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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Thu, 25 Apr 2024 22:23:31 +0200
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On 25-04-2024 17:08, John Larkin wrote:
> On Thu, 25 Apr 2024 10:18:42 +0200, Klaus Vestergaard Kragelund
> <klauskvik@hotmail.com> wrote:
> 
>> On 24-04-2024 16:23, John Larkin wrote:
>>> On Wed, 24 Apr 2024 09:37:24 -0400, legg <legg@nospam.magma.ca> wrote:
>>>
>>>> On Wed, 24 Apr 2024 01:57:36 +0200, Klaus Vestergaard Kragelund
>>>> <klauskvik@hotmail.com> 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
>>>>
>>>> When there are a lot of turns, 3xFEP is not the way to
>>>> go. Too bulky. The three layers is basically a trick to
>>>> avoid creepage requirements for pri-sec safety. That's
>>>> not what you need here.
>>>>
>>>> Anything off the shelf will be a great time saver.
>>>>
>>>> RL
>>>
>>> I sometimes use an autoflyback stage with a DRQ-series dual inductor,
>>> followed by a c-w multiplier using sot-23 dual HV diodes. That's cheap
>>> and easy, given a reasonable supply voltage, like 24.
>>>
>>
>> I cannot use capacitive doubler thingies, there's no output DC voltage.
>>
>>> You can also just buy a potted HV supply and move on to design
>>> something else.
>>>
>>
>> I need it cheap, so cannot buy COTS
>>
>>> There are also potted c-w bricks, but they are a lot more expensive
>>> than buying the diodes and caps.
>>>
>>> Custom magnetics only makes sense at high volume, or for real exotica
>>> like transmission-line transformers.
>>
>> I have almost never used standard magnetics. Most projects has
>> requirements that dictate custom, or in higher volumes price is the key.
>>
>>>
>>> I'm about to embark on a custom tapped inductor and I'm not looking
>>> forward to it. Drawings, quotes, revised drawings, more quotes,
>>> samples, tests, released drawings, MOQs, all that.
>>>
>>
>> Yeah, boring work.
> 
> What input do you have, and what output do you want?
> 

I have 24VDC in, and 3.5kV peak pulse with 10% duty cycle at 100kHz. I 
have a working circuit, but just a little too much loss due to the 
transformer parasitics, so working to change the construction to get the 
optimum transformer design