Both the NPN transistor output and the PNP transistor output function as switches in the circuit to which they’re connected, but the positions where the loads are connected are different.

NPN transistor output

It’s used to connect a load between the + (plus) of the power supply and the sensor output in the connected circuit. The input device to be connected is a plus common type.

PNP transistor output

It’s used when connecting a load between the sensor output and the power supply - (minus) in the connected circuit. The input device to be connected is a minus common type.

It’s often used in Europe from the viewpoint of safety, as the load doesn’t operate even if it’s short-circuited to 0V due to a factor in the wiring of the sensor output line.

The diagram below is a typical output circuit.

NPN transistor output main uses:

• Signal input to PLC, counter, etc
• Commonly used in Japan
• Connect to a positive common input device.

PNP transistor output main uses:

• Signal input to PLC, counter, etc
• Commonly used mainly in Europe
• Connect to a negative common input device.

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