Isolation barrier and switching performance
The CNY17F3SM is a single-channel optocoupler from onsemi that provides 4170 Vrms galvanic isolation between a DC input LED and a phototransistor output. This isolation rating suits it for reinforced insulation in mains-referenced circuits — think industrial PLC digital inputs, motor-drive status feedback, or AC-line zero-cross detection where the control side must stay isolated from the field side. Switching is on the slower side: typ rise/fall times of 4 µs and 3.5 µs, with turn-on/turn-off at 2 µs and 3 µs. That keeps the part in low-speed signal domains — 50/60 Hz line sync, relay coil drive, or fault flag transmission — rather than high-speed data links. The current transfer ratio is binned: 100% min, 200% max at IF = 10 mA. That means with 10 mA forward current the output transistor can sink at least 10 mA into the load, giving a predictable gain for saturating the output into a logic input or relay coil.
Output ratings and temperature range
Output transistor is rated for 70 V collector-emitter max and 50 mA continuous output current, with a Vce(sat) ceiling of 400 mV. The forward voltage is 1.35 V typ at If=10 mA, and the absolute max forward current is 60 mA — typical drive from a 3.3 V GPIO through a 220 Ω series resistor lands around 9-10 mA, right in the CTR test condition sweet spot.
It is ROHS3 compliant. The package is a 6-SMD Gull Wing (6-SMD, Gull Wing), which is a standard surface-mount footprint for optocouplers — the gull-wing leads ease visual solder-joint inspection. The base product number is CNY17F3, and the 'SM' suffix denotes the surface-mount gull-wing package variant.