Ain Shams University
Faculty of Engineering
ECE Dept.
CHEP
Electronic Circuits
COMM 361
Spring 2015
Dr. Sameh A. Ibrahim
Exercise 1
PN Junction Diode
Solutions
1. For the circuit depicted in Fig. 1, plot IX and IR1 as a function of VX for two cases: VB = -1 V and
VB = +1 V.
Fig. 1
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2. Assuming a constant-voltage diode model, plot Vout as a function of Iin for the circuits shown in
Fig. 2.
Fig. 2
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3. Plot the input/output characteristic of the circuits illustrated in Fig. 3 assuming a constant-voltage
model.
Fig. 3
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4. Beginning with VD,on ≈ 800 mV for each diode, determine the change in Vout if Vin changes from
+2.4 V to +2.5 V for the circuits shown in Fig. 4.
Fig. 4
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5. While constructing a full-wave rectifier, a student mistakenly has swapped the terminals of D3 as
depicted in Fig. 5. Explain what happens. Use the exponential model.
Fig. 5
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6. In this problem, we estimate the ripple seen by the load in Fig. 6 so as to appreciate the regulation
provided by the diodes. fin = 60 Hz, C1 = 100 µF, R1 = 1000 Ω, and the peak voltage produced by
the transformer is equal to 5 V. For simplicity, neglect the load.
a. Assuming R1 carries a relatively constant current and VD,on ≈ 800 mV, estimate the ripple
amplitude across C1.
b. Using small-signal model of the diodes, determine the ripple amplitude across the load.
Fig. 6
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7. We wish to design a circuit that exhibits the input/output characteristic shown in Fig. 7. Using
ideal diodes, 1-kΩ resistors, and other components, construct the circuit.
Fig. 7
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8. (Simulation) The half-wave rectifier of Fig. 8 must deliver a current of 5 mA to R1 for a
peak input level of 2 V.
a. Using hand calculations, determine the required value of R1.
b. Verify the result by simulations.
Fig. 8
Assuming VD,on ≈ 800 mV
R1 = (2-0.8)/5m = 240 Ω
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