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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, 22 May 2025 18:12:51 +1000
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On 22/05/2025 11:20 am, KevinJ93 wrote:
> On 5/21/25 12:20 AM, Bill Sloman wrote:
>> On 21/05/2025 3:47 am, KevinJ93 wrote:
>>> On 5/20/25 1:46 AM, Bill Sloman wrote:
>>>> On 20/05/2025 1:13 am, Liz Tuddenham wrote:
>>>>> 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?
>>>>>
>>>>> How about a piezoelectric transformer run in reverse?
>>>>
>>>> The piezoelectric transformer is an interesting idea.
>>>>
>>>>> Neon tubes illuminating a solar cell? 
>>>>
>>>> Neither is all that efficient.
>>>>
>>>>> Capacitive divider using a spare core in the
>>>>> mains supply lead as one plate of the capacitor?  (Depending on supply
>>>>> frequency and required output current.)
>>>>
>>>> I can't see how that could work. Charging up lots of capacitor is 
>>>> series, and discharging them in parallel is one mode of current 
>>>> multiplication, but about the only kind of switch that would work 
>>>> would be a reed relay, and they are slow and don't last long when 
>>>> cycled fast.
>>>>
>>>> Dry reeds are good for 10 million closures, mercury-wetted reeds for 
>>>> about 100 million, and neither is all that cheap or compact.
>>>>
>>>
>>> The Art of Engineering #3 (I think) - describes a "Reverse Marx 
>>> Generator" that does exactly that (charging caps in series and 
>>> discharging in parallel). It uses diodes as the switching element.
>>
>> The forward diode drop is inconsequential at 1kV, but inconvenient at 
>> 3.3V. And you'd need 250 stages in this application.
>>
>> I've got AOE3. It's index doesn't point to any "reverse Marx generator".
>> Google search throws up links, but nothing useful.
>>
>> The classic Marx generator uses spark gaps as its switches. I have 
>> used them myself (to start a xenon arc lamp), but they wouldn't be 
>> useful here.
>>
> 
> Sorry -- it is on page 440 of the X-chapters, not AOE3.
> 
> The reverse Marx generator doesn't need to go all the way down to 3.3V 
> it could just increase the current and reduce voltage to the point where 
> a conventional converter (such as a flyback) can be used without 
> excessive voltage devices being used.

The Baxandall inverter looks as if it would work with sufficiently high 
voltage MOSFET, which clearly exist, even if Infineon is being slow to 
offer a Spice model to let me simulate it.

It's a pretty simple circuit, even if the component parts look to be on 
the expensive side - coping with even 1kV costs money.

-- 
Bill Sloman, Sydney