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Unformatted text preview: 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 4 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 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 (7 points) 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 = 8 V ) Your answer: __________ Ω Continued on the next page Part 1 2 3 4 5 Total 250 Ω 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 4 Problem 1, continued Part 3 (10 points) Suppose that the load resistance is kept at 250 Ω 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 _____________________ 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. Max power (from Part 2) = _________________ mW Max power (from Part 3) = _________________ mW If the power values differ, explain which one is larger and by how many percent....
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- Winter '07
- Rectifier, Alexander Ganago, ___________________________ Discussion section