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I am trying to use the PCA9685 to power a regular desktop pc cooler fan, the idea being to later be able to freely adjust the fan speed depending on the pwm set in the pwm driver.(similar to this) On my Raspi I tried to get the maximum output voltage out of the board using the following python script:

import Adafruit_PCA9685
pwm = Adafruit_PCA9685.PCA9685()
pwm.set_pwm_freq(40)
pwm.set_pwm(7, 0, 4095)

However, this only turns on the led attached to the fan without turning it. Is there a way to amplify it in a way that still accurately represents a multitude of the pwm voltage set in the program?

  • Can't see any relevance to the Raspberry Pi. I thought standard PC fans use PWM at about 25kHz. – joan Dec 31 '19 at 17:25
  • maybe, but I the reason the fan is not turning is most likely due to the pulse having too little voltage to make the average value high enough to move the fan, so I was asking if there was some sort of analog multiplier that would still allow me to modulate the speed at whch the fan is goingi – huehuehuehuehuehuehuehuehuehue Dec 31 '19 at 17:29
  • you are asking a question about driving a fan, but you said nothing about the fan – jsotola Dec 31 '19 at 21:06
  • You do understand that the PCA9685 only powers up to six volts? You could either use a single-transistor driver or an h-bridge driver. – NomadMaker Dec 31 '19 at 22:45
  • Ah, let me see. There seems to be some confusion. The AdaFruit PCA9685 PWM LED/Servo module can output drive 10mA or 25mA sink. So sink driving LED has no problem. However, PCA9685 output signal, thought only 10mA strong, can also drive servos because the output signal is used to input to the signal pin of the servo which has its own 5V to 7.5V, usually 1A+ power supply. Now to drive a cpu cooler fan, you can, as suggested by @NomadMaker, use a NPN BJT such as 2N2222, with maximum 500mA output current, without any problem, to drive a cpu cooling fane which requires much less that 500mA.. – tlfong01 Jan 1 at 6:01

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