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I have been at this problem for months now, and am officially out of ideas why it's not working. I'm trying to use an N-Channel MOSFET to help drive a DC brushed motor from a microcontroller, set up as shown below:

schematic

simulate this circuit – Schematic created using CircuitLab

Unfortunately, all I really know about my motor is that it draws 1.8A at it's maximum current of 4V. My hopes with this circuit is to use my microcontroller's PWM to act as a switch to allow my Motor to draw the current it needs for maximum speed. Unfortunately, it doesn't work the way I hoped in practice. Even when my PWM is at a 100% duty cycle, the Motor is only drawing .45A from the power supply.

Am I missing something? I don't see where my error is here. Can anybody help me out? The datasheet for my MOSFET is provided below:

http://www.ti.com/lit/ds/symlink/csd85301q2.pdf

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  • \$\begingroup\$ I suspect you might need more than 4V for the motor power supply. Have you tried using say a 9V? \$\endgroup\$ – jramsay42 Apr 4 '18 at 5:20
  • \$\begingroup\$ @jramsay42 "9v" batteries are not appropriate for motor projects. However, 6 AA cells could be. \$\endgroup\$ – Chris Stratton Apr 4 '18 at 5:33
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    \$\begingroup\$ To figure out what is wrong, measure while the circuit is trying to drive the motor at 100% duty cycle each of a) battery voltage b) voltage across FET c) voltage across motor. \$\endgroup\$ – Chris Stratton Apr 4 '18 at 5:34
  • \$\begingroup\$ When I drove the recommended 1.8A through the motor, it required 4V. If I connect the motor directly to the power supply under these conditions, it performs optimally. \$\endgroup\$ – Connor Olsen Apr 4 '18 at 5:34
  • \$\begingroup\$ @ConnorOlsen, What's the value of that power supply? \$\endgroup\$ – Dhans Apr 4 '18 at 6:27

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