The difference between the two types is that resistors of different values are placed at their inputs.
In the ULN2003, the we find a 2,700 Ω resistor, matching the characteristics of the IC with TTL logic. In the ULN2004, the resistors at the input of each stage are 10.5 kΩ units, matching its characteristics with CMOS logic.
The circuit in Figure 1 shows how the ULN2002/3 can be used to drive a stepper motor using up to 500 mA. This IC doesn’t need a heat sink and can be powered with voltages up to 12 V.
Figure 1 – Using the ULN2002/2003
