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Pwm

S

s1rlynchalot

n00b
Joined
Nov 19, 2004
Messages
36
I was looking at digital fan controllers, and found one that seemed to be perfect for what I wanted/needed, but it says it uses PWM (Pule Width Modulation), and that it causes led fans to 'blink'. Does this mean they blink only when adjusting fan speeds or all the time? Thanks for any help.

Here is the link to what I was looking at btw- http://xoxide.com/logisys-35-digital-fan-controler-black.html
 
basically all the time. Read how PWM works and everything will make perfect sense.
 
odds are, if it's a decent pwn clock frequency you wont' really see the LED's flashing, they'll just seem dimmer.
 
They blink all the time. However, it usually only becomes annoying when you have the fans running slower. PWM or Pulse Width Modulation is a way to control fans or motors by giving them a constant voltage of say for example 12 vdc. What it does to slow the motor down is to pulse the 12v so that the motor is on for only a certain interval and then it pulses another 12v sequence. The faster you pulse the motor the more often the motor runs and thus it speeds up. Conversely when you decrease the pulse width or interval the motor slows down. PWM has been used for a long time to save energy on items like refrigerator motors that tend to run all the time.

So what's this all mean to you? If the led's on the fan gets it's power from the PWM controller it will pulse right along with the motor. You could eliminate the problem by running your LED's power from some place other than your fan controller. It sometimes causes other problems if you also have your fans rpm sensor hooked up to your MB as well.
 
Just symantics I guess. But in PWM the frequency doesn't change. You actually vary the ratio of time on to time off to make the average voltage applied vary. It's a subtile difference, but it means that the clock frequency is actually what determines whether you see blinking or not.

Also, if you do end up seeing blinking, you can try just putting a cap across the fan terminals. That should smooth out the transistions. But odds are they've already done that on the fan bus.
 
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