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enter image description hereenter image description hereI am trying to control a 12V DC fan with PWM using an IRFZ44N MOSFET. However somehow the fan is not turning on and off when the gate is pulled to either 0V or 5V (on the power supply). And it is definitively not working using the PWM pins on the Arduino Uno. Next to that a 2/6/12V battery charger is used to power the fan. It is rated at 600mA, while the fan is only 300mA.

The question is: what is broken in my circuit? Maybe the power supply can't handle the PWM action, or my MOSFET broke (I might have over-voltaged it on accident)?

I connected it exactly as in this video.

Thanks for your time in advance! Bas

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    \$\begingroup\$ Hi Bas, or Jan, welcome to EE.SE. Can you provide a circuit diagram showing exactly how you connected your parts, in your question? Readers are unlikely to watch a Youtube video to see your circuit, and if the video gets removed, the question becomes useless to future readers. There is a circuit diagram editor integrated in the question editor (one of the buttons in the top bar). Thanks! \$\endgroup\$ – marcelm Aug 19 '19 at 14:42
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    \$\begingroup\$ Please include data sheet for the fan, or at least a catalog picture. If it's a PC "muffin" fan then chances are high that it has an on-board brushless drive, and will not work unless it gets continuous power. \$\endgroup\$ – TimWescott Aug 19 '19 at 14:42
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    \$\begingroup\$ Please describe exactly what you observe, don't just say "not working". Also, you need to include a schematic showing exactly how you have connected your circuit...we're not going to watch a video to find out. The cartoon you include has a different MOSFET, and you should include a link to the datasheet for the actual device you are using. \$\endgroup\$ – Elliot Alderson Aug 19 '19 at 15:04
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My MOSFET was broken after all, I got a replacement and now it works fine!

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You are using the wrong FET for your application.

The IRFZ 44 is a "standard" gate drive FET, and will not reliably turn on with 5 volts of gate drive. If you go to a data sheet, you will find that Vgs(th) (gate turn-on voltage) is 2 to 4 volts. However, this only guarantees 250 uA of current, which is much too small, like 1/1000 of what you need. The fact that you are driving your gate with 5 volts helps, but not nearly enough.

What you need is either a higher gate voltage level or a "logic level" FET. These are specifically designed to turn on with 2 volts or less.

Since you have 12 volts available, I suggest that you try something like

schematic

simulate this circuit – Schematic created using CircuitLab

A few things to keep in mind:

1) The phase of the signal is now inverted. That is, a high at the driver input will produce 0 amps in the fan, and a low will provide full on.

2) R2 should be 1/4 watts. If you only have access to 1/8 watt resistors, increase to 5k.

3) I've shown the added NPN transistor as a 2N3904. That's a common and cheap transistor, but almost any small-signal NPN will work fine.

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  • \$\begingroup\$ Thanks for your quick response! The problem however is that the mosfet doesnt turn off, even when the gate is pulled to 0V. When I the gate is pulled to 12V, nothing changes. \$\endgroup\$ – Jan Aug 19 '19 at 14:51
  • \$\begingroup\$ @Jan Are you saying that the MOSFET is conducting when the gate is at 0V as well as at 12V? \$\endgroup\$ – Elliot Alderson Aug 19 '19 at 15:02
  • \$\begingroup\$ @ElliotAlderson Yes! The same voltages as the input and output of the powersupply. \$\endgroup\$ – Jan Aug 19 '19 at 15:07
  • \$\begingroup\$ @Jan Then you may have swapped the drain and source terminals so you are forward biasing the parasitic diode, or your MOSFET is faulty. \$\endgroup\$ – Elliot Alderson Aug 19 '19 at 15:08
  • \$\begingroup\$ The fan does turn considerably slower (50% speed) when the gate is pulled to 0V, however the fan never turns off (0 RPM) Thanks! \$\endgroup\$ – Jan Aug 19 '19 at 15:16

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