PWM Fan Testing Notes

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Quick test of controlling the speed of various brushless DC fans using PWM at various frequencies.  Speed control of brushless fans using a constant voltage is usually recommended.  However, PWM can be used in most cases. 

PWM signal into IRFZ44 N-CH MOSFET.  Fan +/- to DC power and MOSFET output.  Meter displays % duty cycle.  Osciloscope top trace (CH1) is input PWM signal.  Bottom trace is MOSFET output.  Operating frequency is 400-5000Hz.

The fan is still functional at various operating frequencies with little effect on speed.  The PWM % determines the speed.  At low PMW % (10%), the fan may not startup.  In most cases, 25% PWM is required. 

Audible switching noise is commom when using PWM at less than 20kHz.  Higher operating frequencies may lead to other noise problems.

Recommendation: Use a brushless DC fan with PWM input (4-wire) or constant voltage for speed control.  If using PWM, use a higher operating frequency with some noise filtering.

Arduino PWM Fan Controller:

Another Arduino PWM Controller:   MOSFET based along with Arduino



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