PWM fan controlling

[haris262]

If I connect my CPU 4-pin fans to my CPU fan headers, are they going to be controlled by the motherboard automatically depending on the CPU temperature?

 

[getochkn]

Yup, that's what its there for. The bios will usually let you select what type of cooling curve to use too, example, quiet mode, performace, balanced, etc.

 

[hwc1954]

Yes. There are four wires going to a PWM fan:

Ground
+12 Volts
Tach signal from the fan to tell the computer how fast the fan is turning
+5 volt PWM signal

The PWM signal is pulsed on and off. Very long pulses to spin the fan faster. Short pulses to slow the fan down.

There is a little circuit board inside your PWM fan that reads the pulses from the control signal and varies the +12 volt input to adjust the speed of the fan proportional to the control signal.

The BIOS/motherboard circuitry generates the PWM control signal based on temperature readings (for example, the CPU temperature).

You can also plug a three-pin fan into the 4-pin connectors. There simply won't be a PWM control signal and the fan will run wide open at the full 12 volts. Likewise, you can also plug a PWM fan into a three-pin fan connector. According to the Intel spec, when a PWM fan fails to get a PWM control signal (as would be the case when connecting to a 3-pin header), it is supposed to run wide open based on the input voltage (usually fixed +12 v)