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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Sat, 27 Apr 2024 23:51:14 +0200
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On 27-04-2024 19:17, legg wrote:
> On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> On 27/04/2024 12:24 am, legg wrote:
>>> 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.
>>>
>>> If you wind transformers, they are all pretty straight forward terms.
>>
>> I have wound ferrite-cored transformers from time to time, and they
>> stuck me as unspecific word salad.
>>
>>>> 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.
>>>
>>> The physical limit of saturation at lower frequencies and core loss
>>> at higher frequencies is a basic trade off in ferrite design.
>>
>> Obviously.
>>
>>>>> 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.
>>>
>>> High voltage design is worth serious study, before spending the
>>> shekels. I'd suggest consulting someone with previous experience.
>>> Imagination vs 'Why you can't do that' is a tiring back and forth.
>>>>
>>>> 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.
>>>
>>> In my day, it was considered to be the bible, but I could never
>>> afford a copy, so depended on photocopies and library access.
>>
>> I worked for EMI Central Research at time I thought that I needed it, so
>> access wasn't a problem. The Seimens soft ferrite application notes
>> turned out to be a great deal more useful, and much better organised.
> 
> I believe it was Janson, Barrow and Burgum, with Jongsma at Philips
> (Mullard), who reorganized Snelling's math into useful off-the-cuff
> expressions in the mid 70s. . . using the Steinmetz coefficients etc.
> 
> E.A.B. 32 through 34 are typical, if my records are accurate.
> 
> The Seimens catalog notes for use of power ferrite graphs 'sort of'
> did the same, without actually explicitly stating ANY of them.
> They were free and in book form.
> 
> Anyways, high voltage applications are a different book.
> 
Speaking of a book, I have yet to find a book on HV SMPS design....