What is open collector?

An open collector is a type of output circuit in digital electronics that allows the output to be pulled low (or grounded) by external hardware. The output transistor in an open collector circuit is set up in such a way that it can only pull the output low and cannot drive it high.

Open collector outputs are often used in conjunction with pull-up resistors to create a wired-OR (logical OR) circuit. This allows multiple devices to drive a single output line, with the output line only being pulled low when one or more of the devices activate their open collector output.

Open collector outputs are commonly used in applications where multiple devices need to communicate with a single bus or control line, such as in I2C or SMBus communication protocols. They are also used in some types of sensors, switches, and other devices where a low-power output is required.

Overall, open collector outputs are a versatile and widely-used circuit design that allows for easy interfacing between different devices and components in a digital system.