Electrical – Why did a 1k resistor at the MOSFET gate solve the problem


Why did a 1k resistor solve my problem?

I wanted to control a 3 wire computer fan with PWM(25 kHz 50% duty) from my Arduino NANO pin 10. My Circuit was very simple. I had an IRLB8721F N-Channel MOSFETn a dell HU843-A00(delta ) Chassis fan, a 4148 flyback diode and a pc power supply which I rigged to output 12v. The Arduino was plugged into my computer's USB.

An image of the circuit should be here...<a href="http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html">link</a>...go here bottom of page...with green arrow indicating current flow...this arrow is removed in my post...i also used a mosfet not igbt

This is the circuit, except I didn't have the 1k resistor in place.

With out the resistor the fan was squealing and wouldn't run, but with the resistor it was quiet and ran successfully.Why did the resistor solve my problem?

Best Answer

What may be happening is that your 1k resistor in combination with the gate capacitance is forming a low pass filter. This would cause the fan to experience an oscillating voltage instead of pure pwm. Iirc pc fans have digital controllers that may not play nicely with pwm depending on the frequency. By providing a voltage that never goes to zero, you may be allowing the controller to function continuously instead of resetting over and over again.