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What is PWM??

DankDoodles
By DankDoodles
in Cooling
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Just now, Electronics Wizardy said:

It allows better control of the speed of the fans. Basically instead of lowering the voltage, the fan always gets 12v, and pwm controls the speed of the fans.

If a fan doesn't have PWM, does that mean it will be controlled by the separate controller?

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Posted

PWM = Pulse Width Modulation

 

Basically, the input signal is either on or off, and what portion of the time the signal is on in a given cycle time determines the speed of the fan. The motherboard gives 12V to the fan at all times, and the fourth pin of the fan header sends the pulses that the fan uses to control it's on/off time.

 

The alternative (for fans) is voltage control, which controls the speed by varying the voltage from the motherboard.

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Posted

PWM 3rd pin is tach. 4th pin is control input/output.

Fan current controlled in Pulses. 

Change by component header temps.

 

DC controlled fans is controlling the constant current to create an RPM, thus the 3rd pin, the tachometer.  

Fan current controlled at a constant. 

Change by fan RPMs.

 

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Posted
13 hours ago, emosun said:

PWM basically is really only useful if you need the fan to spin VERY slowly for some reason.

Though i've found that most regular fans at 5v are pretty much silent anyway so idk why you'd need it any slower.

Thats quite different way of thinking from mine. I would say if you are currently looking to buy new fans, only reason not to go with PWM is if your mobo doesn't support PWM, or you can get them for free.

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