How to Switch Electric Current On and Off

By Cathleen Shamieh

Switching is far and away the most important function in electronics. Think about your TV set: You turn it on and off, select a signal source from several different input choices (such as your DVD player, cable box, or gaming system), and change TV channels.

Your TV screen consists of millions of tiny pixels (picture elements), each of which is, in essence, a red, blue, or green light that is either on or off. All those TV control and display functions involve switching, whether it’s simply on/off switching or multiple-choice switching — that is, directing one of several input signals to your TV screen.

Likewise, your smartphone, computing device, and even your microwave rely on on/off states (for instance, key pressed or not, or transmit sound now or not) for their control and operation.

So what exactly is switching?

Switching is the making or breaking of one or more electrical connections such that the flow of current is either interrupted or redirected from one path to another. Switching is performed by components called (you guessed it!) switches. When a switch is in the open position, the electrical connection is broken and you have an open circuit with no current flowing. When a switch is in the closed position, an electrical connection is made and current flows.

Tiny semiconductor transistors are at the heart of most of the switching that goes on in electronic systems today. The way in which a transistor works is a bit complicated, but the basic idea behind transistor switching is this: You use a small electric current to control the switching action of a transistor, and that switching action controls the flow of a much larger current.

Aside from transistor switches, lots of different kinds of mechanical and electrically operated switches can be used in electronics projects. These switches are categorized by how they are controlled, the type and number of connections they make, and how much voltage and current they can handle.