L297 Controller for Unipolar Drives

[shahidmk]

Hi All,

I have been reading up all the contributions being made re chopper controllers for unipolar motors to my great benefit. I came across the following 8amp Unipolar chopper driver based on the L297 that I intend to build.

http://www.ifrance.com/mac1/PAP8A/Pap8aul/index.htm

Any comments!

all past, present and futur info is v. much appreciated.

thanks all..

mks

[pminmo]

I can't read french, but I can see how the 297 can be used as a sequencer for a unipolar or bipolar high power chopper.

Phil

[randyf1965]

http://translate.google.com/translat...language_tools

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[pminmo]

Looks like it's good to go, I'd build it.

Phil

[TigerPilot]

I'm wondering how would you micro step it lower then the half step option. If you want a simple driver look at this one. http://www.p5taylor.btinternet.co.uk/19.pdf. From one chip mentioned only a 1/4 is being used. If you make a 2 or 4 axis driver on one board you don't have to get an other.:-) I was thinking about doing it but gave up on it since I couldn't figure out how to micro step it. :-(

Yoram

[shahidmk]

Thanks for your input phil. I have started converting the schematic into a pcb layout that can be done using tone transfer method. It is hard work I must say. Will keep all posted with my progress.

Yoram: my need isn't for microstepping but for high current. I have progressed from TIP 122 based 4 phase circuits to 5804 circuits driving high current steppers. Where I live the cost of L297 is cheaper than 2 8ohm 20W power resistors hence the employement of current chopping ability of L297. Ideally it would be nice if I could have a current chopping circuit to replace the power resistors in the tip or the 5804 circuits. but my electronics isn't that brilliant that I can muster up such a circuit.

ta
MKS

[shahidmk]

HELP!!!!!!! I managed to build the L297 chopper circuit mentioned in the link. I couldn't get the IRLZ44 here so I replaced it with the IRF510, but there is a problem.

In the test setup, the motor does not rotate and the Mosfets are getting really really really HOT. I have checked the board with the schematics time and time again and cannot find the fault!.. I have traced the signals using a digi V meter and can pick up the pulses generated by the L297 all the way to the end of the 7409.

Any suggestions the direction I should be taking!

Thanks..

MKS

P.S. My motors are 5.2V 1.4A(per phase) 6 wire unipolars!!!!!

[pminmo]

For troubleshooting, pull the motor and put in some resistors that will have a lower current. Your FETS shouldn't be getting real hot, but without a heatsink they will be hot to the touch. Did you build it on a pcb? The 510 isn't as good of a choice as the IRLZ44 for two reasons, the LZ44 has a much lower on resistance show your heat issue won't be as much, but more importantly the gate turn on voltage is lower, more compatable with the 5V logic. Are you getting a low voltage across the current sense resistors r7 and r8?

Phil

[shahidmk]

Phil,

Thanks for your suggestions.

I got the driver hooked upto 5V 8amp PSU. As I am using 0.5ohm 5W sense resistors I set the V ref to .6V. there is humming in the motor but the FETs are still getting v v hot. I am looking for IRLZ44s as soon as I get them I will change over. In the mean time I made a 4 phase driver based on the IRF510 that seems to work. When I connect the 4phase set up to the 7409 it starts getting hot again.

a basic L297 set up without the chopper enabled seems to drive the unipolars ok. but mixing them with the FET gets problamatic....

on the sense resistors I am getting around 0.7 volts......

I do have 4 sla7062s to play with but the difference in total cost of L297 based chopper circuit is coming to USD5.00 for me while the SLA7062 alone is costing 6.50 and is on back order for a month.....!!!!

where to next!!!!!

ta
MKS

P.S. the driver is made on a PCB through toner transfer method...

[pminmo]

how did you connect your 4 phase driver to the 7409's? The commons of the 4 phase would need to go to the appropriate current sense resistor. But you are playing around the point of my concern. By having .7V across that sense resistor, if your 5V is 5V you have a maximum gate to source voltage of 4.3, and that is marginal. Do your fets get hot when u disable the chopping?

Phil

[shahidmk]

Hi phil,
I wasn,t working on the board for a while, I got back to it last night. I am using Turbocnc as the software to test the setup. Last night I changed the pulse width in TCNC to 0!. The motor started spining (what I found was changing the pulse rate in tcnc had no effect on the motor performance). The fet still gets hot. I cannot replase the irf510 with the ilrz as those are not available here at all. The chopping seems to work as well. 5V was the test setup. Today I set up 24V and the board worked. I haven't changed any of the hardware and also have left the V ref at 0.6V. according to TCNC I am running at 35 ipm. If I increase the pulsewidth the motor slows down!! Disabling the chopping stops the FET from getting hot but the motor startes getting warm !. I am baffled...

Ta
MKS

p.s. thanks for patience in coping with my ignorance....

[pminmo]

how fast is your computer? are you running from windows (dos window) or dos with no windows loaded?

Phil