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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Thu, 29 May 2025 11:23:51 -0700
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On Thu, 29 May 2025 16:12:52 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 29/05/2025 3:56 am, john larkin wrote:
>> On Thu, 29 May 2025 02:24:01 +1000, Bill Sloman <bill.sloman@ieee.org>
>> wrote:
>> 
>>> On 29/05/2025 12:26 am, john larkin wrote:
>>>> On Wed, 28 May 2025 21:03:03 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>> wrote:
>>>>
>>>>> On 28/05/2025 3:08 am, Joe Gwinn wrote:
>>>>>> On Tue, 27 May 2025 07:53:12 -0700, john larkin <jl@glen--canyon.com>
>>>>>> wrote:
>>>>>>
>>>>>>> On Tue, 27 May 2025 10:02:27 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> On Tue, 27 May 2025 20:32:49 +1000, Chris Jones
>>>>>>>> <lugnut808@spam.yahoo.com> wrote:
>>>>>>>>
>>>>>>>>> On 18/05/2025 6:11 pm, Bill Sloman 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?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Maybe use an electrostatic motor driving a small generator!
>>>>>>>>
>>>>>>>> Maybe DON'T FEED THE TROLL?
>>>>>>>
>>>>>>> It is an interesting problem, designing a logic supply that runs off a
>>>>>>> 1 KV DC supply. Even when the requirements are confused.
>>>>>>>
>>>>>>> Actually, the uncertainty opens up more circuit possibilities to
>>>>>>> consider. We can thank Sloman for being confused.
>>>>>
>>>>> I don't think that John Larkin needs my help to get confused.
>>>>>
>>>>>> Finally, a purpose ...
>>>>>
>>>>> The first line of my original post was.
>>>>>
>>>>> "I'm looking at a problem where somebody wants to step down a 1kV low
>>>>> current source to 3.3V. "
>>>>>
>>>>> That's been the purpose all along.
>>>>
>>>> Your (still confused and unresolved) specifications opened up a wide
>>>> range of possible implementations. Thanks.
>>>
>>> Since I've now at least got a PSpice model for the IXTH1N450HV 4.5KV
>>> FET, I can - with luck - get on with being confused by an actual (if
>>> simulated circuit). Typical Ciss is depressingly high at 1700pF.
>>>
>>> The higher current (but lower voltage) Infineon IMWH170R450M1 has a
>>> typical Ciss of 506pF and is cheaper than $US45 IXYS part.
>>>
>>> You may find the specification to be confused and unresolved. I haven't
>>> spelt it out in detail because - as the subject line spells out - that's
>>> not what I'm here for. As far as I can see I've been consistent about
>>> what I believe my contact is seeking, and what you are complaining about
>>> is the way you have misconstrued passing comments.
>> 
>> What are the requirements? 1 mA, 3 mA, 1 mW, 10 mW, some microamps,
>> where? There have been all sorts of numbers.
>
>The basic idea is that my contact has 1kV source capable of delivering 
>about 10uA - 10mW - and wants to use it to power some logic from a 3.3V 
>power rail. He'd like better than 50% efficiency, so presumaby he wants 
>something approaching 1.5mA. About the only other number I recall 
>posting was the idea that a switching MOSFET might need to handle up to 
>1mA rather than the 1A the IXTH1N450HV can manage or the 10A the 
>Infineon part  offers.
>
>I've now had an interesting an potentially patentable idea that I'm 
>obviously not going to post on a public forum. Like most patentable 
>ideas it is unlikely to actually work, let alone be be practicable.
>
>> Does cost matter?
>
>He does want it to be inexpensive. There doesn't seem to be any 
>specialised market where a few customers can afford to pay a lot of 
>money for a few devices, or if there is he hasn't mentioned it to me 
>(and probably wouldn't) if there was.

I can imagine some cheap approaches if something like 25% efficiency
were acceptable.