onsemi has marked the 4N283SD as Obsolete. No pin-compatible drop-in replacement exists from onsemi — a board-level redesign would be needed for any alternative.
The 4N283SD provides 5300Vrms galvanic isolation between input and output — this is the withstand voltage for one minute per the isolation spec, certifying the opto for safety-barrier applications in industrial and medical equipment where the primary and secondary circuits must be electrically separated. Minimum current transfer ratio (CTR) is 10% at a forward current of 10 mA. That means with 10 mA through the input LED, the output transistor can sink at least 1 mA — a low CTR floor that forces the designer to budget the output pull-up resistor and the downstream logic threshold around this minimum, not the typical value. Switching is rated at 2 µs turn-on and 2 µs turn-off typical — fast enough for 100 kHz data rates but not for high-speed serial isolation. The output transistor with base access allows the designer to add a base resistor for speed-up or noise immunity, a flexibility not available in Darlington or digital-output optos.
Package and temperature grade for reflow assembly
Housed in a 6-SMD gull-wing package with a supplier device package of 6-SMD, the 4N283SD is designed for surface-mount reflow soldering. The gull-wing leads provide visual solder-joint inspection and some compliance for board flex. Supplied in Tape & Reel for automated pick-and-place. Rated for an operating temperature range of -55°C to 100°C — industrial grade that covers most factory-floor and outdoor telecom enclosures. The 30 V maximum output voltage suits 24 V logic and PLC input rails with margin.