What is a Zener Voltage? (Definition, Characteristics)

Regarding the "Zener Voltage", this article will explain the information below.

• What is a Zener Voltage?
• Variation, Characteristics, and Temperature characteristics of zener voltage

What is a Zener Voltage?

If the reverse voltage \(V_R\) applied to the zener diode is gradually increased, a breakdown phenomenon occurs and current begins to flow rapidly at a certain point.

The reverse voltage \(V_R\) at which the reverse current \(I_R\) begins to flow rapidly is called the zener voltage (breakdown voltage) \(V_Z\). The reverse current \(I_R\) flowing at this time is called the zener current \(I_Z\).

In a zener diode, the zener voltage \(V_Z\) does not change much when the zener current \(I_Z\) changes. Zener diodes are often used in constant voltage circuits to take advantage of this characteristic.

Supplement

The "breakdown voltage of a general rectifier diode" is considerably larger than the "breakdown voltage of a zener diode".

Variation of Zener Voltage

The zener voltage \(V_Z\) of the zener diode is given in the datasheet.

The figure above shows part of the datasheet for ROHM's zener diodes (UDZV series). The zener voltage \(V_Z\) is shown when the zener current \(I_Z\) flows at 5mA.

The datasheet lists the minimum and maximum values of \(V_Z\). In the case of UDZV 20B, the minimum and maximum values of \(V_Z\) are 19.520V and 20.390V, respectively.

This means that the Zener voltage \(V_Z\) varies even within the same model number, and even under the same conditions, the Zener voltage \(V_Z\) may be 19.520V or 20.390V, depending on the individual product.

"Zener Current - Zener Voltage" Characteristics

On some datasheets, the characteristics of "vertical axis: Zener current \(I_Z\)" and "horizontal axis: Zener voltage \(V_Z\)" (\(I_Z\)-\(V_Z\) characteristics) are described. The above figure shows the "\(I_Z\)-\(V_Z\) characteristics" of a ROHM-made zener diode (UDZV 20B).

The "\(I_Z\)-\(V_Z\) characteristic" shows how much the zener voltage \(V_Z\) changes when the zener current \(I_Z\) changes.

The "\(I_Z\)-\(V_Z\) Characteristics" also shows that the zener voltage \(V_Z\) varies depending on the ambient temperature Ta. In the case of "UDZV 20B," the zener voltage \(V_Z\) increases as the ambient temperature Ta rises.

Next, the temperature characteristics of the Zener voltage \(V_Z\) are explained.

Temperature Characteristics of Zener Voltage

Depending on the magnitude of the zener voltage, a zener diode may have a positive or negative temperature coefficient.

Those with a Zener voltage higher than around 5V have a positive temperature coefficient, so the zener voltage increases as the temperature rises.

On the other hand, those whose zener voltage is lower than around 5V have a negative temperature coefficient, so the zener voltage decreases as the temperature rises.

In addition, the positive and negative temperature coefficients cancel each other for zener diodes with a zener voltage near 5V, resulting in a small temperature change.

Summary

In this article, the following information on the "Zener Diode" was explained.

• What is a Zener Voltage?
• Variation, Characteristics, and Temperature characteristics of zener voltage

Thank you for reading.