Path: ...!local-4.nntp.ord.giganews.com!Xl.tags.giganews.com!local-3.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 13 Mar 2025 21:30:54 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: two drums Date: Thu, 13 Mar 2025 17:30:51 -0400 Message-ID: References: <4bs1tj5ua7r2kbcs8na9ij37pn3rk5dqbn@4ax.com> <8e2843da-d792-fb45-6b95-f8d834b527f0@electrooptical.net> <531574ce-36c1-d657-a013-131700df4eaa@electrooptical.net> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 73 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-bd1Hgj4+K1Nuhn0F4KnSoJ2zL3ce/q5vJiKY7FRhYGBjzzuweDvG3C5uKN2270OofQ3G8hLgMmd/TAp!tLkrhTKgyDR66MGT+qaViYaD2tXrdbqxntwuPv3OGgXNFlNbjvW7a2tbZDFRLn6+rA== X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 4215 On Thu, 13 Mar 2025 17:12:08 -0400, Phil Hobbs wrote: >On 2025-03-13 12:22, john larkin wrote: >> On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs >> wrote: >> >>> On 2025-03-13 10:41, john larkin wrote: >>>> On Thu, 13 Mar 2025 07:42:28 -0400, legg wrote: >>>> >>>>> On Tue, 11 Mar 2025 19:35:38 -0700, john larkin 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 >> >> If one core has a north pole up while the other is south, the flux >> makes a tight local loop. That makes L go up. It's approaching an >> all-ferrite gapless inductor. >> >> I tested the theory with a probe coil. Along the centerline of the two >> vertical inductors, induced field is zero. The two 5 mH inductors in >> series add up to 16 mH in this configuration. >> >> If the two series cores have current in the same direction, I get a >> bunch of field radiated and only about 8 mH net. It's kinda like >> winding all that wire onto one big drum core. > >Ah, okay, I forgot that your inductors are actually vertical not >horizontal. My bad. Isn't this the difference between a dipole field and a quadrupole field, regardless of vertical or horizontal? Joe