Method and apparatus for determining fan speed
DC
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Abstract
An operating circuit (1) for controlling the speed of a cooling fan motor (3) for computer cabinetry (7), and for determining an under-speed condition in the fan motor (3) comprises a control circuit (15) which controls a variable output signal generator circuit (18) for outputting a pulse width modulated signal corresponding to the desired fan speed for switching a switching circuit (8) in a power supply circuit of the fan motor (3) for pulse width modulating the power supply to the fan motor (3). A monitoring resistor (R1), a capacitor (C1) and a circuit (12) provides a tachometer signal to the operating circuit (1). A gate circuit (22) gates the second and fourth pulses of the tachometer signal to a counter (20) which counts clock pulses from a clock signal generating circuit (19) between the rising edges of the second and fourth pulses which are in turn stored in a register (23) for comparison with a reference count by a comparator (25). The comparator (25) outputs an alert signal in the event of the count in the register (23) exceeding the reference count indicating under-speed of the fan. The control circuit (15) controls the signal generator circuit (18) for holding the pulse width modulated signal outputted to the switching circuit (8) on during a duty cycle between the rising edges of the second and fourth pulses of the tachometer signal so that the tachometer signal remains available until the fan speed has been determined.
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Specification
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Current AssigneeSemiconductor Components Industries LLC (ON Semiconductor Corporation)
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Original AssigneeAnalog Devices, Inc.
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InventorsBlake, John, Hanrahan, David, Yoshida, Kohji
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Primary Examiner(s)Le, N.
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Assistant Examiner(s)SUNDARAM, T R
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Application NumberUS09/595,953Time in Patent Office988 DaysField of Search324/511, 324/510, 324/515, 324/537, 324/168, 318/471, 318/463, 363/96US Class Current324/168CPC Class CodesG01P 3/489 Digital circuits thereforG06F 1/206 comprising thermal managementH05K 7/20209 Thermal management, e.g. fa...
