Hi all
I had attached an image that shows the output is open collector & has a resistor .Can anyone explain me what does the open collector means & how does it function and what is the use of resistor ?
Open collector means the output transistor collector has no connection, thus the need for a pull-up resistor to the supply voltage to generate a voltage signal.
Open collector output (and open emitter output) means that the chip manufacturer intentionally omitted some essential components required to make a complete circuit. The manufacturer did not commit to a specific output voltage and load resistor.
It means that the circuit designer is free to apply a suitable load and supply voltage according to the needs of the specific application.
It also means that in digital systems, the designer can implement wired-OR (for negative logic) buses or party-line systems without the need for additional gates.
An additional advantage of an open collector output is, for example, the transistor may de driven from a 5V supply control circuit but it can switch a 24V load as the collector does not have a connection to that driving circuit.
The load voltage therefore is wholly dependant on the specs of the transistor. There are quite a few chips that have open collector outputs and are used to drive small motors as things like that. Very handy.