ECE2210 Final given: Spring 08

Transcription

1 ECE Final given: Spring 0. Note: feel free to show answers & work right on the schematic 1. (1 pts) The ammeter, A, reads 30 ma. a) The power dissipated by R is 0.7 W, what is the value of R. Assume that the ammeter is ideal (has no resistance). ammeter reads 30 ma V S =? b). 0 Ω 1 Ω b) What is the value of V S? c) How much power is provided by the source? c) P S =? P R. 0.7 W a) R =?. 5 Ω. (17 pts) a) Find: V 1 & I I S. 0 ma b) I S Supplies how much power to the circuit? V S. 13 V V 1 I V S. V 3. (17 pts) a) Draw the asymptotic Bode plot (the straight-line approximation) of the transfer function below. Accurately draw it on the graph provided. I've done the first section, you do the remainder.. 0 Ω You must show the steps you use to get the Bode plot. That is, show things like the corner frequency(ies), the approximations of the transfer function in each frequency region, calculations of, etc.. H( f) 0.( 0. Hz j. f) ( 30. khz j. f) Magnitude plot H( f) Straight-line approximation Actual b) The asymptotic Bode plot is not exact. Using a dotted line, sketch the actual magnitude of the transfer function H(f) on the plot above. Indicate the point(s) where the difference between the two lines is the biggest (draw arrow(s)) and write down the actual magnitude(s) at that (those) point(s) Frequency (Hz) c) If there are any corners in the Bode plot associated with poles in the transfer function, list that/those. b) If there are any corners in the Bode plot associated with zeroes in the transfer function, list that/those. ECE Final given: Spring 0 p1

2 ECE Final given: Spring 0 p. (13 pts) Find: a) The average, DC (V DC ) voltage. volts 9 b) The RMS (effective) voltage (µ s) c) The voltage is hooked to a resistor, as shown, for seconds. How much energy is transfered to the resistor during that seconds? R L. Ω d) What happened to that energy? 5. ( pts) Assume that diodes D 1 and D DO conduct. Assume that diode D 3 does NOT conduct. a) Find I R3, I D, I D1, & V D3 based on these assumptions. Stick with these assumptions even if your answers come out absurd. I R3 = I D = V S. V LED I D1 D 1 D I D. 0 Ω I D1 = V D3 =. 5 Ω. 150 Ω b) Based on the numbers above, was the assumption about D 1 correct? yes no (circle one) (Specifically show a value which is or is not within a correct range.) V D3 R. 5 Ω c) Was the assumption about D correct? yes no (circle one) d) Was the assumption about D 3 correct? yes no (circle one) (Specifically show a value which is or is not within a correct range.) e) Based on your answers to parts b), c) & e), Circle one: i) The real I D < I D calculated in part a. ii) The real I D = I D calculated in part a. iii) The real I D > I D calculated in part a. ECE Final given: Spring 0 p

3 ECE Final given: Spring 0 p3. (15 pts) A voltage waveform (dotted line) is applied to the circuit shown. Accurately draw the output waveform (v o ) you expect to see. Label important s and voltage levels. LED v o. Ω v o ms 7. (5 pts) A transistor is used to control the current flow through an inductive load (in the dotted box, it could be a relay coil or a DC motor). a) β Assume the switch has been open for a long and the transistor is in the active region, find I, and V CE and P Q. I L =? V CE =? P Q =? b) Was the transistor actually operating in the active region? yes no circle one (Specifically show a value which is or is not within a correct range.) c) What minimum β would be required to achieve saturation?. 50 Ω V CC. V Inductive load I L L L. 0 mh R L d) You can't change the β. Find the maximum value of, so that the transistor will be in saturation. e) The diode in this circuit conducts a significant current: A) never. D) when the switch closes. B) when the switch opens. E) whenever the switch is closed. C) whenever the switch is open. F) always. f), is that found in part d). The switch is opened and closed a few s. What is the maximum diode current you expect. (Answer 0 if it never conducts.) (circle one) is Out of Order. Do you want your grade and scores posted on my door and on the Internet? Yes No (Circle one) If your answer is yes, then provide some sort of alias or password: The grades will be posted on my door in alphabetical order under the alias that you provide here. I will not post grades under your real name. The Internet version will be a pdf file which you can download. Both will show the homework, lab, and exam scores of everyone who answers yes here. ECE Final given: Spring 0 p3

4 ECE Final given: Spring 0 p 7. (5 pts) The same input signal (at right) is connected to several op-amp circuits below. Sketch the output waveform for each circuit. Clearly label important voltage levels on each output. If I can't easily make out what your peak values are, I'll assume you don't know. Don't forget to show inversions. All op-amps are powered by + 15 V power supplies. R. 5 kω a). 5 kω 3V v S ( t) 3V v oa ( t) v S v oa ( t) kω b) v ob ( t) v S v ob ( t). kω. kω c). kω. kω v S. kω v oc ( t) v oc ( t) 1. V R. kω d) v od ( t) v S v od ( t). V ECE Final given: Spring 0 p

5 ECE Final given: Spring 0 p5 L 9. (1 pts) a) Find the s-type transfer function of the circuit shown. You MUST show work to get credit. Simplify your expression for H(s ) so that the denominator is a simple polynomial. Hint: The "output" is a current and the input is a voltage. What is current over voltage? H( s ) =? C V i I o Answers 1. a). 50 Ω b).. V c). 1.3 W. a). 9 V. 1 ma b). 7 mw 3. Magnitude plot 50 (negative because it absorbs power from the circuit) Straight-line approximation Actual \ / / \ 3 7 Frequency (Hz) a). ma..5 ma ma. 1.7 V. b) yes I D1 =. ma > 0 c) yes I D =..5 ma > 0 (volts) d) no V D3 = 1.7. V > 0.7V v o 3.333V e) i) V 3. b). 30 khz c). 0 Hz. a). 3 V b). 7.0 V c). 19. J d) converted to heat 7. a). ma. 1.7 V. 0.7 W b) yes V CE =. 1.7 V >. 0. V c) 7. d). 13 Ω e) D f). 50 ma ms ms. a) Inverted triangle wave that would peak at -15V and then at +15V, but is clipped at -1V and +1V. b) Triangle wave that peaks at +9V and then at -9V. c) Inverted V amplitude triangle wave offset by -V. The negative peak would occur at 1ms and be -1V but it is clipped at -1. The positive peak occurs at 3ms and peaks at at +V, no clipping. d) - 1V between 0 and /3ms. +1V between /3 and /3ms. - 1V between /3 and ms. Extra credit if you show slew effects. 1. s. R. L s 1 R.. L C 9. s 1 R. 1 s. 1 1 R. C L R. L C ECE Final given: Spring 0 p5