The 4N35M_F132: Rated for 4170 Vrms isolation, this opto meets the reinforced insulation requirement for mains-isolated feedback loops in AC-DC power supplies and motor-drive interface circuits — the 4170 Vrms figure is the test voltage between input and output, not the continuous working voltage. Minimum current transfer ratio (CTR) is 100 % at 10 mA forward current — meaning the output transistor can sink at least as much collector current as the LED draws, which is the baseline for driving a logic gate input or a low-power relay coil directly. Typical turn-on and turn-off times are 2 µs each — fast enough for 100 kHz switching signals but not for high-speed digital isolation above 1 MHz; the 2 µs ceiling sets the maximum data rate at roughly 250 kbps in a non-return-to-zero scheme.
No pin-compatible direct replacement from onsemi is documented, but the standard 4N35 footprint means any 6-DIP opto with matching pinout (anode, cathode, base, collector, emitter, NC) can be evaluated as a form-fit-function substitute.