4-pins fan PWM control : help needed

**DeltaFX** · 05-12-2009, 05:33 AM

Hi,

The mobo is use only supports 3-pin fans and can not change fan speed. On the other end, there are 4-pins fans available.

My idea is to control speed of such fans with the open collector PWM outputs of a Velleman K8055 usb board I own.

These fans accept a 21-28 kHz (typical 25kHz) pwm input signal and the k8055 outputs a 23khz PWM so it should be possible.

But I'm a total noob in electronic design, that's why I need help.

**Crinos** · 05-12-2009, 07:12 AM

1) a multi contact switch (3-stages)

1. standard 12v
2. 7v (achieve this by using 12v and 5v).
3. 5v

2) use a potmeter on the + line and you can adjust the voltage.

How to do this with the Velleman K8055 board... I have no clue of... sorry.

**DeltaFX** · 05-12-2009, 03:01 PM

Well well well... Could you please wait a few second till I grab the crossbow then start running ?

My goal is to have the carputer adjust fanspeed by itself, you see ?

**Curiosity** · 05-12-2009, 04:13 PM

What do ya need to know? It could be a direct connection. What's the output voltage of the Vellaman PWM?

EDIT: Oh, open collector. 12V to the collector, 12V to the + on the fan. emitter to the speed control on the fan.

**Curiosity** · 05-12-2009, 05:04 PM

Oops! Just looked and it's probably 5V on the PWM.

**Crinos** · 05-13-2009, 03:08 AM

Originally Posted by DeltaFX

Well well well... Could you please wait a fiew second till I grab the crossbow then start running ?

My goal is to have the carputer adjust fanspeed by itself, you see ?

Hehe... sure. just make sure that you aim stright

The idea is the same, you need to construct a logic that basically do the same as a hardware option.. Either with a switching state, or ... hum... can't find the right word... softer (intervall less).

But why do it the hard way, when there is tons of off the shelf products that do this? And they are usually cheap as well.

**DeltaFX** · 05-13-2009, 10:27 AM

K8055 PWM outputs are open collector, rated for 40 V 100Ma and if I understand right what's said on this page :

http://www.pavouk.org/hw/fan/en_fan4wire.html

and on this pdf
http://www.formfactors.org/developer...e_PWM_Spec.pdf

all I need is to connect the PWM control wire from the fan to the PWM output of the k8055 (and Fan-gnd to K8055-Gnd) and I'm done ?

Plus, at boot the k8055 isn't started, pwm output is open and fans should run at full speed

Why doing it the hard way ? Because I already have the k8055, the carputer is in the trunk so things like manual fan mates are not intersting. My goal isn't only noise, but temperature too.

**Curiosity** · 05-13-2009, 01:05 PM

Yep. You've got it. That's a good design. The fan sources the 5V with a pull-up so the PWM would pull down. Open, it would be full speed. Grounded would be slowest. I just looked at the K8055 schematic and the emitter side of the PWM transistor is grounded, so that's perfect. It's made for PWM inputs like fans use.