X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com X-Virus-Scanned: amavisd-new at cloud9.net Date: Tue, 22 Jul 2014 10:16:16 -0400 (EDT) From: Stuart Brorson To: geda-user AT delorie DOT com Subject: Re: [geda-user] Do you put ground planes under inductors? In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Reply-To: geda-user AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: geda-user AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk 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? >