Zener Diode - Definition, Working, FAQs

Imagine your smartphone charger maintaining a consistent voltage to prevent damage, or your car's electronics running smoothly regardless of fluctuations in the power supply. These reliable performances are made possible by a remarkable electronic component: the Zener diode. This diode ensures voltage stability across a variety of applications, protecting devices from potential electrical issues. As we delve into the world of Zener diodes, we will explore their unique properties and how they have become indispensable in everyday technology, making our gadgets safer and more efficient. Also, we will see some of the solved examples based on this concept.

This Story also Contains

1. What is Zener Diode?
2. VI characteristics of Zener diode
3. Learn Zener Diode From the Video Given Below
4. Solved Examples Based on Zener Diode
5. Summary

What is Zener Diode?

It is invented by C. Zener. A Zener diode is a p-n junction semiconductor device designed to operate in the reverse breakdown region. It is a highly doped p-n junction which is not damaged by high reverse current. It can operate continuously, without being damaged in the region of reverse background voltage. It forms a very thin depletion region and an extremely high electric field across the junction even for a small reverse bias voltage (~5 V).

In the forward bias, the Zener diode acts as an ordinary diode.

Symbol of Zener diode

The symbol of the Zener diode is shown in the below figure.

VI characteristics of Zener diode

• Zener Breakdown

When a reverse bias is increased the electric field at the junction also increases. At some stage, the electric field becomes so high that it breaks the covalent bonds creating electron-hole pairs. Thus a large number of carriers are generated. This causes a large current to flow. This mechanism is known as Zener breakdown.

• Avalanche breakdown

At high reverse voltage, due to the high electric field, the minority charge carriers, while crossing the junction acquire very high velocities. These by collision break down the covalent bonds, generating more carriers. A chain reaction is established, giving rise to a high current.

This mechanism is known as Avalanche breakdown.

The VI characteristics of a Zener diode are shown in the below figure.

When forward-biased voltage is applied to the Zener diode, it works like a normal diode.

When reverse-biased voltage is applied to a Zener diode, it allows only a small amount of leakage current until the voltage is less than the Zener voltage (V_z). As the reverse bias voltage (V) reaches the breakdown voltage of the Zener diode (Vz), there is a large change in current. Also, note that for a negligible change in the reverse bias voltage, a large change in current is produced.

Learn Zener Diode From the Video Given Below

Solved Examples Based on Zener Diode

Example 1: Identify the semiconductor devices whose characteristics are given below, in the order (a), (b), (c), (d) :

1) Simple diode, Zener diode, Solar cell, Light dependent resistance

2) Zener diode, Simple diode, Light dependent resistance, Solar cell

3) Solar cell, Light dependent resistance, Zener diode, Simple diode

4) Zener diode, Solar cell, Simple diode, Light dependent resistance

Solution:

Zener diode

It can operate continuously without being damaged in the region of reverse-biased

wherein

1) It acts as a voltage regulator

2) In forward biasing it acts as an ordinary diode.

Solar cells

It is based on the photovoltaic effect. It converts solar energy into electrical energy.

wherein

One of the semiconductor regions is made so thin that the light incident on it reaches the PN junction and gets absorbed.

(a) represents a simple diode.

(b) represents zener diode

(c) solar cell

(d) light-dependent resistance.

Hence, the answer is option (1).

Example 2: In the given circuit, the current (in mA) through the zener diode is :

1) 3.3

2) 6.7

3) 2.5

4) 5.5

Solution:

In forward biasing it acts as an ordinary diode.

potential difference across R2=10 V
potential difference across R1=5 V
current through R1=5/500=0.01 A
current through R2=10/1500=1/150

current through Zener diode =1/100−1/150=3−2300=1/300=3.3 mA

Hence, the answer is option (1).

Example 3: The value of the resistor, RS′ needed in the dc voltage regulator circuit shown here, equals :

1) (Vi−VL)/nIL
2) (Vi+VL)/nIL
3) (Vi−VL)/(n+1)IL
4) (Vi+VL)/(n+1)IL

Solution:

Total current =(n+1)×IL flowing through RS
Voltage across RS=(Vi−VL)
∴RS=(Vi−VL)(n+1)IL

Hence, the answer is option (3).

Example 4: In the given circuit the current (in mA) through the Zener Diode is close to:

1) 5

2) 6

3) 4

4) 0

Solution:

Zener diode operates continuously without being damaged in the region of reverse-biased

wherein

1) It acts as the voltage regulator.

2) In forward biasing it acts as an ordinary diode.

Since the voltage across the zener must be less than 10 V, therefore it will not work in the breakdown region its resistance is infinite and the current through it is zero.

Hence, the answer is option (4).

Example 5: The figure shows a DC voltage regulator circuit, with a Zener diode of breakdown voltage=6V. If the unregulated input voltage varies between 10 V to 16 V, then what is the maximum Zener current (in mA)?

1) 3.5

2) 1.5

3) 7.5

4) 2.5

Solution:

i1=64=1.5 mA

When the battery voltage is 16 V , the maximum current will be obtained
i=16−62=5 mAimax=5−1.5=3.5 mA

Hence, the answer is option (1).

Summary

A Zener diode is a special kind of diode which allows current to pass in the reverse direction only if a particular voltage known as the Zener breakdown voltage is reached. While typical diodes prevent reverse current flow, a Zener diode is meant to function under the reverse bias condition. Hence it becomes useful in voltage regulation in electronic circuits where the output voltage should be kept constant despite changes in input voltage level or power consumption.