# how to calculate the Resistor for a mosfet so that the Vout 10 V is?

These value are given:

• VDD = 15V
• Zener voltage = 6.8V
• Zener current = 5mA
• Rs = 3kOhm

here is the link to the data sheet: https://nl.mouser.com/datasheet/2/268/supertex_2n7000-1181251.pdf

I have calculated that R1 most be (15-6.8)/5mA =1.6kOhm but I'm stuck there.

• The $V_{DS}$ of your M1 should be negliglible so in a first approximation $V_{A}$ will be $V_{RS}$. Jun 18, 2020 at 5:55
• Look up the threshold voltage of the 2N7000. You know the voltage at the gate (6.2 V) so you can determine the voltage across $R_S$, you know $R_S$ is 3 kohm so you can calculate the current through it. Now check if the 2N7000 needs a large $V_{GS}$ to conduct that current, is that $V_{GS}$ larger than the threshold voltage? (my guess: it is not but check anyway). You know $I_D$ and the voltage across $R_D$ + D1, the rest is easy. Jun 18, 2020 at 8:10