# JFET-Transistor output characteristics in PSpice

I would like to ask if anyone can help me with the following problem. I would like to print the output characteristics of the JFET-transistor in PSpice. This is PMBFJ309, here is the datasheet. My test setup looks like this.

And here is the output.

The values of Vgs goes from top to bottom, starting from 0V to -4V, the increment is 0.25V. But when you compare this result to a datasheet, it's completely different.

So my question is, is there any way to get the same graph as from the datasheet.

There are .model characteristics.

.MODEL  PMBFJ309/PLP   NJF
+             VTO = -2.3973E+000
+            BETA = 3.81468E-003
+          LAMBDA = 3.80761E-002
+              RD = 2.33008E+000
+              RS = 2.33008E+000
+              IS = 3.02702E-016
+            CGS  = 6.50000E-012
+            CGD  = 5.70000E-012
+              PB = 6.83767E-001
+              FC = 5.00000E-001


• Also, the chart you shared does not come from the datasheet you linked. $V_{GS}$ for an n-channel JFET should be negative, and it is shown as negative in the linked datasheet. The chart you used probably comes from a p-channel JFET's datasheet. – The Photon May 21 at 15:09
• It comes from the same datasheet -- see the OP's link to it. For some reason the minus signs are not showing but you can tell there is space for them. – ErikR May 21 at 15:13

You can try to adjust various parameters in the .model, but in the end you have to remember that a SPICE element is only an approximation of the real-life counterpart. You can clearly see that the saturation region is a straight line in the simulation, and the knee points are rather abrupt. Getting a perfect match with the datasheet is quite impossible. Besides, the JFETs are known to have very large variations even compared to their own datasheets. It's one of the reasons you don't see constant current generators with JFETs everyhere. BTW, you used 0...-4 for the Vgs, but in the datasheet it's shown as 0...-1. For this case, you could try adjusting the beta parameter. In LTspice, beta=3.5m seems to come closer to what's shown (the default value is 4.682m).
• @TomášMacháček It looks like you already found the .model definition, so you could try to tinker with the variables, see if you will get a better match. – a concerned citizen May 21 at 17:23