Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Klaus Vestergaard Kragelund Newsgroups: sci.electronics.design Subject: Re: CCFL transformer Date: Sat, 27 Apr 2024 23:51:14 +0200 Organization: A noiseless patient Spider Lines: 98 Message-ID: References: <66rk2jl35lbgd2tnqc6jjoqsd70ig9d485@4ax.com> <1cbq2j1168l9mpeefrghbcdtlt56131h1r@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sat, 27 Apr 2024 23:51:14 +0200 (CEST) Injection-Info: dont-email.me; posting-host="802927b90780904bd0493facb9411aa9"; logging-data="639876"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+AhBDkEiXFK0VpVgu6F/xX62CNwlUdpHM=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:Oqo0pg47RP5s30e4R0EAxfOmeuA= In-Reply-To: <1cbq2j1168l9mpeefrghbcdtlt56131h1r@4ax.com> Content-Language: en-US Bytes: 5257 On 27-04-2024 19:17, legg wrote: > On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman > wrote: > >> 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. > > 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....