The onsemi CNY171S is a single-channel optoisolator in a 6-SMD Gull Wing package, with a DC input driving a phototransistor output that includes a base connection for external bias or feedback. Rated for 5300 Vrms isolation, it provides reinforced galvanic isolation between the input and output circuits — sufficient for mains-referenced control loops and medical equipment where the isolation barrier must withstand a 5 kV surge test. The current transfer ratio (CTR) is specified at 40% minimum and 80% maximum, measured at If = 10 mA. This 2:1 spread means the output collector current can vary by a factor of two across parts — a design that uses the transistor in linear mode must account for the full CTR range; a saturated-switching design is less sensitive.
Switching speed and output drive
Turn-on time is 2 µs typical, turn-off time 3 µs typical, with rise and fall times of 1 µs and 2 µs respectively. This limits the practical data rate to roughly 100 kHz in a saturated-switching application — above that the output waveform degrades and the minimum pulse width is lost. The output can sink up to 50 mA continuous with a maximum Vce(sat) of 300 mV at the rated forward current. The 70 V output breakdown gives headroom for driving 24 V PLC inputs or relay coils without an external level shifter. Forward voltage is 1.35 V typical at If = 10 mA, and the absolute maximum forward current is 100 mA — the LED is not designed for pulsed drive above that without duty-cycle derating.
onsemi has marked the CNY171S as Obsolete. For existing BOM lines, the CNY171S is sourced through independent distribution against an RFQ.