# What is a Zener Voltage? (Definition, Characteristics)

• 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