You are right about no potentiometers on motherboards. But "variable voltage" is not even remotely the same as PWM, and motherboards had variable voltage headers for years before first PWM fan headers showed up.
I am telling you that the way, as an electronic engineer, to regulate an amount of current or voltage or power, is to use a pulse width modulation circuit. "PWM fan control" refers to the 4 pin mechanism we know from PCs as far back as around ATX standard I think?I are right about no potentiometers on motherboards. But "variable voltage" is not even remotely the same as PWM, and motherboards had variable voltage headers for years before first PWM fan headers showed up.
Are you trying to tell us computer industry has been lying to us when they say 'variable voltage' headers and they are really all PWM? Sounds like you think there is some sort of "PWM conspiracy" going on.
"I" was supposed to be "You", sorry.I am telling you that the way, as an electronic engineer, to regulate an amount of current or voltage or power, is to use a pulse width modulation circuit. "PWM fan control" refers to the 4 pin mechanism we know from PCs as far back as around ATX standard I think?
But PWM as a principle can be used elsewhere too e.g. in regulating the voltage at fan headers, or in a power supply for the 3.3/5/12 volt rails. Switch mode power supply just means PWM circuit with extra components to make it efficient and stable. PWM switching, see
It's also used for regulating other stuff like power e.g. in good quality electric induction hobs. Pulse width modulation is a principle, not a PC specific implementation.
The difference between PWM fan control (4-pin) and DC voltage control (3-pin) is that the former is modulating the control signal which directly correlates to fan speed. Whereas DC voltage control is modulating the supply voltage so it averages down before it hits a load.
This may be same thing I was trying to remember.What luckybenski just said sounds right
Have a vague recollection of asus using "fake" pwm headers
They were actually voltage controlled
There were explanations back then from engineers
That sounded similar to what he just said
Though must admit my memory isn't the greatest
So I might also be wrong
And it was confusing back then too since most people
Have no knowledge of pwm other than 4 pin pc fan headers
Again from my dodgy memory
Might have been some explanation that pwm in the way
It's used on 4 pin headers
Allowed lower rpm compared to voltage control
Indeed!The trippiest thing is that the PWM control wire in 4-pin fans is negative true logic. Meaning zero volts is "go", and 5 volts is "off"!
It's so that a fan with no 4th pin e.g. on a 3-pin header, still runs.
I've never looked into soft start motors actually! I'm guessing it isn't just having a capacitor in there to suppress the transient, I think that's even older still than soft start.
I'm familiar with capacitors being used on motors too supply extra power for startup They've been in use for cc100 years, maybe more.
I think that's what I remember as well. They were using variable voltage on some headers and claiming all fan headers were PWM when only CPU fan and CPU OPT were actually PWM.
I've just gone down a rabbit hole reading about this! Good thread on SPCR forums.
Yeah that sounds about right
