I've read a bit about this but there seems to be much ambiguity. When using common cathode seven segment display LEDs would you use NPN or PNP? Or can you use either?
When using common cathode 7 segment leds, you need a NPN type to drive the common cathode to GND. The P base must be driven P(ositive) with a series resistor.
Edit: I misunderstood your question. Please see Long Phams answer and drawings. Although he did not mention the common cathode. This must be connected to GND.