Question

Q3 A MOSFET is used as a low-side switch to control a 15 2 resistive load from a 24 V DC supply. The MOSFET has Rps,on = 0.2 and fon foff= 40 ns. [2] (a) Draw a suitable circuit. (b) Calculate both the drain current ip and drain-source voltage vps when the MOSFET is off and when it is on. [6] (c) Calculate the power dissipated in the load and in the MOSFET while they switched on. are [4] (d) Use a waveform diagram to show how pulse width modulation (PWM) with a duty factor of D is used to control the average power in the load and explain how the average power depends on D. [4] (e) Calculate the total power loss in the MOSFET for a switching frequency of 1 kHz and the load at half power. [4] () Explain how the conduction and switching losses would change if the frequency of the waveform were increased to 100 kHz at the same duty cycle. [2] (g) How should your circuit be modified if the load were inductive and why is the modification necessary? [3]

Answer 1

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