PWM Fan Controller

[marcel.j]

Hi all,
I am new to Electronics. I want to control the speed my PC Fan and had no Idea how to do this. After a day of searching in the internet I crated this circuit.

This is the List of parts I would need:
Resistors
R1   Resistor 1 KOhm 1/4 Watt 5% Carbon Film    
R2   1 KOhm potentiometer
R3   Resistor 4.7 KOhm 1/4 Watt 5% Carbon Film    
Capacitors
C1   0.1 uF ceramic capacitor
C2   1 uF 16 Volts electrolytic capacitor
Integrated Circuits
IC1   555 Timer    
Diodes
D1   1N4148 Switching Diode    
D2   1N4148 Switching Diode    

If anyone could check this Circuit and make it more efficient I would be very grateful.
(sorry for my bad English)

All the best
Marcel

[M. András]

why not use the motherboards pwm headers? btw the pinout for the pwm header gnd, +12v, +tach/rpm, pwm

[marcel.j]

Thank you for the quick reply!
I need to control by my self and my Motherboard Pins are already occupied. 

[TonyPh]

The attached circuit is useful for 4 pin PWM fans only. If you already have PWM on your motherboard then perhaps a PWM splitter cable would be of more use.

[ChrisGreece52]

If you need something manual with cables this is the way to go : simple and usefull
http://en.wikipedia.org/wiki/LM317

[marcel.j]

An LM317 would regulate the Voltage would ´t it? But I want to regulate with PWM so the the Fan become more Quite.

[Paul Price]

Try my first temperature controlled fan manager circuit. Place the thermistor in between the fins of the CPU to monitor the CPU temperature.

If you just want manual but with finely regulated control, you can replace the thermistor with a 1K resistor in series with a 20K pot wired as a rheostat.

If you want really simple manual speed control, look at the second circuit attached.

[ChrisGreece52]

An LM317 would regulate the Voltage would ´t it? But I want to regulate with PWM so the the Fan become more Quite.

Got it sorry but i have nothing 

[ChrisGreece52]

Oh it just occured to me you can use i you want a microcontroller and a pot

[NiHaoMike]

An LM317 would regulate the Voltage would ´t it? But I want to regulate with PWM so the the Fan become more Quite.

That's correct. The newer higher quality fans are using some sort of digital logic (like the Cindy Wu sensorless FOC algorithm used in high end Delta and Nidec fans) that supplies sine waves to the fan motor at low speed and trapezoidal waves (sometimes called overmodulation) at high speed. They do that in order to get the quietness of sine wave drive at low speed and more power at high speed.

If you tried to vary that kind of fan by dropping the voltage, the logic might fail to operate properly (usually when the regulator supplying it drops out) and the MOSFET gate drives might not have enough drive voltage (could possibly damage the inverter, though good fans would trip on UVLO before that). Your fan would also be stuck in trapezoidal wave mode, meaning it won't be as quiet or efficient as it could be at that speed.

Your best option is to make a splitter to split the PWM signal coming from the motherboard. (Simply ignore the extra RPM feedback.) I'm not sure how many fans can be reliably driven, but you can make a buffered splitter (using a 74HC04 or similar) and basically run as many fans as you like. (Use a separate power feed from the PSU since most motherboards can only handle 2A or so.)

[marcel.j]

I need an new circuit to control the Fan because I am not able to connect it to my motherboard there is simply no more space. I am using an external PSU but then the Fan always runs at Full speed.6000 RMP is way too fast for every day use... 

[NiHaoMike]

You can make a splitter so the PWM signal goes to multiple fans.

[darko31]

I've made similar circuit with 555, but my fan is 3 pin only, and I PWM-ed the 12V rail of the fan.

If you have 4 pin fan, that can be controlled by PWM signal from motherboard, as suggested earlier, the most elegant solution is to make splitter cable or buy one. You could 12V and GND from any connector available, and tach and PWM have to be from the fan socket from the motherboard. It's just parallel connection.

Also, if the tach signal is coming from two different fans, on the same motherboard pin, the signal would probably be messed up, and you wouldn't get accurate reading.

[grumpydoc]

If you have 4 pin fan,.....the most elegant solution is to make splitter cable or buy one....., if the tach signal is coming from two different fans, on the same motherboard pin, the signal would probably be messed up, and you wouldn't get accurate reading

Probably wouldn't get any meaningful reading.

You can get fan splitters (which are a good solution to adding more fans when you're out of connectors) but these connect the tacho signal from just one of the fans back to the motherboard connector.

[marcel.j]

so my circuit wold do the same? I don`t need to know the speed