It's called Zener diode. It's called Zener diode. Using the pn junction reverse breakdown state, the current can change in a wide range of the phenomenon of the voltage is basically unchanged, made to play the role of voltage regulator diode. The diode is a semiconductor device with high resistance up to the critical reverse breakdown voltage. At this critical breakdown point, the reverse resistance is reduced to a small value. In this low resistance region, the current increases while the voltage remains constant. Voltage regulator diodes are graded according to the breakdown voltage. Voltage regulator diodes can be connected in series for use at higher voltages, by which higher voltage stability can be obtained.

The forward characteristic of the voltammetry curve of the regulator diode is similar to that of the ordinary diode. The reverse characteristic is that when the reverse voltage is lower than the reverse breakdown voltage, the reverse resistance is very large and the reverse leakage current is very small. However, when the reverse voltage approaches the critical value of the reverse voltage, the reverse current increases abruptly, known as breakdown, at this critical breakdown point, the reverse resistance suddenly drops to a very small value. Although the current varies in a wide range, the voltage at both ends of the diode is basically stable around the breakdown voltage, thus achieving the voltage regulation function of the diode.