Path: ...!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: Fri, 26 Apr 2024 01:36:06 +1000 Organization: A noiseless patient Spider Lines: 61 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: Thu, 25 Apr 2024 17:36:19 +0200 (CEST) Injection-Info: dont-email.me; posting-host="e1588e6f40ac986c41ea6396f515297a"; logging-data="3239961"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+0eY8GzkMlFZutzwo0pHyNNXyGaaK6IsI=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:zTLbx0DpBaSPdxzrhK0WwtzdTX8= In-Reply-To: <66rk2jl35lbgd2tnqc6jjoqsd70ig9d485@4ax.com> Content-Language: en-US Bytes: 3118 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. 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. -- Bill Sloman, Sydney