Every circuit needs a power source, but different circuits have different power requirements. For most small scale electronics, the power consumption is (is or at least could be with better design) very low. For those times when you don't need a lot of power, just a precise voltage level, the simplest means of regulating the supply voltage is by using a Zener diode.
In this Instructable, I will compare a typical voltage regulation circuit with the Zener diode shunt regulator circuit and show you the proper way of selecting the perfect components for your circuit needs. Correct usage of this circuit can save time and money, but it is not well suited for all designs. So grab those breadboards and let's gown to business!
Step 1: Zener Diode Basics
In case you don't know, a diode is a special type of electrical component that lets current flow freely in one direction, but blocks it from flowing in reverse - in the water analogy, the diode would be a one-way valve, only allowing water to flow in a specific direction. A typical diode will have a voltage drop of around 0.7V when forward biased.
All diodes have a "reverse breakdown voltage" which if applied to the diode in reverse will cause current to flow backwards through the component, typically destroying it in the process. This value is typically in the hundreds to thousands of volts. A Zener diode (similar to an "Avalanche Diode") is a special sub-class of diodes that will allow current to flow in the reverse direction if the applied voltage is above a certain level without damaging the component. Of course, there are limitations to the voltage level and/or current flow, but those are things that the design engineer must take into consideration.
Some common Zener diode breakdown voltages are: 1.8, 3.3, 5.1, 7.5, and 12.6, making them ideal for use in many small circuits.