Difference Between SPDT and DPDT (With Table)

Electricity being invented by Micheal Faraday in the 18th century and now the fancy devices and appliances that we use, science has come a long way. There are various elements to create an electrical circuit like resistors, transistors, inductors, diodes, and of course conducting wires made of copper and even aluminum. There are different types of electricity as well Direct current and Alternating Current, which require different setups to use. The importance of electricity is unmatched and undeniably very important so it is also essential to know the way they work to make the most of the appliances. 

The next important elements are the switches we use different kinds of switches as well like pushbutton, pressure, temperature, selector, joystick speed switches, and so on. Coming to connections there are two main types which are single pole double throw(SPDT) and Double Pole Double Throw(DPDT).

SPDT vs DPDT

The difference between SPDT and DPDT is that SPDT has a single input that connects to two outputs while the DPDT has two SPDT integrated together which enables it to control two circuits together at the same time.

Comparison Table Between SPDT and DPDT

Parameters of ComparisonSPDTDPDT
MeaningIt has a single input that connects to two outputs.It has the same mechanism as SPDT but it can control two circuits at the same time.
No.of terminalsHas three terminals Has six terminals.
BenefitsNot as advantageous.More advantageous than the SPDT as it can turn on and off different appliances at the same time.
No.of positionsSPDT has two positions (ON-ON).DPDT can have the two (ON-ON) to three positions (ON-OFF-ON).
Full-formSingle Pole Double Throw.Double Pole Double Throw.

What is SPDT?

The SPDT stands for Single Pole Double Throw, Pole signifies the number of circuits controlled by the switch, and Throw refers to the position of the actuator. SPDT has two positions which means that in the ON-ON position only one of the loads can be energized. There is also the ON-OFF-ON position. An SPDT has three terminals which are power, accessory, and ground terminals.

SPDT is by far one of the most popular switches and it forms the basis for other switches like DPDT, 3PDT, quad DPT and so on. The basic meaning of this is that suppose a lamp and an LED are connected via an SPDT so when the lamp is switched on the LED will be off and when the LED is switched on the lamp will be automatically off. The uses of SPDT vary from creating a Ready mode and Standby in the printer, as an ordinary switch or even switches for kitchen appliances.

SPDT has one circuit which is connected to two appliances that are in parallel connections to one another, thus when one is switched on the other is automatically switched off. The SPDT switches are less disadvantageous than the other counterpart as they can not control two different appliances at the same time. 

What is DPDT?

It stands for Double Pole Double Throw where a pole means the same as the number of circuits and a throw means the position of the actuator. It has six terminals that connect to different appliances which can be controlled at the same time. It has two inputs and four output terminals and it is essentially two SPDT circuits integrated together. Suppose there are two circuits A and B connected to each other in parallel and few appliances connected in parallel as well. Now suppose there is a LED, a lamp in parallel connection, and a speaker and buzzer connected in parallel while the two parallel connections are in series with each other. So when a switch in one way the LED and lamp are on and the buzzer and speaker are off while in the opposite direction the speaker and buzzer are switched on.

In a DPST On-Off situation when both load terminals are or can be energized at the same time and the advantage is that they are independent of each other and thus can be maintained at different voltages. In an ON-ON situation, the circuit acts like two separate SPDT circuits and they can be operated by the same actuator and only two loads can be operated at once. In the final On-Off-On situation it is the same as the ON-ON situation but it is more independent than it. 

The major advantage is that two different appliances can be operated at the same time which cuts down on the circuit costs even though it is a bit more difficult to make or build. 

Main Differences Between SPDT and DPDT

  1. The SPDT has a simple input switch that connects to two output devices whereas DPDT has two SPDT circuits and thus it can control two separate circuits at the same time.
  2. The DPDT switches are thus more advantageous than the SPDT switches are they are capable of controlling two different appliances at the same time. 
  3. The SPDT has two (ON-ON) positions while the DPDT can have two(ON=ON) or three (ON-OFF-ON) positions. 
  4. Making a DPDT connection is thus slightly more complicated than an SPDT connection.
  5. SPDT has three terminals while DPDT has twice of it that is six terminals.

Conclusion

Thus the difference between SPDT and DPDT is that one can control two different appliances while the other cannot control more than one appliance at a time. The SPDT has three terminals while DPDT has six terminals and the former has two positions while the latter has three positions. The DPDT is thus more advantageous than the SPDT and can control different appliances at the same time. However, the SPDT is easier to set up than the DPDT. Thus both have advantages and disadvantages. 

References 

  1. https://www.ingentaconnect.com/content/ben/eeng/2012/00000005/00000003/art00009
  2. https://www.worldscientific.com/doi/abs/10.1142/S0218126612500260
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