Zener Diode
Zener diodes are a special type of diode which permit current to flow in the forward direction as in a normal diode, but where it differs is that it also allows current flow in the reverse direction when the voltage exceeds the breakdown voltage also referred to as Zener voltage or the Zener knee voltage. This electrical property was discovered by Clarence Zener and hence the name Zener diode. The breakdown voltage can be controlled and fixed during the doping process of the diode’s production.
A conventional diode does not let a significant amount of current flow through it in the reverse bias when the voltage is below the breakdown voltage. But when the voltage is exceeded to a point below the reverse breakdown voltage the diode is subjected to high current due to avalanche breakdown and is damaged forever. A Zener diode on the other hand exhibits a controlled breakdown and lets the current keep the voltage across the diode at the Zener voltage. Thus a Zener diode can be used to generate a reference voltage to be used in an amplifier stage, or even as a voltage stabilizer in low current applications.
A Zener diode can be used for a number of applications due to its properties. Apart from the above-mentioned uses, it can also be used to regulate the voltage across the circuit. To do so, it is connected in parallel with the variable voltage source with the diode reverse biased. The Zener diode thus conducts only when the voltage is at the Zener diode’s breakdown voltage, and from then on maintains the voltage at the same value.