Zener diode is a special type of diode. Which operates in the reverse breakdown region during reverse biasing. Zener Diode a P-N junction diode made of Silicon or Germanium. It has a specific voltage called Zener voltage. A circuit is reverse biased and connected in parallel with the load. When the reverse voltage exceeds the Zener voltage, the diode breaks down and a sharp current flows rapidly. Due to this special feature Zener diode is widely used as voltage regulator and voltage stabilizer. Moreover Zener diode is also used as a protector device to protect the meter.
A P-N junction diode made of heavily doped silicon or germanium. Zener diodes are sometimes called voltage reference diodes.
Zener voltage values of Zener diodes are different for different diodes. If the voltage is increased by connecting the zener diode in reverse, the diode produces zener effect up to the zener voltage and if the reverse voltage exceeds the zener voltage, it causes or exhibits avalanche effect. A high reverse bias voltage creates an electric field that causes the covalent bond to break, producing free electrons and holes. This is Zener breakdown.
Again due to high reverse voltage the minority carriers gain a lot of kinetic energy and liberate the valence electrons from normal when they collide with each other. This free valence electron frees another valence electron. In this way a large number of free electrons are created creating a huge reverse current which is called avalanche breakdown.
Md. Husne Fahad
Instructor, Electrical Department