EECE 310 Exam 1, Fall 2006

EECE 310 – Electronics I – Quiz 1 – Fall 2006-2007 - Page 1 of 6 American University of Beirut Department of Electrical and Computer Engineering EECE 310 – Electronics I Quiz 1 – November 3, 2006 Closed Book – No Programmable Calculators 90 minutes Penalty is 5 to 1 Name: _________________________________ ID number: _________________ ▬▬▬▬▬▬▬▬ Consider an amplifier with the following transfer characteristic: 5 2) 4( 30 − − = I O v v for 5 V ≤ Iv ≤ vO + 6 and O v positive. The amplifier is biased to obtain a DC output voltage of 9 V. 1- Find the lower limit L– of O v (in V) a) 30 b) 3.91 c) 1.66 d) 0 e) none of the above 2- Find the small-signal voltage gain at the bias point. a) 7.29 b) 18.33 c) -7.29 d) -18.33 e) none of the above ▬▬▬▬▬▬▬▬ An amplifier uses +10V and –10V power supplies. It provides a 2 Vpeak sine wave to an 80 Ω load when its input is a 0.1 Vpeak sine wave from which a 4.0 mApeak sine wave current is drawn. The amplifier efficiency is 25%. 3- Find the power gain in dB. a) 13.98 b) 20.97 c) 125 d) 41.9 e) none of the above 4- Find the current drawn from each of the two power supplies (in mA). a) 17.7 b) 20.51 c) 5 d) 2.83 e) none of the above 5- Find the power dissipated in the amplifier (in mW). a) 25 b) 100 c) 75 d) 57 e) none of the above ▬▬▬▬▬▬▬▬ 6- Consider the circuit shown below. The Zener diode has a test current and voltage of 10 mA and 9 V, respectively, and a Zener resistance of 20 Ω. The diodes have a VD0 = 0.65 V and rD = 20 Ω. Use the piecewise linear model for all diodes. For vI = 20 sin ωt V, find the peak value of vO (in V). a) 10.66 b) 10.1 c) 11.33 d) 12.66 e) none of the above EECE 310 – Electronics I – Quiz 1 – Fall 2006-2007 - Page 2 of 6 ▬▬▬▬▬▬▬▬ The diode in the circuit below has the I-V characteristic as shown. Assume R1 = R2 = R3 = 100 Ω, VS = 9 V. Construct the appropriate load line on the figure. Hint: Use two points at VD = 0.65 V and VD = 0.75 V. R3 R1 R2 VS + 625 650 675 700 725 750 775 800 mV 5 10 15 20 25 30 35 40 mA EECE 310 – Electronics I – Quiz 1 – Fall 2006-2007 - Page 3 of 6 7- Find the diode current (in mA, to within ±1 mA) a) 25 b) 27 c) 29 d) 31 e) none of the above 8- What is the slope of the load line (in mA/V)? a) -6.7 b) -8.2 c) -10 d) -20 e) none of the above ▬▬▬▬▬▬▬▬ In the circuit shown, IX is a DC current, much larger than IS for the diodes. Assume vs= 2 cos(ωt) mV and vo≈ VO + Vo cos(ωt) V. The capacitor in the circuit is large. It serves as an open-circuit for DC and as a short-circuit for AC signals. 9- What is the value of Vo (in mV)? a) 0.5 b) 1 c) 2 d) 3 e) none of the above ▬▬▬▬▬▬▬▬ In the circuit shown, IX = 22 mA. D1 conducts 1 mA @ 0.7 V voltage drop. D2 conducts 10 mA @ 0.7 V voltage drop. Both diodes exhibit an increase in voltage drop of 0.1 V for a decade of current increase. 