Fan speed monitoring system for determining the speed of a PWM fan
First Claim
1. A fan speed monitoring system for interfacing a fan unit, the fan unit including a fan speed control terminal for controlling a pulse width modulated (PWM) driven fan and the fan unit asserting fan pulses on the fan speed control terminal indicative of fan poles during the power portion of each PWM cycle, the fan speed monitoring system comprising:
- a fan drive and sensing circuit for maintaining the voltage of the fan speed control terminal above a minimum level to maintain continuous power to the fan while also superimposing fan pulses asserted by the fan unit; and
a filter circuit coupled to said fan sensing circuit for amplifying and filtering said fan pulses and for providing corresponding filtered pulse signals.
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Accused Products
Abstract
A fan speed monitoring system for interfacing a fan, including a fan drive and sensing circuit for maintaining the voltage of the fan'"'"'s TFSC pin above a minimum voltage level, thus maintaining continuous power to the fan. The fan drive and sensing circuit includes a control loop having an isolation resistor for enabling superposition of fan pulses asserted by the fan on the TFSC pin. The fan speed monitoring system also includes a filter circuit for filtering and amplifying the fan pulses and providing corresponding filtered pulse signals. The fan drive and sensing circuit includes an active control loop for maintaining the voltage of the TFSC pin at an average level above the minimum voltage level, while also enabling inclusion of the fan pulses. The filter circuit preferably includes an AC amplifier for amplifying the fan pulses and a level transition comparator for converting the amplified fan pulses to the filtered pulse signals having the desired form. In the preferred embodiment, a control circuit activates the fan drive and sensing circuit and receives the filtered pulse signals for determining a time value indicative of the speed of the fan. The control circuit converts the time value into a revolution per minute (RPM) value for identifying fan speed.
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Citations
26 Claims
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1. A fan speed monitoring system for interfacing a fan unit, the fan unit including a fan speed control terminal for controlling a pulse width modulated (PWM) driven fan and the fan unit asserting fan pulses on the fan speed control terminal indicative of fan poles during the power portion of each PWM cycle, the fan speed monitoring system comprising:
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a fan drive and sensing circuit for maintaining the voltage of the fan speed control terminal above a minimum level to maintain continuous power to the fan while also superimposing fan pulses asserted by the fan unit; and a filter circuit coupled to said fan sensing circuit for amplifying and filtering said fan pulses and for providing corresponding filtered pulse signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A fan speed measurement system for a pulse width modulated (PWM) driven fan having a bidirectional thermal fan speed control pin, comprising:
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a bias circuit for providing a bias signal having a voltage level greater than a minimum voltage level necessary for maintaining continuous power to the fan; a fan drive and sensing circuit receiving said bias signal for maintaining the voltage of the thermal fan speed control pin above said minimum level while also superimposing fan pulses asserted by the fan; filter circuit coupled a filter circuit coupled to said fan drive and sensing circuit for filtering and amplifying said fan pulses and for providing corresponding filtered pulse signals indicative of the speed of the fan; and a control circuit for activating said bias circuit and for receiving said filtered pulse signals for determining a time value indicative of the speed of the fan. - View Dependent Claims (19, 20)
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21. A method of monitoring the speed of a pulse width modulated (PWM) driven fan, the fan provided in a fan unit including a fan speed control terminal for controlling the fan and for asserting fan pulses on the fan speed control terminal indicative of fan poles during the power portion of each PWM cycle, the method comprising the steps of:
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maintaining the voltage of the fan speed control terminal above a minimum level to maintain continuous power to the fan while also superimposing fan pulses asserted by the fan unit; and amplifying and filtering said fan pulses and for providing corresponding filtered pulse signals. - View Dependent Claims (22, 23, 24, 25, 26)
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Specification