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From: JM <sunaecoNoChoppedPork@gmail.com>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Tue, 27 May 2025 19:09:37 +0100
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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.