stepper motor driver circuit

[ali shaheen]

hello

i have two stepper motors which i am using in my project...both are from the manufacturer "VEXTA" ...the problem is this that i want a driving IC or a circuit from which I can be able to drive these motors.......I had used ULn2003a but it only can provide 500ma/phase....also i had used transistors HSD313 (its capable of ataining 3Amp ) but of no use....I am using the power supply of personal computer......please help...................

thanks
best regards
ALI SHAHEEN

 

[Reloadron]

Beyond VEXTA you don't mention a model number or the actual current required. That will make if difficult for anyone to suggest a solution.

Ron

 

[4pyros]

What are you trying to control these with??

 

[4pyros]

I had used ULn2003a

Can you post a schematic?

 

[ali shaheen]

hello


the schematic is attached....Its a rough schematic...I had used DARLINGTONS HSD313 (its 3A ) my steppers are working fine but......not giving me the perfect or strong torque....I hope that might be the problem of power supply...but I am using 800w computer power supply....................I hope I had made my self clear....and yes I am using these heavy stepper motors of 1.6A and the second one is 2A stepper motors the are my requirements of my project......

regards
ALI SHAHEEN

 

[ali shaheen]

but there is a problem I am still getting that is I am not getting the full torque from the stepper motors.....I think it due to the power supply.....hey do you know which two wires are shorted in power supply to make it work out from the PC......I had shorted the GREEN AND BLACK one...It is giving me perfect 5v and 12V but the motors is having the holding torque of what it is specified.......

 

[4pyros]

**You need high speed diodes on your motor lines to protect the DARLINGTONS you may have already damaged them.**
What voltage motors are thay? Thay could be 24 volt motors.
Did you cheak the voltage output of the power supply with the motors running?
Have you looked into using controler chips like the L297 and L298 combo?
Andy

 

[Grossel]

Why have you added a DC supply between A and B to the steppers?

The whole schematic seems wrong. I cannot see any paths the current through the stepper can go from positive voltage supply to ground.

All you need is eight transistor. All emitters grounded, aresistor on their base and connect all stepper wires to each transistors collector. You might choose to use the darlington.
Further on, running 12V on a stepper on low speed will probably cause the stepper to overheat. You then might consider getting a couple of PNP transistors so you can switch between heavy duty mode for high torque and high rpm (12V) and economy mode (5V) for slow rpm and less torq.

 

[4pyros]

Why have you added a DC supply between A and B to the steppers?

I missed that! Thay are 6 wire steppers, A and B should go to ground and dont forget the diodes. Andy

 

[shortbus=]

They are wired as unipolar steppers,but still wrong. 'A' and 'B' should be wired to a positive voltage supply. The '1' '2' '3' and
'4' wires should be hooked to the darlingtons and fed to ground when the darlington is conducting, not to a positive voltage. They still need the diodes though.

Steppers are normally not used at their name plate voltages. They are used at up to about no more than 16 times the name plate voltage. Using them at nameplate voltage severely limits the torque and speed they operate at .

Check out this tutorial on steppers for more; Jones on Stepping Motors

 

[4pyros]

Shortbus +1,

They are wired as unipolar steppers,but still wrong. 'A' and 'B' should be wired to a positive voltage

Thanks for fixing my memory. Andy

 

[ali shaheen]

hello

first of all thank you all.
The diagram I had posted is wrong...I accept it....and the way i had used darlingtons on the board is in another way...that is....I had grounded all the emitters and collectors are connected to the motor terminals....and give the positive voltage to the motors supply wire...my motor is working fine but not giving me the maximum torque which I desperatly needed.....my motors are...1.6A vexta 1.8degree/step 5.7volts and the second one is 0.18degree/step 2Amp 12volt stepper motor from vexta......As i am providing the voltage directly to motors the coils inside them are excited to their max and max torque is what I get.....but when through the circuit..and microcontroller based board...those motors are not having a strong torque......I am stuck...should i use MOSFETS inteads of these darlingtons

regards
ALI SHAHEEN

 

[shortbus=]

As I said in my previous post the nameplate voltage is not the voltage you use to drive the motor.

The following is quote from this website; Stepper Motors Other sites give the same basic information.

"Speed and torque performance of the step motor is based on the flow of current from the driver to the motor winding. The factor that inhibits the flow, or limits the time it takes for the current to energize the winding, is known as inductance. The effects of inductance, most types of driver circuits are designed to supply a greater amount of voltage than the motor's rated voltage. The higher the output voltage from the driver, the higher the level of torque vs. speed. Generally, the driver output voltage (bus voltage) should be rated at 5 to 20 times higher than the motor voltage rating. In order to protect the motor from being damaged, the step motor drive should be current-limited to the step motor current rating"

Another thing is the type/size of the motor. The small single stack, round motors from a ink jet printers don't have much torque. The square NEMA double stack motors are much stronger. Vexta motors are usually pretty well documented. Google search the model number of your motor and find out the torque rating curve from the data sheet.

 

[4pyros]

ALI; Your torque will mainly be controled by the software timing. How do you know your PIC program is right? Andy

 

[ali shaheen]

hello

my program is right and there is no problem with it......I also tried to increase the time delay between the steps..but of no use....the holding torque is what I am not getting...i.e when the motor is in halt state......

regards
ALI SHAHEEN

 

[shortbus=]

hello

my program is right and there is no problem with it......I also tried to increase the time delay between the steps..but of no use....the holding torque is what I am not getting...i.e when the motor is in halt state......

regards
ALI SHAHEEN

Holding is done in a dedicated driver by keeping one coil of the motor active.

 

[4pyros]

the holding torque is what I am not getting...i.e when the motor is in halt state......

What voltage are the motors getting in this state?