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Sinking and Sourcing1

Sinking and sourcing refer to the control of direct current flow in a circuit, where sinking digital I/O provides a grounded connection and sourcing digital I/O provides a voltage source. A complete circuit requires a combination of sourcing and sinking inputs or outputs, and using the same type (sourcing-sourcing or sinking-sinking) necessitates an additional resistor. It is crucial to understand the power source of the devices involved, as passive devices sink current while active devices source current.

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32 views2 pages

Sinking and Sourcing1

Sinking and sourcing refer to the control of direct current flow in a circuit, where sinking digital I/O provides a grounded connection and sourcing digital I/O provides a voltage source. A complete circuit requires a combination of sourcing and sinking inputs or outputs, and using the same type (sourcing-sourcing or sinking-sinking) necessitates an additional resistor. It is crucial to understand the power source of the devices involved, as passive devices sink current while active devices source current.

Uploaded by

yaser
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Sinking and Sourcing

Sinking and Sourcing are terms used to define the control of direct current flow in a load. A sinking
digital I/O (input/output) provides a grounded connection to the load, whereas a sourcing digital I/O
provides a voltage source to the load.

Consider a simple circuit that consists of one digital input connected to a digital output. The circuit
needs a voltage source, a ground, and a load. A sourcing digital I/O provides the voltage needed for
the circuit. A sinking digital I/O provides the ground needed in the circuit. The digital input provides
the load required for the circuit to work.

Figure 1 shows a sinking digital output that is connected to a sourcing digital input. In this circuit, the
load is pulled to ground because of the sinking digital input provided.

Figure 2 shows a sourcing digital output that is connected to a sinking digital input. In this circuit, the
load is pulled up to receive voltage because the sourcing digital input has been provided.

Because both a voltage source and a ground reference are needed in order to create a complete
circuit, you must have a sourcing input or output connected to a sinking output or input. If you wish
to connect a sourcing input to a sourcing output or a sinking input to a sinking output, you will need
to add an additional resistor.

When connecting various current inputs and outputs it is important to keep in mind what device is
powering the circuit. Inputs and outputs can either “sink” current or “source” current. A 2-wire
transmitter is a passive device and thus “sinks” current. A 4-wire transmitter operates on an external
power source and thus “sources” or provides power to the circuit.

Note that sinking-sourcing and sourcing-sinking pairing is always used, and never sourcing-sourcing or
sinking-sinking.

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