U.S. patent application number 11/059250 was filed with the patent office on 2006-08-17 for advanced programmable closed loop fan control method.
This patent application is currently assigned to TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Jeffrey David Johnson, Miroslav Oljaca.
Application Number | 20060181232 11/059250 |
Document ID | / |
Family ID | 36815009 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060181232 |
Kind Code |
A1 |
Oljaca; Miroslav ; et
al. |
August 17, 2006 |
ADVANCED PROGRAMMABLE CLOSED LOOP FAN CONTROL METHOD
Abstract
A fan control system and method that maintains the operating
temperature of computer and electronic devices or components at
about a predetermined control level to minimize power consumption
and audible noise. The fan control system is a programmable closed
loop system including a temperature sensor, first and second fan
controllers, and a fan/motor assembly including a power converter,
a motor, and a fan. The first fan controller provides programmable
acceleration/deceleration of the fan during an initial fan spin up,
and the second fan controller runs the fan only as fast as
necessary to keep the sensed temperature level of a computer device
as close as possible to the predetermined control level, thereby
minimizing the power consumption of the system and the audible
noise of the fan.
Inventors: |
Oljaca; Miroslav; (Tucson,
AZ) ; Johnson; Jeffrey David; (Tucson, AZ) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
TEXAS INSTRUMENTS
INCORPORATED
|
Family ID: |
36815009 |
Appl. No.: |
11/059250 |
Filed: |
February 16, 2005 |
Current U.S.
Class: |
318/268 |
Current CPC
Class: |
H02P 29/60 20160201;
G06F 1/206 20130101; G06F 1/3203 20130101; Y02D 10/16 20180101;
Y02D 10/00 20180101 |
Class at
Publication: |
318/268 |
International
Class: |
H02P 7/00 20060101
H02P007/00 |
Claims
1. A fan control system, comprising: at least one temperature
sensor operative to sense at least one first temperature associated
with at least one first location; and at least one fan fuzzy logic
controller having at least one input, wherein the input is
operative to receive a feedback control signal representing a
calculated difference between the first sensed temperature and a
predetermined control temperature, and wherein the fan fuzzy logic
controller is operative to generate at least one first fan control
output signal for minimizing the difference between the first
sensed temperature and the predetermined control temperature.
2. The system of claim 1 wherein the at least one first location is
associated with at least one integrated circuit device, and the at
least one temperature sensor comprises at least one thermal diode
temperature sensor operative to provide a representation of a local
die temperature of the integrated circuit device.
3. The system of claim 2 wherein the predetermined control
temperature is less than a maximum case temperature of the
integrated circuit device.
4. The system of claim 1 further including a DC motor and fan, and
wherein the at least one fan controller comprises at least one
pulse width modulation (PWM) controller operative to control a
speed of the DC motor and fan.
5. The system of claim 4 wherein the PWM controller is operative to
receive the feedback control signal as input, and to provide PWM
pulses having variable duty cycles based on the feedback control
signal.
6. A fan control system, comprising: at least one temperature
sensor operative to sense at least one first temperature associated
with at least one first location; and at least one fan controller
having at least one input, wherein the input is operative to
receive a feedback control signal representing a calculated
difference between the first sensed temperature and a predetermined
control temperature, and wherein the fan controller is operative to
generate at least one first fan control output signal for
minimizing the difference between the first sensed temperature and
the predetermined control temperature, wherein the at least one fan
controller is selected from the group consisting of a proportional
integral derivative (PID) controller, a fuzzy controller, and a
combination of a fuzzy controller and a non-fuzzy controller.
7. The system of claim 1 wherein the first fan control output
signal is operative to run a cooling fan at less than maximum
speed.
8. A method of controlling a cooling fan, comprising the steps of:
sensing at least one first temperature associated with at least one
first location by least one temperature sensor; receiving a
feedback control signal representing a calculated difference
between the first sensed temperature and a predetermined control
temperature by at least one fuzzy logic fan controller; and
generating at least one first fan control output signal for
minimizing the difference between the first sensed temperature and
the predetermined control temperature by the fan fuzzy logic
controller.
9. The method of claim 8 wherein the cooling fan is a DC fan,
wherein the fan controller comprises a pulse width modulation (PWM)
controller, and the receiving step includes receiving the feedback
control signal as input by the PWM controller, and providing PWM
pulses having variable duty cycles based on the feedback control
signal by the PWM controller.
10. A method of controlling a cooling fan, comprising the steps of:
sensing at least one first temperature associated with at least one
first location by least one temperature sensor; receiving a
feedback control signal representing a calculated difference
between the first sensed temperature and a predetermined control
temperature by at least one fan controller; and generating at least
one first fan control output signal for minimizing the difference
between the first sensed temperature and the predetermined control
temperature by the fan controller, wherein the fan controller is
selected from the group consisting of a proportional integral
derivative (PID) controller, a fuzzy controller, and a combination
of a fuzzy controller and a non-fuzzy controller.
