Electrical transmission or interconnection systems – Switching systems – Plural switches
Reexamination Certificate
2000-02-08
2001-12-11
Tso, Edward H. (Department: 2838)
Electrical transmission or interconnection systems
Switching systems
Plural switches
C323S282000
Reexamination Certificate
active
06329727
ABSTRACT:
The present invention relates generally to devices for controlling the speed of a fan, such as a fan for cooling heat generating equipment, by regulating a power supply voltage delivered to the fan, and in particular to a microcontroller based fan controller apparatus and control method.
BACKGROUND OF THE INVENTION
Many systems require a variable speed fan (or blower) to control circuitry temperature and/or heat output. Control of the fan can be accomplished using a series-pass circuit, however this solution generates too much heat and is energy wasteful. Alternatively, fan control can be accomplished using a standard pulse-width-modulated (PWM) power control circuit. Generally, a microcontroller generates a precisely-timed pulse train to drive the power switching circuitry, which outputs a desired voltage that drives the fan. However, the PWM arrangement has several shortcomings. First, there are a number of relatively large discrete components needed to generate, filter and regulate the PWM output voltage. When a power source is significantly above the maximum operating voltage of the fan, extra protection circuitry is needed to prevent a catastrophic failure in the event of a microcontroller crash. An inexpensive microcontroller's software-timing and clock-rate require the PWM circuitry to be designed to operate at a relatively low frequency, thus making the PWM arrangement less efficient and physically larger. Moreover, the microcontroller must communicate in real time with one or more host devices while performing the PWM power supply control as well as other functions; thus, resulting in a difficult and costly firmware programming challenge.
Accordingly, it is an object of the present invention to provide a fan controller system, and a PWM power supply control system, that removes the real-time power control functions from the microcontroller, thereby reducing the parts-count, energy waste and firmware complexity of such systems.
SUMMARY OF THE INVENTION
A microcontroller generates a digital signal in response to input data, such as temperature and/or fan speed data. The digital signal is converted to an analog signal that is used to control a variable power supply. The variable power supply outputs a regulated substantially constant output voltage at a voltage level corresponding to the value of the digital signal. The analog signal is produced by a resistor divider and a plurality of resistive elements that are selectively coupled in parallel with a portion of the resistor divider in response to the digital signal. An upper end of the resistor divider is coupled to the output voltage and a lower end is coupled to a reference voltage such as circuit ground. The resistive elements coupled in parallel with a portion of the resistor divider adjust the voltage generated at the resistor divider's center node. The voltage on the center node is the analog signal that is used to control the variable power supply.
The present invention relieves the microcontroller from having to perform real-time pulse-width modulation power regulation, thereby reducing the parts-count, energy waste and firmware complexity of the control system in which the microcontroller is used. Further, the present invention guarantees at least minimal operation, at a safe operating voltage, in the event of a microcontroller failure.
REFERENCES:
patent: 4419619 (1983-12-01), Jindrick et al.
patent: 5029244 (1991-07-01), Fowler
patent: 5691870 (1997-11-01), Gebara
patent: 5982645 (1999-11-01), Levran et al.
Olson Philip D.
Traveis Gary J.
ADC Telecommunications Inc.
Pennie & Edmonds LLP
Tso Edward H.
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