This part is a kind of semiconductor called IL55.

Function of this product has PHOTODARLINGTON OPTOCOUPLER.

Manufacturers : Siemens Semiconductor Group

Image and pinout :

Some of the text within the PDF file :

SINGLE CHANNEL DUAL CHANNEL FEATURES • Current Transfer Ratio IL/ILD/ILQ30/55, 100% min. IL/ILD/ILQ31, 200% min. • 125 mA Load Current Rating • Fast Rise Time, 10 µS • Fast Fall Time, 35 µS • Single, Dual and Quad Channel • Solid State Reliability • Standard DIP Packages • Underwriters Lab File #E52744 • V VDE 0884 Available with Option 1 D E IL30/31/55 ILD30/31/55 QUAD CHANNEL ILQ30/31/55 PHOTODARLINGTON OPTOCOUPLER Dimensions in inches (mm) Single Channel 3 .248 (6.30) .256 (6.50) 4 5 6 2 1 Pin one I.D. Anode 1 Cathode 2 NC 3 6 NC 5 Collector 4 Emitter .335 (8.50) .343 (8.70) .039 (1.00) min. 4° typ. .018 (0.45) .022 (0.55) .300 (7.62) typ. .130 (3.30) .150 (3.81) 18° typ. .020 (.051) min. .031 (0.80) .035 (0.90) .100 (2.54) typ. .010 (.25) .014 (.35) .300 (7.62) [ ... ]

IL55 PDF Datasheet Download