CPU Smart FAN Mode - voltage vs pwm

[morozaw]

Hello, could somebody from technical support explain how "voltage" mode works?
Somewhere I read in this option the 12V supply voltage connected to fan is in switching mode - PWM.
Is it true?

I mean when voltage option (for 3 pin fan) is checked, the fan is supplied with 12V PWM (without filtration to DC) instead of clear DC voltage.

[wowThatsBad]

I'm not sure if I can really answer your questions, but

1. PWM fans take a constant 12V and the voltage is pulsed to the fan
2. non-pwm fans (3-pin) need voltage varied to vary speed


does that help?

[morozaw]

Hello,
nope, I will explain better what I mean.

In "PWM mode" (for 4 pin fan) voltage ofc is clear DC 12V (at "red" wire) and speed is varied by duty cycle of PWM 5V signal (at "blue" wire).

I found somewhere information that, in "voltage mode" (for 3 pin fan) voltage at "red wire" is not clear voltage mode, but avg from 0-12V PWM voltage.
I mean in "voltage mode" fan is supplied with short spikes (PWM) of 12V voltage, and avg voltage is 12V * Duty cycle of this PWM.

Unfortunately I can't find a source of this measurements - I found only post on other forum about this, so I would like to ask technical support of Gigabyte.
Maybe someone could check this at oscilloscope?

Cheers!

[wowThatsBad]

You could try going to http://www.tomshardware.com/forum. You might get an answer there.

[biernat]

I think, that voltage mode is for 3-pin connected fan. We have here ground, PWM signal and sensor feedback from fan. 4th pin is not used in this mode - it is for 3-pin CPU fans. In PWM mode, we have 4-pin connector - ground, 12V, sensor feedback and PWM signal for rpm control.