Open Collector to drive PNP without Pull-Up
For a project requiring galvanic isolation, I would like to use an optocoupler.
Several fast optocouplers are available that offer an open collector
output.
Can I use this output to drive a PNP transistor (with an appropriate
base resistor) without using a pull-up resistor?

Yes.
The PNP transistor and base drive resistor effectively ARE the pullup.
The only addition which MAY be useful is an extra resistor from PNP base to emitter (V+ usually).
This passes base leakage current when the transistor is off. In most cases it is not needed. In some cases it is possible for the PNP to turn on partially without this resistor.

Along these lines.
R1 optional as above.
R2 value to suit application.



simulate this circuit &ndash; Schematic created using CircuitLab