The Zener diode (also called Zener diode) is a specially designed diode, which is used to provide a stable voltage in the circuit. Its function is to limit the voltage fluctuation in the circuit and ensure that the specific area in the circuit maintains a stable voltage.

The zener diode plays an important role in the following aspects:

1. Voltage stabilizer: The zener diode can maintain the input voltage at a fixed level. When the input voltage is higher than a certain set value, the zener diode starts to conduct, and the voltage of the circuit is stabilized by bypassing the load with excess current. This voltage stabilizer is widely used in various electronic devices and power supply circuits to ensure that circuit components and loads work in the correct voltage range.

2. Voltage regulation: By choosing appropriate zener diode, specific voltage regulation can be realized in the circuit. The voltage of zener diode is usually between several volts and tens of volts, so it can be used to provide these voltage levels.

3. Overvoltage protection: In the circuit, when the input voltage exceeds the set threshold, the zener diode starts to work and conduct. This can prevent excessive voltage from damaging the circuit and load. Therefore, the zener diode is also used as an overvoltage protection device.

In a word, the role of zener diode is to ensure that the voltage in the circuit remains stable, and it can provide voltage regulation and overvoltage protection functions.