Bob Cordell Interview: BJT vs. MOSFET - Page 7 - diyAudio
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Old 16th November 2006, 01:10 AM   #61
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Quote:
Originally posted by Bob Cordell


The p-channel devices are usually inferior to the n-channel devices, but what specifically do you especially not like about the IRF p-channel MOSFETs?

Hi,

I'm not sure what would be JC's answer but.., IR's p-ch have a strange behaviour right in the middle of the audio band as they change transconductance with frequency.

Cheers Michael
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Old 16th November 2006, 01:16 AM   #62
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Look at one on a TEK curve tracer. You will understand, then!
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Old 16th November 2006, 01:45 AM   #63
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IR P channel "flaw"

http://www.diyaudio.com/forums/showt...25#post1042625
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Old 16th November 2006, 03:20 AM   #64
gerhard is offline gerhard  Germany
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Quote:
Originally posted by mikeks
Nothing wrong with my ''skillset'', and i still think MOSFETs are inferior to modern BJTs in audio frequency applications.
D.Self has abt. 11 pages on this in his book, most in favour of bipolars and quite convincing, so I would probably go bipolar with 60V rails.

OTOH I once had to design an amp with 400..500 V rails for scientific purposes and there simply was no contest. For high Vce, bipolar SOAR
melts at a whopping pace, even more for PNPs. By far the best p device I could get was the wimpy TO220 Moto/On MTP2P50E.
Still needed a lot of them in series and parallel.
BTW its spice model had the bias completely wrong IIRC.

Gerhard
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Old 16th November 2006, 03:23 AM   #65
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Thats good Lumanauw, you have saved the post from Charles Hansen!

BTW, here's NP's mos.pdf paper, see page 9, figure 13!

Cheers Michael


EDIT: Oh, and while talking about P-ch FET flaws of IR, please add up your advices on vertical FETs with fairly good complementary pairs, or just P-ch others than IR in my thread Complementary V-FET's other than IRF's???, my hope is that we could make up a list under that thread.
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Old 16th November 2006, 04:31 AM   #66
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Quote:
Originally posted by john curl
Folks, if you want to understand why power vertical mosfets tend to break with higher voltages, just compare the 10ms safe area of the best high speed bipolars to any other pair of practical vertical mosfets.
What I have found: 10ms-100V

2SK3264---5A
IRF130----1.7A
IRF140----2.8A
2SJ201-----3A
Please show me a better vertical power mos pair!

Quote:
Originally posted by MikeB


I don't understand...

2SC5200---2.2A
MJL4281---4.5A
2SC2922---4.5A
2SK1530---5A
Looks quite comparable, BJT <-> Mosfets

Mike
Hi Guys,
If you guys are targetting complementary pairs in VFET's than P-channel Mosfet suffers most in RDS ..and Qg[Total Gate charge]

Though my application requires reliability much important, its evident for me to use N-channel devices only...so if you look at the SOA curve of these mosfets..they were simply amazing....

The APT20M22LVR
Just see the 10mS SOA at 100V =25Amperes
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Old 16th November 2006, 04:36 AM   #67
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Workhorse, your device looks impressive.
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Old 16th November 2006, 04:48 AM   #68
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Also see this APT100GF60LVR

30A at 10mS at 100V
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Old 16th November 2006, 04:59 AM   #69
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Look at this most powerful BJT on this earth

MJ21294 SOA at 10mS at 100V= 10Amperes
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Old 16th November 2006, 03:12 PM   #70
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Bob,
We're just measuring speed in a different way. If you equate speed with ft then certainly VFETs are speedier than BJTs. And the source/emitter follower simulation you suggested is consistent with this.
I'm not just looking at speed in terms of current gain. The design approach I use, which I shall keep under my hat for now, causes me to look at it in a different way and this reduces the advantage of FET over BJT.
From what I have learned it does not surprise me that some have found more sonic success using bipolars than FETs. Many leading brands use bipolars. There are many brands that use FETs that sound mediocre. It is pointless to generalize about this.
Personally, I don't like either of them. The tube folk are blessed.

MikeBettinger wrote:
Quote:
Heresy, and please don't bring what it sounds like into the discussion.
Sorry. Sound quality is hard to measure. That which is easy to measure tends to get the attention and tends to be "improved". Often improved much too far at the expense of that which is more important but hard to measure (or identify).
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