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Difference between P-N Junction Diode and Zener Diode
Both the PN junction diode and the Zener diode are semiconductor devices that are extensively used in various electronic circuits. A PN junction diode is mainly used for rectification (transforming AC into DC), while a Zener diode is used for voltage regulation in the electronic circuits.
There are a number of differences in both PN junction diode and Zener diode which are explained in detail in the below table. Before going into the discussion about the differences between PN junction diode and Zener diode, it is fruitful to get the basic details about the PN junction diode and Zener diode.
What is a PN Junction Diode?
A PN junction diode is a two-terminal semiconductor electronic device. It is constructed by joining a p-type semiconductor material with an n-type semiconductor by the process of alloying. It is named so because at the point of joining of the two semiconductors, a junction is formed called PN junction. The two terminals of the PN junction diode are named − anode and cathode. In the PN junction diode, the current flows from anode to cathode. The circuit symbol of a PN junction diode is shown in Figure-1.
The PN junction diode can conduct only in forward direction, i.e. when anode is connected to positive terminal and cathode is connected to negative terminal of the battery. In the reverse bias, it acts as an open switch and do not conduct. Therefore, the PN junction diode is extensively used for the rectification purpose, i.e. to convert AC into DC.
What is a Zener Diode?
A Zener diode is a special type of semiconductor diode which is designed to operate in the breakdown region. It also has two terminals called anode and cathode. The Zener diode is constructed by joining a highly doped p-type semiconductor material with a highly doped n-type semiconductor material.
Therefore, in case of a Zener diode, the concentration of charge carriers (holes and electrons) is relatively higher than that of an ordinary PN junction diode. Figure-2 shows the circuit symbol for a Zener diode.
A Zener diode behaves as a normal PN junction diode in the forward bias, but also operates in the reverse direction when the voltage across it reaches the Zener voltage. When the reverse voltage across the Zener diode becomes equal to the Zener voltage, the breakdown of the depletion region takes place called Zener breakdown and thus, starts conducting in the reverse direction also. Therefore, the Zener diode can conduct in both forward and reverse directions. It is widely used as a voltage regulator in the electronic circuits.
Difference between PN Junction Diode and Zener Diode
The differences between the PN junction diode and the Zener diode are listed in the following table.
| Parameter | PN Junction Diode | Zener Diode |
|---|---|---|
| Definition | A two-terminal semiconductor device formed by joining a p-type semiconductor with an n-type semiconductor by alloying is known as PN junction diode. | A Zener diode is a special type of two terminal semiconductor device which is optimized to work in breakdown region. |
| Doping level of p-type & n-type semiconductors | The level of doping of p-type and n-type semiconductors used for constructing PN junction diode is low. | The highly doped p-type and n-type semiconductors are used for making Zener diode. |
| Width of depletion layer | As the PN junction diode has low doping level, thus the width of its depletion layer is more. | The Zener diode is highly doped, hence its depletion region is narrow. |
| Effect of reverse current | The high reverse current can damage the PN junction diode. | The Zener diode does not get damaged by the reverse current. |
| Breakdown voltage | In case PN junction diode, the breakdown voltage is high. | The Zener diode has relatively lower breakdown voltage. |
| Biasing condition | The PN junction diode is designed to operate in forward bias only, i.e. current flows from anode to cathode. | The Zener diode is mainly designed to operate in reverse biased conditions. |
| Ohm’s law | The PN junction obeys Ohm’s law. | The Zener diode does not obey Ohm’s law. |
| Manufacturing materials | The PN junction diode is generally made by silicon and germanium. Silicon is extensively used. | The material used for making the Zener diode is selected according to the required voltage. |
| Current flow | In PN junction diode, the current flows only in one direction (or forward direction). | In case of Zener diode, current can flow in both directions. |
| Behave in forward & reverse bias | A forward biased ideal PN junction diode acts a closed switch while in the reverse bias acts as an open switch, i.e. do not conduct. | Zener diode acts as a normal PN junction diode in the forward bias condition, but it also conducts in the reverse bias condition. |
| Application | The PN junction diode extensively used in rectification, clamping, clipping, etc. | The Zener diode is mainly used as a voltage regulator (or stabilizer) in the electronic devices and circuits. |
Conclusion
To conclude, the major difference between a PN junction diode and a Zener diode is that a PN junction diode allows the electric current to pass in only one direction (or forward direction), while a Zener diode allows the electric current to flow in both forward and reverse directions.
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