PWM via the blue wire

------Question for CBM-979433B-135-540-22 Please Put your question below------

If I apply a simple DC voltage to the blue wire between 2.8V and 5.5V will this adjust the fan speed?

Velley, Thank you for your question and welcome to the TechForum!

The fan speed here is controlled by PWM or Pulse Width Modulation. What that means is that regardless of the voltage, as long as it is within range, it will function. To control the speed a digital signal comprised of pulses must be sent.

Notice in this diagram how the High, or on, signal V_{IH} can be anything between 2.8 and 5.5V. Much the same, the Low, or off, signal V_{IL} falls between 0-0.6V. When the signal voltage meets either of these two criteria the circuit interprets a switch to the corresponding zone.

The other factor here is T or Time. T_1 represent the time the pulse is High, where as T represents the total period consisting of the pulse high and the pulse low.

the longer T_1 is, the faster the fan will go.

I do hope this answers your question. If there is anything else, please let us know!

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Just to add to what @AaronRollens stated, the square wave frequency of your PWM signal used to control speed must be between 20Hz and 30kHz. This means that the full period, T, must be between 33.3ยตs and 50ms.

If T1 is high constantly (100% duty cycle), then the fan will run at full speed, if T1 is high 1/2 of the full period, T (50% duty cycle), then the fan will run at approximately half speed, etc.

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