ELD255 LecTest1 - Set A 2

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Seneca College *

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Electrical Engineering

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Dec 6, 2023

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ELD255 Lecture Test 1: Set A – Answer Key Lecture Test 1: Diodes Last Name: Answer First Name: Key Student Number: _____-_____-_____ ELD255NAB Date: June 8, 2023 Score: _____ / 62 +5 Question 1: Honesty Declaration Questions 2 and 3: [6 marks] Given: E = 18 V, R 1 = 5.6 kΩ and R 2 = 8.2 kΩ. 2. Find the source current flowing in this circuit [3] Since D is reverse-biased, the current will be I S = E R 1 + R 2 = 18 V 5.6 k Ω + 8.2 k Ω I S = 1.30 mA 3. Find the voltage across the diode [3] V D = I S R 1 = 1.30 mA ( 5.6 k Ω ) = 7.28 V For the ELD255 Lec Classes of Prof. Ruperto Tumibay 1
ELD255 Lecture Test 1: Set A – Answer Key V D = 7.28 V Questions 4 to 6: [9 marks] Determine the following: 4. Current flowing through R 1 [3] I R 1 = V S V Z R 1 = 10 V 8 V 1.5 k Ω I R1 = 1.33 mA 5. Current flowing through R 2 [3] I R2 = 0 mA The circuit is open because of the capacitor C. 6. Current coming from the voltage source [3] I S = I R 1 + I R 2 = 1.33 mA + 0 mA For the ELD255 Lec Classes of Prof. Ruperto Tumibay 2
ELD255 Lecture Test 1: Set A – Answer Key I S = 1.33 mA Questions 7 to 10: [14 marks] For the circuit below, the 1N4728 Zener diode is conducting with V Z = 3.3 V. Determine the following: R S = 82 Ω, I S = 154.88 mA, and R L = 330 Ω 7. The load current [3] I L = V Z R L = 3.3 V 330 Ω I L = 10 mA 8. The Zener current [3] I Z = I S I L = 154.88 mA 10 mA I Z = 144.88 mA 9. The source voltage [4] E = I S R S + V Z = 154.88 mA ( 82 Ω ) + 3.3 V E = 16 V 10. If the source voltage drops to 15 V, what will be the value of the load current? [4] When E < V Z , Zener diode is OFF I L = I S For the ELD255 Lec Classes of Prof. Ruperto Tumibay 3
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ELD255 Lecture Test 1: Set A – Answer Key I L = I S = E R S + R L = 15 V 82 Ω + 330 Ω I L = 36.41 mA Questions 11 to 15: [15 marks] The 1N4728 Zener diode used for the circuit below has the following specifications: V Z = 3.3 V, I ZK = 1 mA, and I ZM = 276 mA Determine the following: 11. The value of load current anytime Zener diode is conducting [3] I L = V L R L = 3.3 V 3.3 k Ω I L = 1 mA 12. The minimum source current the Zener diode is conducting [3] I Smin = I ZK + I L = 1 mA + 1 mA I S min = 2 mA 13. The minimum source voltage the Zener diode is conducting [3] For the ELD255 Lec Classes of Prof. Ruperto Tumibay 4
ELD255 Lecture Test 1: Set A – Answer Key V Smin = I Smin R S + V Z = 2 mA ( 240 Ω ) + 3.3 V V S min = 3.78 V 14. The maximum source current the Zener diode can safely conduct [3] I Smax = I ZM + I L = 276 mA + 1 mA I S max = 277 mA 15. The maximum source voltage the Zener diode can safely conduct [3] V Smax = I Smax R S + V Z = 277 mA ( 240 Ω ) + 3.3 V V S max = 69.78 V For the ELD255 Lec Classes of Prof. Ruperto Tumibay 5
ELD255 Lecture Test 1: Set A – Answer Key Questions 16 to 21: [18 marks] Determine the following for the circuit shown. 16. Primary peak voltage [3] V P ( pk ) = V P ( rms ) 2 = 120 V 2 V P (pk) = 169.71 V 17. Secondary peak voltage [3] V S ( pk ) = V P ( pk ) a = 169.71 V 6 V S (pk) = 28.28 V For the ELD255 Lec Classes of Prof. Ruperto Tumibay 6
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ELD255 Lecture Test 1: Set A – Answer Key 18. Load peak voltage [3] V L ( pk ) = V S ( pk ) V D = 28.28 V 0.7 V V L (pk) = 27.58 V 19. Average (DC) voltage [3] V DC = V L ( pk ) π = 27.58 V π V DC = 8.78 V 20. Average (DC) current [3] I DC = V DC R L = 8.78 V 1 k Ω I DC = 8.78 m A = I L 21. A 750 µF capacitor is inserted between the rectifier and the load, find the ripple voltage [3] V r = I L f C = 8.78 mA 60 Hz ( 750 μF ) V r = 195.11 mVpp For the ELD255 Lec Classes of Prof. Ruperto Tumibay 7
ELD255 Lecture Test 1: Set A – Answer Key Questions 22 and 23: [+5 marks] If the load needs a regulated dc output voltage of 5 V, what should be the value of R 1 ? The potentiometer R 2 is set at 1.675 kΩ. Using the formula: V out = 1.25 V [ 1 + R 2 R 1 ] 22. Derive the formula for finding the resistor, R 1 [+3] V out 1.25 V = 1 + R 2 R 1 V out 1.25 V 1 = R 2 R 1 For the ELD255 Lec Classes of Prof. Ruperto Tumibay 8
ELD255 Lecture Test 1: Set A – Answer Key R 1 = R 2 V out 1.25 V 1 [derived formula] 23. Find the value of R 1 for the situation mentioned above [+2] R 1 = 1.675 k Ω 5 V 1.25 V 1 R 1 = 560 [value] For the ELD255 Lec Classes of Prof. Ruperto Tumibay 9
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