Device identity and key parametrics
The H11A1SM is a single-channel optocoupler from onsemi with a DC input and a phototransistor output that brings the base terminal out separately. The 4170Vrms isolation rating is the figure a safety engineer checks first — it supports reinforced insulation in mains-referenced circuits such as AC-DC power supplies and motor-drive interfaces. Minimum current transfer ratio is 50% at a forward current of 10 mA. That means the output transistor can sink at least 5 mA when the LED is driven at 10 mA — a straightforward gain to budget into the pull-up resistor on the collector. The typical turn-on and turn-off times are both 2 µs, which is adequate for 50/60 Hz line-frequency isolation and low-speed logic interfaces but not for high-speed data links. Output transistor maximum Vce is 30 V, and the saturation voltage is 400 mV max. The 30 V ceiling suits 24 V industrial logic rails; the low saturation voltage keeps the logic-low level clean when driving a CMOS or TTL input.
Package and mounting for board fit
The H11A1SM is supplied in a 6-SMD gull wing package, surface-mount only. For a BOM position that calls for a through-hole DIP-6, this SMD variant requires a footprint change — confirm the land pattern before committing.
onsemi lists the H11A1SM as Active and ROHS3 compliant.