5300Vrms isolation in a 6-SMD gull-wing package
The CNY172SD is a single-channel phototransistor optoisolator from onsemi, designed to pass a DC signal across a galvanic barrier rated at 5300Vrms. That isolation voltage covers reinforced insulation requirements per IEC 60950-1 for mains-rated equipment — a common spec for medical power supplies, industrial AC-line monitoring, and motor-drive feedback paths where the control side must stay isolated from the high-voltage bus. The current transfer ratio spans 63% minimum to 125% maximum, both measured at 10mA forward current. This CTR window is tight enough that a single resistor on the output pull-up covers the full production spread without a gain trim — useful when the opto feeds a digital input on a PLC or MCU. Switching is spec'd at 1µs rise and 2µs fall typical, with turn-on at 2µs and turn-off at 3µs. That puts the usable data rate around 100 kbit/s — fine for 50/60 Hz zero-cross detect, relay-driver feedback, or slow serial isolation, but not for high-speed comms like CAN or RS-485.
onsemi has marked the CNY172SD as obsolete. No last-time-buy window remains open. The 6-SMD gull-wing package and 5300Vrms isolation rating are the two dimensions that matter most when searching for a functional drop-in. Any replacement must match the footprint (6-SMD, 7.62mm lead pitch typical for this class) and the isolation voltage to avoid a board spin or safety re-certification.
Temperature grade and operating limits
Rated for -55°C to +100°C ambient, the CNY172SD covers industrial and some military-temperature applications. The output transistor can handle up to 70V collector-emitter and 50mA continuous — enough to drive a small relay coil or a logic gate input directly. Forward voltage is 1.35V typical at 10mA, with an absolute maximum forward current of 100mA.