Re: LTSpice model for a SiC MOSFET

On Tue, 27 May 2025 02:43:41 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

On 27/05/2025 1:57 am, JM wrote:

On Tue, 27 May 2025 01:07:36 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
 

On 26/05/2025 4:20 am, JM 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:

>

The drain swing is actually 1.67 times the supply voltage, but it does

>
Where does 1.67 come from?

>
Integrate a series of half-sine peaks that get to 1.67V and the voltage
averages to about 1V.
>
You can do it as purely mathematical exercise, and I did it years ago,
and that's roughly the result I got.
>
There's a voltage drop across the switching FET that's on and the
Baxandall circuit doesn't product perfect half-sine waves, so it hasn't
got a lot to do with precise reality, but it's good enough for
preliminary design.
>
If senile dementia hasn't set in too far I could probably do it again.

 
Yes, but that's the centre tap voltage.  Due to the autotransformer
action the stress across the off transistor will be twice that, or
1000*PI in this application.  The 1700 volt device under consideration
isn't up to the task.

>
It took me a while to wake up to that. I think that there's an option
where you'd use four switching transistors, two to alternately ground
either end of the main inductor and two more to alternately switch the
feed inductor into the other end of the main inductor, but I haven't
worked it out in any detail. It's very much in the brainstorm state at
the moment
>
I have found a 4.5KV MOSFET, the IXYS IXTT02450HV which could survive in
the standard Baxandall configuration.
>
It's $US45.24 each in small volume (which really is excessively
expensive), and I've asked for Spice model, but if Infineon is anything
to go by, I'm not going to get it anytime soon.
>
If either Spice model shows up I'll try and put a simulation together.
It has nearly got to the point where I should try and bodge a MOSFET
model that I have got access to into something that would fit one or
other data sheet, but that's hard work, and my model isn't going to be
all that trustworthy.

You are probably best with bipolar.  If you use a push-pull current
fed half bridge the transistor breakdown rating will be 500*PI (1.57
kV).  Since the off transistor will have a reverse bias of a few volts
on it's base it's breakdown voltage will (typically) be a few hundred
volts greater than it's Vceo spec.  The 2sc4634/4636 would suffice.