The CNY17F4S provides 5300Vrms galvanic isolation between the input LED and the output phototransistor — this is the safety isolation rating that separates low-voltage control circuits from higher-voltage power stages or communication buses, per IEC 60950 reinforced insulation requirements. This means the output transistor can sink at least 16mA when the LED is driven at 10mA — enough headroom to drive a standard logic input or a relay coil through a base resistor, without needing a separate buffer stage.
Switching speed and output drive capability
Rise and fall times are 1µs and 2µs typical respectively, with turn-on time of 2µs and turn-off time of 3µs. This limits the practical data rate through the opto to roughly 100 kbps — adequate for isolated RS-232, status feedback, or PWM at low kHz, but not for high-speed CAN or Ethernet isolation. The output transistor is rated for 70V collector-emitter maximum and 50mA continuous output current. This lets it switch small relays, solenoids, or PLC input modules directly, provided the load current stays within the 50mA ceiling and the collector voltage does not exceed 70V.
onsemi has marked the CNY17F4S as Obsolete. No official successor part number is recorded — the replacement path is a different order code within the CNY17 family or a functionally equivalent optoisolator from another vendor, which requires verifying the CTR bin, package, and pinout against the original BOM position. Sourced through independent distribution against an RFQ. The 6-SMD Gull Wing package is the board-fit constraint — confirm the land pattern matches the original design before committing the replacement.