The ULN2803 is high-voltage, high-current darlington driver IC composed of 8 NPN darlington pairs. All units share the emitter in common, and each unit adopts open-collector output. A 2.7KΩ resistor is connected to each darlington pair in serial, which is compatible with TTL and 5V CMOS for data processing without logic buffer. 

Sink current of ULN2803 is up to 500mA, when it is off state, the withstand voltage is 50V and the output can runs with high load current, which provides solutions for various interface.