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What is the Zener Diode Symbol?

Author: Apogeeweb
Date: 30 Jul 2022
 4786

Catalog

Ⅰ What is a Zener Diode?

Ⅱ What is the Zener diode symbol

Ⅲ Zener Diode Circuit Diagram

Ⅳ How Does a Zener Diode Work?

Ⅴ How to Test a Zener Diode?

Ⅵ Differences in Avalanche Breakdown & Zener Breakdown

Ⅶ V-I Characteristics of Zener Diode

7.1 Forward Characteristics

7.2 Reverse Characteristics

Ⅷ Zener Diode Advantages

Ⅸ Zener Diode Disadvantages

Ⅹ Avalanche Breakdown vs Zener Breakdown 

Ⅺ Applications of Zener Diode

Ⅻ Zener diode as voltage regulator

Frequently Asked Questions – FAQs

Introduction

The Zener diode symbol is extremely similar to that of a standard p-n junction diode, with the sole variation being bent edges on the vertical bar. The Zener diode sign is made up of anode and cathode terminals. The anode terminal is the +ve terminal, whereas the cathode terminal is the -ve terminal. It works in both directions, forward bias and reverses bias. It is mostly used in reverse bias mode.

When reverse biased, ordinary silicon diodes stop all current and are destroyed when the reverse voltage is too high. As a result, these diodes are never deliberately driven in the failure area.

Zener diodes, on the other hand, are unique. They are precisely built to perform without fail in the breakdown zone. As a result, Zener diodes are sometimes known as breakdown diodes.

Ⅰ What is a Zener Diode?

A Zener diode is a form of PN junction diode that can conduct both forward and reverse current. It contains strongly doped areas and is mostly utilized to conduct current in reverse. When the reverse voltage crosses a particular limit known as the reverse breakdown or Zener breakdown voltage, it begins to conduct in the other way.

A Zener diode, unlike a regular diode, can and is particularly engineered to function in the reverse breakdown zone. During the breakdown area, the voltage across the device remains constant while the current changes.

Specifications of Zener Diode

Breakdown Voltage: The breakdown voltage varies between 2.4 and 200 volts.

Current (max) Iz: This is the maximum current at the rated Zener Voltage, with Vz ranging from 200 micro-Ampere to 200 Ampere.

Current Iz (min): The smallest current amount is necessary for diode failure.

Power Rating: This is the maximum power that the diode can consume. It is the voltage and current flowing through the diode.

Temperature Stability: 5V is necessary for the optimum temperature stability of diodes.

Ⅱ What is the Zener Diode Symbol

Electric current passes from anode to cathode and cathode to anode in a Zener diode. The Zener diode symbol is identical to the standard p-n junction diode symbol, but with bend edges on the vertical bar.

Symbol of Zener diode in the circuit diagram

zener-diode-symbol

Zener diode symbol

Ⅲ Zener Diode Circuit Diagram

The Zener diode circuit diagram is given in the image below. In reverse biased, a Zener diode is used. Reverse biasing implies connecting the diode's n-type material to the positive terminal of the supply and the P-type material to the negative terminal of the supply. Because the diode is comprised of strongly doped semiconductor material, the depletion area is quite narrow.

zener-diode-circuit-diagram

Ⅳ How Does a Zener Diode Work?

When used in a circuit with forwarding bias, the Zener diode behaves like any other diode. When the circuit is reverse biased, the current is halted until the Zener voltage is reached. This property is significant because it allows for reliable voltage management while carrying large currents. The Zener voltage may be fine-tuned by doping the device as required.

Although the current-voltage (I-V) curve of a Zener diode resembles that of an ordinary p-n junction diode, there are three distinct zones in the I-V characteristic curve of a Zener diode.

Zener diode-I-V-characteristic-curve-and-the-circuit-diagram

Fig. 2. Zener diode I-V characteristic curve and the circuit diagram for a voltage regulator using a Zener diode

 

The forward bias area is defined as the region where the applied voltage is forward biased and the device permits forward bias current to flow. The applied voltage is reverse biased in the reverse bias zone, as is current flow, which considerably rises in the breakdown region after the applied voltage surpasses the Zener voltage.

