Re: LTSpice model for a SiC MOSFET

On Mon, 19 May 2025 18:19:36 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

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.

You are so smart that you obviously don't need my help.