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?
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?
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.
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.
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
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
darkfenriz said:
How about 2700 °C?
http://ieeexplore.ieee.org/Xplore/l...0659276.pdf?arnumber=659276&authDecision=-203
audioman54 said:
Hey Mark. I'm very familiar with the very nice LME498xx series and the LM4702. You guys all did amazing work on those devices and I've used both the LME49180 and the LMR49830. They outperform anything else I've ever tested. Period!
Part of the appeal of these new devices is using a single pair of for a higher power amplifier than would be possible with a single pair of lateral MOSFETs. Once you get into multiple pairs of the 2SK1057/J161 or 2SK1530/J201 you double the idle dissipation, have matching issues, thermal tracking issues, twice the gate capacitance, etc. I'm also working on my first "double die" design using the BUZ901DP/906DP devices but they're also very expensive.
The higher current IRFP vertical devices have a high Vgs and other problems when used for audio. So I prefer the lateral MOSFETs. But they have their own downside including a fairly high Rds(on) and limited current capability. The new SiC JFETs seem to let us have our cake and eat it too?
AFAIK, Nelson Pass is the only one here on DIYA who actually has gotten his hands on any of the SiC devices. They don't seem to be sold through distribution and the company, understandably, doesn't seem very interested in dealing with DIYers directly. So I think the only way to get any is to have a legitimate company with a legitimate need for them as, apparently, Nelson Pass has done.
I know some engineers, if they're still there after moving a bunch of their operations to China, who work for Xantrex. They make power conversion hardware including solar inverters. So if nothing develops here (i.e. a group buy, etc.) I may try to contact them and see if can ask a huge favor and try to get a couple of SemiSouth samples through them.
Son Of Zen, www.passdiy.com/pdf/sonofzen.pdfWavebourn said:What SOZ stands for, and how to smoke it?
And, in fairness, Wavebourne mentioned Syn08 first mentioned these devices while a search reveals it may have really been suiraMB way back in 2006. So, while Nelson Pass is the first to post results from using them, he may not have been the first to mention them.
And, as others have posted, another advantage to SiC devices is they apparently can handle heatsink damaging temps with ease
So I'm not sure typical SOA concerns apply here?
The low current characteristics would be interesting to know.
And, as others have posted, another advantage to SiC devices is they apparently can handle heatsink damaging temps with ease
So I'm not sure typical SOA concerns apply here?The low current characteristics would be interesting to know.
Wavebourn,
Are these pure class A amplifiers? Also our LME49811 based amplifier has beaten every tube and solid state unit is has gone up against (even Dennis Had at Cary was stunned when I did a demo of the power amps and D/A box at his place in North Car. He was so stunned he designed the new Exciter Dac around the national LME parts in 4 months!...which is quite a thing for a tube guy to do! Also I turned tube guru Joe Curcio into a believer. Joe is also still an FAE at National!) The LME49811 is class A internally by the way.
Listening is #1 of course but I (and Bob Pease) believe it must be combined with good measurements. If something measures poorly, .1 to 1% THD+N or higher, then the listening tests are suspect! We found in our single blind tests at National that small improvements in THD+N, that were linear with increasing power levels, resulted in audible improvements. Also the New LME parts have a unique process that matches the NPN and PNP transistors in such a way that they have identical dimensions, carrier flow, and ft's! Because of this we were able to run much lower bias currents than normal Class A/B amplifiers and still get great measurements and superb sound quality. That is why the opamps are doing so well in the high end community.
Has anyone done any set of measurements with an AP2 Cascade on one of the Pass amplifiers with these new output FETS like the graphs shown in AN-1850 for the LME49830?
I also attached a THD vs Power graph I made of my mono LME49811 based Amplifier with 50VDC rails into an 8-ohm load.
I would love to try these new FET devices with the LME49830 boards and compare them (listen and test) with the LME49811 based power amps I have. Benchtester and I should have the 811 based amps on display at Burningamp!
Best Regards,
Mark / Audioman54
Are these pure class A amplifiers? Also our LME49811 based amplifier has beaten every tube and solid state unit is has gone up against (even Dennis Had at Cary was stunned when I did a demo of the power amps and D/A box at his place in North Car. He was so stunned he designed the new Exciter Dac around the national LME parts in 4 months!...which is quite a thing for a tube guy to do! Also I turned tube guru Joe Curcio into a believer. Joe is also still an FAE at National!) The LME49811 is class A internally by the way.
Listening is #1 of course but I (and Bob Pease) believe it must be combined with good measurements. If something measures poorly, .1 to 1% THD+N or higher, then the listening tests are suspect! We found in our single blind tests at National that small improvements in THD+N, that were linear with increasing power levels, resulted in audible improvements. Also the New LME parts have a unique process that matches the NPN and PNP transistors in such a way that they have identical dimensions, carrier flow, and ft's! Because of this we were able to run much lower bias currents than normal Class A/B amplifiers and still get great measurements and superb sound quality. That is why the opamps are doing so well in the high end community.
Has anyone done any set of measurements with an AP2 Cascade on one of the Pass amplifiers with these new output FETS like the graphs shown in AN-1850 for the LME49830?
I also attached a THD vs Power graph I made of my mono LME49811 based Amplifier with 50VDC rails into an 8-ohm load.
I would love to try these new FET devices with the LME49830 boards and compare them (listen and test) with the LME49811 based power amps I have. Benchtester and I should have the 811 based amps on display at Burningamp!
Best Regards,
Mark / Audioman54
Nelson Pass said: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.
Hi Nelson,
Way to go! VERY interesting new parts.
Let me ask some dumb questions (or make some dumb observations), as it is late in the day and I just got out of a long and dreary design review meeting.
First, these are only available in N-channel sex, right?
So if we wanted to do class AB push-pull, we would need to go quasi complementary, right?
I looked at one of the data sheets, and it looks like in the high current range of drain current, you actually have to source considerable current into the gate; in other words, these seem to be sort of like enhancement mode JFETs where the gate junction is actually forward biased to make them turn on. It looks like one might have to shove over 100 mA into the gate in order to get in excess of 10A of drain current. In some respects, it is almost like they have a finite current gain, like a BJT.
In the circuits you built, were they all class A no-NFB designs?
What do you think is the biggest reason they have such superior distortion characteristics to vertical MOSFETs?
Could we expect the same degree of superiority in class AB push-pull designs?
It looked like the max junction temperature was 175C, which seems a bit low for silicon carbide. Am I missing something here?
I didn't see any gm vs. Id or vs. Vgs curves (and didn't yet calculate it off the slope of the Id vs. Vgs curve), but is it your impression that one gets more gm per mA out of these devices than for vertical MOSFETs?
Thanks again for applying these very interesting devices to audio.
Thanks,
Bob
RocketScientist said:
Actually, it was me who mentioned them in Syn08 thread; I'm waiting for them more than 10 years, so one-two ears more don't matter. They can be used in my current designs where I use MOSFETs, giving great improvements. Until now, I'm unknown among potential customers who can justify such prices on devices, so no need to rush for new devices for any price.
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