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### Author Topic: Temperature slaved 4 wire fan on a 3 pin MoBo header?  (Read 3467 times)

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#### Fan

• Newbie
• Posts: 5
##### Temperature slaved 4 wire fan on a 3 pin MoBo header?
« on: April 24, 2015, 11:08:18 AM »
Hi all
This is my first post here. I already posted this question on the Giorgos' Blog just before I saw it is better to do it here.

A musician friend of me with no money just got an old PC Core 2 Duo mother board with two 3 pin fan headers and a very noisy ~3300 RPM 4 pin CPU fan, so you guess it runs at full speed. After I understood some more about the difference between 3/4 pin fans I hope I could tweak for him some little pcb to drive his CPU fan speed depending on the heatsink temperature.
Is there and already roughly calculated schema that would do the job?
I found this that could be the input : http://english.cxem.net/home/home24.php
and this for the 4 pin output: http://www.pcbheaven.com/circuitpages/High_Frequency_PWM_Fan_Controller/ (4 wires one, and if I read Giorgos correctly, R1 is already in the fan)
But I don't know how to interface. I'd rather not use PICS or Arduino as I'm poorly skilled.
Thank you

#### Fan

• Newbie
• Posts: 5
##### Re: Temperature slaved 4 wire fan on a 3 pin MoBo header?
« Reply #1 on: April 27, 2015, 20:42:21 PM »
I reached to do the 555 oscillator ~23kHz with rough 50% duty cycle (NE555 datasheet page 14 specific wiring, values RA=2k49 RB=1k C=12nF). In the drawers I found a CA3130E and a NTC 6k8
Quote
If you want to use this circuit to vary fan speed based on temperature then one way you can do this is by just adding a comparator. Use the triangle waves generated at the THRES pin and pass them through the inverting input of a comparator. Your reference voltage on the comparator should be connected to a voltage divider (between say a 10k NTC thermistor and a 12k resistor). The output of the comparator could then drive the MOSFET, higher temperature would generate PWM waves with a duty cycle increasingly closer to 100% on.
At the moment I tested with a 6k8 for divider foot: it works with the heat of the fingers but I'll surely have to adjust this later.
My problem is my freind's fan is a 4 wire so I don't need the mosfet to switch the power to the fan, but instead send the OP output PWM to the control (4th) wire of the fan.
The OP out is going from 0V to +12V but Chris says (and I checked)
Quote
... As well, the voltage supplied for the PWM signal is incorrect - it should be 5V. See http://formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf ...
How do I do this? (the CA3130 output stage is a mosfet push-pull able to drive 20mA which are 4 times the max 5mA from the fan spec)
Thank you

#### Fan

• Newbie
• Posts: 5
##### Re: Temperature slaved 4 wire fan on a 3 pin MoBo header?
« Reply #2 on: April 29, 2015, 10:19:21 AM »
Tweaked Giorgos schematic
« Last Edit: April 29, 2015, 10:25:29 AM by Fan »

#### cheerio

• Sr. Member
• Posts: 306
##### Re: Temperature slaved 4 wire fan on a 3 pin MoBo header?
« Reply #3 on: April 30, 2015, 03:39:11 AM »

The OP out is going from 0V to +12V but Chris says (and I checked)
Quote
... As well, the voltage supplied for the PWM signal is incorrect - it should be 5V. See http://formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf ...
How do I do this? (the CA3130 output stage is a mosfet push-pull able to drive 20mA which are 4 times the max 5mA from the fan spec)
Thank you
so the pwm voltage is too high?
try a 5v zener diode or a voltage divider

#### kam

• Hero Member
• Posts: 1849
##### Re: Temperature slaved 4 wire fan on a 3 pin MoBo header?
« Reply #4 on: May 01, 2015, 13:05:13 PM »
the fan can work from 5 to 12v actually. Basically you pull up the ctr to 12v with a resistor and then you drive the pulses with an open collector.
With PWM the circuit youre looking for is rather difficult. Better go with linear which works fine for 3 and 4 wire fans. The principle is here:
http://www.pcbheaven.com/circuitpages/Simple_Linear_Fan_Controller/

Replace of course the potentiometer with your ntc and proper resistors.

#### Fan

• Newbie
• Posts: 5
##### Re: Temperature slaved 4 wire fan on a 3 pin MoBo header?
« Reply #5 on: May 04, 2015, 19:40:07 PM »
The schematics in post #3 just works