4170Vrms isolation with transistor base access
The 4N37SM is a single-channel optoisolator from onsemi that provides 4170Vrms of galvanic isolation between a DC input LED and a phototransistor output with a separate base pin. This base-access transistor output gives the designer flexibility to add a base resistor for speed-up or to configure the transistor as a photodarlington by tying the base to the collector through an external resistor — a feature missing from three-terminal optoisolators. Minimum current transfer ratio of 100% at 10mA forward current guarantees the output transistor will saturate with modest LED drive, making it a reliable choice for logic-level interfacing in PLC digital inputs, motor-drive feedback, and industrial sensor isolation.
Switching speed and temperature envelope
Typical turn-on and turn-off times are both 2µs, which limits the part to signal frequencies below roughly 100 kHz. For higher-speed isolation, a logic-output optocoupler would be needed — but for 50/60 Hz mains sensing, relay-drive, or slow digital signals, this response is more than adequate. Rated for operation from -40°C to 100°C, the 4N37SM fits industrial environments such as factory-floor PLC racks, outdoor telecom cabinets, and under-hood automotive auxiliary circuits (non-AEC). The 100°C ceiling means the part should not be placed near a hot power supply without thermal margin analysis.
Surface-mount gull-wing in tube delivery
Housed in a 6-SMD Gull Wing package (supplier device package 6-SMD), the 4N37SM is designed for reflow soldering on standard PCB land patterns. The 30V maximum output voltage and 300mV Vce saturation at rated current mean the part can directly drive a 5V or 3.3V logic input without a level shifter, as long as the collector load resistor is sized appropriately.
Active production with ROHS3 compliance
ROHS3 compliant. Sourced to order against BOM quantity; current pricing and lead time confirmed at quote.