Construction of a zener diode: Zener diode is a special purpose p-n junction diode. Its symbol is shown in the attached figure. It is fabricated by using heavily doped p-side and n-sides of the diode. This reduces the width of depletion region (thickness ∼10−6m) and increases the strength of electric field in the depletion region drastically (∼5×106V/m). Operation of a zener diode: It is operated in reverse bias. When the reverse voltage applied across the diode is increased to a certain value, the reverse current due to the minority carriers increases suddenly. This happens as the high electric field in the depletion region is strong enough to pull the valence electrons. Beyond this point, voltage across the zener diode remains almost constant.
Breakdown voltage of a zener-diode is the reverse-bias voltage across the diode at which current (from n-side to p-side) suddenly increases across it. This phenomenon results in a practically constant voltage equal to the breakdown voltage across zener-diode.
Zener-diode characteristics(Current voltage variation)
Zener diode as voltage regulator
Circuit diagram for usage of zener-diode as a voltage regulator is shown in the attached figure. Vz=VL is a constant dependent on the zener diode. ∴IL=RVz is a constant Vin=IinR+Vz As Vin is increased, Iz and Iin increases. Note: Vin>Vz is a necessary condition for the zener diode to work as a voltage regulator.