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RocketScientist 12th August 2009 07:17 PM

SemiSouth SiC Power JFETs
I think Nelson Pass first introduced these amazing devices here but now they're being discussed in at least 4 threads. I think the SiC Power JFETs are unique enough to deserve their own thread. So I'm starting one and hope we can discuss the devices themselves (vs a particular amp design) here.

For those not familiar with them, SemiSouth has 3 new Silicon Carbide power JFET devices designed primarily for power conversion applications such as solar power, hybrid/electric car use, etc. Looking at the specs, the devices are a very signficant improvement over the regular power MOSFETs some of us know and love. They have a lower Vgs, lower Rds(on), higher max current (in the largest device), and higher transconductance.

The lower Vgs and higher transconductance, in particular, appear to make them well suited for audio. Nelson Pass has said they have around 1/10th the distortion of power MOSFETs. But using them in a push-pull output stage would involve some design changes over using complimentary pairs of MOSFETs or BJTs.

The most obvious downside is the largest one (the SJEP120R063) is $60 each in sample quantities! And they're not, AFAIK, sold through distribution, and hence not very DIY-friendly. There are posts about the company not responding to emails from DIYers and that's not too surprising.

I would think, however, if there's enough interest here some sort of group buy could be arranged? I'm certainly interested in getting a pair to try out. But I wanted to first start by trying to consolidate the technical discussions into a single thread. Here are the data sheets:

1200V 15A SiC JFET

1200V 17A SiC JFET

1200V 30A SiC JFET

Comments anyone?

darkfenriz 12th August 2009 07:32 PM

In terms of switched characteristics, for which they've been invented, they easily outperform both mosfets and igbts in terms of dynamic behaviour. 1nC of Qgs and no body diodeand no current tail sounds tempting, from this point of view they are worth their price and will find its market in cutting-edge switched mode designs.
Some parameters like maximum operating temperature and parasitic inductances are highly limited by package, we may expect them to come in a utterly different and new packages soon.

Fuling 12th August 2009 07:33 PM

Quite pricey for being semiconductors but cheap compared to most NOS triodes:D

Wavebourn 12th August 2009 07:35 PM

Sure, big copper plates would be desirable for audio, but I doubt they will bother to make them for switched mode converters that are main target applications.

Nelson Pass 12th August 2009 07:35 PM

2 Attachment(s)
I have built four different amplifiers with these parts, and they are
quite superior to Mosfets.

Here is an example with one place in an F2 circuit, which is a simple
Common-Source stage with no feedback.


Michael Rothacher 12th August 2009 07:45 PM

Doh, slobber...

audioman54 12th August 2009 07:56 PM

Rocket Scientist,

What is the best THD+N anyone has gotten out of a complete amplifier using these parts? National made a FET driver in the LME series (Spittinllama from this forum designed and measured the boards, see National Semi AN-1850, and was able to get to 0.0005% THD+N.) The AN-1850 ap-note has complete graphs on the Demo Board Spittinllama designed (who is gone now from National like me). He designed the board along with one of the other apps engineers, who is now the only High Performance audio apps engineer left at National along with the Audio Apps manager who is also a high end audiophile, and a very good guy!

I would like to try these new FET parts with the National FET demo board and compare it (measure and listen) with the LME49811 mono amp(s) which are my favorite sounding units.

I wish I had unlimited funds (and time) to do all the projects I have on my list right now. (Or it would be even better if I was still at National working on these projects and getting paid to do them!) Spending 4-6 hours online everyday job searching limits my audio project time! Thanks to DIY though because I did just get a nice email from a DIY member about some possible contract work! Thanks DIY Group!!!

Mark / Audioman54

Wavebourn 12th August 2009 08:01 PM

Hi Mark;

we are speaking of applications that fully complementary designs can't beat in terms of weighted against audibility distortions.

mlloyd1 12th August 2009 08:16 PM

Re: SemiSouth SiC Power JFETs
2 Attachment(s)
might be time to start thinking again about playing with a power amp version of the leach jfet preamp from (many) years ago; SiC outputs instead of bipolars ...

but, OUCH !$!$!$!



Originally posted by RocketScientist
Comments anyone?

scott wurcer 12th August 2009 08:21 PM


Originally posted by Wavebourn
Hi Mark;

we are speaking of applications that fully complementary designs can't beat in terms of weighted against audibility distortions.

Yes, apples and oranges here there is only one flavor (JFET) anyway. Love to try the SOZ out, the SiC really lets lets you smoke it! I wonder if I can get samples.

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