Three-from-four fan control

摘要

Most PC-motherboards have multiple connectors for plugging in the cooling fans. These are increasingly frequently the four-way connectors. These connectors are mechanically and electrically compatible with the more common three-way connectors, which carry the power supply and tacho signal. On the fourth connection the motherboard supplies a pulsewidth modulated TTL signal, which is used to control the speed of the fan. A separate potentiometer or a temperature dependent speed controller to reduce the noise of the fan is now really history. But the availability of fans with a four-way plug is still rather limited and these fans are generally also more expensive. With the small, additional circuit that is proposed here, it nevertheless becomes possible to use these cheap and ubiquitous fans with their three-way connectors.