You are correct (except that when the LED is activated, the phototransistor gate is injected with current. It's the opposite logic of what you said). It has it's uses though such as flexible output voltages and inherent ORing of signals.

You are correct (except that when the LED is activated, the phototransistor gate is injected with current. It's the opposite logic of what you said). It has it's uses though such as flexible output voltages and inherent ORing of signals.

ADDED:

Using a large resistor minimizes current consumption when the output is pulled LO, but also increases the time it takes to charge the parasitic capacitances on the line and and input capacitances so your rise times get slower which might be unacceptable for some applications (the most common one is a serial bus like I2C).

You are correct. It has it's uses though such as flexible output voltages and inherent ORing of signals.

You are correct (except that when the LED is activated, the phototransistor gate is injected with current. It's the opposite logic of what you said). It has it's uses though such as flexible output voltages and inherent ORing of signals.