I am new to electrical engineering and I am trying to run an n-channel MOSFET (this one) as a PWM switch to a motor. Following some tutorials online I have this setup for my circuit.
simulate this circuit – Schematic created using CircuitLab
When I try to run this circuit, even with no input to the gate, the motor always runs and the MOSFET heats up. The source-drain voltage is 30 max and I'm only running 24V.
Best Answer
With no gate input, it will float and quite possibly turn on the MOSFET - do not run a MOSFET with a floating gate. So, it's quite possible you may have damaged the MOSFET and it will act like a partial short circuit thus the motor always runs.
The next problem is your general circuit. You have wired the MOSFET as a source follower and this is no good for what you want. With an N channel MOSFET this is the best configuration: -
Picture taken from here
Note the use of a diode or snubber network connected across the motor to prevent back-emfs destroying the MOSFET. You also need to pick a MOSFET that adequately turns on with only 3.3 volts gate-source drive.