Isolation and CTR — the two numbers that decide the BOM fit
The onsemi CNY17F3SR2M_F132 is a single-channel optocoupler with a DC input LED driving a phototransistor output, providing 4170Vrms galvanic isolation between the primary and secondary circuits. The current transfer ratio (CTR) is specified at 100% minimum and 200% maximum when the LED is driven with 10 mA forward current — this bracket determines the minimum input current needed to guarantee the output transistor saturates into the load, which directly sets the LED drive resistor value in the design.
Turn-on time is 2 µs typical, turn-off time 3 µs typical, with rise and fall times at 4 µs and 3.5 µs maximum respectively — this limits the usable data rate to low-speed digital signals or 50/60 Hz line-frequency feedback; it will not pass a 100 kHz PWM without pulse-width distortion. The output transistor can sink up to 50 mA continuous and withstand 70 V collector-emitter, with a saturation voltage of 400 mV maximum at the rated forward current — sufficient for driving a PLC input, a logic gate, or a relay coil through a base resistor.
Package, temperature, and lifecycle — what changes when the part goes obsolete
Housed in a 6-SMD Gull Wing package (supplier device package 6-SMD) for surface-mount assembly on a standard PCB footprint — the gull-wing leads provide visual solder-joint inspection access. Rated for continuous operation from -40°C to +100°C, covering industrial enclosure and outdoor telecom cabinet ambient conditions without derating.