Zener diode, Using the reverse breakdown state of PN junction, the current can change in a large range and the voltage is basically unchanged, and the diode with voltage stabilization function is made. This diode is a semiconductor device with high resistance until the critical reverse breakdown voltage. At this critical breakdown point, the reverse resistance is reduced to a very small value. In this low resistance region, the current increases while the voltage remains constant. The zener diode is graded according to the breakdown voltage. Because of this characteristic, the zener diode is mainly used as a regulator or a voltage reference element. The zener diodes can be connected in series to be used at a higher voltage, and a higher stable voltage can be obtained by connecting in series.