Draw circuit diagrams for the flyback and forward converters and describe the main advantages and disadvantages of each circuit in comparison to each other. [6 marks] Explain why a third winding is often used in the forward converter and demonstrate how the choice of turns ratio impacts on the voltage stress experienced by the main switch, and the limitation that the turns ratio has on the maximum modulation depth that the converter can be used with. [6 marks] A forward converter has the following parameters: = 48 V, = 0.4 mH, = 100 F, = 10 , = 35 kHz Vd L C R fs = 1.5, = 1, = 0.4, = 5 mH N1/N2 N1/N3 D Lm Calculate the output voltage Vo. [4 marks] Calculate the average, maximum and minimum currents in the inductor L. [5 marks] Calculate the peak current in the transformer primary winding. [4 marks] QUESTION 6 Fig. 6 The MOSFET switch in fig. 6 is operated at 10kHz with a 0.75 duty cycle to regulate the current in a highly inductive load at 10A. You may assume that the turn-on and turn-off transients of voltage and current of the MOSFET(s) occur along straight lines and that the load current remains constant during the switching transient. The following switching times are appropriate for the MOSFET chosen: = 100 ns; = 150 ns; = 50 ns; and = 100 ns tri tfv trv tfi On graph paper, accurately sketch voltage and current waveforms for both diode and MOSFET during the turn-on and the turn-off transient. [4 marks] Calculate the conduction loss in the MOSFET if its is 0.5 Rds(on) Ω? [2 marks] Calculate the turn-on energy loss and the turn-off energy loss, clearly identifying any assumptions made.
Draw circuit diagrams for the flyback and forward converters and describe the main advantages and disadvantages of each circuit in comparison to each other. [6 marks] Explain why a third winding is often used in the forward converter and demonstrate how the choice of turns ratio impacts on the voltage stress experienced by the main switch, and the limitation that the turns ratio has on the maximum modulation depth that the converter can be used with. [6 marks] A forward converter has the following parameters: Vd = 48 V, L = 0.4 mH, C = 100 F, R = 10 , fs = 35 kHz N1/N2 = 1.5, N1/N3 = 1, D = 0.4, Lm = 5 mH Calculate the output voltage Vo. [4 marks] Calculate the average, maximum and minimum currents in the inductor L. [5 marks] Calculate the peak current in the transformer primary winding. [4 marks] QUESTION 6 Fig. 6 The MOSFET switch in fig. 6 is operated at 10kHz with a 0.75 duty cycle to regulate the current in a highly inductive load at 10A. You may assume that the turn-on and turn-off transients of voltage and current of the MOSFET(s) occur along straight lines and that the load current remains constant during the switching transient. The following switching times are appropriate for the MOSFET chosen: tri = 100 ns; tfv = 150 ns; trv = 50 ns; and tfi = 100 ns On graph paper, accurately sketch voltage and current waveforms for both diode and MOSFET during the turn-on and the turn-off transient. [4 marks] Calculate the conduction loss in the MOSFET if its Rds(on) is 0.5 Ω? [2 marks] Calculate the turn-on energy loss and the turn-off energy loss, clearly identifying any assumptions made.