Can't get MOSFET to turn off

[mkomkom]

Hi,

I'm trying to control some 12V fans with an arduino and am using a N-channel MOSFET to power them. I have it wired up in a fairly typical fashion: Drain is grounded, source to the motor and +12V, gain to the PWM pin.

Variation on the gain has very little effect on the output to the motor. My main problem is I cannot get the MOSFET to turn off! Even if the gain is straight up grounded, the motors are still at (estimating) 90% current draw. I swapped another MOSFET in to check, but with the same result, so I must be doing something wrong. I don't have a lot of experience with MOSFETS, so not sure what I'm doing wrong but it's driving me crazy!!!! Please help! Thanks,

Tyler

[adafruit_support_mike]

If you're using and N-mosfet you need to swap the source and drain.

Source points toward GND, drain points toward VCC.

[mkomkom]

Oh boy. Sorry for such a dumb question and thank you greatly for setting me straight. I guess the current was going right through the internal diode. I swore I tried swapping the source and drain to no avail, but... in any event, you were right. It works great now. Thanks!
Tyler

[adafruit_support_mike]

No worries.. the simple things are the easiest ones to get backwards.

I once melted a nice hole in a breadboard by putting a 6v Zener diode in so it was forward biased. ;-)