What is a key characteristic of Zener diodes?

Zener diodes are specifically designed to operate in the reverse breakdown region, which allows them to maintain a constant output voltage despite variations in load current or input voltage. This ability to regulate voltage makes Zener diodes extremely useful in voltage reference applications and power supply circuits. When the reverse voltage applied to a Zener diode reaches its specified breakdown voltage, the diode turns on and conducts current, effectively clamping the voltage at this level and thus providing stable voltage to the circuit connected to it.

In contrast, Zener diodes do not conduct current in both directions in the same way typical diodes do; they primarily conduct current in the reverse direction when the breakdown voltage is reached. They are also not limited to AC circuits, as they can function effectively in DC circuits to regulate voltage. Lastly, Zener diodes do allow current to pass through them in reverse breakdown mode, which is essential to their operation. This unique characteristic of voltage regulation is what defines Zener diodes and differentiates them from other types of diodes.