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From: John Larkin <jjSNIPlarkin@highNONOlandtechnology.com>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Fri, 26 Apr 2024 11:05:19 -0700
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On Fri, 26 Apr 2024 00:49:52 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>On 25-04-2024 23:29, John Larkin wrote:
>> 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.
>> 
>I have looked into that. I cannot find resonable valued transistors at 
>4kV, prices ranges above 20 USD per piece. But maybe I have not searched 
>in the right place.
>
>On top of that, I need a positive pulse, 3.5kV, and also a negative 
>pulse (600V or so). The can be solved with a transformer.

Oh.