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

A 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:

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 diode, designed 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:

Zener Diode Symbol

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

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.