According to this data sheet at 6v GATE voltage , the saturation drain current is about 1.25A. now I want to switch a device (say a tiny motor) which demands 1.25 A at 2volts , Indicating the resistance 1.6 ohms. now I am supplying the drain source voltage 4 volts.(as usual the motor and the MOSFET is in series) which means the mosfet is saturated , and capable of supplying 1.25A , now the question is , usually we are advised to use ohmic region to switch, but how about this? won't this switch work?
but how about this? won't this switch work?
It will work (for a short period of time) but, the MOSFET will be dissipating about 3.2 volts x 1.25 amps = 4 watts. You'll need a heatsink and this is quite wasteful of power. However, the MOSFET you linked is a 2N7000 and, a heatsink is out of the question hence it will burn in a few seconds: -
What you should be doing is choosing a MOSFET with much much lower on resistance and providing a supply of 2 volts.