Re: mounting a pot core

From	john larkin <jl@glen--canyon.com>
Newsgroups	sci.electronics.design
Subject	Re: mounting a pot core
Date	2026-01-23 08:22 -0800
Organization	A noiseless patient Spider
Message-ID	<v677nktegk32ftr782msgk2k7vrs5h5e34@4ax.com> (permalink)
References	(3 earlier) <10kshda$2ovv2$1@dont-email.me> <80t4nkhljhf05rh1vn0395mjgmcghomki2@4ax.com> <10kv06s$3jqga$4@dont-email.me> <uqv6nkt9fol38q76suchg3cgroo3vef463@4ax.com> <10l02r1$3vsr8$1@dont-email.me>

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On Fri, 23 Jan 2026 16:07:13 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

>On 1/23/26 15:13, john larkin wrote:
>> On Fri, 23 Jan 2026 16:16:00 +1100, Bill Sloman <bill.sloman@ieee.org>
>> wrote:
>> 
>>> On 23/01/2026 6:09 am, john larkin wrote:
>>>> On Thu, 22 Jan 2026 17:51:12 +1100, Bill Sloman <bill.sloman@ieee.org>
>>>> wrote:
>>>>
>>>>> On 22/01/2026 5:18 am, john larkin wrote:
>>>>>> On Thu, 22 Jan 2026 04:49:33 +1100, Bill Sloman <bill.sloman@ieee.org>
>>>>>> wrote:
>>>>>>
>>>>>>> On 22/01/2026 3:45 am, john larkin wrote:
>>>>>>>>
>>>>>>>> https://www.dropbox.com/scl/fi/d7xug1xxazoishocjcwbm/R250_Pot_Core.jpg?rlkey=sakv9lo5ov4a8lx4cjoxzn8f6&raw=1
>>>>>>>>
>>>>>>>> My mechanical design guy is great, and pot cores are a PITA.
>>>>>>>>
>>>>>>>> This will be a transmission-line transformer, and I want all the
>>>>>>>> volt-seconds possible, so the pot core has to be big and barely fit in
>>>>>>>> the box. I've argued that zero vertical clearance is OK - let the top
>>>>>>>> cover and the PCB flex a bit - but mechanical people don't seem to
>>>>>>>> like that idea.
>>>>>>>
>>>>>>> Pot cores aren't the only shaped bits of ferrite you can buy. RM cores
>>>>>>> are another version of the same idea, and the cores that are designed to
>>>>>>> be used with printed circuit windings do seem to be flatter and wider.
>>>>>>
>>>>>> My intern tried several experiments of making the windings from kapton
>>>>>> flex, but they weren't as fast as using coax.
>>>>>
>>>>> The speed of electromagnet propagation is lower in Kapton that it is
>>>>> dielectrics like teflon and polyethylene, which have lower dielectric
>>>>> constants, but your Kapton flex probably wasn't designed to be a planar
>>>>> transmission line.
>>>>
>>>> We made several and we sure intended them to be txline windings.
>>>
>>> The road to hell is paved with good intentions.
>>>
>>>> We
>>>> don't understand why the planar windings were slow, but we need to
>>>> move on with life, and my intern has gone back to Cal Poly, so we'll
>>>> go with connectorized coax. That is known to work.
>>>
>>> Don't mess with stuff you don't understand.
>> 
>> We should mess with stuff we don't understand. We learn things. And
>> it's fun.
>> 
>> Well, maybe you know everything already and don't approve of fun.
>> 
>>>
>>>>>> A regular pot core with connectorized micro-coax wound on a bobbin is
>>>>>> nice, and easy to make in production. No soldering required.
>>>>>>
>>>>>>> The Siemens/TKD ferrite core catalog might be worth reading. Here's a
>>>>>>> small chunk.
>>>>>>>
>>>>>>> https://www.tdk-electronics.tdk.com/en/529402/products/product-catalog/ferrites-and-accessories/pq-cores-and-accessories
>>>>>>
>>>>>> We have samples like that. Seems to me that they would store less
>>>>>> energy than a full pot core.
>>>>>
>>>>> What matters to you is the total volume of ferrite, rather than its
>>>>> precise distribution. If you could find a wider, flatter ferrite core
>>>>> you should be able to store more energy in the same vertical headroom.
>>>>
>>>> We are tight on PCB area, and we need to move on with the project. We
>>>> can experiment with different ferrite materials once the boards are
>>>> built. There's lots available in this pot core size.
>>>
>>> But perhaps not the particular ferrite which would work best.
>> 
>> It's not hard to buy a bunch and try them.
>> 
>>>
>>> The thing about transmission line transformers is that the high
>>> frequency currents are pretty much confined to the transmission line, so
>>> that you can mostly get away with Manganese-Zinc ferrites which are
>>> normally only good for good couple of hundred kHz. If you found that
>>> Nickel-Zinc ferrites would work better you'd be confined to a smaller
>>> range of cores.
>>>
>>> Design is often a question of balancing lots of contradictory
>>> constraints. It pays to know something about all of them before you
>>> commit yourself to a particular volumetric limit.
>> 
>> This pot core uses about all the volume that we have, and it's a
>> standard size that lots of people make.
>> 
>> 
>> John Larkin
>> Highland Tech Glen Canyon Design Center
>> Lunatic Fringe Electronics
>
>I was wondering: Do you actually use this transformer as a balun?
>I mean, does the signal go in at one connector and out the other?
>
>Or is it more like a transformer, where you use the core of the
>coax as one winding and the shield as the other?
>
>Jeroen Belleman

