Isolation and CTR — the two numbers that define fit
The 5300Vrms isolation rating means this opto can withstand a 5.3 kV transient between the input LED and output phototransistor — sufficient for reinforced insulation in mains-powered industrial controls and medical equipment where the safety barrier must survive a surge without breakdown. Current transfer ratio (CTR) is specified at 100% minimum and 200% maximum, both measured at If=10mA. A guaranteed 100% floor means the output transistor can sink at least as much collector current as the LED draws — critical for driving logic inputs or relay coils without an extra gain stage. The 200% ceiling prevents saturation-induced slowdown in high-speed switching. Rise and fall times are 1µs and 2µs typical, with turn-on and turn-off times of 2µs and 3µs typical. This places the CNY17F3 in the medium-speed band — fine for 50/60 Hz line sync, PLC input sampling at a few kHz, or DC bus voltage feedback, but not for high-speed serial isolation.
Obsolete — sourcing reality for the CNY17F3
onsemi lists the CNY17F3 as Obsolete. No official successor part number is published — the CNY17 family has been consolidated into newer isolation technologies (digital isolators, photocouplers with higher CTR binning). The -55°C to 100°C operating range covers industrial and some military-temperature environments. The 70V Vce(max) and 50mA continuous output current suit it for driving low-power loads like logic inputs, small relays, or DC solid-state switches.