Help with driver interfacing

Hey guys/gals, need some help here. I was hoping that someone here has used an ic out of the uln2803a (uln2801,2,3,4 or 5). I am confused beyond belief by this chip.

Basically what I am trying to do is use a Microchip PIC18f4331 to drive stepper motors. These stepper motors are power hogs (require 12V @ 500 mA) to operate correctly. My issue is this. I have the pic sending the stepping signal to a stepper motor via a uln2803a driver IC. However, I am getting no where the 12v @ 500 mA. I was wondering if anyone had encountered this issue, and how I might go about trying to resolve this problem. The constraints that I have to work with however are the fact that this system must be portable, and thus uses a battery to power the system. I have a 12V @ 7Ahour battery, so the power isn't an issue, this IC is however.

If I haven't explained it well enough, then ask whatever I oversaw.

Thanks
Joel

The uln2803 may not be good enough as it has a maximum continuous collector current rating of 500ma.

Could you use a L293D instead? it has a slightly better current rating.
Or the L298, it has a 4A rating.

I could use either of these, supposedly. I took a look at the data sheet for the l298, and I must say that it looks like a great candidate. Just a couple of questions for you (or anyone else that wants to answer) the current sensing on A and B, I am not sure that I understand. I know that I need 0.5A per phase (btw, can someone explain to me what this means), and I am not sure what kind of resistor ranges I am looking at for that.

Overall, I must say that it looks great, however it (unless I am mistaken) will not provide me with the 12V @ 0.5A/phase that I require. Are there other options possibly?

Thanks
Joel

Some important info I left out, the motors are unipolar. Thus the h bridge idea is out. Any other ideas? I have looked into a sk3180 and a 7407 for buffering. I am not sure if this will work, so any help is greatly appreciated.

Joel

Why not just drive it directly using FETS with adequate flyback diodes? The software overhead for driving the stepper sequence is not that complicated, and using PWM to help generate it you can micro step the motor if wanted.