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Switches for Electronic Equipment Tutorial

- Switches are a key element in electronic equipment enabling current to be turned on and off as well as selecting a channel or option.

Switches form a key element within the electronics industry.

Switches can be used for many tasks from controlling the supply of power to a circuit, to selecting a particular circuit element required for a given operation.

As such, switches of many types have been used in electronic equipment from the earliest days. Although different types may be used now, their function is essentially the same.

Switch basics

Switches have a number of requirements. In an ideal world a switch will have infinite resistance and no capacitance across the contacts when the switch is open, but zero resistance when it is closed.

In this way the switch would be able to give complete isolation when it is open, and complete connectivity when closed.

A real or practical switch is not able to achieve this, but often the levels of resistance and such that they approximate to the ideal case, especially for the current and voltage levels required for most electronic applications. For high current electrical systems, this is not as true.

Also the mechanical switches are normally able to give much better levels of isolation and connectivity than many semiconductor switches.

However mechanical switches are often much slower and suffer from a limited life.

As a result, different switch technologies are applicable in different applications, and also differ types of switch are applicable in different uses.

Switch types

There are very many different types of switch that can be bought. Different types of switch are aimed at different applications, and therefore it is useful to use the correct type of switch for a given application.

  • Rotary switch:   As the name implies, this type of switch is operated by rotation. Rotary switches are used when more than two positions are required, for example when changing bands on a radio receiver, etc.. The rotary switch type consists of a spindle or rotor and there is an array of terminals that the circular contactor makes contact with dependent upon the position of the spindle. In this way a particular contact (or contacts can be selected).
  • Toggle switch :   A toggle switch is a form of switch that is manually actuated by a mechanical lever, handle, or rocking mechanism. It generally has two positions. Once the arm is actuated the mechanical mechanism tends to hold it positively in one position or another. The internal mechanics are such that once the arm is moved it and passes a certain point it snaps into the other position. In this way, the switch is held firmly in one position or another.
  • Rocker switch:   This type of switch has many similarities with the toggle switch in that it often has just two positions. However a toggle mechanism is not included and therefore the switching action is not quite as positive.
  • Electronic switch:   FETs and also bipolar transistors as well as SCRs can be used for switching electronic and electrical circuits. When semiconductor technology alone is used to provide switching, these switches are often referred to as electronic switches.

By Ian Poole

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