Zener diode, also called Zener diode. It is the use of PN junction reverse breakdown state, its current can be changed in a wide range of phenomena and the voltage is basically unchanged, made of the role of voltage regulator diode, usually used in constant voltage circuits. And general diodes are used in the forward direction is different, Zener diodes are used in the reverse direction. The reverse breakdown voltage is called Zener voltage (VZ) and the current value is called Zener current (IZ).