Arduino PWM N channel Mosfet, change current?

Discussion in 'Power Electronics' started by Summi ECE306, Aug 15, 2016.

  1. Summi ECE306

    Thread Starter New Member

    Aug 15, 2016
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    The arduino PWM controls the gate of the N channel, which allows the load motor to run.

    Now, when you change the PWM, it really just changes the frequency output at the gate of mosfet, and that changes the speed of motor.

    So throughout the whole thing, the voltage to the motor remains same.

    My question is, when changing PWM does the change the current to the motor and is that why the motor runs fast and slow? If not, is there any way to change the current? Is it possible to have a current changing circuit and pwm, so we have two variables to control?


    Any help would be appreciated.

    Thank you
     
  2. OBW0549

    Well-Known Member

    Mar 2, 2015
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    No. When you change the PWM value, what changes is the percentage of time the MOSFET is conducting, not the frequency. PWM means Pulse Width Modulation. The frequency stays constant throughout.

    No. The instantaneous voltage, which is applied to the motor during the part of the PWM cycle when the MOSFET is on, remains the same; however, the effect of the pulse width modulation is to change the average voltage applied to the motor, which controls the motor's speed.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    ..... and the average current through the motor also changes in response.
     
  4. Summi ECE306

    Thread Starter New Member

    Aug 15, 2016
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    So, right now say, I have a circuit, with micro controller, n-channel mosfet, motor and a power supply of 12v 2A. and control it with PWM, the motor runs at 12V 2A right?

    But, what if, I have a potentiometer connected between power supply and motor, and change the power supply to say 12V 5A, and control the current flow using the pot, will that help with motor speed as well? or only the PWM changes the speed?

    P.s: assuming motor specifications are met.
     
  5. OBW0549

    Well-Known Member

    Mar 2, 2015
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    A "12V 2A" power supply puts out 12 volts and is rated to deliver up to 2 amps of current without danger of being overloaded-- i.e., if you try to draw more than 2 amps from it, it will overheat, burn out, or just go into current limiting mode. But the fact that the power supply is rated at 2 amps DOES NOT MEAN that it will somehow "force" 2 amps through whatever load it's connected to.

    So no, the motor does not "run at 12V 2A."

    I can't make any sense of what you're saying. Why in the world would you want to do that??? Use the PWM value to adjust the motor's speed, that's what it's there for.
     
  6. be80be

    Senior Member

    Jul 5, 2008
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    Better have a 5 amp or bigger pot or you'll have a fire.
    The pot is not a good idea it burns off power and most motors are not made to be controlled by a pot.
    PWM let's the motor maintain it's power without over heating.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,035
    3,242
    The pot will change the motor speed, but it will be inefficient and dissipate a lot of power.
    You would need to have the pot control an added transistor on a heat sink, and that would control the current and dissipate the power.
    That's why PWM is used, it's much more efficient since the control transistors are in the switching mode, not the linear mode.
     
  8. Summi ECE306

    Thread Starter New Member

    Aug 15, 2016
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    Thank you for your response.
     
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