Obsolete lifecycle — sourcing the 4N35 now
That means no ongoing production — the only available units are existing stock in the distribution channel or on the independent market.
5300Vrms isolation and 100% CTR floor
Rated for 5300Vrms isolation between input and output — this is the spec that qualifies it for reinforced insulation in industrial PLC I/O, motor drive feedback, and medical patient-interface barriers. The 100% minimum Current Transfer Ratio at 10mA forward current means the output transistor will saturate with a standard 5V logic input, leaving headroom for LED aging and temperature drift. Forward voltage is 1.18V typical at 10mA, and the maximum continuous forward current is 100 mA. The output side handles up to 30V collector-emitter with a saturation voltage of 300mV max — enough to drive a 5V logic input or a small relay coil directly.
Switching speed and temperature range
Turn-on and turn-off times are both 2µs typical. That limits the useful data rate for status signals, relay drives, and slow serial links.
Package and mounting — 6-DIP through-hole
Housed in a standard 6-DIP (0.300-inch, 7.62mm pitch) through-hole package. The base pin is brought out, allowing the designer to bias the phototransistor for faster switching or to use the Darlington configuration by tying collector and base together.