Servo - February 2008

Building a

STEPPER MOTOR

CONTROLLER Part 1

by Fred Eady

That figures as for the past six months, I’ve been working on an embedded project that is dependent upon the motion provided by the shaft of a stepper motor. So, it would be an understatement to say that I’ve been heads down in the design and implementation phases of deploying the embedded motor control application I’ve been sleeping with for the past six months.

Along the way, I’ve had the opportunity to build up and test various stepper motor control circuits. I’m on the verge of building up yet another stepper motor controller that is based on the STMicroelectronics L6208, which is

a single-IC DMOS driver for bipolar stepper motors. The L6208 can be had in a trio of packages: PowerDIP24, PowerSO36 and SO24. I’ve selected the PowerSO36 package and if you would like to see how this project comes out, keep reading, my friend.

The STMicroelectronics L6208

A close friend of mine owns and operates a machine shop, which contains a multitude of large lathes and milling machines. I can recall walking into his shop one afternoon to find him pouring over a very large piece of electrical gear.

PHOTO 1. This over and under shot gives you a total physical view of the L6208PD. The L6208PD’s heatsink tab runs the length of the bipolar stepper motor driver IC. I’m always thinking of the reader (that’s you) and with this type of package, I’d better make the project easy to build and reliable as lifting a toasted L6208PD from its printed circuit board heatsink pad won’t be any fun at all.

Between his cussing and swearing, I concluded that the large collection of very large electronic components he was working on was part of one of his mills. When I asked him just what the problem was and what he was working on, he explained to me that this particular mill’s stepper motor had seemed to fail.

Obviously, the easy thing to do in this situation is replace the stepper motor before looking elsewhere for the problem. So, he had already swapped out the stepper motor with no joy by the time I had gotten there. Mind you, the stepper motor in the failing mill was quite large. With the stepper motor out of the failure loop, the next logical place to check was the mill’s power supply. According to my buddy, every voltage was present and accounted for. Thus, my machine-head friend was troubleshooting the stepper motor driver electronics when I arrived.

To this day, I envy his courage and adventurous spirit as I would have NEVER removed that massive collection of high-voltage, high-wattage transformers, resistors, and capacitors. Although most of the sensitive control electronics were stuffed onto printed circuit boards, the bulk of the stepper motor driver consisted of large high-voltage/high-amperage electronic components.