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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: those coupled drum core inductors
Date: Mon, 17 Mar 2025 01:30:45 +1100
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On 17/03/2025 1:15 am, john larkin wrote:
> 
> 
> https://www.dropbox.com/scl/fi/cd8gxmlrar3kvv3iz36xe/Mu_twin.jpg?rlkey=dvl8e7fbtjnzz3l9q9urkyyfn&raw=1
> 
> https://www.dropbox.com/scl/fi/nm1ksdn7eufm90ol0b0ec/Murata_Coupled_1.jpg?rlkey=e7yvk464xupz4axy7lt6zj3zk&raw=1
> 
> I was surprised to get K=0.6 by just putting them along side.

Why? And your second url doesn't exactly make the point in a way that is 
easy to follow.

The ferrite in the drums has permeability that is about a thousand times 
higher than that of free space, so the adjacent drum is going to suck in 
a whole lot of flux lines.

The transformer equations are

V1=L1.dI1/dt+M.dI2/dt

V2=M.dI1/dt+L2.dI2/dt

where M=K.sqrt(L1.L2)

-- 
Bill Sloman, Sydney