Asahi Kasei Microsystems Co., Ltd.

Sumner B Marshall, Iii

Mark E Collins

A system and method for reducing fan noise by controlling the drive current to the fan motor. In one embodiment the system approximates a linear drive using a number of transistors in parallel and sequentially deploying the transistors. In another embodiment, a scheme is used to activate and deactivate transistors in discrete steps thereby achieving the benefits of the linear controller topology.

Digital noise reduction for motors

The invention in the simplest form is a technique to provide for sharing of power and signal pins on a motor controller. The switching simply follows the magnetic switching detected by the Hall sensor as the motor magnet passes and uses a diode or resistor instead of a switch. The power transistors are respectively connected to a voltage regulator through a diode or resistor and there are no switches in the circuit. To avoid simultaneous switching, one embodiment is designed by turning &ldquo;On&rdquo; slowly and turn &ldquo;Off&rdquo; quickly. Slow &ldquo;On&rdquo; is accomplished by using a resistor/capacitor (RC) delay such that the gate drive ramps slowly. Fast &ldquo;OFF&rdquo; is obtained by discharging the gate capacitance with an N-CH transistor that bypasses the RC delay.

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Webster, MA, United States of America

Sumner B Marshall, Iii