## Saturday, 21 September 2013

### Previous GATE Questions on Zener Diode as Voltage Regulator

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 :    [GATE’92]

a.       1.2 K ohms
b.      80 ohms
c.       50 ohms
d.      0 ohms

2.       The wave shape of VO in the figure will be   [GATE'93]

3.       A zener diode works on the principle of          [GATE'95]

a.       Tunneling of charge carriers across the junction
b.      Thermionic emission
c.       Diffusion of charge carriers across the junction
d.      Hopping of charge carriers across the junction

4.       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 V0 constant at 6 volts ?   [GATE’96]

a.       0 mA, 180 mA
b.      5 mA, 110 mA
c.       10 mA, 55 mA
d.      60 mA, 180 mA

5.       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 1 amp. Its output resistance and load regulation, respectively are            [GATE’99]

a.       5 and 20%
b.      25 and 20%
c.       5 and 16.7%
d.      25 and 16.7%

6.       The transistor shunt regulator shown in figure has a regulated output voltage of 10 volts, when the 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 volts, β = 99. Neglect the current through RB. Then the maximum power dissipated in the zener diode (PZ) and the transistor (PT) are                     [GATE’01]

7.       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 volts to 50 volts. The zener diode has VZ = 10 volts, and IZK (knee current) = 1 mA. For satisfactory operation                                                                                            [GATE’02]

8.       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                                                                    [GATE’04]

9.       The zener diode in the regulator circuit shown in figure 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                              [GATE’05]

a.       23.7 mA
b.      14.2 mA
c.       13.7 mA
d.      24.2 mA

10.   For the circuit shown below, assume the zener diode is ideal with a breakdown voltage of 6 volts. The waveform observed across R is                                                                                       [GATE’06]

11.   For the zener diode shown in the figure, the zener voltage at knee is 7 volts, the knee current is negligible and the zener dynamic resistance is 10. If the input voltage (Vi)  range is 10 to 16 volts, the output voltage (VO) ranges from                                                                                      [GATE’07]

a.       7.00   to  7.29 Volts
b.      7.14   to  7.29 Volts
c.       7.14   to  7.43 Volts
d.      7.29   to  7.43 Volts

12.   In the following limiter circuit, an input voltage Vi = 10 sin100πt  applied. Assume that the diode  drop is 0.7 volts when it is forward biased. The Zener breakdown voltage is 6.8 volts.
[GATE’08]

The maximum and minimum values of the output voltage respectively are

a.       6.1 volts, -0.7 volts
b.       0.7 volts , -7.5 volts
c.       7.5 volts, -0.7 volts
d.      7.5 volts, -7.5 volts

13.   Consider the following assertions
S1 : For Zener effect to occur, a very abrupt junction is required
S2 : For quantum tunneling to occur, a very narrow energy barrier is required .
which of the following is correct ?                                  [GATE'08]

a.       Only S2 is true
b.      S1 and S2 are both true but S2 is not a reason for S1
c.       S1 and S2 are both true but S2 is  a reason for S1
d.      Both S1 and S2 are false

14.   A Zener diode, when used in voltage stabilization circuits, is biased in  [GATE'11]

a.       Reverse bias region below the breakdown voltage
b.      Reverse breakdown region
c.       Forward breakdown region
d.      Forward bias constant current mode

15.   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.....                                                     [GATE'13]

a.       125   and  125
b.      125   and  250
c.       250   and  125
d.      250   and  250