uln2003 driver vs uln2003

I bought several stepper motors 28byj-48 which has amazing thread on them : http://forum.arduino.cc/index.php?topic=85335.0

To drive the motor everyone use the uln2003 driver, but I have just the uln2003 (only the chip). How can I drive the motor using the chip, the uln2003 chip as far as I know is just a sink.

That chip is just a bunch of darlington transistors with back-EMF diodes. The first picture of google images shows the chip connected to a stepper motor. Leo..

See the schematic on this site how the motor is connected to the driver.


Hi larryD and Wawa Thank you for your answer.

If i understand correctly there is one common positive pin, and 4 pins that are sinks.

Now I'm trying to understand how the uln2003 works, I looked at this : |500x347

Why do they need the "COM" pin ? Current will never flow there because of the diode

It will as it switches off an inductive load.

The ‘com’ pin 9 connects to the motor + supply.
These internal diodes are used for snubbing inductive kickback from the motor coils.

Refer to the schematic in the link I gave.


The "com" pin is also usable as a "lamp test".

so the uln sinks when the in pin is low, right ?

Current flow: +motor supply ------ motor coil in ------- motor coil out -------- ULN2003 pin (collector) -------- GND.

So yes, the ULN transistor sinks the motor current to GND. Low side switch.


tautau123: so the uln sinks when the in pin is low, right ?

No it sinks current when the input pin is high.