11. The method of claim 8 further including the step of using the
at least one first fan control output signal to run the cooling fan
at less than maximum speed.
12. A method of controlling a cooling fan, the method being used to
control a temperature at a first location, comprising the steps of:
sensing a temperature associated with the first location; in the
event the sensed temperature is less than a predetermined control
temperature, providing at least one first fan control signal to run
the cooling fan at one or more speeds sufficient for allowing the
sensed temperature to increase gradually to substantially the
predetermined control temperature; and in the event the sensed
temperature is greater than the predetermined control temperature,
providing at least one second fan control signal to run the cooling
fan at one or more speeds sufficient for gradually decreasing the
sensed temperature to substantially the predetermined control
temperature.
13. The method of claim 12 wherein the first location is associated
with an integrated circuit device, and the sensed temperature is a
representation of a local die temperature of the integrated circuit
device.
14. The method of claim 13 wherein the predetermined control
temperature is less than a maximum case temperature of the
integrated circuit device.
15. The method of claim 12 further including the step of, in the
event the sensed temperature is less than a predetermined minimum
temperature, deactivating the cooling fan.
16. A method of performing a soft start of a cooling fan, the
cooling fan being operative to run at multiple speeds, comprising
the steps of: providing a first fan control signal to the cooling
fan for running the fan at a speed corresponding to a minimum fan
speed; providing at least one second fan control signal to the
cooling fan for gradually increasing the fan speed from the minimum
fan speed to a maximum fan speed over a first predetermined time
period; maintaining the fan speed at substantially the maximum fan
speed over a second predetermined time period; and providing at
least one third fan control signal to the cooling fan for gradually
decreasing the fan speed from the maximum fan speed to an
intermediate fan speed over a third predetermined time period, the
intermediate fan speed being between the minimum fan speed and the
maximum fan speed.
17. The method of claim 16 wherein at least one of the first and
third predetermined time periods is programmable for varying an
acceleration and a deceleration, respectively, of the cooling
fan.
18. The method of claim 16 wherein the intermediate fan speed
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] N/A
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] N/A
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to systems and
methods of controlling a fan to cool computer and electronic
devices, components, and/or equipment enclosures, and more
specifically to a system and method of controlling a cooling fan
based on the sensed die temperature of a CPU. The presently
disclosed system and method provide for reduced system power
consumption and reduced audible fan noise.
[0004] In recent years, operating speeds of computer devices such
as central processing units (CPUs) and microprocessors have
undergone dramatic increases. Because increases in computer device
speeds are typically accompanied by significant increases in the
level of current flowing through the devices, the amount of heat
dissipated by such computer devices has also risen dramatically.
For this reason, there is a need for improved systems and methods
of cooling computer devices and other electronic devices and/or
components associated therewith to remove any excess heat that may
cause high-speed computer systems to fail prematurely.
[0005] A conventional fan control system for cooling computer and
electronic devices is disclosed in U.S. Pat. No. 6,188,189 (the
'189 patent). As described in the '189 patent, a fan control system
includes one or more temperature sensors such as thermal diode
temperature sensors, and a pulse width modulation (PWM) control
circuit operative to control the speed of a DC fan by varying the
width of a PWM pulse. For example, a thermal diode temperature
sensor may be implemented on an integrated circuit (IC) die of a
CPU. In the event the sensed temperature of the CPU exceeds a
predetermined maximum temperature Tmax, the PWM control circuit
increases the PWM pulse width to increase the fan speed to its
maximum level. In the event the sensed CPU temperature is less than
a predetermined minimum temperature Tmin, fan cooling of the CPU
device is deemed unnecessary, and the PWM control circuit therefore
reduces the PWM pulse width to decrease the fan speed to zero. When
the sensed CPU temperature falls within the range Tmin to Tmax, the
PWM control circuit varies the PWM pulse width and consequently the
fan speed linearly, i.e., the variation of the fan speed is
linearly proportional to the sensed device temperature. The '189
patent further describes a power-up sequence for the fan control
system, which includes spinning up the fan directly to its maximum
speed for a limited time period upon power-up, before controlling
the fan speed based on the sensed CPU temperature.
[0006] However, the conventional fan speed control system disclosed
in the '189 patent has several drawbacks. For example, as described
above, when the sensed CPU temperature is within the temperature
range Tmin to Tmax, the system controls the fan speed so that it
varies linearly over the range Tmin to Tmax. Although such linear
control of the fan speed may maintain the CPU temperature within
acceptable limits, it is generally ineffective at minimizing power
consumption because the system including the fan control circuit
and the computer device being cooled is typically dynamically
nonlinear. Moreover, variations in power supply voltages, the
ambient temperature, and the power dissipation of the CPU may
contribute to the dynamic nonlinearity of the overall system.
