Re: LTSpice model for a SiC MOSFET

On 19/05/2025 1:38 pm, john larkin wrote:

On Mon, 19 May 2025 12:23:54 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
 

On 19/05/2025 12:15 am, john larkin 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?

>
I use a Cree/Wolfspeed 1200v part, C2M0280120D, in my Pockels Cell
driver.
>
https://www.dropbox.com/scl/fi/5arhyamrp0bl3tgb2fasn/DSC02771.JPG?rlkey=3ttcc2yt6s9nrtdouuv3aneol&raw=1
>
They do have an LT Spice model library that works.
>
Gate drive for SiC parts is a bear. I did it myself, but I think there
are chips for that now.
>
There are multi-kilovolt silicon mosfets too.
>
Baxandal looks to be inefficient and expensive as a low power
converter. The drain swing is 2x the supply voltage, and it needs two
fets and a difficult custom transformer.

>
It isn't going to be inefficient. That configuration is famous efficient.
>
The drain swing is actually 1.67 times the supply voltage, but it does
need two switching devices and a specially wound transformer (and we
know how reluctant you are to design them or get them made).
>
It is probably going to be too expensive for the application, and we'd
be grateful for your insights into a cheaper alternative. I can't think
of one.

 I'm not sure what the specs are, but I have a few ideas.
 One could make a flyback converter with a high-ratio transformer.
Coilcraft makes some, capacitor charging transformers and CCFLs. There
must be crazy cheap Indian or Chinese CCFL transformers.
 ST makes a 1400v NPN transistor for under a dollar.

But you can't be bothered to post the part number.

It would be cool to put two drum core inductors next to one another,
or on opposite sides of the board, to make a loosely coupled
transformer, exactly what a forward converter needs.

You end up needing a lot more core material than the Baxandall configuration does. Been there, been pissed off by that.

I've finally finished by dummy load board... Gerber day is tomorrow.
The paired Murata drum cores are spaced to tune the coupling factor to
K=0.6
 https://www.dropbox.com/scl/fi/57jecrzc894uvktv72wrg/P978_A18.jpg?rlkey=4095oct5enxqp556xf44oy491&raw=1
  So, how to get the low duty cycle pulsed base drive? I'm thinking
maybe an RC off the HV supply and a diac, a relaxation oscillator.

The Baxandall configuration lends itself to simple drive circuits.

If the rig is a forward converter, we could make a non-saturating
blocking oscillator, and share the transformer secondary to drive the
base and rectify to 3.3v.

Of course you could, but you'd need to be mad to try.

$6 or $7 might be a reasonable parts cost target in modest volume.
Needs Spicing.

Which is why I am looking for a Spice model of the 1.7kV transistor I know I can buy.
--
Bill Sloman, Sydney