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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Thu, 25 Apr 2024 22:25:07 +0200
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On 25-04-2024 17:36, Bill Sloman 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.
> 
I have that book. Only found it useful a couple of times...