Question 3 03 Figure Q3 A Shows A Dual Switch Forward Converter The Input Voltage Vin Is 48 V And The Output Voltage 1 (50.67 KiB) Viewed 109 times
QUESTION 3 03 Figure Q3(a) shows a dual-switch forward converter. The input voltage Vin is 48 V, and the output voltage Vou is 14 V. Other data are given in Table 03(a) V. Di D L1 . TRI T1 Vax D2 N1 N2 D TR2 OV Figure Q3(a). Dual-switch forward converter. Table Q3(a). Data for circuit in Figure Q3(a). Full load output power 50 w Switching frequency 120 KHZ L1 inductance 180 UH Transformer T1 turns-numbers N1:N2 32:26 The transformer is constructed around EFD30 ferrite half-cores in 3C90 material. The manufacturer's data sheet should be consulted to obtain data: http://ferroxcube.home.pl/prod/assets/efd30.pdf Q3a Calculate the following quantities: the duty factor at which the converter operates when it is running in the continuous current mode; ii. the minimum voltage that diode D, must be able to support: . the output power at which the converter will enter the boundary conduction mode: iv. the flux density swing in the transformer's core material: V. the peak magnetizing current drawn by the transformer. 10 marks
Q3b TR1 and TR2 in Figure Q3(a) are normally driven on simultaneously by applying a positive gate-source voltage to each of them. As seen in Figure Q3(b), driving the lower device, TR2, directly from a low-voltage control IC connected to O V is relatively straightforward. However, there is a difficulty with driving the upper device, TR1, as its source voltage swings between 0 and 48 V. TR1 therefore cannot be driven directly from the output terminal of a low-voltage control IC connected to 0 V. With the aid of sketches, explain how circuitry using a bootstrap diode, flying capacitor, high-voltage level-shifting MOSFET and a driver IC can be incorporated to enable TR1 to be driven from the low-voltage control circuitry. V TR1 D1 ti Low-voltage Control D2 TR2 OV Figure Q3(b). Primary side circuitry of dual-switch forward converter in Figure Q3(a). 8 marks Q3c Redraw the circuit in Figure Q3(a), but with the arrangement formed by Dr and De replaced with an arrangement of MOSFETs acting as synchronous rectifiers. Explain what the benefits of this latter arrangement are, and how it operates. Sketch waveforms in your answer as appropriate. 7 marks
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