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Need help with Arduino PWM Motor Control

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timdriedger:
Hi Everyone,

This is my first visit here. Hopefully this is the right crowd for some help.

I'm using the following circuit to control a DC motor with an ATMega (Arduino).

There are many articles out there that refer to a simple circuit like this but I know from doing some reading that they don't really follow best engineering practice. It's kind of just enough info to be dangerous!

What should I change in this circuit to provide good component life and more importantly, noise suppression.

MOSFET Datasheet: http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Components/General/FQP30N06L.pdf

The motor is a truck window lift motor running on 12V, draws about 2-4 amps in our application, 6-9 amps if it heavily loaded. The wires running to the motor are about 10ft long.

The PWM rate is 32kHz.

Thanks,

Tim

Odysseus:
Directly PWM'ing a motor is not ideal.  It's fine for LED's, but DC motors are another story.  I tried it a while back in my very first micro-controllers class.  It worked, but wasted more power than it saved.  :D

That said, the circuit as shown will function, but the turning it into a proper switch-mode speed controller with much lower noise only requires the addition of a couple of caps and an inductor.  It doesn't really change it's fundamental behavior, it's just a filter (in a much simplified view).

Capacitor and inductor values in the attached schematic should work well.  Just make sure everything has sufficient ratings, particularly ripple current for the caps. At least 1 amp RMS for the 100uF and 100mA for the 10uF.  I'd double that to be safe.  Also the inductor needs a DC current rating for the full load current. It's gonna be beefy.  Also, you can use any mosfet or diode that can handle the currents.

When actually constructing this thing, keep the current loops short to avoid radiating noise.  There's one loop through C1, C2, L2, and M1 during the on time of the fet.  Then it changes to D1, L2, and C2 when the fet turns off.  So your motor and voltage supply can be located relatively far away, but keep all of these components physically close together.

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