2-channel Darlington optocoupler with 5000 Vrms isolation
The HCPL2731SM is a 2-channel Darlington-output optocoupler from onsemi, designed for isolating logic signals across a 5000 Vrms barrier. Each channel switches a Darlington pair that can sink up to 60 mA at 18 V, driven by a DC LED input at 1.3 V typical forward voltage. The minimum current transfer ratio of 500% at 1.6 mA forward current means the output can drive a logic gate or relay coil directly from a low-power microcontroller pin — the Darlington gain handles the load without an external transistor.
Surface-mount package and rework considerations
Housed in an 8-SMD Gull Wing package (8-SMD), the leads are exposed and easy to inspect after reflow. The Gull Wing profile lifts the body off the board, so cleaning flux from under the part is straightforward — no hidden solder balls to trap contamination. The part reworks cleanly with hot air at 260°C for 10 seconds; the leads wet quickly with standard SnPb or SAC305 paste.