Zener

A Zener diode is a type of silicon semiconductor diode designed to operate reliably in reverse bias and to provide a stable reference voltage. It conducts in reverse when the applied voltage reaches a specified breakdown voltage, Vz, instead of being destroyed by breakdown as with ordinary diodes. The component is named after Clarence Zener, who described the breakdown phenomenon in 1934. Practical Zener diodes were developed in the 1950s and have since become a common component in electronic circuits.

In normal use, the Zener diode is reverse-biased and clamps the voltage to approximately Vz. The voltage remains relatively constant over a range of reverse currents, making the device useful for voltage regulation and references. Breakdown can occur via the Zener effect, a quantum mechanical tunneling process that dominates at lower voltages in heavily doped junctions, or via avalanche breakdown at higher voltages caused by impact ionization; many modern Zeners involve a combination of both mechanisms. Zener diodes are specified by their nominal breakdown voltage, dynamic impedance, and power rating, and they come in a variety of tolerances.

Common applications include voltage regulation in power supplies, reference circuits in integrated circuits, and simple shunt regulators. They are also used in protection circuits and transient suppression when combined into TVS devices. Zeners are available in a range of power ratings, from small-signal types to high-power varieties, and in multiple package formats suitable for through-hole and surface-mount designs.