Accordingly, varying the fan speed linearly within the temperature
range Tmin to Tmax may result in a fan speed and/or acceleration
that is higher than necessary to cool the computer system, thereby
causing increased system power consumption and increased audible
fan noise. In addition, spinning up the fan directly to maximum
speed during the fan power-up sequence may increase both the power
consumption of the system and the audible noise of the fan.
[0007] Another conventional fan speed control system is disclosed
in U.S. Pat. No. 6,601,168 (the '168 patent). As described in the
'168 patent, a fan speed control system includes a temperature
sensor operative to sense the temperature of an IC chip, and a fan
controller operative to adjust the speed of a cooling fan to a
target speed based on the sensed IC temperature. Specifically, the
fan controller slowly adjusts the fan speed from an initial speed
toward the target speed such that the audible noise associated with
accelerating (or decelerating) the fan is reduced and therefore
made less perceptible to the user of the computer system. However,
although the fan speed control system of the '168 patent may reduce
the audible fan noise, it may be incapable of minimizing the power
consumption of the overall system.
[0008] It would therefore be desirable to have an improved fan
control system and method for use in high-speed computer systems.
Such an improved fan control system and method would be capable of
maintaining the temperature of computer and electronic devices,
components, and/or equipment enclosures at an optimal level for
minimizing both the system power consumption and the audible fan
noise.
BRIEF SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, a fan control
system and method is provided that maintains the operating
temperature of computer and electronic devices or components at
approximately a predetermined control level, thereby minimizing
both the power consumption of the system and the audible noise of
the fan.
[0010] In one embodiment, the fan control system is a programmable
closed loop system that comprises one or more temperature sensors,
first and second fan controllers, and a fan/motor assembly
including a power converter, a motor, and a fan. Both the first fan
controller and the second fan controller are connectable to the
fan/motor assembly. The first fan controller is operative to
control the speed of the fan during the initial fan spin up, and
the second fan controller is operative to maintain the temperature
of a computer device at approximately the predetermined control
level after the initial fan spin up is completed.
[0011] In the presently disclosed embodiment, the first and second
fan controllers comprise respective programmable pulse width
modulation (PWM) controllers, and the fan/motor assembly includes a
DC motor and fan. The first and second PWM controllers are
operative to control the fan speed based on the variable width of a
PWM pulse. In the event the temperature of the computer device
sensed by the temperature sensor rises to meet or exceed the
predetermined control level, the first PWM controller is connected
to the fan/motor assembly and enabled, thereby initiating the spin
up of the fan.
[0012] In the preferred embodiment, the spin up of the fan is
performed in four stages. In a first stage, the first PWM
controller provides PWM pulses to the fan/motor assembly that have
a width corresponding to the minimum start-up voltage of the fan,
as specified by the fan manufacturer. In a second stage, the first
PWM controller provides PWM pulses that have increasing widths for
gradually increasing the fan speed from a minimum level to its
maximum level. In a third stage, the first PWM controller provides
PWM pulses having a width sufficient to maintain the fan speed at
its maximum level for a predetermined time period. In a fourth
stage, the first PWM controller provides PWM pulses that have
decreasing widths for gradually decreasing the fan speed from its
maximum level to a user-defined programmable intermediate level
between the minimum and maximum levels. During the second and
fourth stages of the fan spin up, the fan control system provides
programmable acceleration and deceleration, respectively, of the
fan. Further, at the end of the fourth stage, i.e., after the
initial fan spin up is completed, the first PWM controller is
disconnected from the fan/motor assembly, and the second PWM
controller is connected to the fan/motor assembly for controlling
the fan speed to maintain the sensed temperature of the computer
device at approximately the predetermined control level.
[0013] In the preferred embodiment, the temperature sensor is an
on-die thermal diode temperature sensor configured to provide a
representation of the local die temperature of the computer device.
Further, the fan control system is configured to provide die
temperature feedback from the thermal diode temperature sensor to
the second PWM controller. The fan control system is operative to
compare the sensed die temperature to the predetermined control
level to generate an error signal, which has a magnitude
corresponding to the difference between the sensed die temperature
and the predetermined control level. The fan control system
controls the fan speed based on the magnitude of the error signal.
The second PWM controller is configured to accept the error signal
as input, and to provide PWM pulses having variable widths based on
the error magnitude. The second PWM controller provides the
variable width PWM pulses to control the fan speed to levels
sufficient to maintain the sensed temperature of the computer
device at approximately the predetermined control level.
