8200 Vrms isolation — what it buys you
The CNY65ABST is a single-channel optocoupler from Vishay with a DC input and a phototransistor output, rated for 8200 Vrms isolation between input and output sides. That isolation voltage is the part's defining spec — it supports reinforced insulation in mains-connected equipment, motor drives, and industrial PSU feedback loops where a fault on the primary must not reach the secondary. The transistor output can switch up to 32 V at 50 mA, which covers most logic-level and low-power load interfaces.
CTR window and switching speed
Current transfer ratio is specified at 80% minimum and 240% maximum, both measured at 5 mA forward current. That 3:1 spread is typical for phototransistor couplers — the design must tolerate the full range without saturating or starving the output stage. Turn-on time is 5 µs typical, turn-off 3 µs typical, with rise and fall times of 2.4 µs and 2.7 µs respectively. For 10 kbps to 100 kbps isolated data links these numbers are fine; for faster serial buses like I²C at 400 kHz you would need a logic-output or high-speed optocoupler.
The 4-SMD gull-wing package is surface-mount compatible and suits automated assembly. Forward voltage is 1.32 V typical at 5 mA, and the maximum DC forward current is 75 mA — stay well below that for reliability over the full temperature range.