Question

how does a zener diode act as a voltage regulator?

Answer 1

A zener diode is a diode, thus it conducts unidirectional current .On the contrary a zener diode also conducts current in the opposite direction, but only when the voltage is over a specific value called zener breakdown voltage. So if you connect a 10 V zener in way of condition over a power supply, it won't conduct as long as the voltage is less than 10V, as soon as the voltage goes over 10 V the zener starts conducting and in given case it acts as a voltage regulator thus protecting the equipment from high voltage causing damage.