Title Industrial Electronics-2022_S1.pdf ✅

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Page 3 of 5 Question 1 A Boost DC-DC converter is operating in dc steady state under the following conditions: input voltage Vin = 12V, duty factor D = 0.4, output power Po = 24W, inductance L = 25  H and switching frequency fs = 400 kHz. Assume ideal components. Derive any formula used and state any assumptions made. a) Draw the power circuit of the converter. Calculate and draw typical waveforms of the switching signal, switch voltage, inductor voltage, inductor current, capacitor current and diode current for the continuous conduction mode of operation. [11 marks] b) Draw the inductor voltage and current waveforms for Po = 15W; all else are unchanged. Compare the ripple in the inductor current with that found in part (a) above. [04 marks] c) If the output load is changing in this Boost converter, calculate the critical value of the output load Po below which the converter is in the discontinuous conduction mode of operation. [03 marks] d) In this Boost converter, the input voltage is varying in a range from 9V to 15V. For each input voltage value, the duty ratio is adjusted to keep the output voltage constant at its nominal value (with Vin = 12V and D = 0.4). Calculate the critical value of the inductance L that will keep the converter in the continuous conduction mode at and above Po = 5W for all values of the input voltage Vin. [07 marks] Question 2 An isolated switch-mode power supply is to be designed with the following specification: Input dc voltage Vd = 48V  10% Output dc voltage Vo = 5V (regulated) Output voltage ripple Vo = 10 mV peak to peak Switching frequency s f = 50 kHz Output power Po = 1W - 100W A forward converter operating in a continuous conduction mode with a demagnetizing winding having the same number of turns as the primary winding (N3=N1) is chosen. Assume that all components are to be ideal except the presence of the transformer magnetizing inductance. Deriving any formula used in the calculations: a) Give the circuit diagram of the converter and briefly explain its operation, showing voltage and current waveforms. [07 marks]