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Date:	Tue, 22 Jul 2014 10:16:16 -0400 (EDT)
From:	Stuart Brorson <sdb AT cloud9 DOT net>
To:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] Do you put ground planes under inductors?
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This is really a question for the signal integrity guys over on
SI-List.  However, I'll take a bite, keeping in mind that I am not an
expert.

I'd go with the ground plane since it acts as a shield, and makes
layout easy.  It's always important to have a return path for
currents running around the board, and putting holes/slots in a ground
plane can interrupt return paths in unpredictable ways.

However, I would make it a point to clear other components away from
the inductor on both sides of the board.  As you say, if the
time-varying magnetic flux induces currents in the ground plane, any
component on the opposite side of the board from the inductor might
feel the effects of the induced current.  In particular, a ground
plane with non-zero impedance will experience potential drops
underneath the inductor, so you don't want components living there.

The opinion of a non-expert,

Stuart


On Tue, 22 Jul 2014, Bob Paddock wrote:

> Filippo's question about inductor footprints raised a question in my
> mind about inductor layout placement.
>
> I've read conflicting design advice on if a ground plane should be
> placed under the inductor used in switching power supplies.
>
> One school of though says the ground plane acts as a shield, doesn't
> put slots into the plane to interfere with return currents etc., this
> seems to be the most common approach.  This seems to assume everything
> is perfect in the real world.
>
> The other school of thought is not to put the plane under the inductor
> because the magnetic flux could introduce currents into the ground
> plane modulating 'ground', a type of ground pulling.  This seems to
> assume the real world is not perfect, ie. there are real world effects
> that we don't really want.
>
> Comments?
>

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