Optocoupler identity and isolation rating
The onsemi H11A8173S is a single-channel optocoupler with a DC input and transistor output, housed in a 4-SMD Gull Wing package (supplier device package 4-SMD). The headline rating is 5300 Vrms of isolation — this defines the safety barrier between the primary and secondary sides in a circuit. For a 230 VAC mains-referenced input, 5300 Vrms provides reinforced insulation margin per IEC 60950-1, sufficient for many industrial and medical-grade isolation applications. This wide CTR range means the same part can drive a logic input with a low-50% CTR or saturate a transistor output at 600% — the designer sizes the pull-up resistor based on the minimum CTR to guarantee logic-level switching across temperature and device tolerance. Operating temperature covers -55°C to 100°C, placing it in the industrial/military temperature band.
Output ratings and drive capability
The output transistor can handle up to 70 V collector-emitter and 50 mA continuous current per channel. The 200 mV typical Vce(sat) at rated current means the output drop is low enough to drive a 5 V CMOS input directly when the pull-up resistor is sized correctly. Forward voltage is 1.2 V typical at 5 mA, and the maximum DC forward current is 50 mA.
The H11A8173S is marked obsolete by onsemi. For a BOM line that requires this exact optocoupler, the procurement path is spot-market inventory management, not factory order.