[0014] In the presently disclosed embodiment, if the sensed die
temperature (T.sub.diode) is greater than a predetermined minimum
level (T.sub.min) and T.sub.diode is less than or equal to the
predetermined control level (T.sub.control), i.e., the error
magnitude is less than or equal to zero, then the second PWM
controller provides PWM pulses having variable widths for
controllably decreasing the fan speed, thereby allowing the level
of T.sub.diode to increase such that it gradually approaches the
level of T.sub.control. If T.sub.diode rises to a level greater
than T.sub.control, i.e., the error magnitude is greater than zero,
then the second PWM controller provides PWM pulses having variable
widths for controllably increasing the fan speed, thereby causing
the level of T.sub.diode to decrease such that it again gradually
approaches the level of T.sub.control. If T.sub.diode falls to a
level less than T.sub.min, then the fan control system is
deactivated. If T.sub.diode subsequently rises to a level greater
than T.sub.min and greater than or equal to T.sub.control, i.e.,
the error magnitude is greater than or equal to zero, then the
first PWM controller is operative to initiate the spin up of the
fan, after which the second PWM controller is operative to control
the fan speed based on the error magnitude to move T.sub.diode as
close as possible to T.sub.control.
[0015] By providing a programmable closed loop fan control system
that allows programmable acceleration and deceleration of a fan
upon power-up, and then runs the fan only as fast as necessary to
keep the sensed temperature level of a computer device as close as
possible to a predetermined control level, both the power
consumption of the system and the audible noise of the fan can be
reduced.
[0016] Other features, functions, and aspects of the invention will
be evident from the Detailed Description of the Invention that
follows.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0017] The invention will be more fully understood with reference
to the following Detailed Description of the Invention in
conjunction with the drawings of which:
[0018] FIG. 1 is a block diagram of a fan control system according
to the present invention;
[0019] FIG. 2 is a diagram of fan voltage versus time corresponding
to a fan spin up procedure performed by the fan control system of
FIG. 1;
[0020] FIG. 3 is a flow diagram of the fan spin up procedure
performed by the fan control system of FIG. 1;
[0021] FIG. 4a is a diagram of the maximum case temperature of a
representative computer device versus the device power dissipation,
corresponding to the device being cooled by a fan running at its
maximum speed;
[0022] FIG. 4b is a diagram of the maximum case temperature of the
representative computer device versus the device power dissipation,
corresponding to the device being cooled by a fan running at a
predetermined low speed;
[0023] FIG. 4c is a diagram of the thermal diode temperature of the
representative computer device versus the device power dissipation,
corresponding to the device being cooled by a temperature control
procedure performed by the fan control system of FIG. 1; and
[0024] FIG. 5 is a flow diagram of the temperature control
procedure performed by the fan control system of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0025] A fan control system and method is disclosed that provides
controllable acceleration and deceleration of a fan during an
initial fan spin up, and then runs the fan at speeds sufficient to
maintain the operating temperature of a computer or electronic
device or component at approximately a predetermined control level,
thereby minimizing the power consumption of the system and the
audible noise of the fan. The fan control system provides
programmable closed loop control of the speed and acceleration of
the fan based on the sensed temperature of the device or
component.
[0026] FIG. 1 depicts an illustrative embodiment of a fan control
system 100, in accordance with the present invention. In the
illustrated embodiment, the fan control system 100 comprises a
first fan controller 102, a second fan controller 104, control
logic 118 and 122, a pair of multiplexors (MUXs) 106 and 108, a
fan/motor assembly 112 including a power converter 110 and a motor
and fan 111, a temperature sensor 116, an analog-to-digital
converter (ADC) 120, and a summer 124. The first fan controller 102
is operative to control the speed and acceleration of the fan 111
during an initial spin up of the fan, and the second fan controller
104 is operative to control the fan speed and acceleration to
maintain the sensed temperature of a computer device 114 at
approximately a predetermined control level after the initial fan
spin up is completed.
[0027] For example, the computer device 114 may comprise a
microprocessor or a Central Processing Unit (CPU) within a computer
system such as a desktop or laptop personal computer (PC; not
shown). It is understood, however, that the computer device 114 may
alternatively comprise one or more processors and/or other
electronic devices or components associated therewith within a
computer system. In the preferred embodiment, the fan control
system 100 is implemented on one or more printed circuit boards
(PCBs) within a PC.
[0028] In the presently disclosed embodiment, the fan/motor
assembly 112 comprises a DC motor and fan 111, and the first and
second fan controllers 102 and 104 comprise respective programmable
pulse width modulation (PWM) controllers operative to control the
speed of the fan 111 via PWM pulses having variable widths. Those
of ordinary skill in this art will appreciate that there is a
substantially linear relationship between the duty cycle of PWM
pulses provided by a PWM controller and the speed of a DC fan. In
one embodiment, the PWM controllers 102 and 104 are operative to
provide PWM pulses having duty cycles ranging from about 50% to
100%, in which the 50% PWM duty cycle corresponds to the minimum
fan voltage required to start the fan 111, and the 100% PWM duty
cycle corresponds to the fan voltage required to run the fan 111 at
maximum speed. It should be understood, however, that the minimum
fan voltage required to start a fan is normally specified by the
fan manufacturer, and that the 50% PWM duty cycle corresponding to
the minimum fan voltage, as described herein, is merely provided
for purposes of illustration. Accordingly, it is appreciated that
any other suitable PWM duty cycles may be provided by the PWM
controllers 102 and 104 for starting and for subsequently
controlling the speed and acceleration of the fan 111, in
accordance with fan spin up and temperature control procedures
described herein.
