The ULN2003 is a high voltage, high current array containing seven open collector pairs with common emitters. Each channel rated at 500 mA and can withstand peak currents of 600 mA. Suppression diodes are included for inductive load driving and the inputs are pinned opposite the outputs to simplify board layout.
These useful chips allow you to drive high current loads like relays and motors which require more power than a microcontroller can supply or sink. A high voltage (5V) on an input pin will turn on the pair transistor pulling down the output pin. The load goes between the output pin and the load supply voltage which can be up to 50V. This makes them great for controlling 12V relays, electric motors, unipolar stepper motors and other high voltage or high current loads. Outputs can be connected in parallel to allow higher current loads.
Note: Although this is specified as a 5V chip, it works fine at 3.3V although max output current will be reduced to at max 300mA
Connection to Load
The load connection goes between an output pin and a load supply (max 50V)