Zener diode

A Zener diode helps keep voltage nearly steady, for example at 5.1 V. Connect it in reverse: banded cathode K to +, anode A to −. In the forward direction, it works like an ordinary diode.

Use a series resistor to limit current and stay within the power rating. If the supply is too low or the load draws too much current, the voltage will fall.

In SparkVille’s clock tower, a Zener diode helps keep the clock controller’s voltage steady when its supply fluctuates a little.