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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Tue, 20 May 2025 13:44:14 -0400
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:100ibpi$2at8a$2@dont-email.me...
> On 20/05/2025 11:38 pm, Edward Rawde wrote:
>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:100hb9s$24itl$3@dont-email.me...
>>> On 20/05/2025 4:26 am, Edward Rawde wrote:
>>>> "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.
>>>
>>> I need at least 1.7kV. A 1400V part isn't interesting.
>>
>> Centuries ago they'd put two transistors in series in the TV horizontal deflection department because a single one didn't have
>> enough Vce max.
>
> The transistor was invented in the 1950's. Decades ago is closer to the mark.

LOL sane people would have known what I meant without needing to point that out Bill.
In any case there was no transistor capable of doing horizontal deflection and EHT  for a 20 or more inch CRT before the late 60s.
My Father was never without a spare PL36.

> And if I can buy a 1.7kV SiC MOSFET, why would I bother to stack two transistors?
>
>> And a drive transformer with two secondary windings for the base current in each.
>
> Sure. John Larkin can't be bothered to design special purpose transformers, or get then made, but you want to remind us that that 
> it is still an option.
>
> The classic Baxandall transformer usually has two base drive windings. You tend to need a coil former with lots of pins for its 
> transformer.
>
> -- 
> Bill Sloman, Sydney
>
>