Question about use of optocoupler 4N25

[BGA]

4n25 circuit

The question is about pin-6 of optocoupler that's the base of output transistor.
I'm studing a design in wich the base is not connected; I can't simulate it in Spice because I have an error in the netlist like "pin 6 is unconnected".
So, who can help me to understand why is it possible to connect out of the chip the base of transinstor; is not sufficient that the base is stimolated with the diode light?
Thanks in advance, Bga.

 

[unkarc]

optocoupler 4n25

hi,

My understanding on this is that certain circuit simulators do not 'like' unconnected legs of components and certain other simulators simply do not care...
Those simulators that do not care on unconnected pins are programmed to terminate such pins automatically with a 10 or 100MegaOhm or even GigaOhm resistor to the common ground and solve this problem. You can do the same!

Regarding the base pin of the phototransistor, sometimes it is useful to access it for instance you can feed in some current into the base or take out current to modify the sensitivity and /or the linearity of the transistor wrt light.

rgds
unkarc