Zener Diode

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The Zener diode is an electrical component whose properties are similar to a conventional diode, except that the Zener diode lets the reverse current flow when the latter exceeds the threshold of the avalanche breakdown effect.

A zener diode makes it possible to produce a constant voltage.

Electrical Symbol

the symbol is similar to a diode, unlike the side of the cathode which looks like an inverted Z. The side of the anode is the same as the symbol for a diode.

Zener diode symbol
Zener diode symbol


Operation

characteristic:

Zener diode characterstic
Zener diode characterstic



  • In direct assembly the zener diode conducts but there is "a threshold voltage" as for the diode.
  • In direct Vak <1volt.
  • Conversely, the current is practically zero (I <1µA) if Vak> Vz, we say that the diode is blocked.
  • If Vak <Vz, there is a "zener effect", ie the Vak voltage varies very little.
  • in zener the power lost in the component increases when the current modulus increases. The manufacturer specifies the maximum current in zener.
  • There are commercially available components specified with Vz from 2V to 400V. For high powers, the components must be mounted on a heat sink.
  • Zener diodes are used for their ability to produce a very stable Vak value with respect to the current I in zener. Either as a reference voltage source or as a voltage stabilization.

Applications

Voltage regulator using a zener diode

To be able to use the properties of the Zener diode, it must be wired in reverse:

  • The value of VZ is given by the manufacturer's documentation of the Zener diode or by its reference.
  • The current IZ is imposed by the resistor R.
  • The value of this current is given by the manufacturer's documentation (reverse current to obtain the voltage VZ).
  • The power (Pz = Vz.Iz) dissipated in the diode must always remain lower than the maximum authorized power. Vz varies with temperature and for some applications it is necessary to take this into account.

Much more efficient stabilization can be achieved by using transistor circuits.


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