There are three distinct phenomena involved in the workings of a Zener diode.

  • In the reverse bias voltage, Zener breakdown happens before avalanche breakdown. A Zener breakdown happens when electrons quantum tunnel over the depletion region of a diode, whereas an avalanche breakdown occurs when minority carriers in the depletion zone strike other atoms to form new carriers.
  • The breakdown voltage in the diode where the reverse bias current occurs is referred to as the Zener voltage. The threshold voltage is the point at which the applied electric field becomes high enough to give the energy required for electrons to quantum tunnel through an otherwise prohibited location.
  • In general, Zener diodes are beneficial in circuits with reverse bias. A Zener diode acts like any other diode in the forward bias condition.

Ⅴ How to Test a Zener Diode?

Figure 2 also depicts a basic design for a Zener diode in a voltage regulator. This circuit arrangement may be used to test and determine the Zener voltage characteristic of the device. An input voltage is placed across the Zener diode, and the load resistor is probed using a voltmeter or a similar device to measure the output Zener voltage. The resistor linked in series with the voltage input controls the input current. The voltage measured across the load is the Zener voltage. Assuming that the reverse bias current does not exceed the device's thermal limitations, the diode can carry a significant current while maintaining a steady voltage across a load.

Ⅵ Differences in Avalanche Breakdown & Zener Breakdown

  • Avalanche breakdown is caused by collisions between electrons in the depletion area, whereas Zener breakdown is caused by a high electric field.
  • In weakly doped P-N junction diodes, avalanche breakdown occurs, whereas in substantially doped P-N junction diodes, Zener diode occurs.
  • The diode cannot resume its initial position following the avalanche breakdown, but it can regain it following the Zener breakdown.
  • In the case of Zener breakdown, the electric field in the depletion zone is greater than in the case of avalanche breakdown.
  • Avalanche breakdown produces both pairs of holes and electrons, whereas Zener breakdown produces solely electrons owing to a strong electric field.
  • Avalanche breakdown is caused by a high reverse voltage, whereas Zener breakdown is caused by a low reverse voltage.
  • Avalanche breakdown has a positive temperature coefficient, which means it grows as the temperature rises, whereas Zener breakdown has a negative temperature coefficient, which means it drops as the temperature rises.
  • When contrasted to the avalanche breakdown, theZener breakdown has a strong curve in its V-I properties.

Ⅶ V-I Characteristics of Zener Diode

The V-I characteristic, also known as the Volt-Ampere characteristic, is a graph that depicts the change in current as a function of the voltage applied across the junction. The Zener diode's V-I characteristics are classified into two types: forward characteristics and reverse characteristics. Let us go through them in depth.

V-I-characteristics-of-zener-diode

7.1 Forward Characteristics

The Zener diode's forward-biased properties are seen in the first quadrant of the graph above. The graph clearly shows that the forward-biased properties of the Zener diode are the same as those of a typical P-N junction diode, i.e., increasing the voltage surrounding the terminal increases the current flowing through the circuit. However, due to the increased doping concentration in the Zener diode, the amount of current flowing through it is more than that of a typical P-N diode.

7.2 Reverse Characteristics

When the Zener diode is reverse-biased, only a small amount of leakage current flows through the circuit at first due to minority charge carriers generated thermally, but when the applied reverse voltage is increased further to a certain value of reverse voltage, the breakdown occurs, and a sharp increase in reverse current is observed. The Zener voltage (Vz) is the value of the reverse voltage where the breakdown has occurred, and the Zener Effect is the breakdown effect. The current traveling through the Zener diode may be limited using external resistance. The voltage (V) flowing through the diode may be estimated quantitatively using the formula,

V=Vz+IzRz

Where Vz is the Zenere breakdown voltage, Iz is the Current flowing through the Zener diode, and Rz is the Zener resistance.

