Solved: Fan control doesn't work correctly in RRF 3.3
-
@gixxerfast thanks for confirming that.
The Intel specification for PWM fans says in section 2.1.4:
The following requirements are measured at the PWM (control) pin of the fan cable connector see Figure 7 and Table 1:
PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz
Maximum voltage for logic low: VIL = 0.8 V
Absolute maximum current sourced: Imax = 5 mA (short circuit current)
Absolute maximum voltage level: VMax = 5.25 V (open circuit voltage)
This signal must be pulled up to a maximum of 5.25V within the fan.
Note:New fan designs are strongly encouraged to implement a 3.3V pull up for compatibility with buffer design limits on Hardware Monitor Devices e.g. Super IO devices.So the specification requires there to be a pullup resistor inside the fan, although it doesn't specify a maximum value for it (the maximum current sourced implies a minimum value of about 1K). My guess is that your fans have a pullup resistor with a very high value, so that in conjunction with the capacitance of the cable, it slows down the rise time of the PWM signal excessively. If the fan cable is long, that would make this more of a problem, due to the increased capacitance.
-
@gixxerfast said in Solved: Fan control doesn't work correctly in RRF 3.3:
@dc42
It won't run until 15% but that's sort of expected and not a problem.The Intel spec says behaviour below 20% is undefined. Some fans stop, and some run at a not-very-predictable rate, and some run at the same rpm for all duty values below 20%. Sometimes a manufacturer specifies what a particular fan does in this region, but not always.
-
@achrn Yes, and the fan speed is so low it doesn't really matter if they are on on or not. It makes no difference. Estoy muy contento
