Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 27 Apr 2024 02:36:11 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: CCFL transformer Date: Fri, 26 Apr 2024 19:34:19 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: <60po2j567ogmhdvg3hte0kjlkn7eq0vqpj@4ax.com> References: X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 82 X-Trace: sv3-BE0cnGVOBJFLOSEumj3k6UBYLHrxZkkuW9QEzUpeuyZi6X7pL2kAN3Gl3sidh3Hn22ROTJ+HAb4RMSE!ceAQBN5cluskI3UNuwfJaqbWI5WTbKh9/DiDKdMR5uIv83KZ/WHyMrA/dWl0WXZ56I7aGjxVmHFM!jS4cBQ== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 4276 On Sat, 27 Apr 2024 02:17:23 +0200, Klaus Vestergaard Kragelund wrote: >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 Leakage inductance?