I am working with my first project using stepper motors. I am currently using three used motors of unknown torque spec. 12v 0.16amp 1.8degree 5 wire unipolar. I need more torque than I can get out of these motors and want to switch to a higher torque motor. I am driving them with three uln2004a npn arrays. This array has a current max of 500ma per driver. Most of the motors I am looking at have an amperage of .68 to 5 amp. Is there another transistor array I could use that handles these kind of amperages and preferably comes in dip form?
The problem with using a transistor array at high currents is power dissipation, especially if the transistors are darlingtons. You'd be better off using a mosfet array. See for example HTTP 301 This page has been moved (although I haven't yet found a distributor that stocks that part).
If you are looking at high current bipolar motors, perhaps you want to get an efficient PWM bipolar driver? There are several around, the Pololu A4983 one looks pretty cheap for its spec and does microstepping too...
I am using unipolar motors for ease of wiring programing and the transistor arrays that i have used to drive them thus far (uln2004a) are cheaper than H-bridges arduino tutorials recommend (sn754410ne). I don't mean to be cheap but I have been using these in sculptures that typically use several motors and hence several drivers.