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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Thu, 29 May 2025 16:12:52 +1000
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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.

-- 
Bill Sloman, Sydney