This is a very basic question. As I understand it, in a MOSFET the conductivity from source to drain depends on the voltage from gate to source. I have a a K2718 , the datasheet tells me this: So I set up the transistor like this: With a voltmeter I checked Vgs = 3.8V. From the graph I expect the drain current to be around 150mA. However if I try to short R2 with an ammeter I am effectively shorting my power supply (which starts making funny noises). Why?