Arduino PWM N channel Mosfet, change current?

Thread Starter

Summi ECE306

Joined Aug 15, 2016
10
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
 

OBW0549

Joined Mar 2, 2015
3,566
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.
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.

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

Thread Starter

Summi ECE306

Joined Aug 15, 2016
10
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.
 

OBW0549

Joined Mar 2, 2015
3,566
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?
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."

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?
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.
 

be80be

Joined Jul 5, 2008
2,072
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.
 

crutschow

Joined Mar 14, 2008
34,285
...............
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?
....................
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.
 
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