PWM with adjustable Freq and Duty Cycle

Discussion in 'General Electronics Chat' started by mazur50, May 27, 2008.

  1. mazur50

    Thread Starter Member

    Feb 5, 2007
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    I am looking for a PWM Circuit that i can adjust the Freq and the Duty Cycle independent of each other. and looking for Duty cycle of 0-100%

    thanks
    Mike
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    How are your programming skills? You will probably need to do one from the ground up with a microcontroller running the circuit.
     
  3. mazur50

    Thread Starter Member

    Feb 5, 2007
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    O skills there.
     
  4. mazur50

    Thread Starter Member

    Feb 5, 2007
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    What i am looking to do is make a pwm circuit to control a mosfet to bake a dc motor. and i would like to make it pluse like abs and also have a variable brake.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Why do you need variable frequency in addition to PWM? John
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    The reason we ask is that frequency control in a PWM application may be a bit coarse. Think discrete frequency choices rather than a continuously variable frequency. The microcontroller route may still be the right solution but maybe a dual 555 circuit could also do the job.
     
  7. mazur50

    Thread Starter Member

    Feb 5, 2007
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    I am not sure what i need. I want to be able to notice the pulse
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    If by "notice the pulse" you mean to be able to have a visual indication, then you will need an oscilloscope. A LED will flash too rapidly to let you see the pulse rate - PWM likes to get done at thousands of Hz to hold down the motor noise.
     
  9. mazur50

    Thread Starter Member

    Feb 5, 2007
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    right but i am not using this to control the motor speed I am using it to control the braking of the motor. So would changing the frequency make it work like if i want to make a led blink faster to slower.
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    For braking, the PWM would be applied to drive the motor in reverse (needing a full bridge setup). You would need some device on the shaft to indicate that the shaft had stopped.

    There is another way out. I once worked with a tape drive that used brakes on the reel motors. The braking device was a chamber filled with a magnetic material. The shaft turned a perforated plate inside the chamber. Applying a magnetic field caused the ferrous powder to string along the lines of force. The disk got braked because the strings ran through the perforations and created drag.

    Here's a link to a manufacturer - http://www.ogura-clutch.com/product...ml?PHPSESSID=578be01984d770dc7f369e62b32b331d
     
  11. h.d

    Active Member

    Oct 22, 2007
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    braking or forward drive its the same concept, the diffrence is the value of the duty cycle and its variation direction increasing or decreasing.
    for braking you will start with 100% d.c to trigger the mosfet the for braking start decrease it.
    for abs i theink you should do the decreasing frequently you can do that by microcontroller.
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    This won't do 0 to 100%, but it comes close...

    [​IMG]
     
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