When aging and other conditions are factored in, fan speed can vary up to 20%. Fan to fan variation (of the same model)Ī fan's speed can vary 5% to 10% when new, unless tightly controlled by the fan specification, which adds cost.

The actual fan speed will vary due to a variety of factors including:

The rpm rating for a DC fan is a typical value at full-rated voltage and under specific air-pressure conditions. Many types of consumer and industrial products rely on brushless DC fans for cooling, including desktop and notebook computers, projectors and projection TVs and communications networking equipment. The small geometry IC fabrication processes available today make it possible to provide a rich feature set at an economical cost.īenefits of Closed-Loop Fan Speed Control To help reduce the challenges associated with cooling solutions, engineers can utilize closed-loop fan speed control ICs (FSC-ICs) over open-loop fan drive ICs. Eliminating fan speed variation helps meet product performance and acoustic requirements and provides a competitive advantage in the market. The acoustic noise produced by a fan increases with fan speed, and this variation makes it difficult to optimize cooling efficiency while minimizing acoustic noise. Closed-loop control can drive fans with a wide variety of response characteristics to the same target speed. Figure 1 illustrates the difference between open- and closed-loop speed control as different fans are driven to a target speed from the OFF condition. Aging also affects fan speed, resulting in a wide range of actual fan speeds produced by a particular fan drive setting. Additional variables are introduced when cooling fans are utilized, including a variation of fan speed from fan to fan. Airflow can be affected by different system configurations or external restrictions. The cooling requirements are typically dynamic, and ambient temperatures can vary widely. When implementing cooling solutions for electronic equipment, system designers are confronted with a complex set of variables. UNDERSTANDING CLOSED-LOOP FAN SPEED CONTROL

Fan control