Ⅷ Zener Diode Advantages

  • The Zener diodeis inexpensive.
  • It keeps the input voltage stable and adjusts it.
  • It features a straightforward circuit and is very compatible.
  • It is commonly used to safeguard electronics against overvoltages in electrical circuits.
  • At the output terminal, it delivers a constant voltage.
  • It is capable of controlling the excess current flow in the circuit.
  • It functions as a waveform clipper.

Ⅸ Zener Diode Disadvantages

  • The Zener diodeapplies even more reverse voltage to balance out the excess input voltage, which wastes a lot of power in the process.
  • Because their efficiency decreases at large load currents, Zener diodes are not suited if the load current is too high.
  • The output voltage varies somewhat due to Zener resistance.
  • The circuit has a high internal impedance.
  • For regulating voltages, transistors are preferable over Zener diodes because they have a higher regulation ratio.
  • We cannot alter the output voltage since the Zener voltage equals the output voltage (Vo=Vz).

Ⅹ Avalanche Breakdown vs Zener Breakdown 

The key differences between Avalanche Breakdown and Zener Breakdown are tabulated below:

Parameters

Zener Breakdown

Avalanche Breakdown

Definition

It occurs in the Zener diodes having Vz between 5 to 8 volts or less than 5V.

Avalanche breakdown occurs in the p-n junction when the Vz is greater than 8 volts.

Depletion region

The depletion region is thin.

The depletion region is thick.

Electric connection

The connection is not destroyed.

Connection is destroyed.

Electric field

The electric field is strong.

The electric field is weak.

Temperature coefficient

Negative

Positive

Voltage proportion to the temperature

Inversely proportional

Directly proportional

Structure

PN junction diode

Highly developed p and n region

Ⅺ Applications of Zener Diode

The major applications of Zener diodes are the following:

  • Clipper circuits
  • Voltage shifting
  • Voltage regulation
  • Over-voltage protection

Ⅻ Zener Diode as Voltage Regulator

A voltage regulator aims to maintain a constant load voltage despite variable load current and supply voltages. In the case of Zener diodes, the Zener voltage provides voltage control. In reverse conducting mode, the Zener diode maintains a constant voltage across its terminal while altering the current flow through it. As a result, the voltage across the parallel load remains constant.

CONCLUSION

  • When forward-biased, a Zener diode functions as a simple diode (on).
  • When reverse-biased up to Zener Voltage, a Zener diode can serve as a switch (off) (VZ).
  • From Zener Voltage (VZ) until Avalanche Breakdown, the output of a Zener diode is nearly constant and equals Zener Voltage (VZ).
  • A minor change in input voltage induces a quick increase in Zener Current (IZ) while operating in Zener mode, which can be reduced by employing a series resistor (RS).
  • Power supply, voltage regulators, protective circuits, and waveshapers are the most typical applications for Zener diodes.
  • It is usually suggested to study a Zener diode's datasheet before using it to determine its rated characteristics as per design requirements.

Frequently Asked Questions – FAQs

1. How do you define Zener diode?

A Zener diode is a semiconductor device that permits current to flow in either the forward or backward direction.

2. Why is Zener Diode used as a regulator?

A Zener diode is used as a shunt voltage regulator. The Zener diode is connected in parallel to the load to reverse bias it, and after the Zener diode exceeds the knee voltage, the voltage across the load becomes constant.

3. Does Zener Diode exhibit a controlled breakdown?

Yes, a controlled breakdown occurs in a Zener diode.

4. What is the difference between a Zener diode and a normal diode?

The flow of current is what distinguishes a Zener diode from a regular diode. A typical diode enables current to flow in just one direction, but a Zener diode allows current to flow in both directions.

5. What is Zener Breakdown?

The Zener breakdown is caused mostly by a strong electric field. When a strong electric field is placed across a PN junction diode, electrons begin to flow across the PN junction. As a result, the little current in the reverse bias grows.

6. What is differenece between Zener Diode and normal P-N junction diode?

The primary distinction between a typical P-N junction diode and a Zener diode is that the former allows current to flow only in one direction, whilst the latter permits current to flow in both directions.

7. Does a Zener Diode symbol have a circle?

The circle is an optional style that was popular in the past, but diodes are now typically drawn without it.

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