This is why it can be important to continuously monitor the condition of the fan. Over time, fan speed and therefore cooling efficiency can slowly degrade or fail completely. Fan-Monitoring OptionsĪlthough brushless commutation has gone a long way in increasing the lifetime and the reliability of fans, they are still mechanical devices and prone to mechanical wear and failure. Fan speed versus fan voltage (12V-rated fans). Fan current versus fan voltage (12V-rated fans).įigure 2.
To a first order, speed and current are directly proportional to the DC voltage applied. As the DC voltage applied to the fan is varied, its speed and current draw also vary. To the end user, DC brushless fans are fairly simple to characterize electrically. This has greatly increased the lifetime and the reliability of these fans. The end result is a simple-to-use, reliable, 2-wire device. This commutation circuitry is mounted within the fan itself and is totally transparent to the user. Brushless fans have replaced these mechanical brushes with electronic sensors and switches that now perform the necessary commutation. Over time, the fan would wear and eventually fail. Older DC fans used mechanical brushes, which can cause increased electromagnetic interference (EMI) along with dust particles due to mechanical wear throughout the system. In telecom applications, 48V fans are especially popular.īrushless DC fans are called "brushless" because the electric motor within the fan is commutated electronically. As more systems are designed without a 12V power supply, 5V fans will likely become more prevalent.
Currently, 12V fans seem to be the most widely used. A quick glance at fan catalogs reveals that fans operating at a nominal 5V, 12V, 24V, or 48V are available. The simplest approach to system cooling is to connect a fan to a DC power supply and let it run. The basic DC brushless fan is a 2-wire device over which a DC voltage is applied. These fans couple high reliability with ease of use. Brushless DC fans tend to be the solution of choice for most electronic enclosures. Brushless DC Fansīefore we get into the subject of regulating and monitoring fans, we first need to understand the fans themselves. Fan speed control and monitoring can ease some of these headaches, resulting in quieter, more reliable fans that use less power.
Unfortunately with fan use comes the usual fan headaches of mechanical failures, increased power consumption, and more noise. For many applications, this means using fans. IntroductionĪs IC designers strive to put more transistors running at higher speeds into smaller packages, there can be only one outcome: heat! Couple this with the fact that these high-power ICs are being designed into ever-shrinking boxes, and you end up with a real thermal management problem. This document discusses the operation of the MAX6650 and MAX6651, two fan controllers with linear closed-loop fan speed control.Ī similar version of this article appeared in the Septemissue of EDN. In addition, a fan that is about to fail can be identified so that it can be replaced before it fails. When fan control is augmented by fan-speed monitoring, a speed-control loop can be implemented that is independent of manufacturing variances and wear on the fan. Temperature-based fan control is a necessity in a growing number of systems, both to reduce system noise and to improve fan reliability.
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