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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 18:36:19 +1000
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On 20/05/2025 5:28 am, legg wrote:
> On Mon, 19 May 2025 23:12:50 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> On 19/05/2025 10:48 pm, legg wrote:
>>> On Mon, 19 May 2025 18:27:01 +1000, Bill Sloman <bill.sloman@ieee.org>
>>> wrote:
>>>
>>>> On 19/05/2025 2:12 am, legg 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?
>>>>>
>>>>> 1kv, sitting there all alone and bashfull. Not a common occurEnce.
>>>>> Is this the only power source in the vicinity? Tell us more.
>>>>
>>>> It's not my project. I just got asked about what a Baxandall
>>>> down-converter for a 1kV 10uA source would look like.
>>>>
>>>> Because it's not my project I'm not at liberty to talk about the power
>>>> source. My first thought was an intensely radio-active source pushing
>>>> out a lot of high energy beta rays (electrons) or alpha rays (helium
>>>> nuclei), but it isn't.
>>>>
>>>>
>>> It sort of limits your ability to help.
>>
>> I know what the power source is - in general terms. I haven't got any
>> kind of okay to talk about it
>>
>>> At 1W, you should be able to get away with murder, if efficiency
>>> isn't really an issue.
>>
>> Efficiency is an issue, if only on the sense that a 0.1W power source
>> isn't up to much, so even 50% efficiency would be nice. Jim Williams got
>> about 93% out of the Baxandall configuration, but 50% might be good enough.
> 
> 1KV 1ma 1W. Anything low powered will have efficiency issues
> 
> At 100mW it's a different animal.

The 1ma referred to the current-carrying constraint on the switching 
transistor, not the power source. The Baxandall configuration relies on 
reactive current circulating inside the tank circuit maintain the output 
voltage, and some of that can flow through the switches.

> I was suggesting a repurposed CCFL transformer for use as an
> inductor in a buck reg configuration, because they're cheap,
> available and wound for high voltage with low distributed
> capacitance. The normal drive winding addresses 8-20V bulh
> control. Backwards, like I suggested.

Got a part number?

> Lowest frequency to deal with other caps in the viscinity, as
> the original CCFL will have sensibly done.

Not a good idea. You really want to run a inverter as fast as the core 
material (and the switches) will allow. This isn't a CCFL application so 
the stray capacitances are less of a problem.

-- 
Bill Sloman, Sydney