Difference Between Diode and Zener Diode

Main Difference – Diode vs. Zener Diode

Diodes are common components in electronic circuits, made using doped semiconductors and the main difference between diode and Zener diode is that Zener diodes allow reverse currents to pass through them without becoming damaged, whereas ordinary diodes get damaged if current flows through them in the reverse direction. Diode’s behaviour in a circuit is dependent on which way around they are connected. Therefore, diodes are useful for making circuits where the direction of current flow is important. Zener diodes themselves are a special type of diodes. In Zener diodes, the ability to tolerate reverse currents is achieved by doping the semiconductors that form the p-n junction in a Zener diode to a higher level compared to those in normal diodes.

What is a Diode

diode is a device formed by joining a p-type semiconductor to an n-type semiconductor, forming a p-n junction. An ordinary diode is designed to conduct current only in one direction. i.e., the terminals need to be given a voltage in the forward direction or else current would not be conducted. For this reason, diodes are often used as rectifiers—meaning they ensure that current flows along a preferred direction in a circuit.

The circuit symbol for a diode is:

Difference Between Diode and Zener Diode - Diode Symbol

Diode Symbol

However, this is an idealisation. Under sufficiently large voltages, Zener breakdown and avalanche breakdown occurs and large reverse currents can flow through the diode. This causes ordinary diodes to become damaged.

Below is a typical current vs. voltage characteristic of a diode:

Difference Between Diode and Zener Diode - Diode Current-Voltage Characteristic

Current – Voltage Characteristic of a Diode


What is a Zener Diode

Zener diodes are a special type of diodedesigned to carry reverse currents as well. Zener diodes achieve this by being comparatively highly-doped compared to ordinary diodes. Therefore, the space charge region of a Zener diode is much smaller. Consequently, Zener diodes undergo breakdown at much smaller reverse voltages, called the Zener voltage (V_Z). When this voltage is reached, the Zener diode allows a reverse current to pass through without becoming damaged. Even as the reverse current through Zener diode increases, the voltage is kept around V_Z.

The circuit symbol for a Zener diode is:

Difference Between Diode and Zener Diode - Zener Diode Symbol

Zener Diode Symbol

The figure below shows the current-voltage characteristic for a typical Zener diode:

Difference Between Diode and Zener Diode - Zener Diode Current-Voltage Characteristic

Zener Diode Current-Voltage Characteristic

The shapes of the two characteristic curves may look similar, however, it should be noted that the Zener diode breaks down at a smaller reverse voltage.

The fact that Zener diodes can maintain voltage around V_Z means that they can be used as regulators in circuits for providing a constant voltage across its terminals.

Difference Between Diode and Zener Diode 

Effects of reverse Currents

Diodes: Normal diodes become damaged when reverse currents pass through them.

Zener Diodes: Zener diodes conduct reverse currents without becoming damaged.

Relative Doping Levels

Diodes: Comparatively, doping levels on normal diodes are low.

Zener Diodes: Compared to normal diodes, doping levels on Zener diodes is high.

Relative Value of Breakdown Voltage

Diodes: Typical breakdown voltages for diodes are larger compared to breakdown voltages in Zener diodes (Zener voltage).

Zener Diodes: Typically, Breakdown occurs in Zener diodes at much lower voltages compared to normal diodes.


Image Courtesy
“The circuit diagram symbol for a diode.” by Omegatron (Own work) [CC BY-SA 3.0], via Wikimedia Commons
“Current vs voltage for a semiconductor diode rectifier” by User:Hldsc(Own work) [CC BY-SA 4.0], via Wikimedia Commons
“The circuit diagram symbol for a Zener diode. When used in a circuit diagram, the words “Anode” and “Cathode” are not included with the graphic symbol. (Revised to conform to ANSI Y32.2-1975 and IEEE-Std. 315-1975.)” by Omegatron (Own work) [CC BY-SA 3.0], via Wikimedia Commons
“Schematic V-A characteristics of avalanche or Zener diode. (Note: with breakdown voltage over ca. 6 V avalanche diodes are used instead of Zener diodes.)” by Filip Dominec (Own work) [CC BY-SA 3.0], via Wikimedia Commons

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