MOSFETs:

1. Why MOSFETs don’t suffer with the problem of secondary breakdown?2. Why MOSFETs have a positive temperature coefficient of resistance compared to BJTs

and SCRs which possess a negative temperature coefficient of resistance?3. Why biasing a MOSFET at constant VGS might screw up the operating point? Suggest a

remedy.4. Why MOSFETs have lower switching losses compared to BJTs?5. Why MOSFETs are capable of being operated at considerably higher switching

frequencies than BJTs?6. Why we prefer n-channel MOSFET over p-channel MOSFET for switching applications?7. Identify the region of operation for the n-channel MOSFET(µnCox = 100 µA/V2, W/L = 1

V, VT = 1 V) designated by following parameters:(a)VGS = 2 V, VDS = 5 V(b)VGS = 0.9 V, VDS = 6 V(c) VGD = 2 V(d) VGD = -2.5 V(e) VGS = 1.5 V, VDS = 1.9 V

8. Compute the drain current and transconductance for the n-channel MOSFET (µnCox = 100 µA/V2, W/L = 1 V, VT = 1 V) designated by the following :(a)VGS = 2 V, VDS = 5 V(b)VGS = 0.9 V, VDS = 6 V(c) VGD = 2 V(d) VGD = -2.5 V(e) VGS = 1.5 V, VDS = 1.9 V

DC-DC converters:

1. With the aid of relevant waveforms, please specify the shortcoming which is common to Buck converter and Buck-Boost converter, and explain how ĆUK converter topology overcomes it.

2. With the aid of relevant waveforms, please specify the shortcoming which is common to Boost and Buck-Boost converter, and explain how ĆUK converter topology overcomes it.

3. How do isolated dc-dc converters overcome the limitations of conventional dc-dc converters?

4. Discuss the realization of a buck converter starting with a DC source and a SPDT switch, and arriving at the final converter schematic. Please explain the relevance of different

elements of the converter topology, and the rationale behind the way the different elements are interconnected.

5. Design a buck converter (for continuous inductor current, and assume that all the components are ideal) with the following specifications: dc source voltage = 15 V, output load voltage = 5 V, switching frequency = 50 kHz, load resistance = 10 Ω, output voltage ripple should not exceed 0.1%. Specify (a) the value of the minimum inductance required for continuous inductor current; (b) the value of the minimum capacitance required to limit the output voltage ripple to 0.1 percent; (c) the rms value of the inductor, capacitor, switch and diode current; and (d) peak voltage across inductor, capacitor and switch.

6. Design a boost converter (for continuous inductor current, and assume that all the components are ideal) with the following specifications: dc source voltage = 5 V, output load voltage = 15 V, switching frequency = 50 kHz, load resistance = 10 Ω, output voltage ripple should not exceed 0.1%. Specify (a) the value of the minimum inductance required for continuous inductor current; (b) the value of the minimum capacitance required to limit the output voltage ripple to 0.1 percent; (c) the rms value of the inductor, capacitor, switch and diode current; and (d) peak voltage across inductor, capacitor and switch.

7. The buck-boost converter has following parameters: Vs= 24V, D=0.4, R= 5Ω, L=20 µH, C=80 µF, and f=100 kHz. Determine the output voltage, inductor current average, maximum and minimum values, and the output voltage ripple.

DC to AC converters:

1. A single phase square wave VSI (supplied by a 300 V dc source, output waveform frequency is 50 Hz, and time period is 0.02 s) is feeding a resistive load of 15 Ω.(a) Express the output waveform in Fourier series;(b) Evaluate the fundamental, 3rd, 5th, 7th, 9th, and 11th harmonic.(c) Also evaluate the rms value of the components mentioned in (b).(d) If the Fourier series is truncated at 11th harmonic , compute the error in the rms

value of the voltage computed using truncated Fourier series (up to 13th harmonic), and the actual rms value of the output voltage computed using the output voltage waveform.

(e) Calculate the THD for the output voltage.

2. A single-pulse single phase PWM inverter fed by 500 V dc source (on time in every half cycle = 2π/3), is supplying a 25 Ω resistive load.

(a) Determine the average value of the switch current.(b) Determine the amplitudes of the Fourier series terms for the square wave load

current. Restrict your Fourier series up to 11th harmonic.(c) Determine the power absorbed by the load using the truncated Fourier series up to

11th harmonic.(d) Calculate the THD for the output voltage.

3. A 120o mode three-phase VSI delivers power to a resistive load (star connected load of 13 Ω per phase), from a 650 V dc source.(a) Find out the rms value of the periodic current flowing through the switch.(b) Calculate the THD for the line voltage as well as the phase voltage.(c) Determine the amplitudes of the Fourier series terms for the line voltage. Restrict

your Fourier series up to 11th harmonic.(d) Determine the amplitudes of the Fourier series terms for the phase voltage. Restrict

your Fourier series up to 11th harmonic.

4. A 180o mode three-phase VSI delivers power to a resistive load (star connected load of 10 Ω per phase), from a 250 V dc source. (a) Find the rms value of the periodic current flowing through the switch.(b) Calculate the THD for the line voltage as well as the phase voltage.(c) Determine the amplitudes of the Fourier series terms for the line voltage. Restrict

your Fourier series up to 11th harmonic.(d) Determine the amplitudes of the Fourier series terms for the phase voltage. Restrict

your Fourier series up to 11th harmonic.

5. What is the special significance of PWM inverter in contrast to square wave inverter?