Inductors oppose changes in current flow, similar to the way that an object’s mass opposes changes in its motion.
That’s another question itself I don’t know where I should put it, yet. Yes, I know I should have a flywheel diode in there somewhere. You didn’t describe that, so my bet is on the first case. FETs tend to fail short circuit at first until they explode or become crispy and burnt, at which point they become open circuits. Neglecting to connect your arduino’s ground to the FET’s source would be a likely example of the first case, and the FET being damaged due to static electric discharge or some other factor an example of the second. “cuz ya did something incorrectly” is a correct answer more often than not, with “'cuz ya broke something” coming in second. That would tend to end badly in cases such as this where some substantial amount of power is being switched. Leaving the gate “floating” would leave the FET vulnerable to being turned on by all manner of stray signals, not the least of which is the 50/60Hz floating around everywhere thanks to the electrical grid. Putting it there does indeed discharge the gate in the absence of a drive signal, creating a well-defined “off” state under such conditions. While common practice, it’s not necessary in the strictest sense.
This resource, while perhaps a bit chewy is a rather good summary of various FET properties and their significance. The body diode in a FET is pretty much an inevitable artifact of how they’re made, though one which in various circumstances can be put to good use. However, that’s why I’ve been using a multimeter this whole time instead of watching if the motor started spinning.
NOTE: Yes, I know I should have a flywheel diode in there somewhere. This does NOT turn it on (again, measured with a multimeter and not the actual motor), even though I thought it should. The problem comes when I attach a steady 5V from the Arduino to the gate. I measure 0V on my multimeter when I do that. Third question: why doesn’t this setup work? When the Arduino is unattached, there’s no voltage across the gate, so the motor should not be powered. Second question: Why is that? My guess is that it’s a means of discharging the gate, but I don’t know if that’s right or if that’s a good thing for the MOSFET, anyway. I see everywhere I look that there’s supposed to be a resistor between source and gate. If I had to take a guess, it’s that building up charge while the MOSFET is off with the voltages reversed would somehow hurt the semiconductor inside, but that’s just a guess without any physical knowledge of its inner workings behind it. I’m not sure why it’s there, and I don’t think it affects anything. There is a diode there inside of the MOSFET I have according to the spec sheet. This circuit is somehow wrong, and I don’t know why. The problem is that MOSFET’s clearly don’t work the way I thought they do, because my setup isn’t working like I expected it to. Hypothetically (and idealistically), all I need is for the MOSFET to behave like a switch. A MOSFET is just a device that I found other people using in this way online. That way, I would basically have a 120V PWM signal instead of the 5V PWM signal, and I could change the duty cycle to control the motor’s speed. The MOSFET switch would then be connected to a 120V power supply, which runs a motor (really high voltage rating for a motor, I know, but it’s correct). I have an Arduino to put out a PWM signal, and the hope is that I can use a MOSFET to behave as a switch that turns on and off with the PWM signal. I recently got a MOSFET, and the intention was to use it as a “signal amplifier” of sorts. I’m a physics student, so something as electronically involved as this is a little outside of my wheelhouse, at least in this stage of my education.
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