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1. (20 points) Switching Circuit Transients. A 28V dc voltage source is switched through the network shown in Figure 1. A switching frequency of 200 KHz produces an average current of 1.8 Amperes to a constant voltage load of 16 Volts. Assume an ideal transistor and diode. Consider the 4 μH inductor’s internal resistance to be negligible. a. (15 points) Determine and plot the current waveform in the inductor. b. (5 points) Find the peak energy stored in the inductor during a switching cycle. 28 VDC Constant Voltage Load 16 Volts Ls Ideal Ideal Figure 1. Switching Circuit. 2. (20 points) Diode Rectifiers. A single phase full wave rectifier has an input voltage of 120V ac rms at 60 Hertz. It is providing 10 Amperes DC to a constant current load. The circuit has a commutating inductance of 1.20 mH. Assume ideal diodes. a. (10 points) Determine and plot the input current and input voltage. Label the commutation overlap time with its numerical value. b. (10 points) Find the power factor of this rectifier. Use the voltage and current waveforms that you found to compute this power factor. 3. (28 points) Thyristor Rectifiers. A three phase thyristor‐based rectifier converts a 208V ac rms balanced three phase line to line input voltage to 195 Volts DC. The rectifier’s load is a constant 40Amperes current. Assume ideal switching thyristors and negligible commutation overlap. Use a 2π length for the ac cycle. a. (2 points) Draw and label the circuit that you use for this purpose. b. (8 points) Determine and plot the output voltage waveform. c. (12 points) Determine and plot the voltage across one of the thyristors and the current through the same thyristor. Specify clearly which thyristor you choose. Label the firing angle of this thyristor (with a numerical value) on your plot. Draw the line‐to‐line voltage between lines a and b over your plot to provide a phase angle reference. All three waveforms should be drawn on the same plot with the same phase angle reference system. d. (6 points) Determine and plot the harmonic content of the thyristor voltage that you found in part c. ECE 427 Due: March 7, 2016 Exam #1 4. (20 points) Diode Reverse Recovery. In the circuit shown in Figure 1, when the switch turns ON, the diode turns OFF. For this problem, let the diode conduct 12.0 Amperes when the switch is ON. When turning off, the diode current decreases at the rate of 440 Amperes/microsecond. The diode’s maximum reverse recovery current is 25 Amperes. Its softness factor is 1.50 . a. (10 points) Determine the total turn off time, from the time that the diode’s current begins to decrease until the diode completes its reverse recovery time. b. (10 points) This diode has a forward voltage drop of 0.80 Volts. For operation as described in this problem, it conducts for half of the switching cycle. Model the 28 Volts across the diode in reverse bias as appearing during the time known as tb. If the circuit switches at 200kHz, determine the real power losses in the diode. 5. (12 points) Short Answer. a. (4 points) What is the purpose of a freewheeling diode? b. (4 points) What are the significant differences between a power diode and a Schottky diode? c. (4 points) Why does a power diode have a significant reverse recovery time?