Switches are one of the most common electrical components everyone knows. They are use for breaking and closing circuits. In other words switches are devices use for putting on or off current in a circuit.
Without switches we won't be able to control our electric appliances, they would just work until they get spoilt.
A switch can only works in two modes, fully ON and fully OFF.
Types of switches.
Switches are used in every day life. You might not be familiar with the different type of switches used in different electronics. Switches are built in such a way to perform a special task, for example our smartphones uses a switch to power on and off, and also another switch to control the volume of your phone's sound, in this subtopics we'll learn about the type of switches used.
Circuit Symbol of a switch.
There are basically two types of switches classified according to what activates them, they are;
- Mechanical switches
- Electric switches.
1. Mechanical switches:
They are activated by mechanical power. The mechanical power could be from human, machines or natural forces. Mechanical switches don't require a power source to activate them neither do they use up power except those containing LED indicators, so they are just conductor of electricity which forms part of the circuit they are connected to. Let's know about the switches which falls other this categories.
- Single pole single throw switch (SPST)
- Single pole double throw switch (SPDT)
- Double pole single throw switch (DPST)
- Double pole double throw switch (DPDT)
- Push button
- Limit switch
- Float switch
- Pressure switch
- Toggle switch
- Temperature switch
- Joystick switch
- Rotary switch
Single pole single throw switch.
It can only on or off a circuit at a time. It works as either fully on or off. It has two terminals for connecting to circuits. This type of switch is the most common type, the only disadvantage of this switch is that it can only control one circuit at a time.
Single pole double throw switch.
This type of switch has three terminals one is the input and the other two is the output.
SPDT can control two circuits as opposed to SPST type moreover, it can be use as a change over that is only one circuit can be powered on while the other will remain off. This type of switch is commonly used in radios, lamps and other home appliances.
Double pole single throw switch.
This switch consists of four terminals, the first two serves as the input and the other two is the output.
The DPST is just like two SPST switch controlled by one mechanism, in other words it is a two SPST switch controlled together at time. The two switches can only get on or off at a time. It has one on and off positions , for this ability it can be used to control two different circuit at a time.
Double pole double throw switch.
Also known as DPDT, it consists of six pins with two input terminals at the middle and other two by it sides are outputs.
It has a dual on or off switch consisting of two on positions.
Push button.
It is one of the most commonly used, push buttons is made of brass springs. It can only have an on and off position and only control one circuit at a time. In it on position pressure must be applied to it button, when the pressure is removed it bounces back to an of position.
Limit switch.
This type of switch is operated by the presence of a moving object or objects near it. It differs from other switches that are operated by human hands. It consists of a number when pushed goes to it off position. In other words, it is a type of switch which is in ON state naturally but goes to off state when it bumber is pressed by a force usually from a nearby or moving body.
Float switch.
This type of switch is mainly for controlling AC or DC motor pumps depending on fluids or water level in a reservoir. When it floats on water surface in a reservoir the switch lever is push up by the liquid to form a complete circuit.
Pressure switch.
It is commonly used in industrial machines and robots to sense pressure in hydraulic systems.
Depending on the amount, size or type or pressure to be detected there are three types of pressure switches; piston type pressure switch, metal Bellow pressure switch and diaphragm operated pressure switch.
Toggle switch.
It looks like a motor car gear, this type of switch is manually operated by pushing it up or down.
It comes in different versions of SPST, SPDT, DPPT and DPST.
The toggle switch is usually use for switching high current of about 10A, but can also be used for small current.
Temperature switch.
Just like a bimetallic strip, this type of switch is controlled by temperature and can also be use to sense temperature. It is made of two different metals of different linear expansivity. When heated either by current flowing through it or by hot objects around it it expands to form a closed circuit, when cooled it goes to it off position.
Joystick switch.
This switch is manually operated it can be turned in three dimensions.
Depending on it direction of movement one or more switches are activated. It is usually used in gaming and controlling devices, a good example is a game pad or what you call PES or PS. It is also use in power machines like building machineries or robots. It can be use for lifting, moving objects in any direction.
Rotary switch
Rotary switch is commonly used in celling fan controls, motor speed controls etc.
It is use to connect a line to one of many line.
It is use for selectors in electrical instruments (eg. Digital multi-meter),
channel selectors in communication devices and bandwidth selectors in multi-band radios.
2. Electric switches:
Electric switches are solid state switches made of semiconductor materials. They don't involve any mechanical or moving part.
They are extremely smaller than the mechanical switch that some can't even be seen clearly.
They are present in most of our device used today and are used in mordern and portable electrical appliances. Below are the types of electric switches;
- Bipolar junction transistors
- Metalic oxide semiconductor field effect transistors
- Silicon controlled rectifier
- Power diodes.
Bipolar junction transistor.
It is a three terminal semiconductor that can work in two phases, ON and OFF. It pins are namely emitter, base and collector.
Mosfet(metalic oxide semiconductor feild effect transistor).
It is a unipolar transistor which has three terminals namely, gate(common), drain (output) and source(input). It is a voltage controlled device in which the input current from the source controls the voltage and resistance between it drain and source. It determines the ON and OFF state of the device.
Silicon controlled rectifier (SCR).
An SCR is widely used for high speed switching applications and power control. It is a uni-directional device whose properties imitates that of a diode consisting of three terminals which are anode, cathode and gate.
It is either turned off of on by controlling it gate input and it anode and cathode biasing conditions. It has four four layers of P and N types semiconductors.
Power diodes.
Diodes are made from silicon or germanium. They are mostly use as a switch and rectification. It can only work either in a fully ON state or fully OFF state.
In it ON state it anode is connected to a positive DC source and it cathode is connected to a negative power DC source,this type of connection is called forward bias.
In it OFF state it is connected in reverse as explained above, thus blocking current entirely.