[0029] In the illustrated embodiment, the computer device 114
comprises an integrated cirucit (IC) chip, and the temperature
sensor 116 is a thermal diode temperature sensor implemented on the
die of the IC chip. The temperature sensor 116 is configured to
provide an analog representation of the local die temperature
(T.sub.diode,analog) of the computer device 114 to the ADC 120,
which converts the analog temperature representation to digital
form (T.sub.diode). As shown in FIG. 1, the ADC 120 provides the
sensed die temperature T.sub.diode to the control logic 118 and to
the summer 124. It is understood that, in alternative embodiments,
the function of converting the analog representation of the local
die temperature of the computer device 114 may be provided within
the device itself, thereby rendering the ADC 120 unnecessary.
[0030] The fan control system 100 maintains the operating
temperature of the computer device 114 at about the predetermined
control level by providing programmable closed loop control of the
speed and acceleration of the fan 111 based on the sensed
temperature T.sub.diode of the computer device 114. In an
illustrative mode of operation, the PWM controllers 102 and 104 are
initially disconnected from the fan/motor assembly 112, thereby
causing the fan 111 to be placed in an "off" condition.
Specifically, the control logic 118 provides a Select2 signal to
the MUX 108, in which the Select2 signal initially has a logical
level that causes the MUX 108 to select its second input "2",
effectively providing a 0% PWM duty cycle to the power converter
110. It is noted that the PWM controller 102 initially provides a
Select1 signal to the MUX 106, in which the Select1 signal has a
logical level that causes the MUX 106 to select its first input
"1".
[0031] More specifically, the control logic 118 receives the sensed
temperature T.sub.diode from the ADC 120, and compares the
temperature T.sub.diode to a predetermined minimum level T.sub.min.
In the event T.sub.diode is less than T.sub.min, the control logic
118 provides the Select2 signal to the MUX 108, causing the MUX 108
to select its second input "2" and to provide the 0% PWM duty cycle
to the power converter 110. In effect, the PWM controllers 102 and
104 are disconnected from the fan/motor assembly 112, and the fan
111 is "off". In the event T.sub.diode is greater than or equal to
Tin, the control logic 118 provides the Select2 signal having a
logical level that causes the MUX 108 to select its first input
"1", in preparation of placing the fan 111 in an "on" condition.
Because, as described above, the MUX 106 is also selecting its
first input "1", the MUXs 106 and 108 form an electrical connection
from the PWM controller 102 to the power converter 110.
[0032] As shown in FIG. 1, the summer 124 receives the sensed
temperature T.sub.diode from the ADC 120, and determines the
difference between the temperature T.sub.diode and a predetermined
control level T.sub.control, which is greater than the
predetermined minimum level T.sub.min. In the preferred embodiment,
the predetermined control level T.sub.control corresponds to an
optimal operating temperature of the computer device 114, as
recommended by the device manufacturer. In the event T.sub.diode is
greater than T.sub.control, the summer 124 generates an error
signal having a magnitude that is greater than zero, and provides
the error signal to the control logic 122 and to the PWM controller
104, which at this time is disconnected from the fan/motor assembly
112. The control logic 122 receives the error signal, and compares
the magnitude of the error signal to zero. Because the error
magnitude is greater than zero, the control logic 122 provides an
enable (en) signal to the PWM controller 102, thereby causing the
PWM controller 102 to start performing the fan spin up procedure in
response to the enable signal. For example, the PWM controller 102
may be configured to trigger on an edge of the enable signal.
[0033] FIG. 2 depicts a diagram illustrating the voltage of the fan
111 versus time. The diagram of the fan voltage versus time
corresponds to the fan spin up procedure, as performed by the PWM
controller 102 (see FIG. 1). In the preferred embodiment, the fan
spin up procedure comprises four stages, i.e., a first stage
occurring at time T1, a second stage occurring from time T1 to time
T2, a third stage occurring from time T2 to time T3, and a fourth
stage occurring from time T3 to time T4.
