Zener Diode MCQ Question And Answer With Viva Question

Zener Diode MCQ Question And Answer

1. Zener diode is designed to specifically work in which region without getting damaged?
a) Active region
b) Breakdown region
c) Forward bias
d) Reverse bias
 Answer - b
The Zener diode is a specifically designed diode to operate in the breakdown region without getting damaged. Because of this characteristic, it can be used as a constant-voltage device.

2. What is the level of doping in Zener Diode?
a) Lightly Doped
b) Heavily Doped
c) Moderately Doped
d) No doping
 Answer - b 
A Zener diode is heavily doped so that the breakdown voltage occurs at a lower voltage. If it were lightly/moderately doped, it would breakdown at a comparatively high voltage and, thus, would not be able to serve its purpose.

3. When the reverse voltage across the Zener diode is increased _____________
a) The value of saturation current increases
b) No effect
c) The value of cut-off potential increases
d) The value of cut-off potential decreases
Answer - c
As the frequency of the incident radiation increases, the kinetic energies of the emitted electron are higher and therefore require more repulsive force to be applied to stop them.
The value of saturation current increases, as the intensity of the incident radiation, increases.
The value of cut-off potential decreases, as the frequency decreases.

4. Zener Diode is mostly used as ____________
a) Half-wave rectifier
b) Full-wave rectifierc
c) Voltage Regulator
d) LED

Answer - c
The Zener diode, once in the breakdown region, keeps the voltage in the circuit to which it is connected as constant. Thus it is widely used as a voltage regulator.

5. Which of the following is the correct symbol for the zener diode?

a)
b)
c)
d)
 Answer - d

6. In normal junctions, the breakdown is same as Zener breakdown.
a) True
b) False
Answer - b

In normal p-n unction diodes, the breakdown takes place by avalanche breakdown which is different than the Zener breakdown. Zener diode is specifically made to operate in that region.

7. The depletion region of the Zener diode is ____________

a) Thick

b) Normal

c) Very Thin

d) Very thick

View Answer

Answer: c

Zener diode is fabricated by heavily doping both p- and n-sides of the junction, which results in an extremely thin depletion region.

8. The electric field required for the field ionization is of what order?

a) 104 V/m

b) 105 V/m

c) 106 V/m

d) 107 V/m

Answer: c

In a Zener diode, a very high electric field is produced for even a very small voltage. The electric field required for field ionization is of the order 106 V/m.

9. In a circuit the load current is 5 mA and the unregulated output is 10 V. If the voltage drop across the Zener diode is 3 V, what should be the value of resistance?

a) 50 Ωb

b)100 Ωc

c)125 Ωd

d)150 ΩA

Answer: d

The value of R should be such that the current through the Zener diode is much larger than the load current.

Imagine Iz = 20 mA. The total current is therefore 24 mA.

Thev voltagedrop = 3 V

Resistance = 3 V/24 X 10-3 AR=125 Ω.

Viva Questions

1)  What is a zener diode? 

A  heavily  doped  P-N  junction  which  has  a  sharp  breakdown  voltage  is  called  as  a  zener diode. 

2) What is diode?

The  diode is a  semiconductor device  having  p-n junction. 

3)  On what factor does the  breakdown voltage  of a  zener diode  depends?

The  breakdown  voltage  of  a  zener  diode  depends  upon  the  amount  of  doping. If  the diode  is  heavily  doped,  the  depletion  layer  will  be  thin  and  consequently  the  breakdown of  the junction will  occur  at a lower  reverse  voltage. 

4)  What is breakdown voltage?

When the reverse  bias of  a  zener  diode  is increased,  a  critical voltage  is reached  at which the  reverse  current  increases  sharply  to  a  high  value.  This  critical  voltage  is  called   breakdown voltage.

5)  What is the difference  between  an ordinary  diode  and a  zener diode?

i)  A  zener  diode  is  like  an  ordinary  diode  except  that  it  is  properly  doped  so  as  to  have  a sharp  break down voltage.

ii)  It has  a  sharp breakdown voltage  called zener  voltage.

iii) When forward biased, zener diode  characteristics are  just  that of  ordinary  diode.

iv) A  zener diode  is always  reverse  biased.

6)  Why zener diode  is always  reverse  biased?

Because it utilize  reverse  characteristics for acting  like  a  voltage  regulator.

7)  Mention the  uses of  zener diode.

A  zener  diode  is  used  as  a  voltage  regulator  to  provide  a  constant  voltage  from  a source  whose  voltage  vary  over sufficient range.

