Zener diode. Using the phenomenon that the current of the PN junction can change in a large range while the voltage remains basically unchanged in the reverse breakdown state, a diode is made to stabilize the voltage. "This diode is a semiconductor device that has a high resistance until the critical reverse breakdown voltage. At this critical breakdown point, the reverse resistance decreases to a small value, and in this low resistance region, the current increases while the voltage remains constant. Zener diodes are classified based on the breakdown voltage. Due to this characteristic, Zener diodes are mainly used as voltage regulators or voltage reference elements.". Zener diodes can be connected in series for use at higher voltages, and higher stable voltages can be obtained by connecting them in series.‍