Re: LTSpice model for a SiC MOSFET

On Tue, 20 May 2025 17:49:54 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
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On 20/05/2025 5:48 am, legg wrote:

On Tue, 20 May 2025 03:21:37 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
 

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.
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Does anybody know of a similar - ideally cheaper and smaller - part for
which there is an LTSpice model?

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I use a Cree/Wolfspeed 1200v part, C2M0280120D, in my Pockels Cell
driver.
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https://www.dropbox.com/scl/fi/5arhyamrp0bl3tgb2fasn/DSC02771.JPG?rlkey=3ttcc2yt6s9nrtdouuv3aneol&raw=1
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They do have an LT Spice model library that works.
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Gate drive for SiC parts is a bear. I did it myself, but I think there
are chips for that now.
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There are multi-kilovolt silicon mosfets too.
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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.
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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).
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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.

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<snipped badly formatted list>
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The highest voltage part in there was good for 1.5kV, so not good enough.

>
Bill,  the Baxandal cct is great in lower voltage input applications,
but the one thing you don't want to do with HV sources is ADD voltage
stress.