Monday, December 8, 2014

Previous GATE Questions on Diode Applications & Miscellineous Questions


1.       For the same a.c. voltage and load impedance, which of the following statements about rectifier are correct?
        a.       The average load current in a full wave rectifier is twice than in a half wave rectifier
        b.      The average load current in a full wave rectifier is n times that in a half wave rectifier
        c.       Half wave rectifier will have a bigger sized transformer compared to full wave rectifier
        d.      Half wave rectifier will have a small sized transformer compared to full wave rectifier
Answer:    A & D
  Solution :          


1.       A Ramp voltage v(t) = 100t volts is applied to a RC differentiating circuit with R = 5 k and C = 4 µF. The maximum output voltage is ______
      a.       0.2 volts
      b.      2.0 volts
      c.       10.0 volts
      d.      50.0 volts
Answer:   B

2.       A pulse having a rise time of 40 nsec is displayed on a CRO of 12 MHz bandwidth. The rise time of the pulse as observed on the CRO would be approximately equal to ____________

Answer:   49.5 nsec


1.      In the circuit of the given figure, assume that the diodes are ideal and the meter is an average indicating ammeter. The ammeter will read ________

Answer:   D
             Solution :


1.       A half wave rectifier uses a diode with a forward resistance Rf. The voltage is Vmsinωt and the load resistance is RL. The DC current is given by

Answer:   B             


1.   For full wave rectification, a four diode bridge rectifier is claimed to have the following advantages over a two diode circuit:
        1.       Less expensive transformer
        2.       Smaller size transformer, and
        3.       Suitability for higher voltage application.
  Of these,
                      a.       Only 1 and 2 are true
                      b.      Only 1 and 3 are true
                     c.       Only 2 and 3 true
                      d.      1, 2 as well as 3 are true
Answer:   A & D
        Solution :

2.   For small signal ac operation, a practical forward biased diode can be modeled as
       a.       Resistance and capacitance in series
       b.      Ideal diode and resistance in parallel
       c.       Resistance and ideal diode in series
       d.      Resistance
Answer:   D
        Solution :

3.   For the circuit shown,
a.       Draw the transfer characteristics if both diodes D1 and D2 are ideal.
b.      How would the characteristics change, if D2 is ideal but D1 is non-ideal? Assume D1 has forward resistance of 10 and a reverse resistance of infinity.


1.   a. For the circuit shown, plot Vo under steady state conditions, with and without capacitor C. Assume that the diode is ideal.
   Answer:    With Capacitor, circuit acts as Envelope Detector and With out capacitor, circuit acts as clipper which clips negative half cycle.

     b.       Design a circuit using two ideal diodes, one resistor and two voltage sources that would convert the input voltage to the output voltage as shown in figure. The resistor value need not be specified.




1.   A triangular voltage waveform Vi(t) is applied at the input to the circuit shown. Assume the diodes to be ideal.
a.       Determine the output Vo(t)
b.      Neatly sketch the output waveform superimposed on the input Vi(t) and label the key points.


1.       The circuit shown in the figure is best described as a 
        a.       Bridge rectifier
        b.      Ring modulator
        c.       Frequency discriminator
        d.      Voltage doubler
Answer:   D
               Solution :


1.       In the full wave rectifier using two ideal diodes, Vdc and Vm are the dc and peak values of the voltage respectively across a resistive load. If PIV is the peak inverse voltage of the diode, then the appropriate relationships for this rectifier are
Answer:   B

               Solution :


1.       A square pulse of 3 volts amplitude is applied to RC circuit shown in figure. The capacitor is initially uncharged. The output voltage Vo at time t = 2 sec is
        a.       3 volts
        b.      – 3 volts
        c.       4 volts
        d.      – 4 volts
Answer:   B


Statement for linked answer Questions (1 and 2):
In the circuit shown below, assume that the voltage drop across a forward biased diode is 0.7 votls. The thermal voltage VT = KT/q = 25 mV. The small signal input vi = 100 cos(ωt) mV.
1.       The bias current IDC through the diodes is
        a.       1 mA
        b.      1.28 mA
        c.       1.5 mA
        d.      2 mA
Answer:   A
2.       The ac output voltage VAC is
        a.       0.25 cos(ωt) mV 
        b.      1 cos(ωt) mV
        c.       2 cos(ωt) mV
        d.      22 cos(ωt) mV
Answer:   B
               Solution :


1.       A voltage 1000sinωt volts is applied across YZ. Assuming ideal diodes, the voltage measured across WX in volts is
        a.       Sinωt
        b.      (Sinωt + |Sinωt|) / 2 
        c.       (Sinωt - |Sinωt|) / 2
        d.      0 for all t
Answer:   D
               Solution :

2.       In the circuit shown below, the knee current of ideal zener diode is 10 mA. To maintain 5 volts across the load RL, the minimum value of RL in ’s and the minimum power rating of the zener diode in mW respectively are

              a.       125 and 125
              b.      125 and 250
              c.       250 and 125
              d.      250 and 250
Answer:   B
               Solution :


1.       In the figure, assume that the forward voltage drops to the PN diode D1 and Schottky diode D2 are 0.7 volts and 0.3 volts respectively. If ON denotes conducting state of the diode and OFF denotes the non conducting state of the diode, then in the circuit,

        a.       Both are ON
        b.      D1 is ON and D2 is OFF
        c.       Both are OFF
        d.      D1 is OFF and D2 is ON
Answer:   D
               Solution : 

2.       The diode in the circuit shown, if Von = 0.7 volts but is ideal otherwise. If Vi = 5 sin(ωt) volts, the minimum and maximum values of Vo (in volts) are, respectively,
        a.       -5 and 2.7
        b.      2.7 and 5
        c.       -5 and 3.85
        d.      1.3 and 5
Answer:   C
               Solution :

3.       The figure shows a half wave rectifier. The diode D is ideal. The average steady state current (in Amperes) through the diode is approximately…………

Answer:   0.09
               Solution :

4.       Two silicon diodes, with a forward voltage drop of 0.7 volts, are used in the circuit shown in the figure. The range of input voltage Vi for which the output voltage Vo = Vi, is
        a.       -0.3 volts < Vi  < 1.3 volts
        b.      -0.3 volts < Vi  < 2 volts
        c.       -1.0 volts < Vi  < 2.0 volts
        d.      -1.7 volts < Vi  < 2.7 volts
Answer:   D
               Solution :


  1.   If the circuit shown has to function as a clamping circuit, then which one of the following conditions should be satisfied for the sinusoidal signal of period T?
Answer:     D

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