The MOSFETs I am using to drive fans produce a loud noise

Thread Starter

Jack J. He

Joined Apr 24, 2017
I am using 2 of these mosfets:
to drive 24V fans. I am providing power with a 24V 10A power supply and I drive the gate using a PWM with a frequency of 488Hz. When testing on a protoboard the circuit worked very well, there was some switching noise but it was barely noticeable and I couldn't hear it unless I put my head next to it. I also added a 0.33uF and a 10uF capacitors (to smooth out the output and stop the fans from buzzing) and a diode to protect the mosfet. When I moved the circuit to a PCB the MOSFETs started making a very loud noise that stops when the signal is LOW or HIGH (0 or 255). The only difference is that instead of through hole capacitors (One electrolytic and one ceramic) I used surface mount ceramic capacitors (1206 for 10uF and 0603 for 0.33uF) to save space. Do you think that this change might be the cause of it? I also noticed that the MOSFETs on the board get a lot warmer.


Joined Mar 14, 2008
It would appear that the MOSFETs are oscillating.
Do you have a small resistor (50-100Ω) in series with the MOSFETs as that will help to suppress any oscillations.

Post a schematic of the PWM circuit.


Joined Aug 29, 2017
Capacitors can have a piezoelectric effect, this may be hardly noticeable when using through hole components but due to the fact that surface mount components are physically connected to the pcb, the whole board could be vibrating, amplifying the noise.

I know there are capacitors immune to this effect but I can't remember off the top of my head what they are.