Step motor driver IC advice

Discussion in 'General Electronics Chat' started by geoffers, Jan 10, 2013.

  1. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Hi all,
    I was hoping I could get some advice on step motor driver IC's. I've a bipolar stepper motor I need to drive for a project I'm working on, I've built a driver using a l297/298 combination. However its not in my opinion very good! I've had a quick look at the rs site and see there are several driver chips out there for less money and board space! Has anyone got a opinion on the best one to use? My motor needs 1.5A per phase and a chopper drive (that maybe standard, I'm new to steppers).
    Thanks Geoff
     
  2. Gibson486

    Member

    Jul 20, 2012
    199
    12
    1.5A per phase? That is a pretty big stepper. There is no best chip. it depends on your needs. L293 is what I have used and a vendor told me to use the Allegro 3966, but i got it to work with the L293, so I did not bother with the other chip. that said, these chips are rated for 600mA. In your case, I'd just make my own H bridge circuit drivers with something like a BTN7960. In the end, it is all the same concept. You drive your motor from low current logic signals by using high power transistors. chopper drive is a more special case, but is still the same in terms of getting it to move.
     
    Last edited: Jan 10, 2013
  3. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Thanks for the reply, yep tis a pretty big stepper, runs a little pump. I've had a look at the allegro, shame about the current rating! I was hoping I could use a single chip driver/h-bridge to keep board space down. I think I do need chopper driver to get enough power out (or into!) the motor. I found this on rs, http://uk.rs-online.com/web/p/motor-driver-ics/7264037/
    What do folks think of it? Anyone used it? Its rated to 2.5A and although theres no mention of chopper drive on the datasheet it does have pwm on it and sense resistors so I guess that means chopper drive? Please correct me if I'm wrong?
    Thanks Geoff
     
  4. BReeves

    Member

    Nov 24, 2012
    412
    64
    Google SLA7026M

    It will do what you are asking..
     
  5. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Thanks,
    I had a look at that, it looks like thats for a unipolar stepper motor though? I have a bipolar. I know you can drive a unipolar with bipolar drive by ignoring the centre tap, is there a 'dodge' the other way? As I understand it the unipolar driver doesnt reverse polarity over its outputs?
    Cheers Geoff
     
  6. Gibson486

    Member

    Jul 20, 2012
    199
    12
    chopper method just exploits the inductors on the stepper. The equation for an inductor is v = L di/dt. If you send a fast pulse to an inductive load, the di/dt has to compensate. So effectively, you are just sending it a current pulse instead of a voltage pulse, On the non chopper method, you send it a constant voltage.

    Also, unipolar is just the method of the stepper. With uniploar, current goes in the direction of whatever branch you pick (polarity is fixed). With Bipolar, you dictate the direction of the current by controlling the polarity yourself (ie H bridge).
     
  7. BReeves

    Member

    Nov 24, 2012
    412
    64
    Sorry missed that bit of info, everything I have ever messed with has been unipolar.
     
  8. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Is the idea of the chopper also that you can use a higher driver voltage that the motor is rated for so the current rises faster than it would at a lower voltage then 'chop' it when the current sensing detects the current is at its max. Therefore giving more power for a given step pulse? I want to make sure I've got it clear in my head! The spec for my pump states it needs a chopper drive I guess a normal 5v drive would not deliver enough power?
    Thanks Geoff
     
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