1. Diodes and their applications - Grad Plus

# 1. Diodes and their applications

1.1. Figure shows an electronic voltage regulator. The Zener diode may be assumed to require a minimum current of 25mA for satisfactory operations. The value of R required for satisfactory voltage regulation of the circuit is ___________.   [1991: 2 Marks]

Ans.

1.2. The depletion region (or) space charge region(or) transition region in a semiconductor p-n junction diode has __________. [1996:1 Marks]

(a) electrons and holes

(b) positive ions and electrons

(c) positive and negative ions

(d) negative ions and holes

Ans.

1.3. As the temperature is increased, the voltage across a diode carrying a constant current __________. [1999: 1 Mark]

(a) increases

(b) decreases

(c) remains constant

(d) may increase or decrease depending upon the doping levels in the junction.

Ans.

1.4. The mobility of an electron in a conductor expressed in terms of  _________. [1999: 1 Mark]

(a) cm2/V-sec

(b) cm/V-sec

(c) cm2/V

(d) cm2/sec

Ans.

1.5. A diode whose terminal characteristics are related as i_{D}=I_{s}e^{V/V_{T}} , where Is is the reverse saturation current and VT is thermal voltage(=25 mv), is biased at iD=2mA. Its dynamic resistance is _________. [2000: 2 Marks]

(a) 25 Ω

(b) 12.5 Ω

(c) 50 Ω

(d) 100 Ω

Ans.

1.6. The forward resistance of the diode shown in the figure is 5Ω and the remaining parameters are the same as those of the ideal diode. The DC components of the source current are ________. [2002: 1 Mark]

(a) \frac{V_m}{50\pi}

(b) \frac{V_m}{50\pi\sqrt2}

(c) \frac{V_m}{100\pi\sqrt2}

(d) \frac{2V_m}{50\pi\sqrt2}

Ans.

1.7. The cut-in voltage of both Zener diode Dz and D shown in the figure is 0.7 V, while the breakdown voltage of the Zener is 3.3 V and the reverse breakdown of D is 5 V. The other parameters can be assumed to be the same as those of an ideal diode. The values of the peak output voltage (Vo) are _________. [ 2002: 1 Mark]

(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 cycle.

(d) 4 V in both positive and negative half cycle.

Ans.

1.8. In the single-phase diode bridge rectifier shown in the figure, the load resistor is R=50Ω. The source voltage is V=200 sinωt, where ω=2π × 50 rad/s. The power dissipated in the load resistor R is _______. [2002: 2 Marks]

(a) \frac{3200}\pi W

(b) 400 W

(c) \frac{400}\pi W

(d) 800 W

Ans.

1.9. A voltage signal 10 sin ωt is applied to the circuit with ideal diodes, as shown in the figure. The maximum and minimum values of the output waveform Vout of the circuit are respectively.

(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.

1.10. The current through the Zener diode in the figure is  ______. [2004: 1 Mark]

(a) 33 mA

(b) 3.3 mA

(c) 2 mA

(d) 0 mA

Ans.

1.11 Assuming that the diodes are ideal in the figure, the current in diode D1 is ______. [2004: 2 Marks]

(a) 8 mA

(b) 5 mA

(c) 0 mA

(d) -3 mA

1.12 Assume that D1 and D2 in the figure are ideal diodes. The value of current I is ______.  [2005: 1 Mark]

(a) 0 mA

(b) 0.5 mA

(c) 1 mA

(d) 2 mA

1.13. What are the states of the three ideal diodes of the circuit shown in the figure? [2006: 1 Mark]

(a) D1 ON, D2 OFF, D3 OFF

(b) D1 OFF, D2 ON, D3 OFF

(c) D1 ON, D2 OFF, D3 ON

(d) D1 OFF, D2 ON, D3 ON

Ans.

1.14. Assuming the diodes D1 and D2 of the circuit shown in the figure to be ideal ones, the transfer characteristics of the circuit will be _______.

1.15. The three-terminal linear voltage regulator is connected to a 10Ω load resistor as shown in the figure. If Vin is 10V, what is the power dissipated in the transistor?

(a) 0.6 W

(b) 2.4 W

(c) 4.2 W

(d) 5.4 W

1.16.  The equivalent circuits of a diode, during forward biased and reverse biased conditions, are shown in the figure.  If such a diode is used in the clipper circuit of the figure given above, the output voltage(Vo) of the circuit will be _______.  [ 2008: 1 Mark]

1.17. In the voltage doubler circuit shown in the figure, the switch ‘S’ is closed at t=0. Assuming diodes D1 and D2 to be ideal, load resistance to be infinite, and initial capacitor voltages to be zero. The steady-state voltage across capacitors C1 and C2 will be    [2008: 2 Marks]

(a) Vc1=10 V, Vc2=5 V

(b) Vc1= 10 V, Vc2=-5 V

(c) Vc1=5 V, Vc2=10 V

(d) Vc1=5V, Vc2=-10 V

1.18. Assuming that the diodes in the given circuit are ideal, the voltage Vo is ______. [2010: 1 Mark]

(a) 4 V

(b) 5 V

(c) 7.5 V

(d) 12.12 V

1.19. The transistor used in the circuit shown below has a β of 30 and ICBO is negligible. In the forward voltage drop of a diode is 0.7 V, then the current through the collector will be ______. [2011: 2 Marks]

(a) 168 mA

(b) 108 mA

(c) 20.54 mA

(d) 5.36 mA

Ans.

1.20. A clipper circuit is shown below. Assuming forward voltage drops of the diodes to be 0.7 V, the input-output transfer characteristics of the circuit is ______.

(a)

(b)

(c)

(d)

Ans.

1.21. The i-v characteristics of the diode in the circuit given below are :

i=\;\left\{\begin{array}{l}\frac{v-0.7}{500}A,\;\;\;\;\;\;v\geq0.7\;V\\0\;A,\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;v<0.7\;V\end{array}\right. . The current in the circuit is ______. [2012: 1 Mark]

Ans.

1.22. In the circuit shown below, the knee current of the ideal Zener diode is 10mA. To maintain 5V across RL, the minimum value of RL in Ω and the minimum power rating of the Zener diode in mW respectively are _____.
[2013: 2 Marks]

(a) 125 and 125

(b) 125 and 250

(c) 250 and 125

(d) 250 and 250

Ans.

1.23. A voltage 1000 sin ωt volts is applied across YZ. Assuming ideal diodes, the voltage measured across WX in Volts is _____. [2013: 2 Marks]

(a) sin ωt

(b) (sin ωt+ | sin ωt |)/2

(c) (sin ωt- | sin ωt |)/2

(d) 0 for all t

Ans.

1.24. The sinusoidal ac source in the figure has an rms value \frac{20}{\sqrt{2}} V. Considering all possible values of RL, the minimum value of Rs in Ω to avoid burnout of the Zener diode is _______. [2014: 1 Mark]

Ans.

1.25. Assuming the diodes to be ideal in the figure, for the output to be clipped, the input voltage vi must be outside the range  [2014: 2 Marks]

(a) -1 V to -2V

(b) -2 V to -4 V

(c) +1 V to -2 V

(d) +2 V to -4 V

Ans.

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