EducationZener Diode Definition - Zener diod characteristics and Theory

Zener Diode Definition – Zener diod characteristics and Theory

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Zener Diode

Zener diode definition – also called stabilizer or stabilistor.  It is a member of the semiconductor diodes family. It is often applied in limiter systems (e.g. in frequency modulation (FM) systems, pulse selection systems), voltage stabilizers and as the component, which secures and protects circuits from power surges.

Zener diode symbol
Fig. 1. Zener diode symbol

Its crucial parameter is the breakdown voltage of the “p-n junction”. When diode is forward-biased it operates just like a typical semiconductor diode. It means that it starts conducting current after voltage crosses the threshold voltage of this diode (for a silicon diode approx. 0.7V).

Zener Diode – Tasks for students

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What differs Zener diode from regular semiconductor diode is when Zener is reverse-biased, one can notice that Zener diode is able to conduct electricity after exceeding the specified voltage at the junction, so called Zener breakdown voltage without damaging the component. The value for the breakdown voltage is correlated with high constancy and does not vary with changes in reverse current. After exceeding this voltage, current value rapidly increases. For small voltages (up to 5V) Zener effect plays a crucial role. In the range of 5-7V, the Zener effect and avalanche breakdown is the main one. And lastly, and after exceeding 7V – only avalanche breakdown takes place. It is worth mentioning that Zener breakdown occurs in heavily doped junctions, whereas avalanche breakdown in weakly doped. We can assume that the voltage breakdown of the Zener diode is not relevant with the current that flows through the diode (only in cases of large breakdown current changes very slight changes may be noticed – low dynamic resistance)

Zener Diode – Current-voltage characteristic

Fig. 2. Current-Voltage characteristics of Zener diode (in this case 1N718 diode with Zener Voltage |Vz| = 15V was used)

Zener diode, like the other diodes has its own unique characteristics. At the same time it inherits some of them.

Zener Diode parameters

You can see the list of main zener diode static and dynamic parameters of this component down below:

Static parameters

  • VF – forward voltage at fixed forward current IF,
  • IR – reverse current at given VR reverse voltage (most often VR value is 1V)

It should be noted that these parameters may be irrelevant when diode is operating in “breakdown area”.

  • VZ – Zener voltage, corresponding to the contractual current value of stability (information available in the data sheets of individual diodes)
  • TKVZ – factor temperature of stability voltage (proportion of relative change of stability voltage to the absolute change in ambient temperature at a certain current stabilization).

Zener diode dynamic parameter is the dynamic resistance expressed by the formula:

zener diode parameter dynamic
Dynamic parameter

The resistance rz can also be determined using the static characteristic I(U) at a specific diode stabilization current. The name of such resistance should then be incremental-differential resistance.

Zener diode parameters is characterized by the following limitings:

  • IFMAX – the maximum, constant current conduction,
  • IFMMAX – peak, permitted current of the diode in forward-biased state (conduction state). Usually given for low and medium power diodes,
  • IZMAX – the maximum, permitted current stabilization value, in most cases determined from the quotient of Pad dissipation rate and voltage stabilization Pad VZ,
  • PMAX – maximum power loss.
Zener stabilizer circuit
Fig. 3. Illustration of stabilizer circuit system based on Zener diode

Zener voltage regulator

Voltage stabilization systems are among the most utilized. A few devices are powered with batteries (rechargeable batteries) as well as the output voltage of the power sources may fluctuate within a relatively broad variety.

zener stabilizer

Let us look at methods to create secure voltages. Obviously, you always have the option to utilize an integrated voltage regulator (IC), however, there are quite a few other intriguing approaches, the majority of which just require several (usually different ) components.

zener characteristics

Voltage stabilization isn’t a tricky problem in training as good voltage regulator ICs like the 7805 are easily offered. Because of this, a voltage regulator is commonly utilized in these devices to supply a slightly reduced but steady voltage, like 5V for electronic circuits or to get a microcontroller. When working with an input voltage which range from 7V to 30V, then it offers an output voltage of just 5V. On the other hand, the use of the integrated circuit includes a high number of elements. Alternatively, you can handle 1 semiconductor apparatus, specifically a zener diode. The 7805 stabilizer really comprises a zener diode alongside a significant number of transistors. A zener diode is a sort of diode where a breakdown happens using a well-defined reverse osmosis. The principle of performance of the circuit is a result of the aspects of a common zener diode. The very first breakdown takes place when the reverse voltage rises above a specific value (UZ), which contributes to a sharp gain in the reverse present. The voltage throughout the diode stays stable in the breakdown voltage, so provided that you don’t overdo the opposite current. The next breakdown is a regularly observed disadvantage when using zener diodes. In the event the zener diode gets too hot, then the junction will short-circuit, and following this occasion that the diode elevates the voltage in a level near zero. Simply speaking, the expression zener diode isn’t necessarily appropriate as two distinct phenomena are responsible for its breakdown impact at voltages which range from 3V to 200V. It’s a negative temperature coefficient, inducing the zener voltage to fall to 0.1percent per level. The avalanche impact that overlooks over 5.6V comes with a positive temperature coefficient.

Michal Pukala
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.