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I've got a small motor wired to the drain of an NTE2390, with the other end of the motor hooked up to ground.

When I connect to the source of the MOSFET to power, the motor starts turning even though there are no wires connected to the gate.

Does this mean my MOSFET is broken, or is my circuit wrong?

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    \$\begingroup\$ Ground the gate and see what happens, first. \$\endgroup\$ – jonk Dec 2 '18 at 6:58
  • \$\begingroup\$ @jonk, Just tried that, same result. \$\endgroup\$ – merlin2011 Dec 2 '18 at 7:49
  • \$\begingroup\$ Wire the gate to the Source, and test. In enhancement-mode power MOSFETs, that is the condition wherein you expect NO CONDUCTION. \$\endgroup\$ – analogsystemsrf Dec 2 '18 at 10:10
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  • I've got a small motor wired to the drain of an NTE2390

  • the other end of the motor hooked up to ground.

  • the source of the MOSFET to power

That MOSFET is an N-channel device and its body diode will freely conduct current from a positive supply to a load when incorrectly wired into a circuit: -

enter image description here

You are using it incorrectly. If you want to connect source to positive and load to drain (returning current to ground) then use a P-channel MOSFET.

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  • \$\begingroup\$ Could you explain how to wire it correctly so that the the motor will turn when voltage is supplied to the gate? \$\endgroup\$ – merlin2011 Dec 2 '18 at 18:22
  • \$\begingroup\$ Connect source to 0 volts and motor between drain and power positive. Drive gate with control voltage. \$\endgroup\$ – Andy aka Dec 2 '18 at 19:23

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