CPU fan speed automatic control?

Thread Starter

Jeffo123

Joined Jan 28, 2022
8
Are fan speeds to cool the CPU an automatic system? i.e higher temp = higher rpm? If so how does this work? I know there is a temperature sensor on the CPU, the output for this is a voltage, does this mean the output is filtered and amplified and then fed to the fan through the motherboard? more volts higher speed?

Just need to understand how this feedback system works
 

LowQCab

Joined Nov 6, 2012
2,634
Some Fans are not Controlled.
With a CPU-Temp-Sensor, the Signal it produces is calculated by the CPU in it's built-in Firmware,
then the CPU generates a PWM signal which drives the Fan's PWM-Input-Pin.

You can make a Circuit that lets You externally drive the Fan's PWM-Pin,
normally, the PWM-Pin just needs to be Grounded with the desired Pulse-Width-Waveform.
The Frequency of the Pulse-Width may vary by different manufacturers specifications,
but usually the Frequency is not terribly critical.
.
.
.
 

Thread Starter

Jeffo123

Joined Jan 28, 2022
8
Some Fans are not Controlled.
With a CPU-Temp-Sensor, the Signal it produces is calculated by the CPU in it's built-in Firmware,
then the CPU generates a PWM signal which drives the Fan's PWM-Input-Pin.

You can make a Circuit that lets You externally drive the Fan's PWM-Pin,
normally, the PWM-Pin just needs to be Grounded with the desired Pulse-Width-Waveform.
The Frequency of the Pulse-Width may vary by different manufacturers specifications,
but usually the Frequency is not terribly critical.
.
.
.
Hey, thank you for the response, withr egards to cpu temp sensor output, how exactly is this used to control fan speed? Is the output signal from temp sensor conditioned and then can then used as input for fan?
 

LowQCab

Joined Nov 6, 2012
2,634
"" Is the output signal from temp sensor conditioned and then can then used as input for fan? ""

I don't understand your question.
What are You trying to do ?
.
.
.
 

Reloadron

Joined Jan 15, 2015
7,079
Are fan speeds to cool the CPU an automatic system? i.e higher temp = higher rpm? If so how does this work? I know there is a temperature sensor on the CPU, the output for this is a voltage, does this mean the output is filtered and amplified and then fed to the fan through the motherboard? more volts higher speed?

Just need to understand how this feedback system works
In a quick and simple nutshell we could say it starts with a sensor which senses a CPU core temperature. On a basic home computer the sensor is as simple as a PN junction (a diode) in the CPU. All temperature sensors have output of some type.
How do you get a temperature sensor from a transistor? is a good simple read on the subject. Anyway a sensor be it temperature or anything else like pressure, vibration and other things has an output. The next step is converting what we have to what we want. Signal conditioning is about what it comes down to. I want a usable signal in this case proportional to temperature.

I want, in this case a signal suitable to drive a fan and in this case PWM (Pulse Width Modulation) is the best way to get where I want to be.
Circuits to do this can be built using discrete components or simply done using a portion of a microcontroller or a CPU. The link is mostly discrete component circuits. PWM is just a method which turns a fan on and off very fast. As temperature rises the width of an On time pulse is increased. A simple Google of Fan Speed Control will get you endless hits. In the case of home computers it's all about PWM. :)

Ron
 
Top