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 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: References: <66rk2jl35lbgd2tnqc6jjoqsd70ig9d485@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: Bytes: 4889 On 27/04/2024 12:24 am, legg wrote: > On Fri, 26 Apr 2024 01:36:06 +1000, Bill Sloman > wrote: > >> On 26/04/2024 12:52 am, legg wrote: >>> On Wed, 24 Apr 2024 01:57:36 +0200, Klaus Vestergaard Kragelund >>> 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