NPN / PNP open collector output

The open collector output is an output that uses a transistor.
A transistor consists of three terminals called a base, a collector, and an emitter. When a current flows through the base, a current flows between the collector and the emitter, and when no current flows through the base, the collector and the emitter are in an open state.

The output used as a switch by controlling the current to the base of the transistor using this characteristic is the open collector output.

The direction of the current flowing between the collector and emitter is determined by the transistor configuration.

For NPN type, current flows from the collector to the emitter,
PNP type, current flows from the emitter to the collector.

For NPN open collector output, the emitter is connected to the 0V side of the power supply.
It can be operated by connecting a load between "Power +" and "Output". When the transistor is turned on, the voltage of the output terminal becomes 0V.

For PNP open collector output, the emitter is connected to the + side of the power supply.
It can be operated by connecting a load between "0V" and "output".
When the transistor is turned on, the voltage of the output terminal becomes the + side power supply voltage.

An output that uses a transistor is called a non-contact output because there is no mechanical contact opening and closing.
Compared to the contact output that uses a mechanical relay, the response time is faster, which is effective for high-speed control.
Also, since there is no mechanical operation, there is no life due to the number of uses. Since the direction of current flow is fixed, only DC loads can operate using the output.

Transistor outputs are often used in control equipment. It is well known that it is used for sensors for object detection.