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: Klaus Vestergaard Kragelund Newsgroups: sci.electronics.design Subject: Re: CCFL transformer Date: Sat, 27 Apr 2024 02:17:23 +0200 Organization: A noiseless patient Spider Lines: 76 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sat, 27 Apr 2024 02:17:24 +0200 (CEST) Injection-Info: dont-email.me; posting-host="802927b90780904bd0493facb9411aa9"; logging-data="4185493"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19MW2UXTasQVBAaBkkYDJvwbqWp4jGDzoc=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:jA/TefjQnmscQ3zsK1Cjz997Xvs= Content-Language: en-US In-Reply-To: Bytes: 4028 On 25-04-2024 09:02, Bill Sloman wrote: > On 24/04/2024 3:10 pm, Bill Sloman wrote: >> On 24/04/2024 12:25 pm, John Larkin 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 >>>> step-up 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.... >>> >>> Can you use a C-W multiplier? >>> >>> For low current, you can do resonant tricks too. >> >> It's easier to use a voltage doubler or tripler that it is to find a >> multi-section former off-the shelf. The occasional high voltage power >> supply that I've dismantled clearly used proprietary formers, as do >> the Coilcraft parts >> >> I suppose one could use self-bonding wire to make a series of >> self-supporting pancake windings, but I've never heard of anybody >> doing it. >> >> The Baxandall configuration is definitely a resonant trick, and copes >> with the interwinding capacitance by resonating it with the winding >> inductance. >> >> There's nothing "low current" about it, but if you are working at >> higher currents and powers you can justify even more elaborate >> switching arrangements. >> >> http://sophia-elektronica.com/Baxandall1959JM.pdf >> >> Jim Williams talked about it a lot - application notes AN45, AN49, >> AN51, AN55, AN61, AN65 - but described it as a "a current driven Royer >> inverter" which is simply wrong. >> >> MOSFETs work better as switches than bipolar transistors, and don't >> seem to "squeg". > > The Coilcraft data sheets don't say anything much about the resonant > frequencies of their transformers - except "The FL Series of > transformers is designed for use in cold cathode fluorescent lamp (CCFL) > power supplies at operating frequencies up to 100 kHz" where the "up to > 100kHz" gives them a lot of wriggle room. > > A primary inductance of around 50uH with a 100:1 step-up implies a 0.5H > secondary inductance. 10pF parallel capacitance would give a 71kHz > resonant frequency, which is less than 100kHz. > > Of course once you have one of the Coilcraft parts you can measure the > resonant frequency. > Measurement: https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF