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Need help with Switch Voltage Regulator design

Discussion in 'General Electronics Discussion' started by Gaupa95, Jul 4, 2013.

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  1. Gaupa95

    Gaupa95

    6
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    Jul 1, 2013
    Hi. I'm quite a novice with electronics. But I am working on a Arduino based fan controller.

    I'm going to have 4 separate voltage delivery outputs. for each of the fan groups.
    Each group will be loaded different.
    The output with the most load will have 4 fans connected. Each fan is rated ca 200mA.

    I'm using the pc's own power supply to power this.

    I wanted to adjust the the voltage delivery to the fans. (thus adjust the speed)

    I'm considering to use switch regulation to provide voltage to the fans.

    I wonder how to build this circuit. I would be glad if someone could help me design.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Better use PWM to control the fan's speed.
    PWM minimizes power losses in the controller.

    Using a switch mode controller to generate a variable voltage is akin to PWM in that the input DC is chopped, but you need more components to smooth the output DC of the switch mode regulator.

    When controling a motor, this component overhead in not only unnecessary, on the contrary: a typical DC (fan) motor will stall once the voltage becomes very low. Using PWM the motor sees high voltage pulses durimg the on-time of the PWM cycle. This helps to generate more torque than pure DC and the fan can be controlled to lower speeds than with DC only.
     
  3. Gaupa95

    Gaupa95

    6
    2
    Jul 1, 2013
    I see PMW as an easier solution to the problem. but it would require me to use fans that is capable of being controlled by PMW.

    I want this controller to be able to be more universal. I might add the option to have fans that support it to be controlled by PMW (would have to see what I need in addition to make that work first though)

    In addition this is supposed to be a home project so I want to make it a bit advanced.

    (Guess the 3-4$ extra for the PMW controlled fan is not to expensive though if this would be to hard to make)
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Not necessarily. You can control any DC motor (except brushless) by applying a PWM signal to the power connectors. That is how e.g. electric high performance RC motors are controlled to minimize losses in the controller.

    The "advancement" lies in the necessary power booster (aka transistor amplifier) that you need to design to interface the arduino to the motor. You can probably add some fancy display for actual fan speed and an analog input device (potentiometer) to set the speed, which will require you to digitize the analog input etc. You can make this project as advanced as you like, just don't choose the motor control, that's so simple.
     
  5. Gaupa95

    Gaupa95

    6
    2
    Jul 1, 2013
    You see. That's the problem. These fans that I plan to use is computer case fans. (thus all of them brushless).

    There is two kind of fans I want to use. (Corsair SP120, Corsair AF120/AF140) And most of them dosn't have PWM control support. This requires another way of controlling the fans. (but I guess a linear transistor solution wouldn't be to bad. I could mount it in the HDD cage, providing a steady airflow over the circuitry.)
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,531
    2,656
    Nov 17, 2011
    For a brushless motor you need a dedicated control circuit. You don't control the speed of that kind of motor by varying the dc voltage.

    Look up this article on fan control. A PWM controlled fan is not the same as a PWM controlled DC motor. In a PWM controlled fan the PWM signal is used by the internal electronics of the fan to adjust the speed. If you apply PWM directly to a DC motor it's rpm will follow the PWM's duty cycle.

    The SP120 you mention already comes with a step down adapter for lower speed operation.
     
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