The 4N37FVM is marked obsolete by onsemi.
7500 Vpk isolation barrier
Rated for 7500 Vpk isolation voltage — this is a peak test rating, not a continuous working voltage. For reinforced or basic isolation designs, the working voltage must be derated per the safety standard applied (UL 1577, IEC 60747-5-5). The 1-channel DC-input phototransistor output provides a 100% minimum current transfer ratio at 10 mA forward current. Turn-on and turn-off times are 2 µs typical each, which sets the practical data rate ceiling below 250 kbps in most coupling circuits.
6-SMD Gull Wing — surface-mount footprint
Housed in a 6-SMD Gull Wing package (supplier device package 6-SMD), the 4N37FVM is a surface-mount variant of the through-hole 4N37. The Gull Wing leads reduce board-level stress during thermal cycling compared to J-bend or leadless packages. Operating temperature spans -55°C to 100°C, covering industrial and most military-grade ambient ranges.