Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2002-05-29
2004-03-02
Nappi, Robert (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000, C318S599000, C318S799000, C318S811000, C363S026000, C363S041000, C388S811000, C388S819000
Reexamination Certificate
active
06700339
ABSTRACT:
BACKGROUND OF THE INVENTION
Information handling systems play a vital role in our modern society. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated.
The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information-handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
A computer system, which is one common type of information handling system, may be designed to give independent computing power to one or a plurality of users. Computer systems may be found in many forms including, for example, mainframes, minicomputers, workstations, servers, clients, personal computers, Internet terminals, notebooks, personal digital assistants, and embedded systems.
Information handling systems often include components that require a regulated power supply.
FIG. 1
illustrates relevant components of an information handling system
10
having a CPU
12
coupled to a memory
14
that stores instructions executable by the microprocessor. Information handling system
10
includes an electric fan motor
16
that turns a fan blade (not shown) for cooling the CPU
12
during operation thereof. CPUs require active cooling to operate in a thermal envelope recommended by the manufacturer thereof. Fans are the preferred means for maintaining CPU temperature within the recommended thermal envelope. Ideally, the maximum airflow (fan is fully on) provides the best cooling results. However, it is desirable to be able to gradually vary the fan speed according to the cooling needs in order to save power. Additionally, reducing fan speed reduces acoustic noise produced by the cooling fan. The fan speed can be varied by varying the voltage provided to the power input node of the electric fan motor
16
.
Fan speed depends on the magnitude of voltage provided to motor
16
. Information handling system
10
includes a circuit for regulating the power provided to electric fan motor
16
. The circuit includes a power management circuit (PMC)
18
and power field effect transistor (FET)
20
coupled between the electric motor
16
and PMC
18
. More particularly, the output of PMC
18
is coupled to a gate-input node of FET
20
. The source node of FET
20
is coupled to a first power supply having a voltage VCC
1
, while a drain node of FET
20
is coupled to a power input node of motor
16
.
PMC
18
generates a square wave signal, the duty cycle of which depends upon a control signal provided to PMC
18
.
FIG. 2
illustrates an exemplary square wave generated by PMC
18
. The square wave shown in
FIG. 2
varies between VCC
2
, the voltage of a second power supply provided to PMC
18
in
FIG. 1
, and ground. VCC
2
may be distinct from VCC
1
. The first power supply is capable of providing high current power to fan motor
16
when compared to the current that is provided by the second power supply. As noted above, the duty cycle depends upon the control signal provided to PMC
18
. The period of square wave shown in
FIG. 2
remains constant notwithstanding a change in the duty cycle in response to a change in the control signal provided to PMC
18
.
The square wave signal generated by PMC
18
is provided to the gate-input node of power FET
20
. When the voltage of the square wave signal is at VCC
1
, FET
20
activates thereby coupling the first power supply to the power-input node of fan motor
16
. In response, a shaft (not shown) of motor
16
rotates thereby turning a fan blade (not shown) which in turn produces airflow over microprocessor
12
. When the voltage of the square wave signal provided to the input gate of FET
20
is at or near ground, FET
20
turns off thereby disconnecting the first power supply from the input node of fan motor
16
. In response, the rotational speed of the motor shaft begins to slow and may even stop until FET
20
is again activated by the square wave.
The rotational speed of the fan motors' shaft depends upon the duty cycle of the square wave provided to FET
20
. The higher the duty cycle the higher the average rotational speed of the shaft. To obtain the highest average rotational speed, the duty cycle of the square wave should be 100%. With a 0% duty cycle, no power is provided to fan motor
16
, and the shaft thereof does not rotate. For duty cycles between 0 and 100%, the average rotational speed of the motors' shaft varies accordingly.
The constant coupling and decoupling of the first power supply to the power input node of fan motor
16
according to the square wave provided to the gate input node of FET
20
, stresses fan motor
16
such that fan motor
16
may eventually and prematurely fail. Additionally, the constant coupling and decoupling of first power supply to fan motor
16
corrupts logic within motor
16
that generates a tachometer output signal of fan motor
16
which may be used to determine whether rotational speed of the shaft is set at a desired rate.
SUMMARY OF THE INVENTION
Disclosed is a circuit for regulating a power supply. In one embodiment, the circuit includes a signal generator for generating a square wave signal that varies in magnitude between a first voltage and a second voltage, and a voltage regulation circuit. A duty cycle of the square wave generated by the signal generator varies according to a signal provided to the signal generator. The voltage regulation circuit, coupled to the signal generator, outputs a DC voltage in response to the circuit receiving the square wave signal. The magnitude of the DC voltage varies between the first voltage and a third voltage, wherein the third voltage is greater than the second voltage, and wherein the magnitude of the DC voltage varies directly with the duty cycle of the square wave signal.
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patent: 5848282 (1998-12-01), Kang
patent: 5881298 (1999-03-01), Cathey
patent: 5898288 (1999-04-01), Rice et al.
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patent: 6008603 (1999-12-01), Jones et al.
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“Fan Speed Control is Cool !”; http://www.maxim-ic.com/appnotes.cfm/appnote_number/707; Feb. 2, 2001.
Critz Christian L.
Vyssotski Nikolai V.
Dell Products L.P.
Martin Edgardo San
Nappi Robert
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