8)  What do  you mean by  Characteristics of a  Zener Diode?

A  Graph  showing  the  variation  of  voltage  applied  across  the  terminals  of  a  diode  to  the corresponding  current  is  called  characteristics  of  a  diode.  In  case  of  junction  diodes,  there are  two types of characteristics, forward  and reverse  characteristics.

9)  Explain the flow of  current in zener diode  under reverse  biasing  condition?

In  case  of  reverse  biasing  condition,  the  external  field  is  established  in  a  direction  such  as to  help  internal  field.  Under  this  biasing  the  holes  in  P-  region  and  electrons  in  N-  region are  pushed  away  from  the  junction  with  the  result  that  the  depletion  or  barrier  layer  is thickened  and  hence  increases  the  potential  barrier,  therefore,  the  flow  of  current  stops.  Only  a  few thermally  generated minority  carriers produce  a  very  small  current.

10) Explain the flow of  current in zener diode  under forward biasing  condition?

In  the  case  of  forward  biasing  condition,  the  zener  diode  behaves  like  an  ordinary  p-n junction  diode.  In  this  case  the  external  field  is  established  in  a  direction  such  as  to oppose  the  internal  field.  The  external  field  is  much  stronger  than  internal  field.    In  this arrangement  holes  move  along  the  external  field  from  p-region  to  n-region  and  electrons move  opposite  to  the  field  from  n-region  to  p-region,  that  is,  the  majority  carriers  from each  side  move  across  the  junction.  The  potential  barrier  or  depletion  layer  at  the  junction wiped  out  and  a  substantial  current  flows  depending  upon  the  density  of  n-  and  p- carriers.

11) What do  you mean by  doping?

The  process of introducing  the impurity  in a  semiconductor is called doping.

12) What is Zener breakdown?

If  the  reverse  potential  across  the  zener  diode  is  increased  beyond  a  certain  value,  the current  increases  very  rapidly  due  to  zener  breakdown.  Zener  breakdown  occurs  when  the applied  electric  field  or  potential  is  so  high  that  the  valence  band  electrons  are  pulled  out to  the  conduction  band  in  large  numbers  resulting  in  breakdown.  Thus,  a  zener breakdown,  direct  rupture  of  covalent  bonds  take  place  by  thermally  generated  carriers having  acquired high  energy  due  to strong  electric  field.

13)  What do  you mean by  avalanche  breakdown?

When  the  reverse  voltage  is  made  sufficiently  high  the  thermally  generated  electrons  and holes  acquire  high  energy  from  the  applied  potential  and  make  ionizing  collisions  with the  atoms  of  the  crystal.  These  collisions  produce  further  electrons,  which  in  turn  collide with  further  atoms.  The  commutative  effect  of  such  collisions  results  in  the  breakdown  of the  junction.  Due  to  this  avalanche  multiplication  the  reverse  current  increases  abruptly  to high value. This is called  avalanche  breakdown and may  damage  the  junction. 

14) What are  the differences between avalanche  breakdown and zener breakdown?

In  general  zener  breakdown  occurs  below  8V  and  avalanche  breakdown  occurs  at  higher voltages  (~20  V).  The  Zener  breakdown  is  characterized  by  the  soft  knee,  whereas avalanche  breakdown  is  hard  knee  type.  Zener  breakdown  voltage  has  a  negative temperature  coefficient,  while  the  avalanche  breakdown  voltage  exhibits  positive temperature  coefficient.

15) How the  width of the  depletion region in the reverse  biased diode varies with  the impurity      concentration.

The  width  of  the  depletion  region  of  a  reverse  biased  diode  varies  as  the  square  root  of the impurity  concentration.

16).  How  the  value  of  the  potential  barrier  depends  on  the  amount  of  doping  of  the semiconductor?

The  value  of  potential  barrier  decreases  with  heavy  amount  of  doping  of  the semiconductor. 

17). Why  the silicon diode  is preferred  compare  to  germanium  diode? 

Silicon  diodes  are  preferred  compare  to  germanium  diodes  because  of  its  higher temperature  to current capability. 

18). Under what condition a  zener diode  behaves like an ordinary  p-n junction diode? 

A  zener  diode  behaves  as  an  ordinary  p-n  junction  diode  when  it  is  used  in  forward  bias conditions. 

19). What is the main application of  a  zener diode? 

An  important  application  of  zener  diode  is  its  use  as  voltage  regulator.  The  regulating action  takes  place  due  to  the  fact  that  in  reverse  breakdown  region;  a  very  small  change  in voltage  produces  a  very  large  change  in current.