Zener diode tutorial

Zener Diode – Definition, Characteristic, Symbol

Zener Diode

 

zener diode

Zener diode – 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

If you are a student or simply want to learn how to solve Zener Diode tasks, please visit this section of our website where you can find a wide variety of electronic tasks.


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. 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 – Static and dynamic parameters

You can see the list of main 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

Zener diode is characterized by the following limiting parameters:

  • 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 diode stabilizer circuit

Fig. 3. Illustration of stabilizer circuit system based on Zener diode

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