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DC Motor Control Circuit

Discussion in 'Electronic Projects' started by ElectroMaster, Jul 24, 2002.

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  1. ElectroMaster

    ElectroMaster Administrator

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    Here, S1 and S2 are normally open , push to close, press button switches. The diodes can be red or green and are there only to indicate direction. You may need to alter the TIP31 transistors depending on the motor being used. Remember, running under load draws more current. This circuit was built to operate a small motor used for opening and closing a pair of curtains. As an advantage over automatic closing and opening systems, you have control of how much, or how little light to let into a room. The four diodes surriunding the motor, are back EMF diodes. They are chosen to suit the motor. For a 12V motor drawing 1amp under load, I use 1N4001 diodes.

    [​IMG]
     
  2. iclok

    iclok New Member

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    if wish to control motor speed using pwm?

    i wish to control motor speed by trigger the BJT/mosfet(i m using mosfet in my project). The output voltage(between motor) i get wont come out as my expected(not a rectangular waveform) and got a lot of distortion. Average value of my Vout is higher much than expected, let say pwm duty cycle is 10%, average voltage i get is 40-50%. Why this problem occur? Can give me a solution or suggestion?
     
  3. SteveM

    SteveM New Member

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    Try searching for info on 'H Bridges' and pwm strategies...a good site i've used before is http://www.4qd.co.uk

    Cheers

    ----------------------------------------
    Steve www.circuithut.com - electronic projects site
     
  4. dave

    Dave New Member

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  5. addyismad

    addyismad New Member

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    sorry if i m mistaken but i u r using a mechanical 'push' button... then wats the need of those free wheeling diodes,resistors, etc?
     
  6. kinjalgp

    kinjalgp Active Member

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    You should use a single SPDT switch in place of S1 and S2. This will prevent the circuit from burning out if both S1 and S2 are closed simultaneously.
     
  7. Styx

    Styx Active Member

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    Couple of problems with this design

    1) the LED's around the motor.
    Since they are in anti-parallel it will ensure an LED will light up depending on th evoltage flow

    BUT in doing so you have provided a clamp across the motor, a clamp of 1.2V as a rule of thumb with LED's

    The speed of a brushed-DC is proportional to the voltage at the terminals


    2) inadquate gate-drive
     
  8. akg

    akg New Member

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    No problem . there is a resistor in b/w the led and motor .
     
  9. Styx

    Styx Active Member

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    Very true, but then you set that burn-resistor to drop a certain potontial;

    Say you set it for the DC-link at 12V so the burn-resistor drops 10.8V. THAT is only good IF you go into over-modulation or 100% PWM

    Less and the brightness drops


    Say you set it for a lower voltage, IF you over-drive it then you will burn it out.

    BEst bet would be to have the LED hanging off the gate signal instead
     
  10. akg

    akg New Member

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    Ok..I agree..
     
  11. Styx

    Styx Active Member

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    errr saturday morning, brain kicking in, IF the LED's were hung of the gate-signal they would be provided with a PWM and thus they would dim with lower PWM.

    so looks like no matter where you put the LED's they will dim with low duty, unless you made a FWD/REV signal
     
  12. bananasiong

    bananasiong New Member

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    how if i want the signal only 5v and control the 12 v motor?
     
  13. Hero999

    Hero999 Banned

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    Another problem with this circuit is the top two transistors are configured as emitter followers so they never fully saturate and you don't get any voltage amplification either. If you shift the components about a bit you can swap them for PNP transistors like TIP32s which will sove this problem.

    Another thing, what happens if the user presses both S1 and S2?

    There needs to be some sort of interlock to prevent this - a few logic gates might do.
     
  14. elcopart

    elcopart New Member

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    Very good DC Motor Control solution.
     

    Attached Files:

  15. magoo

    magoo New Member

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    if i may add to this post i would like to say that my learning expereince is that im still learning ..so dont think im a know it all it's just i noticed how you all where discussing the l.e.d. subject on the schematic at the begginig...
    if you remove the led's and add a duel singal throw switch and add the l.e.d's and the requiered voltage to one side of the switch as to indicate dirrection then the problem with clamping would be overcome don't you think?
     
  16. black2sic

    black2sic New Member

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    anyone could help me to design thyristor gate controller?
    (alpha angle control @ firing angle control)
     
  17. HiTech

    HiTech Well-Known Member

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    I have a 3 horsepower 110vDC motor from a treadmill machine. That will likely require some very stout components to operate it!
     
  18. bhusoy

    bhusoy New Member

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    thanks for your advices...
     
  19. cadstarsucks

    cadstarsucks Banned

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    That is exactly what they are for. Normal consumer grade stuff uses 1-2HP. The PWMs that drive it use 50A IGBTs, though the continuous current is limited to 15-25A depending on the unit.

    D.
     
  20. cadstarsucks

    cadstarsucks Banned

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    You should just put the two LEDs anti parallel, as it stands you are breaking the unlit one down. They typically have a 5V reverse breakdown rating.

    And you need to change the 1N4001s to schottkys. 1N4001s are slow diodes that are not worth anything far beyond line frequency.

    D.
     
  21. AND_ECE

    AND_ECE New Member

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    hey its really nice to be a member...
    can you help to build an driver of the step motor (8 coils), to control the direction of torque if the motor
     
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