Re: LTSpice model for a SiC MOSFET

On 19/05/2025 11:33 pm, legg 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'd keep it simple and repurpose a backwards commodity CCFL ($0.50)
  transformer, in a low frequency (20-50KHz) buck regulator 'of sorts'.

Cold cathode fluorescent lamps are cranky beasts, and Jim Williams exploited the Baxandal configuration to get the voltages they need out of low voltage supplies, using bipolar transistor switches. I would not be all that optimistic about finding a CCFL transformer that I could repurpose.
Designing a transformer for the job isn't all that difficult and finding a local transformer shop to wind it wasn't all that hard when I did something similar in the Netherlands  some twenty years ago.

A 1KV mosfet (why SIC?) would act as it's own TVS if the source was
really self-limited. 2$

The SIC part costs about $5.00. The guy I'm talking to came up with $200 regular silicon part with a higher on resistance and about ten times the internal capacitances. I'm not recommending SiC on principle - the limited search I did came up with a SiC part which looked as if might work, even if still too expensive to be attractive.

Trickle charge for start-up, with all control power on the LV side;
an intermediate 8-20V rail.
  From there it's a matter of your tech arranging 'who's on first'
in a sensible manner.

Managing start-up is part of the design process.
--
Bill Sloman, Sydney