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Types of Switches in Electronic Circuits

Switches are an important part of most electronic circuits. In the simplest case, most circuits contain an on/off switch. In addition to the on/off switch, many circuits contain switches that control how the circuit works or activate different features of the circuit.

Switches are mechanical devices with two or more leads (or terminals) that are internally connected to metal contacts which can be opened or closed by the person operating the switch.

When the switch is in the On position, the contacts are brought together to complete the circuit so that current can flow. When the contacts are together, the switch is closed. When the contacts are apart, the switch is open and current cannot flow.

One way to categorize switches is by the movement a person uses to open or close the contacts. There are many different switch designs. The most common are

  • Slide switch: A slide switch has a knob that you can slide back and forth to open or close the contacts.

  • Toggle switch: A toggle switch has a lever that you flip up or down to open or close the contacts. Common household light switches are examples of toggle switches.

  • Rotary switch: A rotary switch has a knob that you turn to open and close the contacts. The switch in the base of many tabletop lamps is an example of a rotary switch.

  • Rocker switch: A rocker switch has a seesaw action. You press one side of the switch down to close the contacts, and press the other side down to open the contacts.

  • Knife switch: A knife switch is the kind of switch Igor throws in a Frankenstein movie to reanimate the creature. In a knife switch, the contacts are exposed for everyone to see.

  • Pushbutton switch: A pushbutton switch is a switch that has a knob that you push to open or close the contacts. In some pushbutton switches, you push the switch once to open the contacts and then push again to close the contacts. In other words, each time you push the switch, the contacts alternate between opened and closed.

    Other pushbutton switches are momentary contact switches, where contacts change from their default state only when the button is pressed and held down. The two types of momentary contact switches are

    • Normally open (NO): In a normally open switch, the default state of the contacts is open. When you push the button, the contacts are closed. When you release the button, the contacts open again. Thus, current flows only when you press and hold the button.

    • Normally closed (NC): In a normally closed switch, the default state of the contacts is closed. Thus, current flows until you press the button. When you press the button, the contacts are opened and current does not flow. When you release the button, the contacts close again and current resumes.

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