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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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