU or less formal) standards, and US/North American standards. For example, many components are shown as simple rectangles in the European tradition, while we here in the US more often use more representative symbols like the zig-zag line for resistors, the "S-curve" symbol for fuses, etc.

And one of the things that I liked about the European capacitor symbols was using open "boxes" on both sides for non-polarized capacitors, and using a black-filled rectangle for the negative side of a polarized capcitor.

As others have already suggested, it seems silly to try to decide on one style to use "from now on". Which one you use in any particualr situation depends on the context and you should be flexible enough to deal with ALL the different standards.


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