Re: two drums

On 14/03/2025 1:41 am, 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.

It doesn't use the whole universe - just the bit in the immediate vicinity of the inductor. The bonus L comes from the field lines that go through the adjacent ferrite. A inductor wound onto a toroid can be completely shielded - but only if the winding is non-progressive.
Something wound around a pot core is less perfectly shielded, so the semi-shielded inductor was invented a long time before people realised that toroidal cores were a good thing.
--
Bill Sloman, Sydney