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Useful information about Z-diodes
Usually, diodes only allow the current flow in the direction of flow and block it in the opposite direction, for example as a rectifier diode to ensure the current flow in only one direction. The Z-diode is used as a special type of diode, however, mainly for stabilizing voltages. However, it can also be used to limit voltages in a power circuit. This guide explains how exactly the Z-diode works, what advantages and disadvantages it offers and in which areas it can be used. In addition, there are a few things to consider when you buy to select the right diode for your needs.
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How do Z diodes work?
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What are the advantages and disadvantages of Z diodes?
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How temperature-dependant are Z-diodes?
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What are Z diodes used for?
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Stabilization circuit with a Z-diode
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Voltage stabilization with Z-diode and transistor (collector circuit)
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What is important when purchasing Z-diodes?
How do Z diodes work?
While the Z-diode is operated in reverse direction, it operates in forward direction like a common diode. Z diodes are called Zener or avalanche effects, which cause the current to increase abruptly as soon as a certain blocking voltage is reached.
Both effects occur at different voltages. This is referred to as the Zener effect at a reverse voltage of less than 5 V. It occurs when the electrical field strength in the barrier layer is large enough to break the electron pair bonds. The electrons are dissolved from their lattice and thus increase the electrical conductivity, as well as the reverse current or also called Zener current.
From a voltage of more than 5 volts, Zener effect and avalanche effect occur simultaneously, whereby the avalanche effect ensures that the built-in barrier layer is occupied with the released charge carriers. As of a reverse voltage of more than approx. 6.5 volts, only the avalanche effect occurs. The tension rises to a level at which the charge carriers are accelerated so much that further charge carriers are released from other lattice atoms.
The sequence repeats itself and increases the number of charge carriers released was the result of sudden conductivity of the barrier layer. The name of the avalanche effect is therefore derived from the sudden "roll over" of the barrier layer with released load carriers. Diodes, which only dissolve by this effect above the breakdown voltage, are called Avalanche diodes. As soon as the voltage drops back below the breakdown voltage value, the barrier layer is immediately restored, so that only a very low current flow in the reverse direction is possible.
There are different types of diodes that are operated with different reverse voltages. These can be characterized as follows:
| Diode type | IP in Voltat IZ = 5 mA | RZ in Ohmbei IZ = 5 mA | αZ· 10− 4/Kat IZ = 5 mA |
|---|---|---|---|
| ZPD 2.7 | 2.4 3.1 | 70 | 9 5 |
| ZPD 4.7 | 4-in-1 5/2 | 60 | 6− 0 |
| ZPD 6.8 | 6:1 7.5 | 4 | 1 +4 |
| ZPD 8.2 | 7.3 9.2 | 4 | +2 ... +7 |
| ZPD 12 | 10.7 13.4 | 15 | +6 ... +9 |
| ZPD 15 | 13.0 ... 16.5 | 20 | +7 ... +9 |
What are the advantages and disadvantages of Z diodes?
Z diodes are ideal for voltage stabilization, as they are comparatively cheap and simple to use. Thus, despite variable current flow, you can keep the voltage constant to protect sensitive components against voltage fluctuations. Nevertheless, there are different disadvantages depending on the scope of application, which must be taken into account.
If you are working with signals, the Z diode can distort signals due to the non-linearity of the component. Any distortion can occur in both the flow direction and the reverse direction.
Practical advice
Z-diodes are only suitable for circuits with low and relatively constant current consumption. Voltage regulators are better suited for larger current fluctuations and current flows.
How temperature-dependant are Z-diodes?
Z-diodes hardly heat up during normal operation. However, if there is a heavy load, a very high temperature development can occur. If the load exceeds the maximum permissible power loss, the high heat will cause very fast material fatigue, was one of the reasons for this, which could lead to the destruction of the component. Temperature dependence is a disadvantage, especially in applications that require an exact voltage. The temperature dependence of a Z diode is indicated by the temperature coefficient.
Practical advice
When you connect Z diodes with positive and negative temperature coefficients in series, the temperature coefficients are optimized to increase and thus reduce the temperature dependence to a minimum.
What are Z diodes used for?
Z-diodes are particularly useful for voltage stabilization, especially in circuits with low current flow. This can be used, for example, in power supplies, as it stabilizes the DC voltage and thus minimizes the remaining ripple.
Stabilization circuit with a Z-diode
Voltage stabilization with Z-diode and transistor (collector circuit)
However, they can also be helpful for voltage limitation and overload protection. Measuring instruments can be protected by Z-diodes, because they limit the voltage at full deflection in the measuring device. As a result, the current in the measuring device does not rise any further and it is protected against overload. If you want to use Z diodes as a safety barrier in explosion protection, this is usually referred to as a Zener barrier. It prevents the penetration of impermissibly high energy into a highly flammable area.
In addition, Z diodes are often used to represent faults that are used, for example, to describe faults in a transmission channel. These disturbances are called white noise and can be well generated by the avalanche effect of the Z diodes. The stronger the current flow, the greater the noise effect. The noise caused by the movements of the charge carriers within the diode is also called scrap noise and is amplified by the above described avalanche effect in the Z diodes.
What is important when purchasing Z-diodes?
When purchasing Z-diodes you will always find detailed product descriptions and information on the technical data of the diode. Of course, it depends on the purpose for which you want to use your Z-diode. However, you should always make sure that you never exceed the maximum permissible power loss. This is indicated as P(DEAD) in the technical data of the diode. Otherwise, the diode can be destroyed very quickly.
In addition, you should pay attention to the specified reverse voltage and its tolerance. This is as CURRENTLY Spg. (UZ) in the technical data and gives you information on the voltage at which the Z diode can be operated. The specified reverse voltage and its tolerance result in the maximum permissible reverse voltage as well as the minimum required reverse voltage in order to be able to operate the diode correctly.
Furthermore, the different types of housing are important, which are tailored to specific applications. Depending on the design, they can be used for through-hole mounting or surface mounting. The respective housing type can be found in the title of the article and in the product description. The housings can be made of metal, glass or plastic and differ depending on the manufacturer.
However, you should always make sure that you never exceed the maximum permissible power loss. This is indicated as P(DEAD) in the technical data of the diode. Otherwise, the diode can be destroyed very quickly.
Depending on the application of the Z-diode, there are many other requirements and key figures that must be observed. You can also find these in the technical data or in the category "Documents & Downloads", in which you can find a comprehensive product sheet for each diode. Here you can see all the details and key figures of the respective diode.
Practical advice
Housing with integrated metal cooler enables a much better heat dissipation. This increases the maximum permissible power loss, i.e. P(DEAD) minimum.