High voltage (>60V) P-channel JFET?

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Jocko Homo

Jocko Homo

RIP
Joined 2002
Get your Digi-key catalog out, SY....

I've used some Zetex parts.......I believe that they are good for that voltage, maybe more.

No, I don't remember the number. Memory is not as sharp these days. (I bet Cap'n P. knows the number. Unless his memory is over the hill too.)

But as Phred would probably say:

"Search engine! Do I have to research all this stuff for you guys?" [joke]

Jocko
 
john curl

john curl

Member
Joined 2003
I doubt if there is anything available. Usually, P channel is lower voltage than N channel, all else being equal. Cascode with 1/2 A Hitachi mos fet like the 2SJ79 gets you up to 200V. Works great, been using it for more than a decade. Other, low current, mosfets will also work.
 
SY

SY

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Joined 2002
SYclotron.com
Well, even high voltage n-jfets are pretty rare birds- Siliconix makes some, so did Teledyne some years back, but that's about it. My guess, as a materials guy, is that it's more a matter of demand than technology. How much of a mass market is there for a 200V jfet? Not much. Mosfets won't work for my application, but audio is pretty niche-y, and high end audio is microminiscule. For the high volume stuff, Mosfets work just fine and have better perfomance in areas like gm and on-resistance that are important in mass applications. I can't think of anyone outside of audio who would need a 200V jfet with a 1nV/rt-Hz noise density.
 
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Petter

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Joined 2001
The main problem I have found with JFET's is power dissipation. I have found higher power units, but they lack many of the fundamental qualities one likes in the "smaller" devices.

In the long run, materials technology will come to your rescue. The first Silicon Carbide (SiC) devices which will be made available will have high voltage ratings (way above what you are looking for) and probably great power dissipation ratings as well - in part due to the ability to work at significantly elevated temperature as well as material thermal conductivity.

As for noise, we will have to wait and watch :)

Petter
 
Jocko Homo

Jocko Homo

RIP
Joined 2002
OK, Sy.......

Make a cascode with a P-channel JFET, into a P-channel MOSFET. It should not be hard to make a swinging bias string referenced to the source of the JFET. It can be a very low current string.

Try it.....it just may work.

Yeah....I know.......enhancemant mode parts........still noisy. Depending on the circuit, and where it is, you may find that noise is not that much of an issue.

Jocko
 
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jcx

Member
Joined 2003
supertex makes depletion mode n mosfets to 500 V, don't think p depletion mosfets exist

the gordon micpre guy claimed to get n fets selected by the manufacturer to > 2x nominal part rating, maybe just measuring some pfets would work

cascoding with Zetex ZVP0545 450 V enhancement mosfet biased with lithium batt could work for >10 yrs without replacement, some batt are thru hole pcb mount
 
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
Make a cascode with a P-channel JFET, into a P-channel MOSFET. It should not be hard to make a swinging bias string referenced to the source of the JFET. It can be a very low current string.

Try it.....it just may work.
Click to expand...

It probably would, but it gets rid of the main virtue of my circuit compared to all-tube cross-coupled inverters: simplicity (especially in how the bias is set) and low parts count. As much of an agnostic as I am about "designing for sound," I'm a fiend about esthetics.;)
 
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