Logic and the MC33033 motor driver

Discussion in 'General Electronics Chat' started by shortbus, Nov 27, 2012.

  1. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    I have a different application I'm want to try for the MC33033 BLDC motor driver, and would like some input on the logic input.

    The driver is expecting input from three Hall sensors to signal the commutation of the motor stator. The original use of the chip is to make a bi-polarity shift to the stator coils also.

    What I need is a uni -polar output from the chip, for a switch reluctance motor (SRM).

    In the BLDC use the chip is expecting in put from the Hall's as follows -
    100 - 110 - 111 - 011 - 001 - 000 A six step commutation of the stator coils results from this.

    In the SRM, it only needs a three step commutation -
    100 - 110 - 111

    My question is, is there going to be a problem with the chip logic only receiving three of the expected signals and repeating? Instead of getting all six signals and repeating.

    The data sheet for the MC33033 and page 11 from the data sheet that shows the logic truth tables. The 60 degree logic is the one I would use. Thank you for any input.
     
  2. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    No logic experts? Need more details?
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    I haven't checked the IC or it's PDF, but it sounds like you need a unipolar driver for a 3 coil SRM?

    It would be very simple to use 3 FETs to drive the 3 coils unipolar, and you can use any logic circuit microcontroller etc you like to drive those 3 coils.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    1. About the output drivers, you can use PNP transistors, it shows on page 15.
    2. You also can use the P channel MOSFET to be the drivers.
    3. The page 16 shows :
    Figure 35. Three Phase, Six Step, Full Wave Commutation Waveforms
    Rotor Electrical Position (Degrees)

    So, if you only using three steps, the waveforms shows that rotating 180 degrees, you can try it, what will it happen if you start over from 100.
     
  5. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    RB, I keep coming across things that knowledge of microcontrollers are the way to go. But at 65yrs old and after two small strokes it's really hard to learn on your own.

    I had thought about using a Johnson counter with the Hall outputs but then I found the MC33033 and MC33035 chips and thought I could adapt them to my project.

    The Hall out puts are needed sense the rotor position. This is to get full power from the motor.

    Thanks for your input!
     
  6. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    Scott, The difference between the stators in a BLDC and SRM, make the need for a repeating sequence of 3. A BLDC has a distributed winding, like a induction motor. A SRM has a concentrated/salient pole winding.

    Another difference is the BLDC uses a bipolar or reversing voltage, kind of like a square wave AC. The SRM is unipolar DC voltage square wave. Instead of the "three phase full wave commutation", the "three phase half-wave commutation" is closer to my needs.

    I guess I'll have to rig up a test/simulator rig to check out what happens when I use only three of the six steps. I'm much better at the mechanical part of things than the electronic.

    Thank you for the response to my question.
     
Loading...