Datasheet for the ULN2004, a seven-channel Darlington transistor array with built-in clamp diodes, part of the ULN200x family used to drive relays, solenoids, lamps and stepper motors. This small 64.8 KB PDF gives the pinout, input resistor configuration suited to 6 to 15 V logic, current ratings and switching data. Technicians use it to check outputs, the common diode pin and supply connections when loads fail to switch. Note the ULN2003 has a different input resistor for 5 V logic.
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