Quad Darlington array for medium-current switched loads
The STMicroelectronics ULN2068B integrates four NPN Darlington pairs in a single 16-PowerDIP through-hole package, each rated for a continuous collector current of 1.75 A and a collector-emitter breakdown voltage of 50 V. Each channel includes the base resistor and a clamp diode for inductive flyback, so a relay, solenoid, or stepper-motor winding connects directly between the output and the supply rail without an external catch diode. The 1.4 V maximum saturation voltage at 1.25 A (2 mA base drive) sets the per-channel conduction loss — at full load that is about 2.2 W total across four channels, which the PowerDIP's leadframe and the PCB copper must sink.
1.75 A per channel — where the current rating lands
The 1.75 A maximum collector current per Darlington is the absolute ceiling at 25°C case temperature; the practical continuous current in a 85°C ambient, still-air environment is lower because the 1 W package power limit and the junction-to-ambient thermal path through the 16 leads set the real derating. For a 12 V relay bank pulling 500 mA per coil, the ULN2068B runs with 2.8 V of headroom and about 0.7 W total dissipation — well within the thermal budget. For a 24 V solenoid at 1.2 A, the 1.4 V saturation drop leaves 22.6 V across the load and dissipates 1.68 W per channel, which requires airflow or a heatsink on the PowerDIP body.
Through-hole PowerDIP — board integration note
The 16-PowerDIP (0.300-inch row spacing, 7.62 mm body width) is a through-hole package intended for wave-solder assembly or manual insertion in prototype runs. The 20 mm × 7.10 mm body has staggered lead exits that increase the copper cross-section from the die to the PCB pad, improving thermal conduction compared to a standard DIP-16. For best thermal performance, connect all GND pins (pins 9 and 10) to a continuous ground plane with wide traces, and avoid routing sensitive analog signals under the package — the Darlington outputs switch inductive loads and couple switching noise into the substrate.
The base product number ULN2068 covers the full family including the A and B suffix variants.