Hi i am trying to find a way to determine the range of the drain source resistance (RDS) for a N-JFET only with the parameters given on its datasheet.
I know that the drain source resistance is related to the drain source voltage and the drain current or the source current that is the same, because no current flows through the gate.
I don't remember where I got it from, and I don't even know if it is true, I have this written on some old notes I found.
I know VGS is the rating for the maximum voltage that can be tolerated between the gate and source terminals.
I know VGS(off) is the gate source cut-off voltage, this is the voltage at which the device turns off and starts working on the ohmic region.
I know IDSS os the maximum current that can be handled by the device.
So given the following datasheet:
But on the datasheet this parameter indicates the absolute maximum voltage that the device is able to withstand, but I read practically this should be used up to around 60%.
I don't understand how VGS(off) could be lower than VGS max.
And at last IDSS:
I don't really understand how to use the datasheet values to calculate the range of RDS given a range of voltages for VDS.
I plotted RDS against VGS(off) and IDSS, using VGS = -2.5V and the ranges given on the datasheet and got this: