Re: two drums

On 2025-03-13 10:41, john larkin wrote:

On Thu, 13 Mar 2025 07:42:28 -0400, legg <legg@nospam.magma.ca> wrote:
 

On Tue, 11 Mar 2025 19:35:38 -0700, john larkin <jlArbor.com> wrote:
>

>
https://www.dropbox.com/scl/fo/qpfhkvbfig7elysx78lq3/ALGqgMaRq1tx8aIiN3p1TfM?rlkey=36bcqfdb9di22ko48j89vocut&dl=0
>
If I put two of these drum core inductors close together, and get the
phasing right, I get an extra 5 mH for free, without any more ESR. And
external mag fields drop too, I think.

>
Check ripple and transient load response (load one - measure the
other).
>
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
>
RL

 The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
 I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
 The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately.  Coupled inductors in series have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same direction in both cores, so the in the low frequency limit, the B field contributions add everywhere.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com