Isocom tlp521 series optoisolators high density mounting isocom tlp521 4gb a photoisolator that uses an ir led optically coupled to an npn silicon photo transistor in a space efficient through hole package suitable for applications such as computer terminals industrial systems controllers test and measurement equipment signal transmission isocom tlp521 4gb optoisolator 4 channel 100 600 ctr 53kv dil 16