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From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Sun, 01 Sep 2024 19:49:39 -0700
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On Sun, 01 Sep 2024 17:43:32 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:

>On Sun, 01 Sep 2024 13:17:03 -0700, john larkin
><jlarkin_highland_tech> wrote:
>
>>On Sun, 01 Sep 2024 15:53:46 -0400, Joe Gwinn <joegwinn@comcast.net>
>>wrote:
>>
>>>On Sun, 1 Sep 2024 17:55:58 -0000 (UTC), Phil Hobbs
>>><pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>>john larkin <jlarkin_highland_tech> wrote:
>>>>> On Sun, 1 Sep 2024 17:45:46 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>>> wrote:
>>>>> 
>>>>>> On 30/08/2024 2:21 am, Jan Panteltje wrote:
>>>>>>> On a sunny day (Fri, 30 Aug 2024 00:43:39 +1000) it happened Bill Sloman
>>>>>>> <bill.sloman@ieee.org> wrote in <vaq1f2$jdj$1@dont-email.me>:
>>>>>>> 
>>>>>>>> It's lot easier and quicker to bread-board a circuit in LTSpice than it
>>>>>>>> is to wire up a test circuit, but what that means is that you need to
>>>>>>>> make fewer real circuits and they are a lot more likely to work when tested.
>>>>>>>> 
>>>>>>>> That, on it's own, is enough to explain why labs look different today
>>>>>>>> than they did in the dark ages.
>>>>>>> 
>>>>>>> All it explains is boeings falling apart and astronuts ending up stuck at the ISS
>>>>>>> and no moonlanding from the US, not even a probe.
>>>>>>> Slimulations are _not_ realty and never will be.
>>>>>> 
>>>>>> But they can capture useful parts of reality, if you know what you are 
>>>>>> doing.
>>>>>> 
>>>>>> John Larkin's simulated inductors tend not to have any parallel capacitance.
>>>>> 
>>>>> The trick is to know when it matters. ESR and core loss are usually
>>>>> more important.
>>>>> 
>>>>> I designed this surface-mount inductor for my Pockels Cell driver,
>>>>> after several tries using commercial parts. They all smoked.
>>>>> 
>>>>> It's wound on a specially marked Sharpie pen that we have carefully
>>>>> reserved.
>>>>
>>>>It better have a regular calibration schedule, or your semiconductor
>>>>customers may give you the raised eyebrow. 
>>>
>>>Hmm.  To be overly serious:  With traceability to NIST (US) or NPL
>>>(UK) or the like.
>>>
>>>The trend in standards is to eliminate standards tied to a physical
>>>object.
>>>
>>>I have a Sharpie in hand.  The barrel that is not covered by the cap
>>>is a truncated cone, being 11.0 mm at the blunt end and 12.32 mm near
>>>the cap, 73 mm away.
>>
>>Mine is pretty cylindrical for the length of the coil. I expect that
>>the operator's (ie, my)  applied tension affects the radius too.
>
>Most likely.
>
>
>>That inductor sees 25 amps p-p, roughly a sawtooth, at 4 MHz. The
>>Coilcraft parts that I tried all smoked, I guess from skin effect and
>>proximity effect.
>>
>>>
>>>Actually, all that's needed is to specify an ideal geometric shape,
>>>with tolerances, in the formal documentation.  
>>>
>>>Joe Gwinn
>>
>>I'll have someone start on a SolidWorks model.
>
>I bet you need the standoff, so the lossy FR4 material isn't too
>close.  That should be in the requirements as well.

The turns squish down into the gap-pad gunk, which is an OK heat
conductor. The PCB under the pad is a big copper pour, top and bottom,
with a zillion thermal vias.  There's more gap-pad on the underside of
the board to dump heat into the baseplate.

At 4 MHz, skin depth is 32 microns, so most of the copper is wasted.
That's why it gets so hot.

I tried three of the Coilcraft 1010VS parts in series, but they
smoked, probably skin+proximity effect.  Maybe parallel would have
been better.

>
>I'd specify the coil dimensions, not the mandrel dimensions, which may
>be provided as a helpful suggestion only.
>
>Joe Gwinn

I could have a mandrel machined or 3D printed, to more accurately wind
the inductor. The improvement would be mostly cosmetic.

Inductors are a pain.