TUTORIAL 1: POWER SEMICONDUCTOR DEVICES

TUTORIAL 1: POWER SEMICONDUCTOR DEVICES

1. List four characteristics of an ideal electronically operated switch and compare with the practical power switches. (4 Marks) 2. With the aid of voltage and current waveforms during turning ON of a switch, briefly explain how switching loss exists in the actual devices and describe how it increases with the increase in the switching frequency. (6 Marks) 3. As a converter designer, you are provided with a selection of Power BJT, Darlington pair BJT, Power MOSFET, IGBT, thyristor, triac and GTO. State which type of device you would choose to be incorporated in each of the following cases and give your reasons:(i) A 200 W, 400 kHz resonant inverter for low power induction heating (ii) A 80 W, 240 V, 50 Hz light dimmer (iii) A six-stage single-phase 50 Hz multilevel inverter with 500 W output power (iv) A 500 W, 240 V, 50 Hz PWM inverter with 20 kHz carrier frequency (8 Marks) 4. Two new DC/DC converter circuits namely converter A and converter B were tested. Converter A and converter B consists of power BJTs and MOSFETs respectively as the main power switching devices. Both converters were switched at 10 Hz. It was observed that converter B generate more heat than converter A. However, when the switching frequency for both converters were increased to 30 kHz, the converter A generate more heat than converter B. Explain why the heat generate differently in both converters when switching at low and high frequency. State which device would you recommends if it is used in a low power switched mode power supply circuit.

(5 marks) 5. With the aid of I-V curve diagram, describe the steady state characteristic of Power BJT, MOSFET and IGBT. State the drive requirements of each device and compare their on-state voltage drops and power losses for the same amount of collector or drain current. Discuss also the major difference in applications such as power range and switching frequency using those devices. (10 marks)