Switch & Types of Switches – Construction, Working & Applications

Different Types of Electrical & Mechanical Switches

What is a Switch?

In electrical and electronic systems, a switch is a device, which can make or break an electrical circuit automatically or manually. In other words, an electrical switch is a controlling device, which interrupts the flow of current or changes the direction of current in a circuit.

Almost all the electrical and electronics systems contain at least one switch, which is used to make the device ON or OFF. In addition, a switch is used to control the circuit operation where a user may activate or deactivate the whole or certain parts or process of a connected circuit.

Types of Switches

Types of Switches

We will discuss various types of these switches in details given below:

Generally, Switches can be categorized as.

Both of these types of switches are widely used in electrical and electronics systems. Switch type selection depends on the system in which they are going to be incorporated. Switches can also be categories on many different bases. We will discuss them one by one later in this article.

Switches can also be categories on the basis of holding the current state.

The latch switch holds its state whether ON or OFF until the new commands initiated.

Momentary switch holds the state only when the specific command is presented only.

Switches Wiring Diagrams:

Types of Mechanical Switches

Mechanical switch is a switch in which two metal plates touch each other to make a physical contact for the current to flow and separate from each other to interrupt the flow of current. There are different types of Mechanical switches which can be additionally categorized on the basis of power handling capacity. The contact material is chosen by keeping in mind that the metal oxides, which are produced due to corrosion, are mostly insulator and layers of such oxides on the switch plates will hinder the normal operation of the switch.

Mechanical Switches can be categories on the basis of their operation:

SPST (Single Pole Single Through)

This is a simple ON/OFF switch. It is also called as a “One Way” or “Single Way” Switch (known as  Two-Way Switch in the US). When a user presses the button of the switch, then the plates of the switch connect with each other and the current starts to flow in the circuit and vice versa.

SPST (Single Pole Single Through) Switch

Here is the basic construction and working of a SPST (Single Pole Single Through) also known as one way switch.

Construction & Working of one way SPST (Single Pole Single Through) Switch

SPDT (Single Pole Double Throw)

SPDT switch has three pins (terminals). One pin among three is used as common and called a Two-Way Switch (known as Three-Way Switch in the US). We can send two different signals to the same pin by using this switch. Because of this functionality, this switch is also known as selector switch.

Other switches related to SPDT are SPCO (Single Pole Changeover) and SPTT (Single Pole Center Off or Single Pole Triple Throw).

SPDT (Single Pole Double Throw) Switch

Below is a diagram of construction and operation of Single Pole Double Through (SPDT) switch also known as 2-way switch.

Construction & operation of two way SPDT (Single Pole Double Through) Switch

DPST (Double Pole, Single Throw)

This switch is basically two SPST switches in one package and can be operated by a single lever. This switch is mostly used, where we have to break both ground and lines at the same time.

DPST (Double Pole, Single Throw) Switch

DPDT (Double Pole Double Throw)

This switch is equivalent to two SPDT switches packaged in one pack. This switch has two common pins and four signal pins. Total four different combinations of singles can be applied to the input pins of this switch. Another switch, related to DPDT is DPCO (Double Pole Changeover or Double Pole, Centre Off).

DPDT (Double Pole Double Throw) switch

2P6T (Two Pole, Six Throw)

It is a type of the changeover switch with a common (COM) which may be connected to six lines with a second two pole switch, which controlling and the operation of the switch is same.

2P6T (Two Pole, Six Throw) Switch

Intermediate Switch

Intermediate switch is also known as a four way switch in the US. We have posted a detailed post about it which can be seen below.

The figure below shows the basic construction and working principle of the intermediate switch.

Construction & Working operation of Intermediate Switch

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Types of Latch and Momentary Operation Switches

Push Buttons Switch

This button is used in many electronics circuits and can handle a small amount of current. When a user presses the button, its metal plate connects with each other, hence the circuit is completed. When the user removes its finger from the button, contact of the pins are detached.

Toggle Switch

Toggle switches are actuated by a lever angled in one or more directions. This switch is stable in state and remains in that state unless or until the lever is pushed in another direction. Most of all household applications have toggle switch and it can fall into any category as mentioned above e.g. SPST, DPDT etc.

Related Switches Wiring Tutorials:

Electrical and Electronic Switches

The Above discussed switches are Mechanical switches and they are user manually operated. Now, we are going to discuss Electrical switches, which are faster in response than mechanical switches and can be switched automatically by an electronic circuit like a microcontroller or microprocessor. They can also be categorized on the basis of current and voltage rating like mechanical switches.

There are the most widely used electronic switches

The question arises here, why do we need an electronics switch? The answer of the question is that sometimes, it is necessary that circuits, which make decisions also turn OFF or ON certain devices based on the decision. If only a mechanical switch is used, then there should be one person present there all the time to make the device ON and OFF after getting an indication message from the circuit.

To eliminate this problem, electronics switches are used then. They are very much fast and accurate as compared to mechanical switches. Electronic switches are small in size and do not make noise while switching operation and they make sure the stability and reliability of the system.

Let’s discuss types of electronic switches in detail.

Transistor as a switch:

Transistors can be used in different modes of operation but we are going to discuss the transistor as a switch. If we apply a large amount of current at the base of the transistor (keeping in mind the maximum allowed current for this type of transistor) then we can run this transistor in deep saturation mode i.e. this transistor can be used as a switch.

Typical Circuit of Transistor as a Switch:

No current flows, when there are 0 volts at the base of the transistor.

When the base is at logic level 1.

Lamp Starts glowing.

Mosfet As a Switch:

Mosfets can also be used for switching purposes at high frequencies. They can operate at Mega-hertz  (MHz) frequencies. Mostly, Mosfets used for PWM (pulse width modulation).

Mosfets have three terminals.

  1. Gate
  2. Drain
  3. Source

If we apply logic 1 by keeping in mind the maximum allowed voltage for the base, then the resistance between the drain and source become low and current starts flowing in this channel and vice versa

So the lamp would not glow, i.e. it would be Off, when the Gate at logic 0.

Gate at logic 1, lamp is glowing.

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Relay as a Switch

A Relay is an electromechanical device, which consists of an electromagnet. When a current is flowing through the coil, it becomes an electromagnet and this electromagnet can be used for switching purposes. Their contacts can fall into any category, e.g. SPDT, DPDT etc. You may read more about solid state (SSR) relays in our previous post. We also covered the basic circuit and working of relay as switch.

When we energize the coil, Lamp will glow.

Relay as a Switch

When we de-energize the coil, the lamp would not glow.

These were the types of switches. We will discuss in detail their construction, operation and application one by one in detail in next coming posts. Thanks.

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