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 OP1

Sourced /
Sinked
Outputs

 

Note: The following outputs are "non-inductive", as they do not contain coils or motors which could generate high voltages known as back emf. These types of outputs are mentioned in OP2.

To make the output devices work below, they need to be either sinked or sourced by the previous subsystem.

 

Examples of Non Inductive Outputs being "Sinked"

 



 

The three outputs above will only work if their lower connections (bottom of arrow) are taken down to the minus supply rail by the previous subsystem. This will then allow the current to flow through them. If the previous process subsystem allows the current to flow, then we say the output has been "sinked" to make it work.


Examples of Non Inductive Outputs being "Sourced"

 


 


The three outputs directly above will only work if their upper connections (tip of the arrow) are taken up to the positive supply rail by the previous subsystem. This will then provide a positive voltage to allow the current to flow through them. If the previous process subsystem does this, then we say the output has been "sourced" to make it work.

Example of "Sourcing and Sinking", at the same time....

 




 

These LEDs have been connected in series between the positive and negative supply rails. If their midway point is taken down to the negative supply rail, we will sink the upper LED and it will illuminate. If the midway point is taken up to the positive supply rail, then the lower LED will be sourced and it will come on. A 555 Astable circuit could provide this type of switching (see P7).

The higher than usual 1K protection resistors are used to avoid both LEDs lighting at the same time. This is because there is already a potential across them, as they are connected in series between the two power supply rails.