Thank you .The voltage across R1 is very dependent on what MOSFET is used. Also depends on temperature. The data sheet for this part is needed but even then the voltage is only approximant.
If R1 was across V1 you will have 40mA. I know from experience that you will get closer to 35mA. So lets say M1 D-S current is about 35mA. In the data sheet there is a Gate Threshold voltage listed for current of 10uA (or some very low current). There should be a graph of Gate Voltage, Voltage D-S, and Drain Current. There is probably not a graph-line for 35mA. You will have to guess.
Is this a school project?
If you use SPICE to find the answer, pick a real MOSFET. Using a "NMOS" may not work well.
I don't think the answer is particularly revealing regardless of how it is answered. You or they need better questions.Thank you .
This is an interview question
Thank you.I think he is expecting something like this. I was not able to give any answer. Try to play around MOSFET saturationThe simplest answer is that it takes a "Gate Turn on Voltage" to get the MOSFET to turn on. It takes 4 or 5 volts across G-S to turn on the part. That voltage must come from the 40V. So the Source must be below the 40V by that 4 volts.
Another way to look at it. Think of a junction transistor. They take 0.6V (approx) to turn on the transistor. So the Emitter must be below the supply by about 0.6V.
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by Jake Hertz
by Jake Hertz
by Jerry Twomey
by Jake Hertz