Galvanic barrier for industrial signal isolation
The CNY171SR2VM is a single-channel optoisolator from onsemi that uses a DC-input LED and a phototransistor with base access to provide 4170Vrms of galvanic isolation between input and output. This isolation rating suits safety barriers in motor drives, switch-mode power supply feedback loops, and PLC digital input modules where the primary and secondary sides must not share a ground path. The transistor-with-base output allows the designer to bias the base for faster switching or to use the base as a photodiode for analog feedback — a flexibility not available in Darlington or simple phototransistor optos.
CTR range and switching timing for BOM sizing
Current transfer ratio is specified at 40% minimum and 80% maximum at If=10 mA. The 2:1 spread is tighter than many general-purpose optos, which simplifies worst-case pull-up resistor calculations across temperature and aging. Turn-on time is 2 µs typical, turn-off 3 µs typical, with rise/fall times of 4 µs and 3.5 µs max respectively. For 10 kHz switching applications, the propagation delay adds about 5 µs of dead time — budget that in the controller timing if the opto is in a feedback or fault-signal path.