Name:__________________________________________ Massachusetts Institute of Technology Department of Nuclear Science and Engineering Department of Electrical Engineering and Computer Science 22.071/6.071 – Introduction to Electronics, Signals and Measurement Spring 2006 Quiz 3 • Please write your name on each page of the exam in the space provided • Please verify that there are 12 pages in your exam. • To the extent possible, do your work for each question within the boundaries of the question or on the back side of the page preceding the question. Extra pages are also provided for computation. • Note that the total number of points is 100. • Closed book. No Calculators • Partial credit adds up so make sure that you show your work. 22.071/6.071 Spring 2006 Quiz#3 Page: 1Name:__________________________________________ General Useful Information Diodes: Ideal diode model AnodeCathode+-VdId IdVdReverse-BiasRegionForward-BiasRegion 0.7 Volt offset model Vg = 0.7 Volts +-VdId0.7 V IdVdVg Full diode model exp 1TVdId IsV⎡⎤⎛⎞=−⎢⎥⎜⎟⎝⎠⎣⎦ +-VdId Zener Diode Ideal model Vz Id Vz IdVdVzReverse biasregion BJTs Ie = Ic + Ib For operation in the active region Ic = Ibβ Vbe=0.7 V IbIccollectorbaseemitterVbe+_Ie Reactives Capacitor ccdVI=Cdt CVcIc+- Inductor LLdI=LdtV VLIL+-L 22.071/6.071 Spring 2006 Quiz#3 Page: 2Name:__________________________________________ Problem 1 - (15 points) For the following circuit the switch S has been open for a long time. At time t=0 the switch is closed and it is opened again at time t=1 sec. Sketch vc(t) for all t. Indicate all relevant values in your sketch. (This is the homework problem. One of the element values has been changed for easier algebraic operations) 10uF 50kΩ 50kΩ 12 V+-vc+-S t (sec)vc(t)1 22.071/6.071 Spring 2006 Quiz#3 Page: 3Name:__________________________________________ 10kΩ VBVCE+-RC+20 VICIBProblem 2 - (15 points) The transistor used in this circuit has the characteristics shown on the graph below. Α) Calculate the load line, draw it on the graph and locate the Q-point for IB=6uA 6(6 10 A)−× 51015 20 252VCEIC(mA)(Volts)11.50.5IB=4uAIB=6uAIB=8uAIB=10uA Β) Estimate the value of the transistor β.22.071/6.071 Spring 2006 Quiz#3 Page: 4Name:__________________________________________ Problem 3 - (15 points) t=0Cv(t)+-R1R2Is In this circuit, the switch is closed for a long time and opens at time t=0. A. What is the voltage v just before opening the switch v(t=0-)? B. What is the voltage v just after opening the switch v(t=0+)? C. What is the value of the time constant τ governing the evolution of v for t>0? D. Draw v(t) versus time and give an expression for v(t). tv(t)0 22.071/6.071 Spring 2006 Quiz#3 Page: 5Name:__________________________________________ Problem 4 - (10 points) For the following circuit, the switch is closed for a long time then opens at time t=0. i(t)LRCVst=0v(t)+- A. What is the voltage v and current i just before opening the switch v(t=0-), i(t=0-)? B. Obtain the differential equation for the subsequent (t>0) evolution of voltage v(t). C. Obtain two initial conditions to apply at t=0+ D. In the space below draw the general possible forms of the voltage v(t) tv(t)0 22.071/6.071 Spring 2006 Quiz#3 Page: 6Name:__________________________________________ Problem 5 - (15 points) The graph below shows the i-v characteristic curve of a certain diode. + Vd -Id The diode is used in the following circuits. Draw on the above plot and label, the load-line you would use for each circuit in order to obtain the diode voltage and current. 500 Ω 1.5 V +- (A) 500 Ω 1.5 V +-(B) 1kΩ 4 V +-1kΩ (C) 5 pt Extra credit Problem 6 - (15 points) 22.071/6.071 Spring 2006 Quiz#3 Page: 7Name:__________________________________________ The Zener diode used in this circuit has a Vz = 6.7 Volts and it is used for biasing the npn transistor which has β=100. 6.7 V 10kΩ 100kΩ 10kΩ Vcc=+20 VICRER1RCIEIBVCE+- Determine the Q-point (CQI and ) of the transistor CEQV 22.071/6.071 Spring 2006 Quiz#3 Page: 8Name:__________________________________________ Problem 7 - (15 points) 5.7 V VccRER 1VZC V o+ - Voltage Vcc applied to the above circuit has the form shown below. It has a DC offset of about 7 Volts with considerable fluctuations about that value. The Zener diode used in the circuit has Vz = 5.7 Volts. The output is taken across the emitter resistor ER as indicated in the schematic. A. Draw the form of the output voltage Vo on the same graph. B. What is the role of resistor and capacitor C? 1R 22.071/6.071 Spring 2006 Quiz#3 Page: 9Name:__________________________________________ Blank page: For computation 22.071/6.071 Spring 2006 Quiz#3 Page: 10Name:__________________________________________ Blank page: For computation 22.071/6.071 Spring 2006 Quiz#3 Page: 11Name:__________________________________________ Problem Points 1 2 3 4 5 6 7 Total 22.071/6.071 Spring 2006 Quiz#3 Page:
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