Forums

Dots on inductors

Started by Raveninghorde November 26, 2012
I read many years ago (National app note from memory) that one should
connect the inner layer of an inductor to the switch in a buck
regulator and the outer layer to the capacitor as the outer layer will
then act as a screen.

I don't know if it makes a difference in practice but it's free.

With many modern inductors it is impossible to see how they are wound
so the only indication of "polarity" is the dot. Is the dot arbitary
and down to the winder or does it actually relate in anyway to the way
the inductor is wound?
On Mon, 26 Nov 2012 16:48:51 +0000, Raveninghorde
<raveninghorde@invalid> wrote:

>I read many years ago (National app note from memory) that one should >connect the inner layer of an inductor to the switch in a buck >regulator and the outer layer to the capacitor as the outer layer will >then act as a screen. > >I don't know if it makes a difference in practice but it's free. > >With many modern inductors it is impossible to see how they are wound >so the only indication of "polarity" is the dot. Is the dot arbitary >and down to the winder or does it actually relate in anyway to the way >the inductor is wound?
It indicates phasing alone. Constructional details, where critical, will only show on the winding sheet. You won't get the winding you want without including winding instructions in the transformer drawing and then batch inspecting each purchased lot. RL
On Mon, 26 Nov 2012 16:40:18 -0500, legg <legg@nospam.magma.ca> wrote:

>On Mon, 26 Nov 2012 16:48:51 +0000, Raveninghorde ><raveninghorde@invalid> wrote: > >>I read many years ago (National app note from memory) that one should >>connect the inner layer of an inductor to the switch in a buck >>regulator and the outer layer to the capacitor as the outer layer will >>then act as a screen. >> >>I don't know if it makes a difference in practice but it's free. >> >>With many modern inductors it is impossible to see how they are wound >>so the only indication of "polarity" is the dot. Is the dot arbitary >>and down to the winder or does it actually relate in anyway to the way >>the inductor is wound? > >It indicates phasing alone. Constructional details, where critical, >will only show on the winding sheet. > >You won't get the winding you want without including winding >instructions in the transformer drawing and then batch inspecting each >purchased lot. > >RL
The dot is for phasing of a TRANSFORMER. In such a case, it indicates the winding START point. In many cases, it is already part of the bobbin. In some cases, it gets painted on as part of the winding process. There is no need to mark the winding start of an inductor. An inductor is a non phased device. No, it matters not which 'way' it gets utilized. AT ALL.
On Mon, 26 Nov 2012 15:44:04 -0800, SoothSayer wrote:

> On Mon, 26 Nov 2012 16:40:18 -0500, legg <legg@nospam.magma.ca> wrote: > >>On Mon, 26 Nov 2012 16:48:51 +0000, Raveninghorde >><raveninghorde@invalid> wrote: >> >>>I read many years ago (National app note from memory) that one should >>>connect the inner layer of an inductor to the switch in a buck >>>regulator and the outer layer to the capacitor as the outer layer will >>>then act as a screen. >>> >>>I don't know if it makes a difference in practice but it's free. >>> >>>With many modern inductors it is impossible to see how they are wound >>>so the only indication of "polarity" is the dot. Is the dot arbitary >>>and down to the winder or does it actually relate in anyway to the way >>>the inductor is wound? >> >>It indicates phasing alone. Constructional details, where critical, will >>only show on the winding sheet. >> >>You won't get the winding you want without including winding >>instructions in the transformer drawing and then batch inspecting each >>purchased lot. >> >>RL > > > The dot is for phasing of a TRANSFORMER. In such a case, it indicates > the winding START point. In many cases, it is already part of the > bobbin. In some cases, it gets painted on as part of the winding > process. There is no need to mark the winding start of an inductor. > > An inductor is a non phased device. > > No, it matters not which 'way' it gets utilized. AT ALL.
I don't think that's entirely true. Which way you use it doesn't change the inductive behavior of the part, but it does change the parasitic capacitance of the part to neighboring parts on the board, and/or how it radiates. If the outside windings are on the "cold" end of the inductor they'll tend to provide some measure of electrostatic shielding. If they're on the "hot" end they'll tend to provide a bit of electrostatic coupling to the world at large, much the same as if you had a similar-sized cylinder of metal attached to that circuit node. This may not matter for most practical purposes, but it certainly feels like something that would have an effect on EMI, depending on how the circuit is built. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
On Mon, 26 Nov 2012 15:44:04 -0800, SoothSayer
<SaySooth@TheMonastery.org> wrote:

