Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2002-10-15
2003-11-18
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000, C318S599000, C318S799000, C318S811000, C363S026000, C363S041000, C388S811000, C388S819000
Reexamination Certificate
active
06650074
ABSTRACT:
BACKGROUND OF THE INVENTION TECHNOLOGY
1. Field of the Invention
The present application is related to information handling systems, and more specifically, to information handling systems having variable speed cooling fans.
2. Description of the Related Art
Information handling systems play a vital role in 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 these 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.
The computer system may include microprocessors that require active cooling to operate in a thermal environment recommended by its manufacturer. To achieve adequate cooling, various thermal solutions are used with fans being integral parts of such solutions. Ideally, maximum airflow (fan fully on) allows for best cooling results, however, acoustical noise from the fan and fan power consumption are also at maximum. Therefore, it is desirable to have the ability to gradually vary fan speed in a thermal solution. However, robust implementation of a variable speed fan controller is hard to achieve due to different fan manufacturers' requirements for supply voltage stability and available signal quality of fan tachometer (rotational speed) output (especially at low rotational speeds).
The noise and power usage problems have been addressed by using pulse width modulated (PWM) signals to periodically interrupt supply voltage to the fan. This provided desirable results regarding fan noise and power consumption, but in some fans it caused premature failures and corruption of logic generating the tachometer output signals from the fan.
Another way that the noise and excess power problems have been addressed was to use a fully integrated fan controller integrated circuit (IC) having an SMB or I
2
C compatible interface. This allowed for seamless fan control, however, if the fan controller IC implemented direct PWM control, then the same fan reliability issues were still present. A significant drawback of using the fan controller IC was cost.
Linear regulators have been used with power management controllers by setting the fan voltage based on binary states of one or more control signals (essentially, a crude DAC is used as a reference for linear regulator). However, a drawback was requiring dedicated binary outputs and only course resolution for fan speed control (e.g., most often there are only three fan speed settings: OFF, LOW, HIGH).
Heretofore, low fan speeds could not be utilized below a certain voltage because the fan digital circuits for producing a rotational speed tachometer output were failing to produce acceptable logical levels due to the low supply voltage to the fan motor. In other words, the supply voltage would be sufficient to run the fan at a low speed but the tachometer output became non-functional at low speeds corresponding to the low voltages.
FIG. 1
illustrates relevant components of an information handling system
10
having a central processing unit (CPU)
12
coupled to a memory
14
that stores instructions executable by the CPU
12
. 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
12
require active cooling to operate in a thermal environmental envelope recommended by the processor manufacturer. 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 the fan motor
16
. Information handling system
10
includes a circuit for regulating the power provided to the 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 the PMC
18
is coupled to a gate-input node of the FET
20
. The source node of the FET
20
is coupled to a first power supply having a voltage VCC
1
, while a drain node of the FET
20
is coupled to a power input node of the fan motor
16
.
The PMC
18
generates a square wave signal, the duty cycle of which depends upon a control signal provided to the PMC
18
.
FIG. 2
illustrates an exemplary square wave generated by the PMC
18
. The square wave shown in
FIG. 2
varies between VCC
2
, the voltage of a second power supply coupled to the PMC
18
in
FIG. 1
, and ground. VCC
2
may be distinct from VCC
1
, or from the same power supply. The first power supply is capable of providing high current power to the 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 the PMC
18
. The period of the 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 the PMC
18
.
The square wave signal generated by the PMC
18
is coupled to the gate-input node of the power FET
20
. When the voltage of the square wave signal is at VCC
1
, the FET
20
activates (becomes a low resistance), thereby coupling the first power supply (VCC
1
) 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 the CPU
12
. When the voltage of the square wave signal provided to the input gate of FET
20
is at or near ground, the FET
20
turns off, thereby disconnecting the first power supply from the input node of the fan motor
16
. In response, the rotational speed of the motor shaft begins to slow and may even stop until the FET
20
is again activated by the square wave being at VCC
1
.
The rotational speed of the fan motor's shaft depends upon the duty cycle of the square wave provided to the gate input of the FET
20
. The higher the duty cycle results in the higher the average rotational speed of the shaft. To obtain the highest average rotational speed, the duty cycle of the square wave would be 100%. With a 0% duty cycle, no power is provided to the fan motor
16
, and the shaft does not rotate. For duty cycles between 0 and 100%, the average rotational speed of the fan motor's shaft varies accordingly.
The constant coupling and decoupling of the first power supply to the power inp
Critz Christian L.
Vyssotski Nikolai
Baker & Botts L.L.P.
Dell Products L.P.
Martin Edgardo San
Nappi Robert E.
LandOfFree
Fan speed controller with conditioned tachometer signal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fan speed controller with conditioned tachometer signal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fan speed controller with conditioned tachometer signal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3184658