What this optoisolator does in the assembly
The CNY17F4SR2VM is a single-channel optocoupler from onsemi that provides galvanic isolation between a DC input LED and a phototransistor output. With a 4170Vrms isolation rating, it is suited for breaking ground loops and protecting low-voltage logic from high-side transients in industrial controls, PLC digital inputs, and motor-drive feedback paths. The current transfer ratio is guaranteed between 160% and 320% at a forward current of 10mA, which means the output transistor can sink at least 16mA when the LED is driven at 10mA — enough to directly drive a 5V logic input or a small relay coil without a buffer stage.
Switching speed and output drive
Typical turn-on time is 2µs and turn-off time is 3µs, with rise and fall times of 4µs and 3.5µs respectively. These edges are clean enough for 10–20 kHz PWM or serial data at moderate baud rates, but the 3µs turn-off delay means the output transistor holds conduction briefly after the LED is switched off — a consideration for fast-switching applications like high-frequency SMPS feedback. The output transistor is rated for 70V maximum collector-emitter voltage and 50mA continuous current, with a saturation voltage of 400mV at rated drive. This gives enough headroom to interface with 24V industrial logic rails or 12V automotive circuits while keeping the voltage drop low enough to avoid thermal stress in the output stage.
Package, mounting, and temperature range
Housed in a 6-pin SMD gull-wing package (6-SMD), the CNY17F4SR2VM is supplied on tape and reel or cut tape for automated pick-and-place assembly. The 6-SMD footprint is common across the CNY17 family, making it a drop-in replacement for other CTR-binned variants in the same package. At the high end, the LED forward voltage and CTR both drift; the 100°C ceiling is below the typical derating knee for the phototransistor, so the 50mA output current is still available at the top of the range.