Path: ...!weretis.net!feeder9.news.weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Sat, 27 Apr 2024 01:26:09 +1000
Organization: A noiseless patient Spider
Lines: 103
Message-ID: <v0gh2v$3otv6$1@dont-email.me>
References: <v09htg$1tjdf$2@dont-email.me>
 <66rk2jl35lbgd2tnqc6jjoqsd70ig9d485@4ax.com> <v0dt9i$32s0p$1@dont-email.me>
 <aldn2j9kf84stcb23q3or9o70ga9laguku@4ax.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Fri, 26 Apr 2024 17:26:25 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="37e01aa39ad71e591c97e77262d7e9b8";
	logging-data="3962854"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18ih6J7aGQi63y3UOiGT04Cx6qChAItg3s="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:M/+tPJep7bfLgmfZPdJJIRYh5M8=
Content-Language: en-US
In-Reply-To: <aldn2j9kf84stcb23q3or9o70ga9laguku@4ax.com>
Bytes: 4889

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.

The late great Tony Williams passed out .pdf copies to his s.e.d. mates

They started off with the transformer equation, and I don't think that 
that ever showed up in Snelling's book.

> One of the earliest comprehensive studies of ferrite material apps.

Comprehensive perhaps, but vilely organised and incoherent.

> There's an electronic version of the first edition on line, for
> those interested.

And silly enough to risk it.

> It has a later revision (~Y2K), that I also can't afford.

Don't bother.

-- 
Bill Sloman, Sydney