Question

SECTION B: Attempt any Two) questions 150 marks total! Q3 A MOSFET is used as a low-side switch to control a 15 2 resistive load from a 24 supply. The MOSFET has RDSan VDC 0.2 ? and ton-tof-40 ns. (a) Draw a suitable circuit. (b) Calculate both the drain current ip and drain-source voltage ups when the MOSFET is off and when it is on. 161 (e) Calculate the power dissipated in the load and in the MOSFET while they are (d) Use a waveform diagram to show how pulse width modulation (PWM) with a duty switched on. factor of D is used to control the average power in the load and explain how the average power depends on D (e) Calculate the total power loss in the MOSFET for a switching frequency of I kHz and the load at half power. Explain how the conduction and switching losses would change if the frequency of the waveform were increased to 100kHz at the same duty cycle. (t) (g) How should your circuit be modified if the load were inductive and why is the modification necessary? Continued overleaf

Please answer all the parts of the question clearly and fully! Thank you!

Numerical Answers:

(b) (0.0 A, 24 V), (approximately 1.6 A, 0.32 V)

(c) 38.4 W, 0.5 W

(e) 0.26 W + 1.5 mW

Answer 1

(a) (b) when misfit is off V_D = OA V_DS = V_DD - I_D R_D V_DS = V_DD = 24 v (I_o = OA) misfit is ON I_D = V_DD/R_d + R_DS = 24/15 + 0.2 Tilde Equal 1.6 I_D = 1.6 A V_DS = I_D R_DS V_DS = R_S I_D = 1.6 times 0.2 V_DS = 0.32 V (c) power dissipated in the load P_L = I_D V_DS = 1.6 times 0.32 = 0.5 w p_2 = 0.5 w power dissipated by the circuit p_L = V_DD I_D = 24 times 1.6 p_2 = 38.4 w (d) duty cycle (D) = T_on/T_on + T_off times 100% = 40/40 + 40 times 100 = 50% D = 0.5 = 50% P = f_s V_D/2 (t_on + t_off) times I_n = 1 k/2 times 24 (40 + 40) n times 1.6 D_m = 1.5 w toatla power = p_in + p_switching p_t