L297/298 - Will it drive these?

[Micro_CNC]

So this is whats happening....
I currently have a 5 pound block of PCB that was full of 2N3055's, buffers, amps and L297 chips for controlling my 3-Axis machine. Well, at least half of the 2N3055's have blown since its conception and it struggles just to rotate the motors now. The power supply went with it.

So I have been looking to rebuild the drives with a L297/298 combo per stepper. My question is, will L298's drive these motors and if so what component values will I need to utilize for current sensing/chopper? If a L298 can't drive one of these motors can I put L298's in parallel for more amps? I am using the reference schematic from the L297/298 data sheets.

Schematic in here - L298
http://www.st.com/stonline/books/pdf/docs/1773.pdf

The X and Y are Identical bipolar steppers
----2.5A per Phase
----Insulation Class B
----Made by Minebea
----They just get warm to the touch at 12V
----1.1 ohm per phase (measured - not labeled)

The Z is also a bipolar stepper
----2.8A
----1.8V(I've been running at 12 and they are cool to the touch)
----Insulation Class B
----Made by Superior Electric
----0.95 ohm per phase (measured - not labeled)

I plan on running the machine at 5 volts for the next month or so then change it over to 12V, reason being I have a 17A 5V supply at hand and the motors seem to have enough power (wired straight to the 5V source) for my uses and I will have enough spare cash in a month for a proper 12V 50A source. Right now my only 12V source peaks at 4.5A. both the 17A-5V and the 4.5A-12V supplies are regulated.

I would love to get Geckos and proper steppers etc. in the future but I cannot afford them now. I only have enough $$$ to build a controller from parts right now. I only need full stepping it is a very basic robust machine I only need the axis to receive the step/direction signals and move in full step accordingly. I'm pretty sure I will need the chopper drive functional to prevent the 298 from overheating but I may be wrong. I'm using EMC2 through the parallel port if that is of interest.

Thank you in advance.

[Tim Tanner]

Hi,

Yes you can parallel up L298's even if current chopping is used. A pair of L298's is good for about 3.5A/phase.

You can use one L298 per winding as per Fig. 7 or just connect every pin on one L298 to every pin on the other L298. I have successfully paralleled three L298's using the second method.

Don't forget to uprate the diodes in the bridge too. I guess you can salvage these from your existing design?

You certainly will need chopper drive if you are using a 12V supply.

Regards,

Tim.

[Micro_CNC]

Does anyone have a link to a thorough description / formulas regarding how chopper drives work? Are they PWM with a carrier wave or are they voltage based? I'd like to be able to figure out what values I need for my passives that set how the chopper functions.

Can the L297's supply enough current to drive multiple L298's or would I need to put some type of preamp between them (3904/3906's)?

So the diode is equal to the max current the drive can supply? 2A on one L298, 4A on two L298, etc..

Also, I trust my wiring and have been designing/building digital electronic devices for years - very little motor control though, should I run a buffer between the machine and the computer for other reasons such as voltage spikes or are they few and far between?

No, I can't salvage anything but the L297's from the old drive, That is the last time I will use an unregulated supply too. For some reason I got a spike or something which just killed it. The L297's were being powered off the parallel port then they connected to the actual drives through optoisolators. Everything else in it is split open, has melted leads, or is at least partially melted - It was quite spectacular to watch, It was like a couple of firecrackers together.

Regards,
Matt