The inductor on default library has no polarity mark. Normally is not necessary a mark because an inductor have not polarity, (at end of day an inductor is a wire with turns)
But you work on Switching power supply this become important. The inductor mark point to the internal point of espires, this point need to be connected to Switching net and not on stabilized. This simple thing reduce the EMI and need to be marked on schema if you need pass any certification process .
2 Likes
See Elektuur Style Symbol Library (and Generic Symbol Library) in PCM on how to add an Indicator field with ●, + or − (on symbols, but also on schematics without the need to modify symbols), and also:
I design electronic power converters professionally and I have not previously encountered inductor polarity marks. I can think of two (unlikely but not impossible) reasons why it might be helpful:
- It is true that there is often much more voltage swing on one end of the inductor than the other. If that noisier end is on the inside of a multilayer coil, then there may be less tendency for capacitive noise coupling (to nearby circuits) than if it is on the outside. That being said, the vast majority of noise coupling problems seem to involve inductive coupling rather than capacitive coupling. I do not think that the inductive coupling will be affected by swapping ends of the inductor.
This reminds me of the “outer foil” marking on some very old wound film-foil type leaded capacitors. The idea was to connect ground to the outer foil of the capacitor. The only way I know of for me to see such a capacitor is to go digging through some ancient components I have in my lab. I think those components were pulled out of a TV set that originally belonged to Julius Caesar. 
But there was a big problem with TV’s in his day; there was a shortage of working power outlets.
- They are rare, but there is such a thing as a magnetic core (you could add a wound bobbin to make an inductor) with a biasing magnet. This inductor is designed to be driven with electromagnetic flux in only one direction. But I do not remember seeing such inductors from distributors. IF the cores are still available, it would be possible to build such an inductor. I think this would be a large inductor. such as at least 2-3 cm on a side.
1 Like
If I recall correctly outer winding of an inductor can in fact couple capacitively to other conductive elements and if it’s connected to the switching node it can increase EMI slightly. Polarity marks in some industries (esp. automotive) are most definitely a thing.
Obviously i make my own symbol, but the point of suggestion was not start a discussion about polarity or EMI.
Yes, Dawid is right. In my job we need certify all circuits about emission and inmunity into paid labs. We take care of this. I think that if sometimes is important is not problematic the inclussion of L_pol to the standard Lib
2 Likes
Murata has a nice explanation and some plots about it:
3 Likes
See also EN IEC 60375 for current international and European convention standard.
Also clarified my comment above (i.e. you can add an indicator as a field, with ☐ Allow autoplacement unchecked, to a symbol on a schematic and then simply duplicate that symbol without having to actually modify the graphical symbol itself).
I think that is not the point.
I think that include a polarized inductor don´t require break the code or a deeper and can help to the kicad users. Make a goodness without any damage for anybody.
i dont want start in the thesis, because Is easy make my own resistor or a capacitor too, but i think that a so common part is alread included to make easy to the kicad users
My point is that it takes only slightly more work than setting a component’s value by simply copying and pasting one of the symbols I provided above, and you can even choose your non-standard indicator. Sure, why not have an invisible, pre-set field by default (but I think current KLC wouldn’t allow it – I’m referring to the links in my first reply), but why force a particular indicator using fixed text or graphics?
I never say replace the actual L indicator, and my need was solved, i only suggest the addition of L_polarized.
2 Likes
I only suggested your need to be a bit more inclusive…
This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.