Isocom smd optoisolators 1 channel so 4 isocom is121 the is121 is an optically coupled isolator with a current transfer ratio of 50 to 600 the optoisolator consists of an ir led and npn silicon phototransistor in a space efficient surface mounting 4 pin package ideal for use in computer terminals industrial systems controllers measuring instruments potential and impedance matching in signal transmission systems isocom is121 smd optoisolator 1 channel 50 600 ctr so 4