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JFET Questions

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eev_carl:
Hi,

I'm trying to reproduce the load lines in the JFET J211 datasheet.  When my Vgs is 0 and Vds is 5, I get 8.2mA of current and not the 20mA in the datasheet.  I was wondering if there was something wrong with my test setup or if my JFET was bad (I just replicated my results with a new one though).

The attached schematic shows the JFET with a positive Vds and a negative Vgs. In the simulation, Vgs is 0.  I'm also unsure as to why the simulation shows only .4mA of current.  (Differently spec'd JFET?)

https://www.mouser.com/ds/2/149/J211-889304.pdf

Thanks,
Carl

Wimberleytech:
You need to supply the model for the transistor you are simulating.  That model needs to be the model of the device in the datasheet.

I found this but cannot vouch for it:
.model J211   NJF(Beta=1.808m Betatce=-.5 Rd=1 Rs=1 Lambda=10m Vto=-2.9
+      Vtotc=-2.5m Is=101.9f Isr=977.5f N=1 Nr=2 Xti=3 Alpha=13.92u
+      Vk=88.13 Cgd=3.913p M=.3448 Pb=1 Fc=.5 Cgs=3.496p Kf=701.5E-18
+      Af=1)

Benta:
According to the data sheet, drain current can be anywhere between 7.0 and 20 mA at zero gate voltage, so your results are within spec.

TimFox:
The data sheet value for Idss (drain current at zero gate-source voltage) ranges from 7 to 20 mA across production, so your 8.2 mA value is within specification.

Ian.M:
 I've set up a .dc sweep with Vgs stepped to attempt to reproduce the datasheet curves Carl posted, using Wimberleytech's J211 model.  It seems to be somewhat better than the default NJF one, but it still doesn't look much like the curves in the datasheet.  It has a sharper knee, and much lower output resistance in the saturation region.

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