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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Fri, 26 Apr 2024 10:57:24 -0400
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On Fri, 26 Apr 2024 01:36:06 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 26/04/2024 12:52 am, legg wrote:
>> On Wed, 24 Apr 2024 01:57:36 +0200, Klaus Vestergaard Kragelund
>> <klauskvik@hotmail.com> wrote:
>> 
>>> Hi
>>>
>>> I need a low distributed capacitance winding transformer, for a HV
>>> stepup function (3.5kV)
>>>
>>> I am zeroing in on similar concept as CCFL transformers with
>>> sectionalized bobbin.
>>>
>>> For example:
>>>
>>> https://www.coilcraft.com/en-us/products/transformers/power-transformers/ccfl-transformers/fl/
>>>
>>> Possibly using Triple Insulated Wire to create some distance between the
>>> individual turns.
>>>
>>> Not many sells CCFLs these days.
>>>
>>> Guess I will keep it alive....
>>>
>>> Regards
>>>
>>> Klaus
>> 
>> Stress between turns is limited by v/n limit of core. It's layer
>> stress and section stress that you have to deal with.
>> That's what the multisection bobbin and pancake windings do.
>
>They also reduce the parallel capacitance of the windings, and give you 
>are higher resonant frequency for the transformer as a whole.
>
>"Layer stress" and "section stress" aren't specific electronic 
>engineering terms, and the "v/n" limit of the core is pretty vague.
>
>There is a volt per turn limit imposed by the magnetic field that 
>saturates the core - but at higher frequencies you can tolerate more 
>volts per turn before the core saturates - it's a linear function of 
>switching frequency, up to the point where resistance around the current 
>loops inside the core lets enough current circulate to heat the core 
>above its Curie temperature.
>
>> If the CCFL transformer will allow only 1600V, imagine the
>> precautions required for 3x that stress. I'm not sure you
>> can avoid vacuum impregnation / potting in anything 'small'.
>
>Imagination does seem to be what's being applied here.
>
>There's a least one truly horrible 1969 text book on transformer design
>
>https://www.amazon.com.au/Soft-Ferrites-Applications-C-Snelling/dp/0408027606
>
>and it took me years to realise quite how confusing it was.

https://archive.org/details/SNELLING__SOFT-FERRITES__1969/page/n13/mode/2up?view=theater

RL