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What is a Zener Diode?

The Zener diode is a surface-contact crystal diode made of silicon material, referred to as the Zener diode. The diode is a semiconductor device with high resistance up to a critical reverse breakdown voltage. When the Zener tube breaks down in the reverse direction, within a certain current range (or within a certain power loss range), the terminal voltage is almost unchanged, showing voltage stabilization characteristics. Therefore, it is widely used in regulated power supplies and limiting circuits. Zener diodes are graded according to their breakdown voltage. Because of this characteristic, Zener tubes are mainly used as voltage regulators or voltage reference components. Zener diodes can be connected in series for use at higher voltages, and more stable voltages can be obtained through series connection, which is called a bidirectional voltage regulator.

How Zener Diodes Work

The Zener tube is also a crystal diode, which works by using the characteristic of stable voltage in the breakdown region of the PN junction. Zener tubes are widely used in voltage stabilizing equipment and some electronic circuits. This type of diode is called a Zener tube to distinguish diodes used in rectification, detection and other unidirectional conduction occasions. The characteristic of the Zener diode is that after breakdown, the voltage at both ends remains basically unchanged. In this way, when the Zener tube is connected to the circuit, if the voltage of each point in the circuit changes due to fluctuations in the power supply voltage or other reasons, the voltage at both ends of the load will remain basically unchanged. After the reverse breakdown of the Zener tube, although the current changes in a wide range, the voltage at both ends of the Zener tube changes very little. Utilizing this characteristic, the Zener tube can stabilize the voltage in the circuit. Because of this characteristic, Zener tubes are mainly used as voltage regulators or voltage reference components. Its volt-ampere characteristics can be seen that Zener diodes can be connected in series for use at higher voltages, and more stable voltages can be obtained through series connection.

Strictly speaking, the three-terminal voltage regulator belongs to the integrated circuit. After comparing the output voltage with the internal reference voltage, the regulator is driven to adjust to a stable value. A single component can be roughly judged whether it is damaged by measuring the resistance between each pin with a multimeter, and it is best to connect it to the circuit for measurement. Indicators such as voltage regulation rate and ripple can only be tested with professional instruments. An oscilloscope can also be used for qualitative inspection under amateur conditions.
The Zener tube is also a crystal diode, which works by using the characteristic of stable voltage in the breakdown region of the PN junction. Zener tubes are widely used in voltage stabilizing equipment and some electronic circuits. We call this type of diode a Zener tube to distinguish it from diodes used in rectification, detection and other unidirectional conduction occasions.
(1) Stable voltage Uz: Uz is the breakdown voltage of the PN junction, which varies slightly with the operating current and temperature. For the same type of Zener tube, the voltage regulator value has a certain dispersion.
(2) Stable current Iz: The reference current value when the Zener tube is working. It usually has a certain range, namely Izmin - Izmax.

(3) Dynamic resistance rz, which is the ratio of the voltage change at both ends of the Zener tube to the current change, as shown in the figure above, that is, this value changes with the operating current. Generally, the larger the working current, the smaller the dynamic resistance and the better the voltage regulation performance.
(4) Voltage temperature coefficient, which is a coefficient used to explain that the stable voltage value is affected by temperature changes. Different types of Zener tubes have different temperature coefficients of stable voltage, and there are positive and negative points. For Zener tubes with voltage regulation values lower than 4v, the temperature coefficient of the stable voltage is negative;
The temperature coefficient of the stable voltage of the voltage regulator tube with a voltage regulation value higher than 6v is positive;
Between 4V and 6V, it can be positive or negative. In the case of high requirements, two tubes with opposite temperature coefficients can be used in series for compensation (such as 2DW7).
(5) Rated power consumption Pz: It has been pointed out before that the larger the working current, the smaller the dynamic resistance and the better the voltage regulation performance, but the maximum working current is limited by the rated power consumption Pz, exceeding Pz will damage the voltage regulator tube.

Types of regulator tubes

There are two types of voltage regulator tubes: low voltage and high voltage. The Vz value of the low-voltage Zener tube is generally below 40V, and the high-voltage Zener tube can reach up to 200V. In the past, domestically-made Zener tubes were packaged in metal shells, which were not only bulky but also expensive. In recent years, a large number of full series of glass-sealed voltage regulator tubes have come out, and its advantages are complete specifications (Vz=2.4～200V), good voltage stabilization characteristics, small size (DO-35 package, tube diameter φ2.0mm, length 4mm), Inexpensive.
Semiconductor Zener diodes are also known as Zener diodes (ZenerDiode) or voltage adjustment diodes. Both Zener tubes and semiconductor diodes have unidirectional conductivity, and sometimes it is difficult to distinguish them only by observing their appearance. For example, 2CW7 looks like a low-power diode, and 2DW7 looks like a transistor. The dynamic resistance is also relatively large. For Zener tubes, when the reverse voltage exceeds its operating voltage Vz (also known as Zener voltage or stable voltage), the reverse current will suddenly increase, while the voltage across the device remains basically constant. The corresponding reverse volt-ampere characteristic curve is very steep, and the dynamic resistance is very small. Zener tubes can be used as voltage regulators, voltage references, overvoltage protection, level shifters, etc. In this paper, the Dz symbol is used to represent the Zener tube.

Zener tube and diode difference

1. Diodes generally work under forward voltage, while Zener tubes work under reverse breakdown state. The usage of the two is different;

2. 2. The reverse breakdown voltage of ordinary diodes is generally above 40V, and the high one can reach hundreds of volts to thousands of volts, and the reverse breakdown section of the volt-ampere characteristic curve is not steep. That is, the range of the reverse breakdown voltage is relatively large, and the dynamic resistance is also relatively large. For Zener tubes, when the reverse voltage exceeds its operating voltage Vz (also known as Zener voltage or stable voltage), the reverse current will suddenly increase, while the voltage across the components remains basically constant. The corresponding reverse volt-ampere characteristic curve is very steep, and the dynamic resistance is very small. Zener tubes can be used as voltage regulators, voltage references, overvoltage protection, level shifters, etc.