[Physics Class Notes] on Types of Switches Pdf for Exam

A Brief Description of A Switch

As we all use switches to control various electronic devices in our day-to-day life, this article deals with switches and their types. It aims to give a basic idea about switches and their types. Switches are important but they are not given the respect that they should be getting since their availability. 

Meaning of a Switch

What do you understand from the terminology Switch? A switch is an electrical device that is used to interrupt the flow of electricity or in simple terms turn on or turn off any electronic appliance like – fans, lights, television, computer, washing machine, etc. A switch is used to make or break the electronic circuit when the switch is on it means the circuit is closed and the current is flowing and when it is off, the circuit is open and there’s no flow of current.

Mechanical Switches.

Depending upon poles and throws mechanical switches can be classified into various types. These can be explained as follows along with sub-categories: 

1. Single Pole Double Throw

 Single pole double throw switch which has two terminals; one input terminal which is referred to as pole and one output terminal known as throw. Hence it got the name single pole single throw. This switch is one of the simplest examples of switches. This switch is generally used in a single loop, which means the circuit requires to control only one close path.

2. Single Pole Double Throw

It has three terminals, two output terminals, and one input terminal. We can also use this switch to supply current to two loops. It is also known as a selector switch.

3. Double Pole Single Throw

These   Double pole single throw switches are used to control the two circuits at the same time. It consists of four terminals, two input terminals, and two output terminals. These types of circuits have two switches and are connected with a single lever so that they can operate at the same time. It can be said that DPST switches are very similar to two SPST.

4. Double Pole Double Throw

This switch has six terminals, two input terminals (poles), and four output terminals (throw), two for a terminal for each pole. In a double pole double throw switch, one pair of output or throw is connected with two terminals of input or pole.

5. Two Pole Six Throw

It is made up of 12 output terminals- six output terminals (throw) for each pole and one input terminal (pole). This type of switch is generally used for change-over in the circuit with a common input terminal.

6. Momentary Control Switches

These are further divided into various categories. Few of them are as follows: 

Temperature switch: Various temperature sensing devices like RTD (resistance temperature device) are composed in this type of switches. This switch operates according to the value of measured temperature.

Toggle Switch: This type of switch is very common and used in household applications to ON and OFF electrical appliances. It has a lever by which we can move up or down to ON and OFF appliances. 

Rotary Switch: This type of switch is used for connecting one line with another of the many lines. Nob of multimeter, channel selector, range selector metering device band selector in communication devices is the example of this type of switch. This switch is similar to a single pole multi throw switch. But the arrangement of this switch is different. 

Electrical Switches

Power Diode

To construct power diodes silicon is used. When the pn junction is reverse biased the power diode acts as switch off and it acts as switch on when the pn junction is forward biased.

Bipolar Transistors

A transistor works similar to that of a normal switch.  Transistor’s active region is not used for switching applications. When the transistor works in the saturation region, it is on and it is off when it works in the cut-off region. For npn and pnp transistors, to operate it as a switch when it’s on a base current needs to be supplied.

MOSFET

MOSFET- Metal Oxide Semiconductor Field Effect Transistor which is a unipolar switching device. It is made up of three terminals: drain (output), source (common), and gate (input). As the device is voltage controlled, the on and off state of the device can be determined by controlling the input voltage and resistance across the drain and the source.