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Old 12th July 2006, 04:43 AM   #1
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Default how much is the transconductance of lu1014d

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Old 12th July 2006, 04:47 PM   #2
EUVL is offline EUVL  Europe
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If you just look at the datasheet, you can estimate it to be about 30S. In practice (e.g. ZV9), your effective transconductance would be determined by the source resistor, which is about 0.5 ohm, or 2S. The transconductance of the JFET is in comparison negligible.

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Old 13th July 2006, 01:28 AM   #3
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I have looked at the datasheet but I'm just not that intellagent??? Don't we need to know early voltage or something??? Is that on the datasheet???
This is one of the model parametors that I see varied numbers for in every different model???
EUVL, Could you enlighten us DIY Physicists a little more??? Thanks.
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Old 13th July 2006, 06:25 AM   #4
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There are enough semiconductor physicists on this forum, so it should not be a mechanical engineer here doing the explanation. But I shall try.

One can define transconductance as roughly Id / Vgs.
If you look at Figure 8 of the datasheet, take Vds = 2V. The current Id jumps from almost 0 at Vgs=-1V (magenta curve) to above 30A at Vgs = 0V (cyan curve). So delta Id / delta vgs = 30A/V.

Or not ?


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Old 13th July 2006, 11:57 PM   #5
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EVUL, Thanks, I'm not sure you are willing to take questions??? BTW, I work in "the industry", just not in this disipline. After work I generally tend to be much more mechanical myself!
The simple formulae you suggest, (I think most of us new that) is using data points way outside our operating range(30A). I beleive we are operating in a highly variable area of I vs Gfs or whatever, at only a few amps?... However, I might think, I should try to "curve trace" a few of these babies to get some of those same numbers closer to where we are using these devices for a more accurate answer??? I think I can figure that out... I havent used an HP SPA in years... Sounds like fun...
That would also allow me to enter "user data" into my Pspice model...
Not intending to polute the thread or anything but, any other ideas on the gfs, or other perameters are also welcome
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Old 14th July 2006, 06:12 AM   #6
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> I beleive we are operating in a highly variable area of I vs Gfs or whatever, at only a few amps?...

There are 3 curves on the data sheet: Vgs 0V, -0.5V & -1V.
If you plot the 3 points Id vs Vgs, you get pretty much a straight line.

I am still waiting for my JFETs, so I cannot provide more measurement data. I asked Nelson once in the Newtron thread. And he kindly referred to ZV9.

But who cares, if Y is approx. 60 times larger than Rsource.


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Old 14th July 2006, 09:12 AM   #7
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I also got about 35 S at Vds=4V from the Fig 8.

At Vds=2V, about 30 S.
At Vds=3V, about 33 S.
At Vds=4V, about 35 S.

Average about 33 S (i.e. transimpedance=abt 0.03 Ohms)
on the assumption of the operating Vds of 3V.
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