资料介绍
Pulse Width Modulation (PWM) fan speed control
methodology pulse-width modulates a fan’s full-rated
power supply voltage at a low frequency, typically
30 Hz. A typical PWM circuit, consisting of a transistor
in series with a fan, can be small and inexpensive
because it is either fully on or completely off. This effi-
cient control methodology affords a very wide speed-
control range (typically 10% to 100% of full speed)
because the fan motor is exposed to its full-rated
voltage during the active portion of the PWM cycle.
PWM control works with standard, two-wire Brushless
DC (BDC) fans of various sizes. However, very large
fans (with operating currents of 0.5A or more) can
sometimes produce an unwanted acoustic noise com-
ponent when operated with PWM control. In most
cases, this is remedied by slowing the edges of the out-
put switching transistor with the addition of a small
capacitor. In the most severe cases, this may not be
sufficient, which forces the user to consider linear
voltage speed control. M AN770
Linear Voltage Fan Speed Control Using Microchip's
TC64X Family
Linear voltage speed control operates by continuously
Author: Microchip Technology Inc.
varying the DC supply across the fan. The lower the
voltage, the slower the fan operates. While this meth-
INTRODUCTION odology eliminates the acoustic noise issue described
Pulse Width Modulation (PWM) fan speed con
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