Actions
Forum Thread Details
  • State Not Answered
  • Replies 16 replies
  • Subscribers 289 subscribers
  • Views 4388 views
  • Users 0 members are here
Related

Linear or Switch Mode Power supply for PWM Driven Stepper Motors?

Catwell

I used to use linear power supplies for all my motor control applications. Stepper and servo drivers were all fed with raw linear power. However, recently I have switched to less expensive switching power supplies for the same application. Although I have not seen any performance drop in the motors, I am wondering if I should still stick with a linear supply.


So, to all the motor drive designers out there, is there any real problems with using a switching supply? Would I get smoother motor commutation going linear?


For those who want to know, I am driving 2.1 - 3A per phase stepper motors at 36V. The power supply I am now using supplies switch mode regulated power of 36V at up to 8.8A (350W).


Cabe

  • 0 in reply to D_Hersey

    Thanks for the detailed answer.

     

    Picture is not loading here ...

  • 0

    If the sense resistor is one ohm, about one ampere of current should flow through the load.

     

    Faster version:

     

    image

  • 0 in reply to D_Hersey

    Wow... this was an old question.

     

    Glad to finally get some answers! Keep it up!

     

    Cabe

  • 0

    The simplest way to get this done is just to insert some dropping resistors and scale up the supply.  Most of my stepping motors are in the attic, the rest are arrayed around here.  My machine shop is currently being run by my son in Portland Or.  BTW, he has a job, but it isn't that good.  He just got his master's in statistical bio, knows his drops/RF, math/physics, good programmer and writer.  So if anyone knows of anything out that way. . .

     

    So, I will have to make up some numbers for completeness.  Remember though, that their etiology is roughly from my office chair.  Let's say that we have a 5V motor with a 1.2@ coil.  We'll reckon the ESL of the coil to be about H/10, if we need to talk reactance.  If we have a unipolar supply, we will have to run four coils.  Really two cores with counter-wound coils.  The effect magnetically is as though we had two coils that we could push-pull.  The resistance of our coil is (R=V/I) 4 1/6 ohms.  Using standard resistor values, we could, instead of naively using the nominal 5V to power the motor coils, use a twelve volt supply and 5.6 ohm dropping resistors.  Statically, the resistors would be consuming a little more power than the motor, the ratio of their resistances, seeing that current through them is the same.  Dynamically, however we would see some improvements.  We would be less prone to stalling.  We would be less prone to resonating, a situation in which the motor doesn't really turn.  Adding mechanical resistance helps with resonance as well.  Our motor would stop whining and start humming.  Our top speed would be higher.  One neat thing would be that we could split the dropping resistors and put the clamp between them.  With HV enough Qs this will be survivable, and my motor rotor wont 'knuckle under' the moment it is de-energised.

     

    Adding the linear CCS that I have drawn would not help the thermal picture, the dissipation that was in the resistors would now be in the power Qs is all.

     

    However, if I added a window comparator and maybe a latch, and operated the power Q in saturation mode, things would get ripply, but efficiency would be clearly benefited.  A chopper is to a CCS as a SMPS is to a linear supply.

  • 0

    Hi

    To control the initial current in the flyback,DCM. is it better to increase the number of revolutions and frequencies relatively or to limit the duty cycle?

  • 0 in reply to Jeniva

    You have added a comment to an 8 year old thread.

    It would be a good idea to start a new thread and explain your question with a lot more detail and background.

    Diagrams and pictures will help.

    MK