Voltage Regulators and Power Supplies
Circuits usually require a dc power supply that can maintain a fixed voltage while supplying enough current to drive a load. Batteries make good dc supplies, but their relatively small current capacities make them impractical for driving high-current, frequently used circuits. An alternative solution is to take a 120-V ac, 60-Hz line voltage and convert it into a usable dc voltage.
There are two approaches to this. The more traditional approach is to use a step-down transformer. The other approach is to use a “switch-mode” power supply. This latter method has all but taken over from step-down transformers in recent years, and is the reason your “wall-wart” black plastic power adapters have become ...