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Maxim > Design Support > Technical Documents > Application Notes > Temperature Sensors and Thermal Management > APP 3530
Keywords: fan drive, fan controller, thermal management, temperature sensing, noise control, PWM, fan noise,
acoustic noise, PWM modulation
APPLICATION NOTE 3530
Circuit Converts PWM Fan Drive to Linear and
Reduces Acoustic Noise
By: Kerry Lacanette
Jun 20, 2005
Abstract: This application note describes an alternative to the standard method of controlling cooling fans. The
typical approach of using temperature sensing with PWM output could result in excess acoustic noise. In
contrast, a circuit that converts the PWM fan drive to linear reduces the acoustic noise.
A similar version of this article appeared in the February 21, 2005 issue of EE Times magazine.
Fans are a necessary part of many thermal management strategies, but fans can cause excessive levels of
audible noise when operating at full speed. Adjusting the cooling-fan speed as a function of temperature is a
good way to reduce acoustic noise in a system. The standard way to make that adjustment (shown in
simplified form in Figure 1) uses an IC that combines temperature sensing with a PWM output, which in turn
controls the power supply for a DC brushless fan.
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