10- What is the voltage across the diodes (in V)? a) 0.71 b) 0.73 c) 0.75 d) 0.76 e) none of the above ▬▬▬▬▬▬▬▬ For a certain diode it is given that: vD = 0.690 V @ iD = 1 mA vD = 0.730 V @ iD = 4 mA 11- What is the value of n for this diode? Assume VT = 25 mV. a) 1.00 b) 1.15 c) 1.25 d) 1.40 e) none of the above EECE 310 – Electronics I – Quiz 1 – Fall 2006-2007 - Page 4 of 6 12- What is vD @ iD = 8 mA? a) 0.740 V b) 0.745 V c) 0.750 V d) 0.755 V e) none of the above ▬▬▬▬▬▬▬▬ In the circuit shown below, assume that the diodes are ideal, and that R = 1 kΩ, V1 = -5 V, V2 = -10 V. R V2 V1 I 13- What is the value of I (in mA)? a) 10 b) 5 c) 1 d) 0.5 e) none of the above ▬▬▬▬▬▬▬▬ In the circuit of Figure 1, the diode drops 0.7 V when conducting. The source has a peak value of VS = 4 V. Figure 1 14- Find the maximum value of the diode current, in mA. a) 38 b) 18 c) 23 d) 28 e) 33 15- Find the average value of the output voltage, in V. a) 0.802 b) 0.441 c) 0.560 d) 0.681 e) 0.324 16- A capacitor is connected in parallel with the resistor. Find the minimum capacitance needed (in μF) to have a ripple voltage in the output of at most 0.1 V. Assume T = 1 msec, and that the capacitor discharges during the period t ≈ T/4 to t ≈ 5T/4, and so on. a) 375 b) 175 c) 225 d) 275 e) 325 ▬▬▬▬▬▬▬▬ In the circuit of Figure 2, the diodes drop 0.6 V when conducting. The input voltage vI is sinusoidal with a peak value of 11 V. Assume VA = 2.5 V and VB = 2 V. EECE 310 – Electronics I – Quiz 1 – Fall 2006-2007 - Page 5 of 6 Figure 2 17- Find the maximum value of the output voltage vO, in V. a) 3.6 b) 4.6 c) 2.6 d) 3.1 e) 4.1 18- Find the minimum value of the output voltage vO in V. a) -7.3 b) -6.8 c) -5.3 d) -5.8 e) -6.3 ▬▬▬▬▬▬▬▬ The Zener regulator shown in Figure 3 uses a diode with the following parameters: VZ0 = 5.9 V, rZ = 10 Ω, IZK = 1 mA, and IZmax = 250 mA. Assume that R = 330 Ω. Figure 3 19- Find the output voltage VO (in V) with no load. a) 6.00 b) 6.13 c) 5.62 d) 5.74 e) 5.87 20- A load that draws a current IL is connected from the output node to ground. Find the change in the output voltage VO (in mV) when IL increases from 1 mA to 21 mA. a) -194.1 b) -165.8 c) -78.8 d) -108.1 e) -137.1 EECE 310 – Electronics I – Quiz 1 – Fall 2006-2007 - Page 6 of 6 21- A resistor is now connected (as the only load) from the output node to ground. Find the minimum value of resistance (in Ω) that keeps the Zener diode in the breakdown region. a) 258.0 b) 492.4 c) 411.7 d) 352.2 e) 298.1 ▬▬▬▬▬▬▬▬ 22- The input vI to the circuit shown in Figure 4 is a +/– 10 V symmetrical square wave. Find the average value of the output voltage (in V) if the Zener diodes drop 0.7 V in the forward direction, VZ1 = 4.7 V, and VZ2 = 5.6 V. a) -0.55 b) 0.85 c) 0.45 d) -0.95 e) -0.25 + R1 100 + - vO Z1 Z2 vI vI t T 2T 10V -10V Figure 4 ▬▬▬▬▬▬▬▬ 23- In the circuit of Figure 5, find the voltage VX (in V) across R2. Assume V1 = 7 V, and V2 = 9 V. The diodes are ideal. a) 8 b) 9 c) 7.5 d) 7 e) 6 Figure 5 ▬▬▬▬▬▬▬▬ 24- A full-wave rectifier uses a center-tap transformer with a primary winding of 100 turns, and two secondary windings of 10 turns each. The primary of the transformer is connected to a 220V RMS, 50 Hz source. Find the peak-inverse voltage (PIV), in V, of the diodes in the circuit, assuming that the diodes drop 0.8 V when conducting. a) 86.3 b) 80.1 c) 61.4 d) 73.9 e) 67.6 ▬▬▬▬▬▬▬▬