This part is a kind of semiconductor called 4N39.

Function of this product has PHOTO SCR OPTOCOUPLERS.

Manufacturers : Fairchild Semiconductor

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Some of the text within the PDF file :

PHOTO SCR OPTOCOUPLERS DESCRIPTION The 4N39 and 4N40 have a gallium-arsenide infrared emitting diode optically coupled with a light activated silicon controlled rectifier in a dual in-line package. 4N39 4N40 FEATURES • • • • 10 A, T2L compatible, solid state relay 25 W logic indicator lamp driver 400 V symmetrical transistor coupler Underwriters Laboratory (UL) recognized  File #E90700 6 1 6 SCHEMATIC 1 ANODE 1 6 GATE APPLICATIONS • • • • • Low power logic circuits 6 Telecommunications equipment Portable electronics Solid state relays Interfacing coupling systems of different potentials and impedances. CATHODE 2 5 ANODE 1 N/C 3 4 CATHODE Parameter TOTAL DEVICE *Storage Temperature *Operating Temperature *Lead Solder Temperature *Total Device Power Dissipati [ ... ]

4N39 PDF Datasheet Download