What this opto does on the board
The 4N36SM is a single-channel optocoupler from onsemi that isolates a DC input from a transistor output with a base terminal. Its 4170Vrms isolation rating lets it bridge logic and power domains in industrial controls, motor drives, and PLC I/O modules where galvanic separation is mandatory for safety and noise immunity. The base pin on the output side gives you the option to bias the phototransistor for faster switching or to configure it as a photodarlington with an external transistor — a flexibility not available on simpler optos. Typical turn-on and turn-off times are 2µs each, fast enough for 24V digital inputs running at a few kHz.
Key ratings that drive BOM decisions
Current transfer ratio is guaranteed at 100% minimum with 10mA forward current. That means for every 10mA you push through the LED, the output transistor can sink at least 10mA collector current — enough to drive a TTL or 5V CMOS logic input directly. If your logic family needs less than 1mA at the input, you can drop the LED current well below 10mA and still have margin. The output transistor is rated for 30V maximum with a saturation voltage of 300mV max. That 300mV drop at full load matters when you're switching a 5V rail — the logic-high level at the collector will be 4.7V, which is still above the 3.5V threshold for most 5V CMOS inputs. For 3.3V logic, you'll want to check the input threshold of the receiving device against the Vce(sat) plus pull-up resistor drop. Forward voltage is 1.18V typical at the rated forward current. That's a standard red-LED drop, so any 3.3V or 5V GPIO can drive it through a current-limiting resistor. The maximum continuous forward current is 60mA, but you'll normally run it at 10–20mA for the CTR knee.
Lifecycle and sourcing reality
The 4N36SM is listed as Active and ROHS3 compliant. The surface-mount Gull Wing leads reflow well with standard lead-free profiles; the lead pitch is wide enough that hand-soldering or hot-air rework is straightforward. Pricing and lead time are confirmed at quote time against your BOM quantity. Submit an RFQ through the site — we source direct from authorized channels and can provide current availability and pricing for your volume.