1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

PWM controller

Discussion in 'Electronic Projects' started by Dr.EM, Jun 3, 2006.

Thread Status:
Not open for further replies.
  1. Someone Electro

    Someone Electro New Member

    Joined:
    Sep 10, 2003
    Messages:
    2,579
    Likes:
    2
    Location:
    A boring village in Europe (slovene)
    Thats what basicly makes DC motors lose tork at high speeds.The inductance of there coil.

    I dont see how higher frq. are more eficent anyway. I know that 500Hz is more eficent then 50Hz in AC motors.
     
  2. Dr.EM

    Dr.EM New Member

    Joined:
    Oct 27, 2004
    Messages:
    1,009
    Likes:
    1
    Location:
    UK
    Yeah, I made the mistake of touching a clamping diode after a few seconds of use and it was burning hot. That was a 6A one, so it really needs a bigger one (the practical solution would be a 10A TO220 diode I think, heatsinked).

    I tried both the 120Hz and 3Khz frequencies on it and found the 3Khz to be more effective. For one thing, the 120Hz really was too loud, and it had the typical stalling on lower RPM. 3Khz gave perfectly good control, but like I say the whistling noise is irratating. After a while, you can hear the motor noise over it, and of course on full, it dissapears altogether.

    My attempt at hosting the video:

    http://media.putfile.com/Motor-PWM-control
     
  3. Someone Electro

    Someone Electro New Member

    Joined:
    Sep 10, 2003
    Messages:
    2,579
    Likes:
    2
    Location:
    A boring village in Europe (slovene)
    Ouch this motor give ot a lot of sound when PWM controled!

    If it has high enugh resistace try conecting this to a audio amp it would act as a speaker quite good.Hehe
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,585
    Likes:
    950
    Location:
    Canada, of course!

    Hi Dr. EM,
    I made a motor speed control very similar to yours for an electric powered model airplane. I also used a switching frequency of about 3kHz and it whistles loudly when 1st turned on then the air noise from the propeller drowns it out.
    I didn't use a diode across the motor, maybe I should for better efficiency. Instead I rely on the zener diode in the Mosfet to protect it by "wasting" the voltage spike when the controller switches off the current.
     
  6. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    audioguru, you're also falling into the all to common trap of believing the protection myth believed by many nubes, the diode isn't used for protection but for efficiency's sake.

    Another myth, it actually works better at higher frequenies as the self-inductance of the motor is enough to sustain the current flow through the diode in between pulses, think of it like an inductor in a SMPS.
    http://www.4qdtec.com/pwm-01.html
     
    Last edited: Jul 1, 2006
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,330
    Likes:
    653
    Location:
    Derbyshire, UK
    I did tests when I wrote my PIC PWM tutorial, trying different frequencies driving a 6V DC motor - in the end I settled on 2.5KHz, this gave the best performance - moving to 20KHz produced hardly any power at all.
     
  8. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    Interesting, possibly the diode wasn't switching fast enough.
     
  9. Someone Electro

    Someone Electro New Member

    Joined:
    Sep 10, 2003
    Messages:
    2,579
    Likes:
    2
    Location:
    A boring village in Europe (slovene)
    Then the diode would overheat.The inductance of the motor is restricing the curent flow a lot at such a high freq.
     
  10. Dr.EM

    Dr.EM New Member

    Joined:
    Oct 27, 2004
    Messages:
    1,009
    Likes:
    1
    Location:
    UK
    I tried this circuit at over 20Khz in prototyping and found it worked very poorly operating a small computer fan.
     
  11. antpsai

    antpsai New Member

    Joined:
    Mar 14, 2006
    Messages:
    5
    Likes:
    0
    Hi all. The terms like "efficiency" and "protection" applied to the diode across the motor in a PWM circuit are both correct and both misleading. Its like saying that the wheels in a car are there for efficiency (rolling) and protection (suspension?), yes but the wheel is there to make the car run. Same thing with the diode - it is there to make the circuit run by letting the current circulate (free wheel is the term) through the motor -without the diode the circuit would be a BAD circuit. BTW the diode can be replaced by a transistor to improve efficiency (lower drop) when it is suitably switched.
     
  12. muki55

    muki55 Member

    Joined:
    Aug 29, 2006
    Messages:
    44
    Likes:
    0
    2 Simple PWM

    Try this simpliest PWM:)
     

    Attached Files:

    • pwm1.JPG
      pwm1.JPG
      File size:
      62.6 KB
      Views:
      2,016
    • pwm2.JPG
      pwm2.JPG
      File size:
      53.2 KB
      Views:
      2,342
  13. svdv

    svdv New Member

    Joined:
    Sep 5, 2006
    Messages:
    1
    Likes:
    0
    Hello

    Hello the circuits seems good to for study. I would like to know the specifications of Q2, the power MOS and the diode to be place across the load.

    Thanks in advance.
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,585
    Likes:
    950
    Location:
    Canada, of course!
    The spec's must match your load's requirements and the switching frequency.
    You can lookup the spec's in Google or at www.datasheetarchive.com like everyone else does.
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,585
    Likes:
    950
    Location:
    Canada, of course!
    Won't your beer can freeze to your mouth?
     
  16. AirWalker83

    AirWalker83 New Member

    Joined:
    Aug 14, 2006
    Messages:
    6
    Likes:
    0
    hi, everybody........
    i need some help here.......
    i am using power window motor for my project.....
    Now i am searching a suitable motor driver in IC package for the power window motor.....
    As i know, the L293B is not suitable because it only support up to 1A per channel.......
    So, do u all have any suggestion of the motor driver for the power window motor???
     
  17. chiba

    chiba New Member

    Joined:
    Jun 4, 2005
    Messages:
    128
    Likes:
    1
    Location:
    Australia
    Your choice is simple: drive a mosfet and live in peace, or pursue your present course and your ic's face obliteration. We shall be waiting for your answer. The decision rests with you.
     
  18. AirWalker83

    AirWalker83 New Member

    Joined:
    Aug 14, 2006
    Messages:
    6
    Likes:
    0
    Mosfet need to build the circuit?
    Cause i still a beginner, not quite understand the MOSFET.
    Beside MOSFET, got any other motor driver IC that can replace L293D?
     
  19. chiba

    chiba New Member

    Joined:
    Jun 4, 2005
    Messages:
    128
    Likes:
    1
    Location:
    Australia
    Do you like Salsa? because trying to drive a Window winder that could draw anywhere from 5-30A is going to bake all your chips. However, using a simple low cost ic to drive one of them awfull mosfet thingys will work out cheaper and easier. I'm sure PWM ic's that can handle 30A are available in the future but first we have to get that time line thing sorted.
     
  20. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    No, not that I know of anyway. I recommend that you should do some Googling and research about MOSFETs, they're not that complex, they're basically electronic switchs.
     
  21. tankist80

    tankist80 New Member

    Joined:
    Dec 18, 2006
    Messages:
    4
    Likes:
    0
    all, thanks for the info. lurked for month's now and learned a lot of things.
    i plan to build H bridge for wheelchair motor and IRF3205 looks very suitable. at least on paper looks like significant improvement over ifrz44n (and not much more expensive) i thought using first.

    any recomendations for a VERY good one ? HIP4081??
     
    Last edited: Dec 18, 2006
Thread Status:
Not open for further replies.

Share This Page