Zener Diode

A particular type of semiconductor which acts as a normal rectifier until the voltage applied to it reaches a certain point, or threshold voltage. At this point — at the "Zener voltage", "avalanche voltage" or "Zener knee voltage" — the Zener diode becomes either conducting (i.e., "turns on") or non-conducting (i.e., "turns off"). These types of circuits include computer equipment (turn on), voice-activated circuits such as telephone wiretap devices (turn on), and surge protectors (turn off). As the main use of a Zener diode is to provide a reference voltage, it often is known as a "reference diode". In a RF (Radio Frequency) clamp application, the Zener diode is used to clamp (i.e., supply) a specific voltage for other, protected components, perhaps in an integrated circuit (IC). The Zener diode is the device that made it possible to make digital integrated circuits. Without Zener diode on-chip reference voltage (and, thereby, the benefit of voltage regulation and transient voltage protection), we would not be able to just "hook them together", as we do now.


Figure: a) Current versus voltage of a zener diode and b) schematic symbol for a zener diode