Patent ID: 7092623

Claim:
A system for determining speed of a fan powered by a power supply configured to provide a pulse width modulated (PWM) signal to the fan, wherein the fan is operable to generate tachometer pulses indicative of a current speed of the fan, the system comprising: a test circuit operable to generate test pulses and to provide the test pulses to the fan, wherein a current frequency of the test pulses is proportional to a current frequency of the tachometer pulses; a frequency divider operable to generate control pulses and configured to receive the tachometer pulses, wherein each one of the tachometer pulses is operable to reset the frequency divider; and a latch configured to receive the tachometer pulses and the control pulses, wherein each one of the tachometer pulses is operable to reset the latch and each one of the control pulses is operable to set the latch; wherein a current frequency of the control pulses is lower than the current frequency of the test pulses; wherein the latch is operable to output recreated tachometer pulses; wherein a current frequency of the recreated tachometer pulses corresponds to the current speed of the fan; and wherein the test pulses operate to provide power to the fan.