Please help me answer these questions. Thank you. Suppose that a power MOSFET is

Question

Please help me answer these questions. Thank you.

Suppose that a power MOSFET is being used to switch a current through a resistive load of value 5-ohms using a 12V power supply. Suppose that the MOSFET is biased such that the ON resistance is RDS = 1.25 ohm. Calculate the power dissipated in the MOSFET and also in the load. Now suppose that the MOSFET is biased such that the ON resistance is RDS = 0.05 ohm. (This would require a higher gate voltage to achieve.) Calculate the power dissipated in the MOSFET and also in the load.

Explanation / Answer

(a)

total resistance =5+1.25 ohm =6.25 ohm

current =12/6.25 = 1.92A

power dissipation through mosfet = 1.92^2*Rds =4.608W

Power dissipated though load = 1.92^2*5=18.432 W

(b)

total resistance =5+0.05 ohm =5.05 ohm

current =12/5.05 = 2.376A

power dissipation through mosfet = 2.376^2*Rds =0.282W

Power dissipated though load = 2.376^2*5=28.232 W

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