[0034] At time T1, the PWM controller 102 provides about a 50% PWM
duty cycle (DC %.sub.1) to the power converter 110. As described
above, when the PWM controller 102 is enabled to perform the fan
spin up procedure, the MUXs 106 and 108 are controlled to select
their first inputs "1", thereby forming an electrical connection
from the PWM controller 102 to the power converter 110. In the
presently disclosed embodiment, the 50% PWM duty cycle corresponds
to the minimum fan voltage required to start the fan 111. It is
understood that the PWM controller 102 may alternatively provide
any suitable PWM duty cycle sufficient to start the fan 111, as
recommended by the fan manufacturer. The power converter 110
receives the 50% PWM duty cycle, and converts the 50% PWM duty
cycle to electrical energy, which is subsequently applied across
the phase windings (not shown) of the DC motor to start the fan
111. When the fan 111 starts, the fan runs at its minimum
speed.
[0035] From time T1 to time T2, the PWM controller 102 provides PWM
duty cycles (DC %.sub.1) ranging from about 50% to 100% to the
power converter 110. As described above, the 100% PWM duty cycle
corresponds to the fan voltage required to run the fan 111 at
maximum speed. As shown in FIG. 2, the PWM duty cycle (fan voltage)
ramps up over the time period T1 to T2, thereby gradually
increasing the fan speed from the minimum speed to the maximum
speed. In effect, the PWM controller 102 provides for a PWM soft
start of the fan motor, thereby reducing the initial electrical
current surge to the motor. In the preferred embodiment, the
acceleration of the fan 111 from time T1 to time T2 can be
programmed to minimize the system power consumption and the audible
noise generated while the fan accelerates.
[0036] From time T2 to time T3, the PWM controller 102 provides the
100% PWM duty cycles (DC %.sub.1) to maintain the fan speed at its
maximum level. Providing 100% PWM duty cycles to the fan 111 for a
predetermined time period is particularly useful in the event the
recommended minimum fan voltage (e.g., corresponding to the 50% PWM
duty cycle) fails to start the fan 111.
[0037] From time T3 to time T4, the PWM controller 102 provides PWM
duty cycles (DC %.sub.1) ranging from about 100% to 75% to the
power converter 110. As shown in FIG. 2, the PWM duty cycle (fan
voltage) ramps down over the time period T3 to T4, thereby
gradually decreasing the fan speed from the maximum speed (e.g.,
corresponding to the 100% PWM duty cycle) to a user defined
intermediate level (e.g., an intermediate level corresponding to
the 75% PWM duty cycle) between the minimum speed (e.g.,
corresponding to the 50% PWM duty cycle) and the maximum speed. In
the preferred embodiment, the deceleration of the fan 111 from time
T3 to time T4 can be programmed to minimize the system power
consumption and the audible noise generated while the fan
decelerates.
[0038] At time T4, the PWM controller 102 provides the Select1
signal having a logical level that causes the MUX 106 to select its
second input "2", thereby disconnecting the PWM controller 102 from
the fan/motor assembly 112 and completing the fan spin up
procedure.
[0039] Accordingly, the presently disclosed fan spin up procedure
provides for a PWM soft start of the fan motor. Such a PWM soft
start significantly reduces the average current requirements of the
motor, and maintains good control of the fan acceleration. As
described above, the ramp time during the second stage, i.e., soft
start portion, of the fan spin up procedure can be varied to obtain
a higher or lower acceleration of the fan 111. Similarly, the ramp
time during the fourth stage of the fan spin up procedure can be
varied to obtain different levels of fan deceleration. Because the
fan spin up procedure provides for soft starting the fan motor, the
speed of the fan can be increased to its maximum level with reduced
mechanical stress, thereby increasing the lifetime of the motor and
fan 111. Further, in the event a mechanical problem prevents the
fan 111 from starting during the PWM soft start of the motor, the
fan may be started during the third stage of the fan spin up
procedure when the full fan voltage is applied and maximum motor
torque is achieved.
[0040] A method of performing the presently disclosed fan spin up
procedure is illustrated by reference to FIGS. 1 and 3. It should
be understood that when the fan spin up procedure is performed, the
motor and fan 111 are initially in the "off" condition, and the
MUXs 106 and 108 are configured to connected the PWM controller 102
to the fan/motor assembly 112. As depicted in step 302, a
determination is made as to whether the sensed temperature
T.sub.diode of the computer device 114 is greater than or equal to
the predetermined control level T.sub.control. In the event
T.sub.diode is greater than or equal to T.sub.control, a
predetermined minimum PWM duty cycle is applied, as depicted in
step 304, by the PWM controller 102 to the fan/motor assembly 112
to cause the fan 111 to start and to run at its minimum speed. For
example, the minimum applied PWM duty cycle may be about a 50% duty
cycle. The PWM duty cycles are then ramped up, as depicted in step
306, from the minimum PWM duty cycle to a maximum PWM duty cycle to
cause the fan speed to increase gradually from the minimum speed to
a maximum speed. For example, the maximum applied PWM duty cycle
may be about a 100% duty cycle. Next, the fan speed is maintained,
as depicted in step 308, at the maximum speed for a predetermined
time period. The PWM duty cycles are then ramped down, as depicted
in step 310, from the maximum PWM duty cycle to a user defined
intermediate PWM duty cycle to cause the fan speed to decrease
gradually from the maximum speed to an intermediate speed between
the minimum and maximum speeds. For example, the intermediate
applied PWM duty cycle may be about a 75% duty cycle. At the end of
step 310, the fan spin up procedure is completed.
