[lm-sensors] ASUS P5B DELUXE WiFi with Winbond W83627DHG - here 3-pin and 4-pin cpu fans

[Christian Mahr]

Hi David and others on the list,


some more internet research revealed more details on the differences between 3-pin and 4-pin fans (at least to me):

First: Intels intention with this 4-pin definition (black, yellow, green, blue wires) and the related pinning from "PC-user" perspective are shown here:
 
http://www.intel.com/support/motherboards/desktop/sb/cs-012074.htm 
      and
http://www.intel.com/cd/channel/reseller/asmo-na/eng/products/box_processors/desktop/proc_dsk_p4/technical_reference/188115.htm

So Intel made sure that 4-pin fans ("the newer ones") will work on 3 pin MBs, but 3-pin fans on a 4-pin MB connectors do work only with speed supervision, but without speed control.

Some earlier motherboards seem to have a jumper to be able to select between power control on pin 2 and pwm control on pin 4, but the ASUS P5B Deluxe/Wifi seems not to offer this choice.

Some more technical explanation I found here:

http://www.analog.com/library/analogDialogue/archives/38-02/fan_speed.html
 
including the explanation why 4-pin Fans are the technical better options on the long term.

The very technical details of the 4-pin fan interface definition are given here by Intel:

http://www.formfactors.org/developer/specs/REV1_2_Public.pdf

Intel issued the spec in July 2004 and seems to promote this solution somehow since then. Nevertheless such fans are far less widespread than the 3-pin ones. Most cooler/fan manufacturer still offer mainly 3-pin fans as part of their CPU-cooler solution.
In this specification we are told the the pwm control signal is actually not modulating the 12V power as it does with 3-pin fans. 
The pwm fan control pin (pin4) contains a 0..5 V logic ("TTL-like") pwm signal (only 5mA loadable!) at 25kHz, which is intented to control the internal eletronics of the respective fan directly. 

So this type of pwm control is completely useless for a 3 pin fan which expects modulated 12-V-power, unless....
 
What might be possible is to use some external circuitry to translate the 0..5V logic signal into a pwm-modulation of the +12V supply, i.e. a power switch.


Before I start experimenting in hardware, just my question: 
 - did anybody find already a ready-made-solution for this kind of adapation circuitry?
 - if not: Is there any suitable IC known which does all in one (otherwise I might need at least 4 resistors and 2 transistors...)

Sorry for the lengthy explanation but the whole might be of interest for other MB owners as well who try to control their CPU fan and don´t succeed....

Best regards
	Christian

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