W08_314_HW8_solutions

W08_314_HW8_solutions - EECS 314 Winter 2008 Homework set 8...

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EECS 314 Winter 2008 Homework set 8 Student’s name ___________________________ Discussion section # _______ (Last, First, write legibly, use ink) (use ink) Instructor is not responsible for grading and entering scores for HW papers lacking clear information in the required fields above © 2008 Alexander Ganago Page 1 of 5 Scores for the HW set: Problem 1 2 3 4 5 6 7 Total Score Problem 1 Circuits with semiconductor Diodes at DC voltages 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 In Parts 1, 2 and 3, consider a Light-Emitting Diode (LED) with V DO = 1.7 V Part 1 (8 points) Assume a DC voltage source V S = 8 V and a load resistor equal to 250 . Calculate the following parameters and write your answers in the blanks: a) The current in the circuit: _________25.2_____________ mA b) The power dissipated by the LED: ___42.84 ___________ mW Part 2 (7 points) Assume that the LED can sustain currents up to 40 mA. Calculate the minimal load resistance in 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 = 8 V ) Your answer: ___157.5 _____ Continued on the next page Part 1 2 3 4 5 Total 250
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EECS 314 Winter 2008 Homework set 8 Student’s name ___________________________ Discussion section # _______ (Last, First, write legibly, use ink) (use ink) Instructor is not responsible for grading and entering scores for HW papers lacking clear information in the required fields above © 2008 Alexander Ganago Page 2 of 5 Problem 1, continued Part 3 (10 points) Suppose that the load resistance is kept at 250 but the source voltage can vary. Calculate the range of source voltage values V S such that the current flows through the LED (the LED shines) but does not exceed 40 mA. Your answer: from ______1.7________ to ______11.7________ 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. Max power (from Part 2) = _______68__________ mW Max power (from Part 3) = _______68__________ mW If the power values differ, explain which one is larger and by how many percent. Your answer: ____ No difference in maximum power as I D0 and V D0 are same in both parts ___________________________________________ Show your work Continued on the next page
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EECS 314 Winter 2008 Homework set 8 Student’s name ___________________________ Discussion section # _______ (Last, First, write legibly, use ink) (use ink) Instructor is not responsible for grading and entering scores for HW papers lacking clear information in the required fields above © 2008 Alexander Ganago Page 3 of 5 Problem 1, continued Assorted diode circuits (expect similar problems on the final exam) 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:
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W08_314_HW8_solutions - EECS 314 Winter 2008 Homework set 8...

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