发明授权
- 专利标题: Method and apparatus for determining fan speed
- 专利标题(中): 确定风扇转速的方法和装置
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申请号: US09595953申请日: 2000-06-19
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公开(公告)号: US06528987B1公开(公告)日: 2003-03-04
- 发明人: John Blake , David Hanrahan , Kohji Yoshida
- 申请人: John Blake , David Hanrahan , Kohji Yoshida
- 主分类号: G01P3489
- IPC分类号: G01P3489
摘要:
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.