Question about Rds(on) of a power MOSFET


Joined Aug 1, 2013
It isn't calculated. It is stated on the datasheet, usually under specific conditions such as a 10 V drive signal and a stated pulse width.



Joined Apr 24, 2011
How fast is this thing switching?

If just every so often than Rds on times source current is a decent estimation of device power.

Switch that sucker on and off fast, as is done in a switching power supply, and the losses are dominated by switching losses as the device goes off to on (minority) and on to off (mostly).

These are due to the short period when the device voltage is increasing but the load current is still on. It is but a brief period but they do add up.