4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification

Introduction
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1 Introduction
1.1 Overview
This specification defines the intended operation of a fan that implements the Pulse Width
Modulation (PWM) control signal on the 4-wire fan interface. The introduction of 4 wire PWM
controlled fans is a means to reduce the overall system acoustics. The expectation is a 4 wire
PWM controlled fan when properly implemented will be significantly quieter than a similar 3
wire fan.
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