Eight Darlington pairs in a DIP — the workhorse relay driver
The ULN2803ANG4 is an 8-channel NPN Darlington transistor array from Texas Instruments, packaged in a through-hole 18-DIP (0.300", 7.62 mm body). Each pair can sink 500 mA continuous with a collector-emitter breakdown of 50 V, and the saturation voltage is held to 1.6 V max at 350 mA load — tight enough to keep a 12 V relay coil fully energised without excessive heat in the package.
The 500 mA per-channel limit is per Darlington, not per package — if you drive all eight channels at 350 mA, the total die dissipation is 8 × 1.6 V × 0.35 A ≈ 4.5 W, which the DIP can handle with adequate copper on the board or a socket with airflow. The 50 V Vceo gives headroom for 24 V industrial loads and snubbing transients; stay below 40 V steady-state if you want margin on the avalanche rating. Operating temperature spans -40 to 85 °C, so this array is comfortable in motor-drive cabinets, outdoor telecom pedestals, and factory-floor panels where the ambient can swing. The 18-PDIP body is socket-friendly — a turned-pin socket makes field replacement straightforward if a channel fails shorted.
Expect last-time-buy pricing on remaining stock; no further factory orders are being accepted.