>On Mon, 26 Nov 2012 16:40:18 -0500, legg <legg@nospam.magma.ca> wrote: > >>On Mon, 26 Nov 2012 16:48:51 +0000, Raveninghorde >><raveninghorde@invalid> wrote: >> >>>I read many years ago (National app note from memory) that one should >>>connect the inner layer of an inductor to the switch in a buck >>>regulator and the outer layer to the capacitor as the outer layer will >>>then act as a screen. >>> >>>I don't know if it makes a difference in practice but it's free. >>> >>>With many modern inductors it is impossible to see how they are wound >>>so the only indication of "polarity" is the dot. Is the dot arbitary >>>and down to the winder or does it actually relate in anyway to the way >>>the inductor is wound? >> >>It indicates phasing alone. Constructional details, where critical, >>will only show on the winding sheet. >> >>You won't get the winding you want without including winding >>instructions in the transformer drawing and then batch inspecting each >>purchased lot. >> >>RL > > > The dot is for phasing of a TRANSFORMER. In such a case, it indicates >the winding START point. In many cases, it is already part of the >bobbin. In some cases, it gets painted on as part of the winding process. >There is no need to mark the winding start of an inductor. > > An inductor is a non phased device. > > No, it matters not which 'way' it gets utilized. AT ALL.
It can matter, just like the "outside foil" of a film cap (black band) sometimes matters. There's less capacitive coupling to the outside world, less radiated EMI, of the outside of the winding is at AC ground. Also, sometimes magnetic coupling between inductors matters, like in filters. Polarity could matter there, too. Someone used to, maybe still does, make choke inductors that have internal biasing magnets, to increase saturation current in one direction. There are hum-bucking applications, too. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Raveninghorde wrote:
> I read many years ago (National app note from memory) that one should > connect the inner layer of an inductor to the switch in a buck > regulator and the outer layer to the capacitor as the outer layer will > then act as a screen. > > I don't know if it makes a difference in practice but it's free. > > With many modern inductors it is impossible to see how they are wound > so the only indication of "polarity" is the dot. Is the dot arbitary > and down to the winder or does it actually relate in anyway to the way > the inductor is wound?
Nope, no standard there. Fastest way to find out is crack one open and look. Watch out for ferrite shrapnel. The gentle method is to measure the RF leaking out with one end grounded and the other energized, then reverse. Then talk to the mfg whether their production procedure (SOP) calls out to always connect in this particular way. Typically they are but it can be tough to obtain something in writing about it. -- Regards, Joerg http://www.analogconsultants.com/
On Nov 27, 10:44=A0am, SoothSayer <SaySo...@TheMonastery.org> wrote:
> On Mon, 26 Nov 2012 16:40:18 -0500, legg <l...@nospam.magma.ca> wrote: > >On Mon, 26 Nov 2012 16:48:51 +0000, Raveninghorde > ><raveninghorde@invalid> wrote: > > >>I read many years ago (National app note from memory) that one should > >>connect the inner layer of an inductor to the switch in a buck > >>regulator and the outer layer to the capacitor as the outer layer will > >>then act as a screen. > > >>I don't know if it makes a difference in practice but it's free. > > >>With many modern inductors it is impossible to see how they are wound > >>so the only indication of "polarity" is the dot. Is the dot arbitary > >>and down to the winder or does it actually relate in anyway to the way > >>the inductor is wound? > > >It indicates phasing alone. Constructional details, where critical, > >will only show on the winding sheet. > > >You won't get the winding you want without including winding > >instructions in the transformer drawing and then batch inspecting each > >purchased lot. > > >RL > > =A0 The dot is for phasing of a TRANSFORMER. =A0In such a case, it indica=
tes
> the winding START point. =A0In many cases, it is already part of the > bobbin. In some cases, it gets painted on as part of the winding process. > There is no need to mark the winding start of an inductor. > > =A0 An inductor is a non phased device. > > =A0 No, it matters not which 'way' it gets utilized. =A0AT ALL.
Wrong. If the outermost layer of a multilayer winding is connected to ground at one end, the inductor as a whole will radiate appreciably less than it would if one end of the outermost layer were connected to a high AC voltage. It only the stray capacitative coupling that changes, but that can matter quite a lot. -- Bill Sloman, Sydney
On Mon, 26 Nov 2012 17:27:46 -0800, Joerg <invalid@invalid.invalid>
wrote:

>Raveninghorde wrote: >> I read many years ago (National app note from memory) that one should >> connect the inner layer of an inductor to the switch in a buck >> regulator and the outer layer to the capacitor as the outer layer will >> then act as a screen. >> >> I don't know if it makes a difference in practice but it's free. >> >> With many modern inductors it is impossible to see how they are wound >> so the only indication of "polarity" is the dot. Is the dot arbitary >> and down to the winder or does it actually relate in anyway to the way >> the inductor is wound? > > >Nope, no standard there. Fastest way to find out is crack one open and >look. Watch out for ferrite shrapnel. The gentle method is to measure >the RF leaking out with one end grounded and the other energized, then >reverse. Then talk to the mfg whether their production procedure (SOP) >calls out to always connect in this particular way. Typically they are >but it can be tough to obtain something in writing about it.
I've just checked with a German manufacturer and they confirm the dot on their inductors is the start of the inner winding. I appreciate not all manufacturers will necessarily be as consistent.
Raveninghorde wrote:
> On Mon, 26 Nov 2012 17:27:46 -0800, Joerg <invalid@invalid.invalid> > wrote: > >> Raveninghorde wrote: >>> I read many years ago (National app note from memory) that one should >>> connect the inner layer of an inductor to the switch in a buck >>> regulator and the outer layer to the capacitor as the outer layer will >>> then act as a screen. >>> >>> I don't know if it makes a difference in practice but it's free. >>> >>> With many modern inductors it is impossible to see how they are wound >>> so the only indication of "polarity" is the dot. Is the dot arbitary >>> and down to the winder or does it actually relate in anyway to the way >>> the inductor is wound? >> >> Nope, no standard there. Fastest way to find out is crack one open and >> look. Watch out for ferrite shrapnel. The gentle method is to measure >> the RF leaking out with one end grounded and the other energized, then >> reverse. Then talk to the mfg whether their production procedure (SOP) >> calls out to always connect in this particular way. Typically they are >> but it can be tough to obtain something in writing about it. > > I've just checked with a German manufacturer and they confirm the dot > on their inductors is the start of the inner winding. > > I appreciate not all manufacturers will necessarily be as consistent.
Great, then at least you found one where they have a system to it. If this is for a product design I'd still get that in writing though. -- Regards, Joerg http://www.analogconsultants.com/
On Mon, 26 Nov 2012 15:44:04 -0800, SoothSayer
<SaySooth@TheMonastery.org> wrote:

>On Mon, 26 Nov 2012 16:40:18 -0500, legg <legg@nospam.magma.ca> wrote: > >>On Mon, 26 Nov 2012 16:48:51 +0000, Raveninghorde >><raveninghorde@invalid> wrote: >> >>>I read many years ago (National app note from memory) that one should >>>connect the inner layer of an inductor to the switch in a buck >>>regulator and the outer layer to the capacitor as the outer layer will >>>then act as a screen. >>> >>>I don't know if it makes a difference in practice but it's free. >>> >>>With many modern inductors it is impossible to see how they are wound >>>so the only indication of "polarity" is the dot. Is the dot arbitary >>>and down to the winder or does it actually relate in anyway to the way >>>the inductor is wound? >> >>It indicates phasing alone. Constructional details, where critical, >>will only show on the winding sheet. >> >>You won't get the winding you want without including winding >>instructions in the transformer drawing and then batch inspecting each >>purchased lot. >> >>RL > > > The dot is for phasing of a TRANSFORMER. In such a case, it indicates >the winding START point. In many cases, it is already part of the >bobbin. In some cases, it gets painted on as part of the winding process. >There is no need to mark the winding start of an inductor. > > An inductor is a non phased device. > > No, it matters not which 'way' it gets utilized. AT ALL.
It is highly unlikely that a dot will occur on a magnetic drawing that has only one winding. Inductors with multiple, tapped and phase-coherent windings do exist and are constructed with all of the precautions required for transformers. The are called inductors simply as a convention to indicate their intended use. Every line-powered computer you've ever seen probably has one of the more common examples; a common-mode choke to assist with EMC compliance. Such a part becomes unpredictable (if not completely useless) if phasing or winding instructions are ignored. There are many intentional constructional details in magnetic components that are not immediately obvious, even to the experienced technician, that can determine their effectiveness in many ways. RL