In attached circuit I expect the FET to be biased fully on, with RDSON = 6 ohms. Current through the loop is 10V/(100 + 6 ohms) = 94mA.

Drop across M1 should be 566mV.
Drop across R1 should be 9.43V.

V1 Rser = 0, so no drop there. I tried several other FET models but I am seeing similar strangeness, so I wonder if my sim config settings are wrong.

 

hi m12,
Have you considered the effect of the voltage drop across R1, that decreases the Vg to Vs voltage,
E

 

hi m12,
Have you considered the effect of the voltage drop across R1, that decreases the Vg to Vs voltage,
E

Oops, dummy me. Thanks!

 

Drop across M1 should be 566mV.

No.

The MOSFET is connected as a source-follower, so the drop will be at least the Vgs(th) value.

R2 has nothing to do with it as the gate current through it is essentially zero.

 

No.

The MOSFET is connected as a source-source follower, so the drop will be at least the Vgs(th) value.

Right!! The thing about a source follower such as this; Vout is more variable between FETs then it would be with a BJT in emitter follower configuration. This because the Vgs threshold voltage usually has a range of 2-3 volts.

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