What is NPN/PNP open collector?
NPN type has an N-type semiconductor for the emitter of the output transistor, a P-type semiconductor for the base, and an N-type semiconductor for the collector.
In the PNP type, the emitter of the output transistor is a P type semiconductor, the base is an N type semiconductor, and the collector is a P type semiconductor.
The positive and negative charges are opposite in PNP type and NPN type.
An open collector is a transistor output circuit that uses the transistor collector as it is as an output terminal.