Patent ID: 6836092
Filing Date: 2004-12-28
Classification: G05B

Abstract:
A method of detecting operational information about a DC fan of a device where the DC fan is powered by pulse width modulation and produces an output pulse in proportion to rotational speed, comprising:providing a pulse width modulated voltage to the DC fan and providing a voltage to an input of a control circuit when the DC fan is present in the device; producing a temporary reduction in the voltage to the input of the control circuit upon receiving the output pulse from the DC fan when present; holding the input of the control circuit at a low voltage when the DC fan is not present; detecting through the control circuit that the DC fan is not present in the device when the input of the control circuit is continuously at the low voltage; and detecting the rotational speed of the DC fan when present in the device through the control circuit from the number of temporary reductions in the voltage per unit of time at the input of the control circuit.