NTE3041 NPN optoisolator , transistor output
The NTE3041 is an optoisolator in a 6–Lead DIP type package consisting of a gallium arsenide infrared emitting diode optically coupled to a monolithic silicon photo transistor detector.
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Image for illustrative purpose only

Features:
High Current Transfer Ratio: 100% Min @ Spec Conditions
Guaranteed Switching Speeds

Applications:
General Purpose Switching Circuits
Interfacing and Coupling Systems of Different Potentials and Impedances
Regulation Feedback Circuits
Monitor & Detection Circuits
Solid State Relays

Manufacturer datasheet - NTE3041 (Adobe Reader required to read datasheet)