Re: LTSpice model for a SiC MOSFET

On 27/05/2025 9:09 am, john larkin wrote:

On Wed, 21 May 2025 18:20:25 -0700, KevinJ93 <kevin_es@whitedigs.com>
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 specs, as far as I can tell, suggest 1KV at 1 ma in and 3.3v at 3
ma out. The required efficiency is then 1%.

Actually 1kV at 10uA in. The one 1mA was a constraint on the switching transistor based on the current that might circulate in the resonant tank.

So use a resistor and a zener to make 36 volts and dump it here:
 https://www.digikey.com/en/products/detail/mornsun-america-llc/K78L03-1000R3/16571443
 That will be about 3% efficient and cost under $2.

Misunderstanding the constraints can lead people to propose inappropriate solutions.
--
Bill Sloman, Sydney