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La question
Le lecteur superutilisateur darkAsPitch se demande:
What happens if I do not plug it into the motherboard and it does not have a switch?
I have seen fans before with an “off/low/high” switch that allows you to manually set their speed.
I have seen fans that plug into the motherboard and are controlled by the OS.
I am curious… what does a fan do by default when plugged into a PSU? Does it run at 100% unless otherwise told to go slower? This is what I would expect…
Alors, comment fonctionnent-ils? Alésage complet sauf indication contraire?
La réponse
Journeyman Geek, contributeur de SuperUser, offre les informations suivantes:
Well, kind of. Fan speed control is done by varying voltage or through Pulse Width Modulation (using a constant voltage and cutting it up into pulses to vary speed). If you’re plugged into a motherboard, that’s what it does. If it has 3 wires, the third wire tells the motherboard what’s the speed the fan is running as. If you have a 4th wire, fan speed control is done via PWM rather than voltage control.
You can plug in a 2 wire fan to a 3 or 4 wire connector (though you lose speed feed back), and a 3 wire to a 4 wire connector (where you lose PWM control). You can also use a fan controller to control speeds.
Else, assuming the power source is unaware it’s a fan (as it would be connected through molex for example), and is at a fixed voltage, yes, it goes at full speed all the time.
Hyperslug, un autre contributeur, explique comment se jouent les exceptions:
Like the other guys said, pretty much yes, but I can think of 3 exceptions:
1. A few fans have a built in thermistor that will adjust speed depending on temperature.
2. PSU’s with specially marked Fan-Only PSU connectors (Antec TruePower 550W) can adjust the speed of the fan:
Et voilà: en dehors du contrôle externe par un mécanisme (que ce soit l'entrée de la carte mère, un thermomètre de boîtier ou un bloc d'alimentation intelligent), les ventilateurs fonctionneront à la vitesse la plus rapide autorisée par la source d'alimentation.
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