Phototransistors

Hi

can anyone tell me what a phototransistor does ? I have seen the circuit diagram and it looks like a circuit built using LEDs and transistors. What does it do then ?? What part does the LED play ??



thanx

your describing an optoisolator. There are many differnt types but one type is transister based. The basic Theroy is more light (more current flow), more satuated the transister will be. The light is driving the base of the transister