i can't understand how, in a MOSFET N, to get an expression of the voltage Vds with respect to time if Vgs > Vth (closed circuit) and if Vgs < Vth (open circuit). I saw many equations with current, but none of them was like

\$\ Vds = a(1-e^{-t}) \$

I wrote an expression like this because it seems to fit with this kind of curve. Is anybody know how can i get this Vds without the current ? I'm not a pro with circuits then sorry for my missing knowledges. enter image description here


closed as unclear what you're asking by Hearth, Finbarr, JRE, RoyC, Warren Hill Apr 28 at 15:06


  • \$\begingroup\$ You need a circuit to have current and datasheet to see RdsOn vs Vgs \$\endgroup\$ – Sunnyskyguy EE75 Apr 17 at 23:24
  • 1
    \$\begingroup\$ Why do you expect there would be such an equation, when you don't have any sort of capacitor or inductor charging to give you that exponential? Or are you referring to the gate capacitance? In general I can't tell what you're asking. \$\endgroup\$ – Hearth Apr 17 at 23:26

A MOSFET is a transconductance device. That means you get amps out for volts in. It also means that any formula you see contains \$I_{D}\$ (amps out) and \$V_{GS}\$ (volts in) rather than \$V_{DS}\$ (volts out).

If you want a formula that contains \$V_{DS}\$, use the formula that contains \$I_{D}\$ and multiply it by the circuit resistance in the drain connection.

