Tag: zener diode

Questions Related to zener diode

A zener regulated power supply consists of a $9 V $ battery connected in series with a and a zener diode. The zener diode maintains a constant voltage drop of $4V $ The current drawn by the load resistance will be :

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $0.025 A$

  2. $0.050 A$

  3. $0.01 A$

  4. $0.015 A$

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Correct Option: A

Zener breakdown takes place if:

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. Doped impurity is low

  2. Doped impurity is high

  3. Less impurity in N-part

  4. Less impurity in P-type

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Correct Option: B
Explanation:

 Zener breakdown occurs due to heavily doped diodes.In this process electrons crosses the barrier from 

the valence band of the p-type  to the conduction band of the lightly filled n-type material.

If, a Zener diode ($V _z = 5V$ and $I _z = 10 mA$) is connected in series with a resistance and 20 V is applied across the combination, then the maximum resistance one can use without spoiling zener action is

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. 20 $k\Omega$

  2. 15 $k\Omega$

  3. 10 $k\Omega$

  4. 1.5 $k\Omega$

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Correct Option: C

The main cause of Zener breakdown is

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. the base semiconductor being germanium.

  2. production of electron-hole pairs due to thermal excitation.

  3. low doping.

  4. high doping.

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Correct Option: D
Explanation:

Zener breakdown occurs in heavily doped p-n junctions. The heavy doping makes the depletion layer extremely thin. So that, carriers cannot accelerate enough to cause ionization. Thus, current will increase in reverse bias only due to reverse breakdown voltage.

The main cause of avalanche breakdown is

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. collision by ionisation.

  2. high doping.

  3. recombination of electrons and holes.

  4. low doping.

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Correct Option: A
Explanation:

Avalanche breakdown is caused by impact ionization of electron-hole pairs. A very little current flows under reverse bias conditions and depletion region increases. The electric field in the depletion region of a diode can be very high. Electron/holes that enter the depletion region undergo a tremendous acceleration. As these accelerated carriers collide with the atoms, they can knock electrons from their bonds, creating additional electron/hole pairs and thus additional current. As these secondary carriers are swept into the depletion region, they too are accelerated and the process repeats itself.

The avalanche breakdown in p-n junction is due to

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. shift of Fermi level.

  2. cumulative effect of conduction band electron.

  3. widening of forbidden gap.

  4. high impurity concentration.

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Correct Option: B
Explanation:

The avalanche breakdown in p-n junction is due to cumulative effect of conduction band electron. In reverse bias, due to applied electric field, electrons acquire enough energy to free more electron bound to the atom. The abundant number of electron-hole pairs are created for conduction, this is cumulative effect.

A Zener diode

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. is a lightly doped junction diode.

  2. heavily doped junction diode.

  3. is either p-type or n-type.

  4. has no p-n junction.

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Correct Option: B
Explanation:

The reverse breakdown voltage depends on doping of the diode. Hence, in the Zener diode the heavy doping of its p-n junction is done. The depletion region formed in the diode is very thin ($<1\ m$) and the reverse bias voltage of about $5\ V$ which is less than ordinary diode.

The current flow in a Zener diode is mainly due to

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. thermally generated charge carriers

  2. minority charge carriers

  3. collision generated charge carriers

  4. ions

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Correct Option: C
Explanation:

When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Avalanche breakdown occurs in reverse bias when the applied voltage is high enough, the free electron may move fast enough to knock other electrons free, creating more free-electron-hole pairs (i.e., more charge carriers), increasing the current. Thus, the current flow in a Zener diode is mainly due to collision generated charge carriers

Zener diode works on

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. zero bias

  2. reverse bias

  3. forward bias

  4. infinite bias

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Correct Option: B
Explanation:

We know that zener diode works on the reverse bias. When the reverse bias is equal to the break-down voltage, the voltage across the zener remains almost constant and the current increases rapidly.

Zener diode acts as a/an

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. oscillator

  2. regulator

  3. rectifier

  4. fliter

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Correct Option: B
Explanation:

Zener diode is used to supply constant voltage in voltage regulator circuit hence option (b) is correct.