We are using them as transformers. We drive the shield as the primary
and use the inner conductors as the secondary. 

The usual config has a high-voltage power supply on one end of the
primary and a mosfet (now a GaN fet) slamming the other end to ground,
with programmable pulse delay and width. 

The sec gives us an isolated pulse out of either polarity.

Since the windings are a transmission line, I guess the length of the
line limits how short a pulse we can make.

If we worked in balun mode, we couldn't make long pulses. 


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

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Thread

mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-21 08:45 -0800
  Re: mounting a pot core Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-01-21 12:28 -0500
  Re: mounting a pot core Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-01-21 12:28 -0500
    Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-21 10:11 -0800
  Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-22 04:49 +1100
    Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-21 10:18 -0800
      Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-21 23:47 +0100
        Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-21 16:34 -0800
          Re: mounting a pot core Joe Gwinn <joegwinn@comcast.net> - 2026-01-21 19:48 -0500
            Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-21 17:06 -0800
            Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-22 13:17 +0100
              Re: mounting a pot core Joe Gwinn <joegwinn@comcast.net> - 2026-01-22 12:47 -0500
                Re: mounting a pot core Joe Gwinn <joegwinn@comcast.net> - 2026-01-22 15:49 -0500
                Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-22 23:49 +0100
          Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-22 17:57 +1100
            Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-22 08:31 -0800
              Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-23 15:57 +1100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-23 06:24 -0800
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-24 03:35 +1100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-23 08:40 -0800
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-24 17:01 +1100
          Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-22 12:59 +0100
          Re: mounting a pot core legg <legg@nospam.magma.ca> - 2026-01-22 10:58 -0500
            Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-22 10:57 -0800
              Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-23 16:01 +1100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-23 06:19 -0800
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-24 03:19 +1100
                Re: mounting a pot core liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-01-24 19:25 +0000
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-25 14:33 +1100
                Re: mounting a pot core liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-01-25 11:07 +0000
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-26 02:46 +1100
                Re: mounting a pot core legg <legg@nospam.magma.ca> - 2026-01-25 08:51 -0500
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-25 08:08 -0800
                Re: mounting a pot core legg <legg@nospam.magma.ca> - 2026-01-25 22:44 -0500
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-26 17:56 +1100
                Re: mounting a pot core legg <legg@nospam.magma.ca> - 2026-01-26 10:50 -0500
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-27 03:23 +1100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-26 08:51 -0800
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-26 07:53 -0800
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-27 03:36 +1100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-26 08:48 -0800
                Re: mounting a pot core Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-01-26 13:12 -0500
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-26 10:58 -0800
                Re: mounting a pot core Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-01-26 20:36 +0000
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-27 14:30 +1100
      Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-22 17:51 +1100
        Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-22 11:09 -0800
          Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-23 16:16 +1100
            Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-23 06:13 -0800
              Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-23 16:07 +0100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-23 08:22 -0800
                Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-24 12:17 +0100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-24 07:54 -0800
                Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-25 13:04 +0100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-25 07:33 -0800
                Re: mounting a pot core Jeroen Belleman <jeroen@nospam.please> - 2026-01-25 17:32 +0100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-25 11:12 -0800
                Re: mounting a pot core JM <sunaecoNoChoppedPork@gmail.com> - 2026-01-25 19:44 +0000
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-25 13:07 -0800
                Re: mounting a pot core JM <sunaecoNoChoppedPork@gmail.com> - 2026-01-25 22:40 +0000
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-25 17:29 -0800
                Re: mounting a pot core JM <sunaecoNoChoppedPork@gmail.com> - 2026-01-25 19:40 +0000
              Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-24 03:39 +1100
                Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-23 10:09 -0800
                Re: mounting a pot core Bill Sloman <bill.sloman@ieee.org> - 2026-01-24 16:49 +1100
  Re: mounting a pot core legg <legg@nospam.magma.ca> - 2026-01-22 10:46 -0500
    Re: mounting a pot core john larkin <jl@glen--canyon.com> - 2026-01-22 11:16 -0800

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