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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Mon, 19 May 2025 14:26:55 -0400
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:100epio$1h4ca$1@dont-email.me...
> On 19/05/2025 1:38 pm, john larkin wrote:
>> On Mon, 19 May 2025 12:23:54 +1000, Bill Sloman <bill.sloman@ieee.org>
>> wrote:
>>
>>> On 19/05/2025 12:15 am, john larkin wrote:
>>>> On Sun, 18 May 2025 18:11:58 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>> wrote:
>>>>
>>>>> I'm looking at a problem where somebody wants to step down a 1kV low
>>>>> current source to 3.3V.
>>>>>
>>>>> The Baxandall class-D oscillator could do it, but it needs a pair 1.7kV
>>>>> MOSFETs for the job. The Infineon SiC IMH170R450M1 would do it - though
>>>>> it's a much higher current part (10A) than the job needs (about 1mA).
>>>>>
>>>>> I've dived into the Infineon rabbit-hole which promises LTSpice models,
>>>>> but wasn't able to find one.
>>>>>
>>>>> Does anybody know of a similar - ideally cheaper and smaller - part for
>>>>> which there is an LTSpice model?
>>>>
>>>> I use a Cree/Wolfspeed 1200v part, C2M0280120D, in my Pockels Cell
>>>> driver.
>>>>
>>>> https://www.dropbox.com/scl/fi/5arhyamrp0bl3tgb2fasn/DSC02771.JPG?rlkey=3ttcc2yt6s9nrtdouuv3aneol&raw=1
>>>>
>>>> They do have an LT Spice model library that works.
>>>>
>>>> Gate drive for SiC parts is a bear. I did it myself, but I think there
>>>> are chips for that now.
>>>>
>>>> There are multi-kilovolt silicon mosfets too.
>>>>
>>>> Baxandal looks to be inefficient and expensive as a low power
>>>> converter. The drain swing is 2x the supply voltage, and it needs two
>>>> fets and a difficult custom transformer.
>>>
>>> It isn't going to be inefficient. That configuration is famous efficient.
>>>
>>> The drain swing is actually 1.67 times the supply voltage, but it does
>>> need two switching devices and a specially wound transformer (and we
>>> know how reluctant you are to design them or get them made).
>>>
>>> It is probably going to be too expensive for the application, and we'd
>>> be grateful for your insights into a cheaper alternative. I can't think
>>> of one.
>>
>> I'm not sure what the specs are, but I have a few ideas.
>>
>> One could make a flyback converter with a high-ratio transformer.
>> Coilcraft makes some, capacitor charging transformers and CCFLs. There
>> must be crazy cheap Indian or Chinese CCFL transformers.
>>
>> ST makes a 1400v NPN transistor for under a dollar.
>
> But you can't be bothered to post the part number.

What you should have said is that you couldn't be bothered to use a search engine.

https://www.google.com/search?q=1400v+npn+st

>
>> It would be cool to put two drum core inductors next to one another,
>> or on opposite sides of the board, to make a loosely coupled
>> transformer, exactly what a forward converter needs.
>
> You end up needing a lot more core material than the Baxandall configuration does. Been there, been pissed off by that.
>
>> I've finally finished by dummy load board... Gerber day is tomorrow.
>> The paired Murata drum cores are spaced to tune the coupling factor to
>> K=0.6
>>
>> https://www.dropbox.com/scl/fi/57jecrzc894uvktv72wrg/P978_A18.jpg?rlkey=4095oct5enxqp556xf44oy491&raw=1
>>
>>
>> So, how to get the low duty cycle pulsed base drive? I'm thinking
>> maybe an RC off the HV supply and a diac, a relaxation oscillator.
>
> The Baxandall configuration lends itself to simple drive circuits.
>
>> If the rig is a forward converter, we could make a non-saturating
>> blocking oscillator, and share the transformer secondary to drive the
>> base and rectify to 3.3v.
>
> Of course you could, but you'd need to be mad to try.
>
>> $6 or $7 might be a reasonable parts cost target in modest volume.
>> Needs Spicing.
>
> Which is why I am looking for a Spice model of the 1.7kV transistor I know I can buy.
>
> -- 
> Bill Sloman, Sydney
>
>