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Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Bill Sloman <bill.sloman@ieee.org> Newsgroups: sci.electronics.design Subject: Re: LTSpice model for a SiC MOSFET Date: Tue, 20 May 2025 03:02:06 +1000 Organization: A noiseless patient Spider Lines: 100 Message-ID: <100fo6f$1nipq$1@dont-email.me> References: <100c4og$t4lo$1@dont-email.me> <n7qj2kpht38kdk82o1hn10sss3ie2vnbrf@4ax.com> <100e4nq$1dhk3$1@dont-email.me> <9n8l2k9pc9jq3iichdq1baq04uqqk13ksg@4ax.com> <100epio$1h4ca$1@dont-email.me> <necm2ktlcg0kk4ce50a1vsqaai02h9ior0@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Mon, 19 May 2025 19:02:08 +0200 (CEST) Injection-Info: dont-email.me; posting-host="ce5aaf6936c6909f88ba6fd07b08faf9"; logging-data="1821498"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18USUywaC9/h8zfPWqVF4lbUUSZlouhOqc=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:1pde+/W+lP8992oQn8vopHRhoFA= In-Reply-To: <necm2ktlcg0kk4ce50a1vsqaai02h9ior0@4ax.com> X-Antivirus-Status: Clean Content-Language: en-US X-Antivirus: Norton (VPS 250519-2, 19/5/2025), Outbound message Bytes: 5354 On 19/05/2025 11:29 pm, john larkin wrote: > 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. I clearly need help here, but you don't seem to interested in being helpful. -- Bill Sloman, Sydney