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I have a question regarding a mosfet simulation I am trying to perform.

Here is the circuit in question.

enter image description here

We can see that Vd=1kV , Vs=0V and Vg=10V(it is a pulsed source)

Now to my understanding I should be seeing the 1kV at the output when the we have the saturation equation satisfied. enter image description here

When I simulate it on the other hand I do not see that response.

Here is the response I see: enter image description here

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    \$\begingroup\$ Why did you connect the load resistance to the source side instead of the drain side? In this case the Vout = Vg - Vgs. Also, the default Mosfet model is not suitable for this application. Try to use the real part model available in LTspcie. \$\endgroup\$
    – G36
    Commented Jul 19, 2023 at 15:34

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Your circuit is a source follower. This means that the voltage at the source "follows" the gate. In fact it lags behind by a couple of volts so, if the gate is at (say) 10 volts you might see 6 to 8 volts (typically) at the source.

A source follower has no voltage amplification just like an emitter follower has no voltage amplification. If you want either to act as a switch then, the gate needs to be driven with respect to the source by 10 volts.

  • Your circuit is operating in the saturation region
  • The MOSFET's triode/ohmic region is where it acts as a switch: -

enter image description here

Image from this question and answer. Or from this answer: -

enter image description here

The answer explains that the saturation region for a BJT is not the same region for a MOSFET.

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  • \$\begingroup\$ I understand, If I wanted for the mosfet to act like a switch but the discrepancy between the Gate and Drain is more than 10V, what configuration would work? \$\endgroup\$
    – DRF
    Commented Jul 19, 2023 at 17:24
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    \$\begingroup\$ The maximum gate source voltage is defined in the device data sheet and is usually around plus or minus 20 volts. The data sheet also indicates how much gate source voltage you need to remain in the triple region for a particular load current. \$\endgroup\$
    – Andy aka
    Commented Jul 19, 2023 at 18:33

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