Sinking VS Sourcing Digital Outputs

A sinking digital (input/output) provides a grounded connection to the load, whereas a sourcing digital(input/output) provides a voltage source to the load.


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

Sinking Output: the device’s output signal does not provide power. It must be connected to a device that provides power for the output signal or sinking input with a loop power supply in the circuit.

Sinking Input: the device receiving the signal does not provide power. It acts as a resistive load, it must be connected to a device that sources its output signal, or to a sinking output with a loop power supply in the circuit.

 


 

float switch circuit output sourcing

Figure 2: Sourcing digital output 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.

Sourcing Output: The device’s output signal powers the output circuit. It must be connected to a receiving device that provides no power and acts as a resistive load, such as a 2-wire passive transmitter.

Sourcing Input: The device receiving the signal provides power for the input signal. It must be connected to sink output, such as a 2-wire transmitter which uses the power from the receiving device.