Zener Diode (Regulator)

A Zener diode is a heavily-doped p-n junction designed to operate in REVERSE BREAKDOWN.

Below breakdown: behaves like normal diode (low reverse current).

At V = V_Z (Zener voltage): reverse current suddenly grows, but voltage stays nearly constant.

This sharp clamp at V_Z is exploited for VOLTAGE REGULATION — line voltage or load may vary, output stays at V_Z.

Breakdown mechanisms: Zener effect (tunnelling, V_Z < ~5 V, has negative T-coefficient) vs avalanche (impact ionisation, V_Z > ~5 V, positive T-coefficient). At ~5 V both contribute and T-coefficient is minimal — used in temperature-stable references.

Always operate with a SERIES RESISTOR to limit current. Otherwise the diode burns out at breakdown.

Used in: voltage regulators, surge protectors, waveform clippers, reference voltages.