无论是在笔记本电脑、台式机上，甚至是游戏机上，我们都听到了后台系统迷的呼呼声。这些小小的冷却风扇到底是怎么知道什么时候该向上、向下旋转，或者调节它们所移动的空气量的？

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

问题

超级用户读者darkAsPitch：

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…

那么它们是如何工作的呢？全通径，除非另有指示？

答案

超级用户贡献者Journeyman Geek提供了以下见解：

Well, kind of. Fan speed control is done by varying voltage or through Pulse Width Modulation (using a c***tant 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.

另一位投稿人Hyperslug强调了例外情况是如何发生的：

Like the other guys said, pretty much yes, but I can think of 3 excepti***:

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:

3. If you plug it into the PSU molex using the 12/5 volt rails (7 volt) or 12/7 rails (5 volt) it’ll be run slower, but at this point you’re modding.

在某种机制的外部控制之外（无论是主板的输入、外壳温度计还是智能PSU），风扇将以电源允许的最高速度运行。

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