Zener is a type of diode designed for operation in a reverse-breakdown mode and are characterized according to their behavior when used in this fashion. Useful as a voltage reference or for voltage limiting purposes, they are also capable of functioning as a one-way valve for current flow in the manner of rectifier diodes, though their behavior in this mode is generally less ideal than that of purpose-built devices. Products within this family implement exactly one instance of this function per device package.