Electronic – MOSFET Rds(on) question


I have a question related to the Rds(on) property of a MOSFET (IRF630N).

Once the MOSFET is turned on (Vgs > Vth) will Rds(on) vary with the increase of Vgs? Or it is not affected by the gate voltage once the MOSFET is on. Will it be affected only by the junction temperature? How is Rds(on) related to the Drain current?

Best Answer

\$R_{DS(ON)}\$ is an important parameter, and many datasheets start with mentioning values for them.
For the FDC885N two values are mentioned in the Features section at the start of the datasheet:

Max \$R_{DS(ON)}\$ = 27m\$\Omega\$ at \$V_{GS}\$ = 10V, \$I_D\$ = 6.1A
Max \$R_{DS(ON)}\$ = 36m\$\Omega\$ at \$V_{GS}\$ = 4.5V, \$I_D\$ = 5.3A

From the same datasheet:

enter image description here

So, yes, \$R_{DS(ON)}\$ varies with \$V_{GS}\$, and yes, it's higher at higher temperatures.

If your manufacturer can't give you the information and you really need it, move on to another manufacturer.