Hi there,
Can anyone tell me the difference between the L 293 chip and the PBL 3717 chip? And are they interchangable?
Thanks
Tony

Hi Tony,

Although they both perform a similar function they are not interchangeable. The 3717 is essentially a single phase device and you would need two chips to drive one bipolar motor. Although they are OK for printers and scanners etc neither are really suitable for CNC use because the drive current is just not sufficient. (Most bipolar stepper motors require a minimum 24 Volts at 2 Amps to provide sufficient torque to drive a CNC). There are better Stepper Motor chips available – take a look at the Alegro range for starters.  http://www.allegromicro.com/en/Products/Categories/ICs/motor.asp

Tweakie.

Hi Tony,

Although they both perform a similar function they are not interchangeable. The 3717 is essentially a single phase device and you would need two chips to drive one bipolar motor. Although they are OK for printers and scanners etc neither are really suitable for CNC use because the drive current is just not sufficient. (Most bipolar stepper motors require a minimum 24 Volts at 2 Amps to provide sufficient torque to drive a CNC). There are better Stepper Motor chips available – take a look at the Alegro range for starters.  http://www.allegromicro.com/en/Products/Categories/ICs/motor.asp

Tweakie.

Or, better still, look at the Toshiba TB6560HQ.  They are much higher performance than the Allegro, and much more robust.  I've blown up several of the Allegros.  And, even at their best, the 30V/2.5A limits are rather, well, limiting...

Regards,
Ray L.

Ray,

You can blow up anything if you operate it outside the manufacturers specification. Blowing up several Alegro's could be classed as careless. 

Tweakie.

Thanks very much, that is very usefull information.

I have a schematic for a driver which I got out of a CNC Robotics book, but I am not convinced it is the best one for running a CNC.
Does anyone have a good design that they wouldnt mind sharing. I would like ideally to micro step. I am really new at this electronic stuff, but am learning fast!

Tony,

Personally, I would rather buy a ready made, multi-axis, controller board but there is nothing wrong with building your own if you can (certainly learn a lot more by building your own).
Here are a few websites you may like to check out and as one leads to more there could be a lot of browsing here.

http://www.fromorbit.com/projects/picstep/index.php
http://www.edingcnc.com/index.php?pagina=8_download
http://www.embeddedtronics.com/
http://www.pminmo.com/
http://store.qkits.com/moreinfo.cfm/QK179

Good fortune with your project,

Tweakie.

Thanks Tweakie

Ray,

You can blow up anything if you operate it outside the manufacturers specification. Blowing up several Alegro's could be classed as careless. 

Tweakie.

Tweakie,

Twice, after operating perfectly for years, one of my three 3977s went up in smoke in the middle of a job.  Not doing anything it hadn't done 1000 times.  The problem is the 3977 has virtually no self-protection against even the briefest transients.  Other drivers, like the Toshiba, and Geckos, are FAR better at protecting themselves against unavoidable transients.  Search on Xylotex, which also uses the 4977, and see how many others have had the exact same thing happen.  I was operating well below rated voltage and current limits, and well heat-sinked.  I don't know why they died, but they did.  And when they do, they typically take out the PCB and several other components as well.

Regards,
Ray L.

Ray,

The Xylotex boards, particularly within their enclosures are not exactly renown for their reliability. Whether this is due to the chip or the design of the board would be a difficult call but I get your point - the more robust the chip the better.

Tweakie.