Can you parallel the transistors in ULN2003?
As you now realise, you can parallel them rather than "cascade" them.







simulate this circuit &ndash; Schematic created using CircuitLab

Since transistors have a negative temperature coefficient of VCE (collector to emitter voltage) when on if one starts to run hot it will hog the current from the other, thereby getting hotter, etc., until it is destroyed.

The simplest way to prevent this is to add, say, 0.5 &Omega; series resistance to the collector (output) of each. That way if one starts to hog the current the voltage drop across its resistor will rise and limit the current.

Also, take care of the maximum current for the whole chip which, from memory, is 1.5 A. Remember that it all has to go through a tiny gold wire and out one little pin in the corner of the package!