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I am using a FQP30N06 MOSFET to PWM a motor. When I test it with an LED and a PC fan it worked fine, but when I connected it to a big motor it just turns on by itself. I am using the analogWrite function on digital pins and 1k ohm resistor from gate to source. The Arduino ground is connected to the source, the motor is connected to drain, it’s an Arduino uno r3.

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    \$\begingroup\$ Welcome to EE.SE. We need a schematic and/or diagram please, or we cannot help you. I will clean up your text, you do the rest. \$\endgroup\$ – VTNCaGNtdDVNalUy Apr 6 '18 at 2:25
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    \$\begingroup\$ Did you put a flyback diode across the motor? \$\endgroup\$ – RoyC Apr 6 '18 at 5:57
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Positive surges on the drain will couple thru drain-gate capacitance; non-linearity in that capacitance will leave a net charge on the gate, perhaps of the polarity and magnitude to turn on and sustain an ON gate voltage bias.

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