Re: squeezing a field

On 23-10-2024 19:22, john larkin wrote:

I'm designing a small PCB with essentially 5 sync buck switching
regulators. Board space is tight so I want to put the inductors on the
bottom of the multilayer board. There's a 0.2" gap between the bottom
of the board and a big aluminum flange.
 Unshielded drum cores have the most energy storage per volume or
dollars. They store energy in the universe instead of in ferrite. Good
cooling too.
 Something like this just fits
 https://www.digikey.com/en/products/detail/bourns-inc/SRN8040TA-470M/6155133
 Its mag field lines will bounce off the PCB planes and the flange,
change from the classic bar magnet pattern into a pancake . I wonder
what that will do to its electrical behavior.
 

The proximity of the aluminum is probably close to the effects of having ground plane or not below the inductor.
Steve Sandler has tested this:
https://www.signalintegrityjournal.com/blogs/17-practical-emc/post/2694-dc-dc-converters-solid-return-plane-or-cutouts-under-switch-node-and-inductor
Found very little effect.
Similar test:
https://www.monolithicpower.com/en/learning/resources/when-is-it-beneficial-to-place-a-copper-layer-beneath-dc-dc-power-supplies?srsltid=AfmBOoq_cYcCoGN57iR4TXaq9n4hlYK1VWLt5m6yYGpVBdRF6RF7L7hz