314_HW8_solutions[1]

314_HW8_solutions[1] - EECS 314 Winter 2007 HW 08 Grading...

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EECS 314 Winter 2007 HW 08 Grading Policy © 2007 Alexander Ganago This document corrects the typos made in early versions of problems 4, 5, and 7. Problem 1 – 25 points Problem 2 – 25 points Problem 3 – 25 points Problem 4 – 30 points (one point for each correct answer) Problem 5 – 30 points (one point for each correct answer) Problem 6 – 15 points (one point for each correct answer) Problem 1 – 25 points (5 points for each part) = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Total = 175 points, as usual
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EECS 314 Winter 2007 HW 08 Problem 1 Student's name ___________________________ Discussion section # __________ (Last name, first name, IN INK) Alexander Ganago Page 1 of 2 The big picture Semiconductor diodes are non-linear circuit elements: they do not obey Ohm’s law. The voltage-current characteristics of diodes can be approximated using one of several models; for simplicity, each problem assignment specifies which model to use. In this problem, use the offset diode model: the diode acts as an open circuit unless it is biased at V DO ; the voltage drop across the diode does not exceed V DO (see the sketch). Problem Part 1 Assume a DC voltage source V S = 6 V, Light-Emitting Diode (LED) with V DO = 1.7 V, and a load resistor equal to 330 Ω . Calculate the following parameters and write your answers in the blanks: a) The current in the circuit: __________________________ mA b) The power dissipated by the LED: __________________________ mW Part 2 Assume that the LED can sustain currents up to 40 mA. Calculate the minimal load resistance in Ω such that the current through the LED does not exceed 40 mA and the LED shines. (In this part, assume a DC voltage source V S = 6 V ) Your answer: __________ Ω Part 3 Suppose that the load resistance is kept at 330 Ω but the source voltage can vary. Calculate the range of source voltage values V S such that the current through the LED does not exceed 40 mA and the LED shines. Your answer: from _____________________ to _________________ volts From the given information and your results obtained above, determine whether the maximal power dissipated by the LED in Part 2 is the same as that in Part 3. If the power values differ, explain which one is larger and by how many percent. Your answer: _________________________________________________________ _____________________________________________________________________ The problem is continued on the following page 330 Ω
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EECS 314 Winter 2007 HW 08 Problem 1 Student's name ___________________________ Discussion section # __________ (Last name, first name, IN INK) Alexander Ganago Page 2 of 2 Assorted diode circuits. (Expect similar problems on exam 3 ;) Use the offset-diode model (the diode acts as an open circuit unless it is biased at +0.7 V; the voltage drop across the diode does not exceed +0.7 V) and calculate the following parameters for each circuit: a) The current through the circuit b) The output voltage V 0 Show your work on a separate page. Part 4 Your answers: I = _______ mA V 0 = ________ V Part 5 Your answers: I = _________ mA V 0 = _________ V Part 6 Your answers: I = ________ mA V 0 = ________ V 16 V 10 V 8 V
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Solution (Barry Mullins) Part 1 First we assume the diode is not forward biased. In this case I=0 and V D0 = 6V, telling us that our assumption was wrong and that the diode is in fact forward biased. Thus, it can be replaced with an voltage source with a voltage equal to the diode offset voltage.
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314_HW8_solutions[1] - EECS 314 Winter 2007 HW 08 Grading...

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