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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Tue, 20 May 2025 03:02:06 +1000
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On 19/05/2025 11:29 pm, john larkin wrote:
> On Mon, 19 May 2025 18:19:36 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> 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.
>>
>>> 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.
> 
> You are so smart that you obviously don't need my help.

I clearly need help here, but you don't seem to interested in being helpful.

-- 
Bill Sloman, Sydney