A Zener Diode is a form of diode where the reverse breakdown is well-defined. When wired in reverse, it will conduct if the voltage across it exceeds the reverse breakdown voltage, and will clamp to that voltage. It is often used as a voltage regulator for low-current applications, as voltage references, and as a constant voltage drop when making extended-scale voltmeters. In schematics, it is usually wired with the reverse polarity (cathode positive) from normal diodes.
[file]zener.JPG|thumb[/file]
[file]zener.JPG|thumb[/file]