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Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

Q1: In the given circuit, the diodes are ideal. The current I through the diode D1 in milliamperes is ______ (rounded off to two decimal places). (2024)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE) (a) 1.12
(b) 2.25
(c) 1.67
(d) 2.92
Ans:
(c)
Sol: Assume D2 OFF
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Tested: DON
Assume D1 OFF
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Tested: D1 ON
V= 2 mA × 1kΩ
= 2 V
States: D1 and D2 ON  
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)3VX = 13
VX = 13/3 = 4.33 V
I1 + ID1 = I2
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)IDI = 3 mA - 1.33 mA
= 1.67 mA

Q2: The Zener diode in circuit has a breakdown voltage of 5 V. The current gain β of the transistor in the active region in 99. Ignore baseemitter voltage drop VBE. The current through the 20Ω resistance in milliamperes is ____ (Round off to 2 decimal places). (2023)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 287.36
(b) 145.36
(c) 250
(d) 547.36
Ans:
(c)
Sol: Redraw the circuit :
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)We know,
IE = (1 + β)IB
= 100IB
⇒ IB = IE/100
Apply KVL in loop,
25 - (IE/100) x 7000 - IE x 10 x IE x 20 = 0
⇒ IE = 0.25 A or 250 mA

Q3: For the circuit shown below with ideal diodes, the output will be (2022)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) Vout = Vin for Vin > 0
(b) Vout = Vin for Vin < 0
(c) Vout=VinVout= −Vin for Vin > 0
(d) Vout=VinVout = −Vin for Vin < 0
Ans: 
(a)
Sol: Case (i): For positive half cycle of Vi
Diode D1 & D2 are in forward biased.
Redraw the circuit:
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)So, Vo = Vin
Case (ii): For negative half cycle of Vi
Both diodes D& Dare in reverse biased.
Redraw the circuit:
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Hence, V= Vin for Vin > 0.

Q4: In the circuit shown, a 5 V Zener diode is used to regulate the voltage across load R0. The input is an unregulated DC voltage with a minimum value of 6 V and a maximum value of 8 V. The value of RS is 6Ω. The Zener diode has a maximum rated power dissipation of 2.5 W. Assuming the Zener diode to be ideal, the minimum value of R0 is _______ Ω. (2021)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE) (a) 25
(b) 28
(c) 34
(d) 30
Ans:
(d)
Sol: To calculate R0 min' we must find IL max
Is min = Izmin + Imax
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)For ideal zener diode, Izmin⁡ = 0
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)IL max = 1/6 A
R0 min = Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)


Q5: Assuming the diodes to be ideal in the figure, for the output to be clipped, the input voltage vmust be outside the range (SET-2 (2014))
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) -1V to -2 V
(b) -2 V to -4 V
(c) +1V to -2 V
(d) +2 V to -4 V
Ans: 
(b)

Sol: CASE-I:
V≤ −4V
D→ conducts
D1 → OFF
So, V= −2V
CASE-II:
−4V ≤ Vi ≤ −2V
Both the diodes will be OFF V= V1
CASE-III:
V≥ −2V
D→ conducts
D→ OFF
Vo = −1V

Q6: The sinusoidal ac source in the figure has an rms value of  (20/√2) V. Considering all possible values of RL, the minimum value of Rs in Ω to avoid burnout of the Zener diode is _____. (SET-2 (2014))
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 100
(b) 200
(c) 300
(d) 400
Ans: 
(c)
Sol: I≥ IZ + IL
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)⇒ Rs ≥ 300Ω  
Hence, Rs(min) = 300Ω

Q7: A voltage 1000sin ωt Volts is applied across YZ. Assuming ideal diodes, the voltage measured across WX in Volts, is  (2013)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) sin ωt
(b) (sin ωt + ∣sin ωt∣)/2
(c) (sin ωt − ∣sin ωt∣)/2
(d) 0 for all t
Ans:
(d)
Sol: For positive half cycle,
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)VWX = 0
For negative half cycle,
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Short circuit condition,
VWX = 0

Q8: In the circuit shown below, the knee current of the ideal Zener dioide is 10 mA. To maintain 5 V across RL, the minimum value of RL in Ω and the minimum power rating of the Zener diode in mW, respectively, are (2013)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 125 and 125
(b) 125 and 250
(c) 250 and 125
(d) 250 and 250
Ans: 
(b)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Iload = 50mA − 10mA = 40mA
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Pmin = 50mA × 5V = 250mW  

Q9: The i-v characteristics of the diode in the circuit given below are
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)The current in the circuit is (2012)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 10 mA
(b) 9.3 mA
(c) 6.67 mA
(d) 6.2 mA
Ans:
(d)
Sol: By applying kVL in loop,
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)10 = 103i + V
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)10 = 2V − 1.4 + V
3V = 11.4
⇒ V = 3.8
⇒ i = (10 − 3.8) × 10−3 = 6.2 mA  

Q10: A clipper circuit is shown below.
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Assuming forward voltage drops of the diodes to be 0.7 V, the input-output transfer characteristics of the circuit is (2011)
(a) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(b) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(c) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(d) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Ans:
(c)
Sol: For positive voltage the waveform clips at +5.7 V.
For negative voltage at -0.7 V, the zener diode conducts and clips out.
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
Q11: The transistor used in the circuit shown below has a β of 30 and ICBO is negligible
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)If the forward voltage drop of diode is 0.7 V, then the current through collector will be (2011)
(a) 168mA
(b) 108mA
(c) 20.54mA
(d) 5.36mA
Ans:
(d)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)= 11.8/2.2k = 5.3636 mA
This is the maximum current possible in any case.

