UNDERSTANDING CLOSED-LOOP FAN SPEED CONTROL By Ken W. Gay, SMSC When implementing cooling solutions for electronic equipment, system designers are confronted with a complex set of variables.

The weakness of the open-loop system is clear: without any feedback, the system cannot automatically adjust its process to change its output. This rigidity, the inflexibility of an open-loop system, ...

Withclosed loop speed control, the fan controller ensures that the fan isrunning at the desired speed by measuring the actual speed and adjustingthe duty cycle accordingly. Here the host specifies the ...

Though simple, this “open loop” form of fan control has disadvantages. Since there is no feedback mechanism, speed accuracy depends entirely on mechanical tolerances of the fan. Although it may not ...