Monday, December 8, 2014

Previous GATE Questions on Voltage Regulators (1987 - Till Date)


1.     The 6 volts Zener diode shown in figure has zero zener resistance and a knee current of 5 mA. The minimum value of R so that the voltage across it does not fall below 6 volts is ……

   Answer:     B
                Solution :


1.     A Zener diode in the circuit shown has a knee current of 5 mA, and a maximum allowed power dissipation of 300 mW. What are the minimum and maximum load currents that can be drawn safely from the circuit, keeping the output voltage Vo constant at 6 volts ?

                              a.       0 mA,  180 mA
                              b.      5 mA, 110 mA
                              c.       10 mA, 55 mA
                              d.      60 mA, 180 mA
Answer:    C
                  Solution :

1.   In a series regulated power supply circuit, the voltage gain Av of the pass transistor satisfies the condition
                       a.       Av ->
                       b.      1 << Av <
                       c.       Av 1
                       d.      Av << 1
Answer:    C
                Solution :


   1.  A DC power supply has a no-load voltage of 30 volts, and a full load voltage of 25 volts at a full  

         load current of one amp. Its output resistance and load regulation, respectively are
                              a.       5 and 20 %
                              b.      25 and 20 %
                              c.       5 and 16.7 %
                              d.      25 and 16.7 %
Answer:    B


1.       The transistor shunt regulator shown in figure has a regulated output voltage of 10 volts, when input varies from 20 volts to 30 volts. The relevant parameters for the zener diode and the transistor are: VZ = 9.5 volts, VBE = 0.3 votls, β = 99. Neglect the current throught RB. Then the maximum power dissipated in the zener diode (PZ) and the transistor (PT) are

Answer:    C
                Solution :


1.     A zener diode regulator in figure, is to be designed to meet the specifications : IL = 10 mA, Vo = 10 volts and Vin varies from 30 to 50 volts. The zener diode has VZ = 10 volts and IZK (knee current) = 1 mA. For satisfactory operation

Answer:    A
             Solution :


1.       The output voltage of the regulated power supply shown in the figure is 
           a.       3 volts
           b.      6 volts
           c.       9 volts
           d.      12 volts
Answer:    C
                Solution :


1.   In the voltage regulator shown, the load current can vary from 100 mA to 500 mA. Assuming that the zener diode is ideal (i.e. the zener knee current is negligibly small and zener resistance is zero in the breakdown region), the value of R is 

Answer:               D
               Solution :


1.     The zener diode in the regulator circuit shown has a zener voltage of 5.8 volts and a zener knee current of 0.5 mA. The maximum load current drawn from this circuit ensuring proper functioning over the input voltage range between 20 and 30 volts is

Answer:    A
                 Solution :


Statement for Linked Answer Questions (1 and 2):
A regulated power supply shown in the figure below has an unregulated input of 15 volts and generates a regulated output Vout. Use the component values shown in the figure.
 1.       The power dissipation across the transistor Q1 shown in the figure is
           a.       4.8 volts
           b.      5.0 volts
           c.       5.4 volts
           d.      6.0 volts
Answer:    D
2.       If the unregulated voltage increases by 20%, then power dissipation across the transistor Q1
           a.       Increases by 20%
           b.      Increases by 50%
           c.       Remains unchanged
           d.      Decreases by 20%
Answer:    B
             Solution :


1.       A Zener diode when used in voltage stabilization circuits, is biased in
              a.       Reverse bias region below the breakdown voltage
              b.      Reverse breakdown region
              c.       Forward bias region
              d.      Forward bias constant current mode
Answer:    A
               Solution :


1.     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 voltage regulator circuit shown in the figure, the Op-Amp is ideal. The BJT has VBE = 0.7 volts, and β = 100, and the zener voltage is 4.7 volts. For a regulated output of 9 volts, the value of R (in ) is ……..
              Answer:    1090
               Solution :


14.   For the voltage regulator circuit shown,the input voltage (Vin) is 20 V ± 20% and the regulated output voltage (Vout) is 10 volts. Assume the OP-AMP is ideal. For a load RL drawing 200 mA, the maximum power dissipation in Q1 (in Watts) is _________________
Answer:    2.85

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