Q12: Assuming that the diodes in the given circuit are ideal, the voltage V(2010)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 4V
(b) 5V
(c) 7.5V
(d) 12.12V
Ans:
(b)
Sol: Diode D1 is On and diode D2 is OFF.
So, V0 =10 ×(10/(10+10)) = 5V  

Q13: In the voltage doubler circuit shown in the figure, the switch 'S' is closed at t = 0. Assuming diode Dand D2 to be ideal, load resistance to be infinite and initial capacitor voltages to be zero. The steady state voltage across capacitor C1 and C2 will be (2008)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) Vc1 = 10V, Vc2 = 5V
(b) Vc1 = 10V, Vc2 = −5V
(c) Vc1=5V,Vc2=10VVc1 = 5V, Vc2 = 10V
(d) Vc1=5V,Vc2=10VVc1 = 5V, Vc2 = −10V
Ans:
(d)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Forst capacitor charge through Diode (D1) upto Vmax(5V) with shown polarities.
∴ Vc1 = 5V  
Now diode D1 will be reversed biased and Dwill be forward biased and capacitor C2 will charge in reverse direction through diode D2 upto 2Vmax
∴ Vc2 = −10V

Q14: The equivalent circuits of a diode, during forward biased and reverse biased conditions, are shown in the figure.
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
If such a diode is used in clipper circuit of figure given above, the output voltage v0 of the circuit will be  (2008)
(a) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(b) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(c) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(d) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Ans:
(a)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)= 5 sinωt
Since maximum voltage across at the point P may be 5 V, hence voltage across the diode always will be less than or equal to zero. So it will be reversed always.
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
Q15: The three-terminal linear voltage regulator is connected to a 10 Ω load resistor as shown in the figure. If Vin is 10 V, what is the power dissipated in the transistor ? (2007)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 0.6W
(b) 2.4W
(c) 4.2W
(d) 5.4W
Ans:
(b)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)V0 = V− VBE
= 6.6V − 0.7V = 5.9V
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)VCE − V− V0
= 10 − 5.9 = 4.1V
PQ = VCE × IC
= 4.1 × 0.59A = 2.4W

Q16: Assuming the diodes D1 and D2 of the circuit shown in figure to be ideal ones, the transfer characteristics of the circuit will be (2006)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(b) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(c) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(d) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Ans:
(a)
Sol: Vi < 10V (D1 OFF, D2 OFF)
Vo = 10V
Vi > 10V (D1 ON, D2 OFF)
Vo = Vin

Q17: What are the states of the three ideal diodes of the circuit shown in figure ? (2006)Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) D1 ON, D2 OFF, D3 OFF
(b) D1 OFF, D2 ON, D3 OFF
(c) D1ON,D2OFF,D3OND1 ON, DOFF, D3 ON
(d) D1 OFF, D2 ON, D3 ON
Ans:
(a)
Sol: Analyzing the circuit, we can see that D1 and D2 are in forward bias and D3 is in reverse bias. But no current flow through D2, bcause current gets shortest path through D1.

Q18: Assume that D1 and D2 in figure are ideal diodes. The value of current is (2005)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 0 mA
(b) 0.5 mA
(c) 1 mA
(d) 2 mA
Ans:
(a)
Sol: Current will pass through its simplest path (or) low resistance path. D1 become forward biased and D2 is reverse biased
I = 0 mA

Q19: Assuming that the diodes are ideal in figure, the current in diode D1 is (2004)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 8 mA
(b) 5 mA
(c) 0 mA
(d) -3 mA
Ans:
(c)
Sol: From the circuit, if 'D1' is 'ON' Kirchoff's law is not satisfied
∴ D1 is OFF and D2 is ON
∴ I = 0 mA

Q20: The current through the Zener diode in figure is (2004)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 33 mA
(b) 3.3mA
(c) 2 mA
(d) 0 mA
Ans: 
(c)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
Q21: A voltage signal 10 sin ωt is applied to the circuit with ideal diodes, as shown in figure, The maximum, and minimum values of the output waveform Vout of the circuit are respectively (2003)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) +10 V and -10 V
(b) +4 V and -4 V
(c) +7 V and -4 V
(d) +4 V and -7 V
Ans: 
(d)
Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)Fpr positive cycle , when Vin > 4V
(Vin > 4V) D2ON, D1OFF, Vout = 4V
where Vin < 4V, then Vout = Vin because Dalso become (OFF).
For negative cycle, when Vin < −4V
DON, D2 OFF
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)but, Vin = −ve  
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(∵ for minimum output Vin = −10V)
Vout = (-3/10) x 10k − 4 = −7V

Q22: The cut-in voltage of both Zener diode Dz and diode D shown in figure is 0.7 V, while break down voltage of Dz is 3.3 V and reverse breakdown voltage of D is 50 V. the other parameters can be assumed to be the same as those of an ideal diode. The values of the peak output voltage (V0) are (2002)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) 3.3 V in the positive half cycle and 1.4 V in the negative half cycle
(b) 4 V in the positive half cycle and 5 V in the negative half cycle
(c) 3.3 V in both positive and negative half cycles
(d) 4 V in both positive and negative half cycles
Ans: 
(b)
Sol: For positive half cycle, at peak input voltage
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)So, V0 = 4V
For negative half cycle, at peak input voltage
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)So, Vo = 10 × (1/(1+1)) = 5V

Q23: The forward resistance of the diode shown in figure is 5Ω and the remaining parameters are same as those of an ideal diode. The dc component of the source current is  (2002)
Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)(a) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)

(b) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
(c) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
(d) Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE)
Ans: (a)

Sol: Previous Year Questions- Diodes and their Applications | Analog and Digital Electronics - Electrical Engineering (EE) = Vm/50π

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