arduino - stepper motor - ULN2803 - zener diode

Can anyone help with this...

I have a 3.15v stepper motor, and a ULN2803 Darlington Array. The motor is rated as 1 amp per phase at 3.15 Ohms per phase (Sanyo Denki 103H546-0440).

I have parralleled the inputs to the ULN2803 and I am currently driving the stepper with 6 volts. It works fine except... Pin 10 of the ULN2803 is marked as 'common free-wheeling diode'. At the moment I am just running 6 volts straight in to this Pin (although if I take that out it doesn't seem to affect the operation of the stepper - but then it might be being driver direct from the Arduino pins). I am not using a Zener Diode. I understand that I should really use a zener diode to protect the ULN 2803 (and Arduino?) from 'back EMF'.

My question: Do I need a zener diode? What sort of zener diode do I need?

Many thanks,



you don;t need a zener- the freewheeling diode(s) in the ULN2803 are there to clamp the motor noise/reverse current. Sounds like you have it wired correctly from what you say- just connect the +6 to the "common freewheeling diode".



sorry, i forgot to reply. thanks very much for your answer. very helpful.