Sourcing vs Sinking Current

[Sparky2003]

Can someone explain the difference betwen sourcing and sinking current when powering components.
Thanks.

 

[dpc]

Try posting this in Circuit Engineering Forum.

 

[lrob]

Sparky2003,

If a device is a sourcing unit it will supply the positive for the circuit. A PNP sensor is a sourcing device.

A sinking device will supply the negative of the circuit and will also handle the current draw. A NPN device is a sinking device.

So if your unit has sinking inputs you need sourcing devices wired into the inputs, and vice versa.

 

[IRstuff]

Please be careful of what you're saying. NPN devices can source as well.

Standard TTL uses only NPN transistors and the transistors are used to source and sink current. The TTL totem-pole output uses a common-emitter NPN for output current sinking and an emitter-follower for output current sourcing.

TTFN

 

[lrob]

I stand corrected. I was only looking from an industrial 24 vdc typical control system viewpoint with PLC base.

 

[jbartos]

Suggestion: Reference:
IEEE Std 100-2000 Dictionary:
Source/Sink Device:
Source devices originate signals, whereas sink devices terminate signals. Examples of source/sink devices include channel banks and digital cross-connect systems.

 

[skiier]

Sourcing or sinking is in reference to a ground point which can be + or - .
When u "source" one side of the load is always connected to ground and the other side is connected thru some "switching device" to the "source" be it + or - .
When u "sink" one side of the load is always connected to the "source" ( be it + or - ) and the other side of the load is connected thru some "sinking/switching device" to ground.
"Polarity" is unimportant in this discussion. The physical connection determines whether the cct is "sourcing" or "sinking".

skiier

 

[GGOSS]

Hello Sparky2003,

Svereral people here have answered your question correctly already. The following is another & possible more simple explanation.

Sourcing means the positive of a DC supply is being switched to the load. In a sourcing circuit the load is perminantly connected to the negative supply. The switching element of optic sensor, proximity sensor, limit switch etc is connected to the positive of the supply. When it is activated (switched) it makes the positive connection to the load.

Sinking means the negative of a DC supply is being switched to the load. In a sinking circuit the load is perminantly connected to the positive supply. The switching element of optic sensor, proximity sensor, limit switch etc is connected to the negative of the supply. When it is activated (switched) it makes the negative connection to the load.

Sourcing and sinking circuits can be produced using either NPN or PNP transistors. To generalise an say (for example) that all sourcing circuits are PNP would in fact be incorrect.

I hope the above helps.

Regards,
GGOSS