[0041] After the fan spin up procedure is completed, the PWM
controller 102 provides the Select1 signal to the MUX 106, in which
the Select1 signal has a logical level that causes the MUX 106 to
select its second input "2". As a result, an electrical connection
is formed from the PWM controller 104 to the power converter 110.
At this time, the PWM controller 104 is operative to perform the
temperature control procedure to maintain the operating temperature
of the computer device 114 at about the predetermined control level
T.sub.control. In the presently disclosed embodiment, the PWM
controller 104 receives the error signal generated by the summer
124, and operates to minimize the magnitude of the error
signal.
[0042] For example, the PWM controller 104 may be implemented as a
proportional integral derivative (PID) controller, a fuzzy
controller, a combination of a fuzzy controller and a non-fuzzy
controller, or any other suitable controller. Implementing the PWM
controller 104 as a PID or fuzzy controller allows the fan control
system 100 to anticipate changes in the sensed temperature of the
computer device 114, and to adapt the speed of the fan 111 to these
sensed temperature changes.
[0043] The temperature control procedure performed by the PWM
controller 104 will be better understood with reference to FIGS.
4a-4c. FIG. 4a depicts a plot 402 of the maximum case temperature
of the computer device 114 (see FIG. 1) versus the device power
dissipation. It should be appreciated that the case temperature of
the device 114 is substantially equal to the device die
temperature. As shown in FIG. 4a, there is a linear relationship
between the maximum case temperature of the device 114 and the
device power dissipation. Specifically, as the power dissipation of
the device increases (decreases), the maximum case temperature also
increases (decreases). The maximum case temperature may therefore
be easily determined for any power level. It is noted that the
maximum case temperature (T.sub.max) corresponding to a
predetermined thermal design point (TDP) of the computer device 114
occurs at the highest temperature level of the plot 402. For
example, the actual power dissipation of the computer device 114
may be measured to be about 70 watts, and the measured power may be
plotted to obtain the maximum allowable case temperature of about
61.degree. C. for that power level. To assure compliance with the
plot 402 and optimal system reliability for all device operating
conditions and power levels, the fan 111 would normally be run
continuously at its maximum speed.
[0044] FIG. 4b depicts the plot 402 and a second plot 404 of the
maximum case temperature of the computer device 114 (see FIG. 1)
versus the device power dissipation. As described above, compliance
with the plot 402 can be achieved by running the fan 111
continuously at its maximum speed. The plot 404 represents a
situation in which the fan 111 is run at a speed significantly
slower than the maximum speed (e.g., the minimum speed). As shown
in FIG. 4b, there is no longer a linear relationship between the
maximum case temperature of the computer device 114 and the device
power dissipation when running the fan 111 at the slower speed. For
example, when the fan 111 is run at the slower speed, the maximum
case temperature may be reached at a first intermediate power level
P.sub.int1, which is significantly less than the thermal design
point (TDP) of the device 114. However, up to this intermediate
power level P.sub.int1, the maximum case temperature remains below
T.sub.max, even though the fan 111 is not running at its maximum
speed. Allowing the case temperature of the computer device 114 to
rise above T.sub.max is not recommended because damage to the
device 114 may result.
[0045] FIG. 4c depicts a plot 406 of the thermal diode temperature
T.sub.diode of the computer device 114 (see FIG. 1) versus the
device power dissipation. The plot 406 results when the fan 111 is
run in accordance with the temperature control procedure performed
by the PWM controller 104 (see FIG. 1). The plot 406 has two
portions, i.e., a substantially flat portion 406a that remains at
the predetermined control level T.sub.control within the power
level range 0 to a second intermediate power level P.sub.int2, and
a ramp portion 406b that corresponds to the range P.sub.int2 to
TDP. As shown in FIG. 4c, the predetermined control level
T.sub.control is less than the maximum case temperature
T.sub.max.
[0046] The PWM controller 104 is operative to perform the
temperature control procedure to maintain the thermal diode
temperature T.sub.diode of the computer device 114 at about the
predetermined control level T.sub.control within the power level
range 0 to P.sub.int2. Because T.sub.control is less than
T.sub.max, the fan 111 may be run at speeds that are less than its
maximum speed within the range 0 to P.sub.int2. For example, within
the range 0 to P.sub.int2, the fan 111 can be run at speeds greater
than its minimum speed but less than its maximum speed, and within
the range P.sub.int2 to TDP, the fan 111 can be run at its maximum
speed.
