Open collector

[1] An open collector/open drain/open emitter/open source is an IC output configurations processing the IC's internal function through a transistor via an exposed terminal internally unconnected ("open"). One of the IC's internal high/low voltage rails often connects to that transistor's other terminal. If the transistor is off, the output is internally disconnected from any internal power rail, a state called "high-impedance" (Hi-Z). Open outputs configurations thus differ from push–pull outputs, which use a pair of transistors to output a voltage/current.