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 1 Name General Useful Information Diodes Id Ideal diode model Anode Id Cathode Reverse Bias Region Forward Bias Region Vd Vd Id 0 7 Volt offset model Vg 0 7 Volts 0 7 V Vd Vg Id Vd Vd Full diode model Id Is exp 1 VT Id Vd Id Zener Diode Vz Vz Ideal model Id Vd Reverse bias region Vz BJTs collector Ie Ic Ib For operation in the active region Ic Ib Vbe 0 7 V Ic Ib base Vbe Ie emitter Reactives Capacitor C dV Ic C c dt Ic Inductor dI VL L L dt 22 071 6 071 Spring 2006 Quiz 3 Vc L IL VL Page 2 Name 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 S 50k 50k 12 V 10uF vc vc t 1 22 071 6 071 Spring 2006 Quiz 3 t sec Page 3 Name 20 V Problem 2 15 points RC 10k The transistor used in this circuit has the characteristics shown on the graph below IC IB Calculate the load line draw it on the graph and locate the Q point for IB 6uA 6 10 6 A IC VCE VB mA IB 10uA 2 IB 8uA 1 5 IB 6uA 1 IB 4uA 0 5 5 10 15 20 25 VCE Volts Estimate the value of the transistor 22 071 6 071 Spring 2006 Quiz 3 Page 4 Name Problem 3 15 points t 0 Is R2 C R1 v t 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 governing the evolution of v for t 0 D Draw v t versus time and give an expression for v t v t 0 22 071 6 071 Spring 2006 Quiz 3 t Page 5 Name Problem 4 10 points For the following circuit the switch is closed for a long time then opens at time t 0 t 0 i t Vs L C v t R 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 v t 0 t 22 071 6 071 Spring 2006 Quiz 3 Page 6 Name Problem 5 15 points The graph below shows the i v characteristic curve of a certain diode Id Vd The diode is used in the following circuits Draw on the above plot and label the loadline you would use for each circuit in order to obtain the diode voltage and current 500 1 5 V 500 1 5 V 4V 1k 1k A B C 5 pt Extra credit Problem 6 15 points 22 071 6 071 Spring 2006 Quiz 3 Page 7 Name The Zener diode used in this circuit has a Vz 6 7 Volts and it is used for biasing the npn transistor which has 100 Vcc 20 V IC RC R1 100k IB 6 7 V 10k VCE IE RE 10k Determine the Q point I CQ and VCEQ of the transistor 22 071 6 071 Spring 2006 Quiz 3 Page 8 Name Problem 7 15 points Vcc R1 C VZ 5 7 V RE Vo 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 RE 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 R1 and capacitor C 22 071 6 071 Spring 2006 Quiz 3 Page 9 Name Blank page For computation 22 071 6 071 Spring 2006 Quiz 3 Page 10 Name Blank page For computation 22 071 6 071 Spring 2006 Quiz 3 Page 11 Name Problem Points 1 2 3 4 5 6 7 Total 22 071 6 071 Spring 2006 Quiz 3 Page 12
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