[0047] Accordingly, the presently disclosed temperature control
procedure allows the speed of the fan 111 to be adjusted to make
the sensed temperature of the computer device 114, as indicated by
the thermal diode temperature T.sub.diode, as close as possible to
the predetermined control level T.sub.control. In the event the
sensed temperature is below T.sub.control, the fan speed is
decreased. In the event the sensed temperature is above
T.sub.control, the fan speed is increased. In this way, the
temperature of the computer device 114 is prevented from
significantly exceeding the predetermined control level
T.sub.control for a substantial length of time, and the fan 111
runs only as fast as necessary to assure that the device
temperature is brought below the maximum case temperature T.sub.max
and remains as close as possible to the control level
T.sub.control. As a result, both the system power consumption and
the audible fan noise are minimized. It should be noted that the
fan speed is not only dependent upon the temperature and power
dissipation of the computer device 114, but it may also be affected
by other factors including but not limited to the ambient
temperature, the supply voltage, the specific characteristics of
the fan, and the elevation at which the fan control system is
employed.
[0048] A method of performing the temperature control procedure is
illustrated by reference to FIGS. 1 and 5. It should be understood
that when the temperature control procedure is initially performed,
the speed of the fan 111 is at about a user defined intermediate
level (e.g., the intermediate level corresponding to the 75% PWM
duty cycle). Further, the MUXs 106 and 108 are configured to
connect the PWM controller 104 to the fan/motor assembly 112. As
depicted in step 502, a first determination is made as to whether
the sensed temperature T.sub.diode is less than the predetermined
minimum level T.sub.min. In the event T.sub.diode is not less than
T.sub.min, a second determination is made, as depicted in step 504,
as to whether the sensed temperature T.sub.diode is equal to the
predetermined control level T.sub.control. In the event T.sub.diode
is equal to T.sub.control, the method loops back to step 502. In
the event T.sub.diode is not equal to T.sub.control, variable PWM
duty cycles are provided, as depicted in step 506, by the PWM
controller 104 to the fan/motor assembly 112 to control the fan
speed in an effort to move the level of T.sub.diode as close as
possible to the level of T.sub.control, thereby minimizing the
magnitude of the error signal |T.sub.diode-T.sub.control| generated
by the summer 124. For example, if T.sub.diode is less than
T.sub.control, i.e., the error magnitude is less than zero, then
the PWM controller 104 provides PWM pulses having variable widths
for controllably decreasing the fan speed, thereby allowing
T.sub.diode to increase such that it gradually approaches
T.sub.control. If T.sub.diode is greater than T.sub.control, i.e.,
the error magnitude is greater than zero, then the PWM controller
104 provides PWM pulses having variable widths for controllably
increasing the fan speed, thereby causing T.sub.diode to decrease
such that it again gradually approaches T.sub.control. In the event
T.sub.diode falls to a level less than T.sub.min, fan cooling of
the computer device 114 is deemed unnecessary, and the fan control
system 100 is deactivated, as depicted in step 508. To that end,
the control logic 118 provides the Select2 signal to the MUX 108,
in which the Select2 signal has a logical level that causes the MUX
108 to select its second input "2", effectively providing a 0% PWM
duty cycle to the power converter 110.
[0049] Having described the above illustrative embodiments, other
alternative embodiments or variations may be made. For example, it
was described that the fan control system 100 (see FIG. 1) includes
the first fan controller 102 for controlling the speed and
acceleration of the fan 111 during an initial spin up of the fan,
and the second fan controller 104 for controlling the fan speed and
acceleration to maintain the sensed temperature of the computer
device 114 at about the predetermined control level after the
initial fan spin up is completed. However, it should be understood
that in alternative embodiments, the fan control system 100 may
include one, two, or any other suitable number of fan controllers
for performing the presently disclosed fan spin up and temperature
control procedures.
[0050] It was also described that the fan control system includes a
DC motor and fan, and that the first and second fan controllers are
configured as PWM controllers for controlling the DC motor/fan.
However, in alternative embodiments, the fan control system may
comprise any other suitable types of motor, fan, and fan
controller(s) for performing the fan spin up and temperature
control procedures described herein.
[0051] It was also described that the temperature sensor 116
provides a representation of the local die temperature of the
computer device 114. However, in alternative embodiments, the
temperature sensor may comprise one or more temperature sensors
operative to provide representations of temperatures associated
with any suitable article(s) or device(s), or associated with one
or more locations within a space or enclosure such as an
electronics enclosure.
[0052] It will further be appreciated by those of ordinary skill in
the art that modifications to and variations of the above-described
advanced programmable closed loop fan control method may be made
without departing from the inventive concepts disclosed herein.
Accordingly, the invention should not be viewed as limited except
as by the scope and spirit of the appended claims.
* * * * *