5300Vrms isolation in a rework-friendly package
The H11A817BS is a single-channel optocoupler from onsemi with a transistor output and DC input. Its 5300Vrms isolation rating suits it for galvanic separation in power supplies, motor drives, and industrial I/O where you need to break ground loops or protect low-voltage logic from high-side transients. The 4-SMD Gull Wing package is a surface-mount part with visible leads — easy to inspect and rework with hot air if needed. The leads are on a 0.1-inch pitch, so the footprint is forgiving for hand assembly or touch-up.
CTR range and output drive — what they mean for the BOM
Current transfer ratio (CTR) is specified at 130% minimum to 260% maximum, measured at 5mA forward current. This means the output transistor can sink 1.3 to 2.6 times the input current — enough to drive a logic gate input or a small relay coil directly without a buffer transistor. Maximum output voltage is 70V, and the output can sink up to 50mA continuous. That 70V ceiling covers most 24V and 48V industrial rails with margin; the 50mA limit is the hard ceiling for the output transistor's safe operating area. For sub-microsecond edges you would step up to a digital isolator or a faster optocoupler family.
onsemi lists the H11A817BS as Obsolete. The operating temperature range of -55°C to 100°C covers industrial and some military-grade environments. The 200mV Vce saturation at max drive means the output drops less than 0.2V when fully on — negligible in most logic-level circuits.