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From: John Larkin <jjSNIPlarkin@highNONOlandtechnology.com>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Thu, 25 Apr 2024 14:29:52 -0700
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On Thu, 25 Apr 2024 22:23:31 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>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

You could make 3.5KV DC, and then switch. There are high-voltage fets
around.

If you need fast rise/fall, or clean pulses, the transformer could be
difficult.