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Question 1

Question 1. a) Reduce this circuit to a single value. 2 m F. 15 m F. 3 m F. 1.25 m F. continued. Question 1. b) Reduce this circuit to a single value. 5H. 2 H. V a. V in. Question 2. a) Does the circuit use positive or negative feedback.

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Question 1

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  1. Question 1 a) Reduce this circuit to a single value. 2 mF 15 mF 3 mF 1.25mF continued ... EET 124, Spring 2006, Exam no. 2

  2. Question 1 b) Reduce this circuit to a single value. 5H 2 H EET 124, Spring 2006, Exam no. 2

  3. Va Vin Question 2 a) Does the circuit use positive or negative feedback. b) How many trip points should this circuit have. c) If the amplifier’s spec sheet states Vupper rail = -Vlower rail = 5 V when the amplifier is powered by bipolar supply rails with a potential of 7 volts (not shown in diagram). Identify the value(s) of the trip point(s) and output voltage levels. d) Sketch the transfer characteristic curve of the comparator. EET 124, Spring 2006, Exam no. 2 continued ...

  4. Question 2 e) This is the input to the amplifier on the prior page. On the same graph, sketch how the voltage at node a varies with time. EET 124, Spring 2006, Exam no. 2

  5. Question 3 t=0 500 W 1 kW SW 1 kW 20V 5mF a) Find (i) the capacitor current; and (ii) the capacitor voltage before the switch is closed. b) Draw the Thevenin equivalent circuit, not including the capacitor, after the switch is closed by finding VTh and RTh EET 124, Spring 2006, Exam no. 2 continued ...

  6. Question 3 t=0 500 W 1 kW SW 1 kW 20V 5mF c) What is the circuit’s time constant after the switch is closed. d) After the switch is closed, identify the initial conditions for (i) the capacitor current; (ii) the capacitor voltage. e) Determine the final values for (i) the capacitor current; (ii) the capacitor voltage. EET 124, Spring 2006, Exam no. 2 continued ...

  7. Question 3 t=0 500W 1 kW SW 1 kW 20V 5mF f) After the switch is closed, write the equations that express how (i) the capacitor current and (ii) the capacitor voltage vary with time. g) Make simple sketches of the current and voltage waveforms of the capacitor after the switch is closed. Show the initial and final values. EET 124, Spring 2006, Exam no. 2 continued ...

  8. Question 3 t=0 500 W 1 kW SW 1 kW 20V 5mF h) What is the capacitor’s voltage at 15 milliseconds. i) How much time is needed for the current to reach 10mA. EET 124, Spring 2006, Exam no. 2

  9. Question 4 ein In parts a, b, c, e, and f, ignore any nonlinearities of the operational amplifier due to limited power supply rail. vout 1Vp 10 MegW • Calculate the circuit’s AC gain ein/vout = point E / point A. • b) Calculate the circuit’s DC gain. = point D / point B • c) A seasoned engineer would not find it necessary to measure the DC voltage gain from • point A to point E. Why ? EET 124, Spring 2006, Exam no. 2

  10. Question 4 d) Complete the table For partial credit, you must explain your responses. Use the next page if necessary. 10 Meg ohm Voltage MaximumMinimumAverage Point A Point B Point C Point D Point E ?V ?V EET 124, Spring 2006, Exam no. 2 continued ... continued ...

  11. Question 4 extra space for part (d) response: continued .... EET 124, Spring 2006, Exam no. 2

  12. Question 4 Point F Point G 10 Meg Ohm e) Calculate the circuit’s AC gain ein/vout if the capacitor C3 is shorted. f) Calculate the circuit’s DC gain = point G / point F if the capacitor C3 is shorted. EET 124, Spring 2006, Exam no. 2 continued ...

  13. Question 4 • Complete the table for the amplifier with the shorted capacitor • For partial credit, you must • explain your responses. • Use the back of the page the • if necessary 10 Meg Ohm Voltage MaximumMinimumAverage Point F Point G EET 124, Spring 2006, Exam no. 2

  14. Extra Credit Why is the period of an oscillation of this relaxation oscillator independent of +/-Esupply, Vupper, and Vlower. Be certain to explain you response in sufficient detail. Hint: Start with the charging-cycle equation and consider the symmetrical nature of the circuit. EET 124, Spring 2006, Exam no. 2

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