Midterm Exam 3 -- E84, Fall 2008

• Due Tuesday 12/17 5 pm at Parsons 2372.
• Take home, open notes, course web, reference books.
• Mark your start and end times. Don't spend more than 3 hours.
• Mark your name and question number clearly on top of each page. Indicate the total number of pages submitted.
• When solving a problem, list all the steps. In each step, describe what you are doing in English, then show the calculation and the result of the step. A final answer, even if correct, without evidence of the steps leading to the answer will not receive credit.

1. Problem 1. (33 points)

An inductive load is connected to a AC voltage source of 220 Volts (RMS) and 50 Hz. It is known that the average power is 1.1 kW and the power factor is . If the power factor is to be improved to 0.866 by including a capacitor in paralle with the load, what is the its capacitance?

2. Problem 2. (33 points)

Find the DC operating point of the transistor circuit given below, where , , , , and . If you find the DC operating point is not in the middle of the linear region of the output characteristic plot, modify so that the DC operating point is in the middle of the linear region (to maximize the dynamic range of the AC output).

3. Problem 3. (34 points)

The circuit shown below is called Darlington transistor amplifier which is composed of two transistors and with their collectors connected and the emitter of connected to the base of . Assume and both transistors have .

1. Give the expressions of , , , all in terms of and .
2. Given , find so that the DC operating point is in the middle of the linear region of the output V-I characteristic plot.
3. Given and the same as before, find the proper DC voltage so that the Q point is in the middle of the linear region.
For simplicity, assume for both transistors .