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how about using J111 J175 Jfets in F5
how about using J111 J175 Jfets in F5
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Old 6th October 2017, 08:47 AM   #21
Zen Mod is offline Zen Mod  Serbia
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how about using J111 J175 Jfets in F5
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Old 11th October 2017, 07:00 PM   #22
BesPav is offline BesPav  Russian Federation
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Comprehensive information including fab masks could be accessed there:
http://www.onsemi.ru.com/PowerSoluti...N-6609.pdf.pdf
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Old 11th October 2017, 07:48 PM   #23
JohnLopez is offline JohnLopez  Canada
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Default What does that mean-

Quote:
Originally Posted by WalterW View Post
I see it in more datasheets from JFET's: "Sourced from process 51" .....
What does that mean? What is the manufacturer trying to tell us with that information?
Hi Walter. It refers to FET Process 51, - defined for example, in my copy of National Semiconductor Corporations manual for Field Effect Transistor Data Book dated 1982. There are different number classes for these Fet devices based on their physical Die structure, with data on the various preferred 2N types by number and packaging, and intended application. Process 51 is an N Channel J-Fet designed for switching applications amoung other things. See if you can access the information on-line. Bye for now John.
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Old 11th October 2017, 08:28 PM   #24
Nelson Pass is offline Nelson Pass  United States
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how about using J111 J175 Jfets in F5
Quote:
Originally Posted by rhythmsandy View Post
That's Idss I believe is not a drawback.
Actually I think it is. The Idss of those parts is typically higher than you
might imagine. The J112's are typically 40-50 mA Idss and those J111's are
even higher. Same story to a lesser extent with J175's.

It takes a lot of degeneration to get them down to the 10 mA or so that the
amp works with. If you don't take that approach, the Idss figures with the
voltages involved will exceed dissipation limits of the parts. Even if they
didn't, the Drain load resistance would have to be made low to bias the
Mosfets that follow, low enough to severely impact the gain.

Either way, it's a pain in the butt. Easier to pick parts that are lower Idss
to begin with, and the K170's and J74's are still a preferred choice.
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Old 11th October 2017, 10:26 PM   #25
Mark Johnson is offline Mark Johnson  United States
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how about using J111 J175 Jfets in F5
Serious question: why don't you (rhythmsandy) modify the circuit design to accommodate the higher-gm, easier-to-buy, JFET types? Maybe it's as simple as changing the values of resistors R1-R2 and R5-R8.

You will have to buy two dozen of each type and sort them by Idss to get a pair that are in the range your redesign requires. When I test a bunch of Fairchild J113s, I routinely see a 5-to-1 spread of Idss.

_
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Old 12th October 2017, 06:17 AM   #26
rhythmsandy is offline rhythmsandy
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Quote:
Originally Posted by Nelson Pass View Post
Actually I think it is. The Idss of those parts is typically higher than you
might imagine. The J112's are typically 40-50 mA Idss and those J111's are
even higher. Same story to a lesser extent with J175's.

It takes a lot of degeneration to get them down to the 10 mA or so that the
amp works with. If you don't take that approach, the Idss figures with the
voltages involved will exceed dissipation limits of the parts. Even if they
didn't, the Drain load resistance would have to be made low to bias the
Mosfets that follow, low enough to severely impact the gain.

Either way, it's a pain in the butt. Easier to pick parts that are lower Idss
to begin with, and the K170's and J74's are still a preferred choice.
what about those Jfets in double differential input stage? wouldn`t they work there?
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Old 12th October 2017, 06:40 AM   #27
rhythmsandy is offline rhythmsandy
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Quote:
Originally Posted by Mark Johnson View Post
Serious question: why don't you (rhythmsandy) modify the circuit design to accommodate the higher-gm, easier-to-buy, JFET types? Maybe it's as simple as changing the values of resistors R1-R2 and R5-R8.

You will have to buy two dozen of each type and sort them by Idss to get a pair that are in the range your redesign requires. When I test a bunch of Fairchild J113s, I routinely see a 5-to-1 spread of Idss.

_
jfet matching is anyway inevitable.
would like to use those jfets in double differential input stage. Where the current through the source resistor is hardly 2ma.
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Old 13th October 2017, 05:28 AM   #28
PRR is offline PRR  United States
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Thanks, JohnLopez.

The "process" is mainly the die layout, first picture. P51 is a fairly large die with a fairly large JFET on it. P52 is a slightly smaller die with a much smaller JFET on it.

This gives a *spread* of curves, second picture. All the curves are much the same shape. Where a specific device falls left-to-right (Vgs) depends on "baking", time temp and chemistry (not precisely controlled). But the P51 curves lie 10X higher in current than the P52 curves, because P51 is a bigger device than P52.

But what do you know about picking? They give you a "Proper JFET" table, third picture. JFETs can be good for 100MHz, so our <100KHz audio is Low Freq and we want Low Noise. Buying N-type Singles, we are led to P51 as one suggestion. However this is a 10mA-100mA Igss part. If we realize we may run nearer 1mA, we may look at General Purpose Amps and P52 is a suggestion.

I never found "Process" to be much help (good insight thought). There's some trends: P53 must be a teeny device which makes sense for low-low Gate leakage- indeed that is what P53's description shows and suggests. P58 is a fat beast and parts from the right end of the curve may be low-R switches (and cost more due to large 3-row die).

But we have to buy *parts*, not processes. A part is selected from a Process and the left, center, or right areas of the spread curve. Then further sorted for breakdown, leakage, or other valuable features. Then put in a Package, giving dissipation and pinout. Yes, if say 2Nxxxx is "almost right", you might look up its process and find similar parts with the difference you want. I've never done that.
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File Type: gif prop-JFET-curves.gif (23.7 KB, 96 views)
File Type: gif proper-JFET-process.gif (34.0 KB, 97 views)
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Old 13th October 2017, 05:26 PM   #29
Nelson Pass is offline Nelson Pass  United States
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how about using J111 J175 Jfets in F5
Quote:
Originally Posted by Mark Johnson View Post
When I test a bunch of Fairchild J113s, I routinely see a 5-to-1 spread of Idss.
In current batches of that Fairchild part, I'm not seeing that. Out of couple
thousand parts, a few are maybe 14 mA, and the bulk are 19-20 mA or so, with
a few at 22 or 23. Nothing outside that, and they are not all from the same
boxes.

Maybe they learned something from Toshiba....
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Old 13th October 2017, 05:47 PM   #30
BesPav is offline BesPav  Russian Federation
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Default how about using J111 J175 Jfets in F5

Quote:
Originally Posted by Nelson Pass View Post
It takes a lot of degeneration to get them down to the 10 mA or so that the amp works with. If you don't take that approach, the Idss figures with the voltages involved will exceed dissipation limits of the parts.

Papa, you say nothing about cascodes...
how about using J111 J175 Jfets in F5
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