U.S. patent application number 14/994845 was filed with the patent office on 2017-07-13 for coordinating cooling fans.
This patent application is currently assigned to Hewlett Packard Enterprise Development LP. The applicant listed for this patent is Hewlett Packard Enterprise Development LP. Invention is credited to Hung-Chu Lee, KaiChun Su, Ting Wen Tsai, Yuan-Hung Wang.
Application Number | 20170198706 14/994845 |
Document ID | / |
Family ID | 59274831 |
Filed Date | 2017-07-13 |
United States Patent
Application |
20170198706 |
Kind Code |
A1 |
Wang; Yuan-Hung ; et
al. |
July 13, 2017 |
Coordinating Cooling Fans
Abstract
In one example in accordance with the present disclosure a
system for coordinating cooling fans in a housing includes a first
fan for cooling a power supply; a second fan; a control board to
provide a first pulsed wave modulated (PWM) signal to the second
fan; and a logic element to provide a control signal to the first
fan based on a second PWM signal from the power supply and a third
PWM signal from the control board.
Inventors: |
Wang; Yuan-Hung; (Taipei,
TW) ; Lee; Hung-Chu; (Taipei, TW) ; Su;
KaiChun; (Taipei, TW) ; Tsai; Ting Wen; (New
Taipei City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hewlett Packard Enterprise Development LP |
Houston |
TX |
US |
|
|
Assignee: |
Hewlett Packard Enterprise
Development LP
Houston
TX
|
Family ID: |
59274831 |
Appl. No.: |
14/994845 |
Filed: |
January 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 25/166 20130101;
F04D 27/004 20130101; F04D 25/068 20130101; F04D 29/325 20130101;
F04D 25/08 20130101 |
International
Class: |
F04D 27/00 20060101
F04D027/00; F04D 25/08 20060101 F04D025/08; F04D 29/32 20060101
F04D029/32; F04D 25/06 20060101 F04D025/06 |
Claims
1. A system for coordinating cooling fans, the system comprising: a
first fan for cooling a power supply; a second fan; a control board
to provide a first pulsed wave modulated (PWM) signal to the second
fan; and a logic element to provide a control signal to the first
fan based on a second PWM signal from the power supply and a third
PWM signal from the control board.
2. The system of claim 1, further comprising a lookup table which
indexes the third PWM signal to the first PWM signal.
3. The system of claim 1, wherein the second PWM signal is
independent of the third and first PWM signals.
4. A system for coordinating cooling fans in a housing, the system
comprising: a first fan; an OR-logic element that outputs a control
signal to the first fan; a power supply to provide a first pulsed
wave modulated (PWM) signal to the OR-logic; and a controller to
provide a second PWM signal to the OR-logic, wherein the second PWM
signal is used to increase a duty cycle applied to the first fan so
as to prevent backflow in air circulation when a second fan is
operated.
5. The system of claim 4, wherein the OR-logic controls an
electrical connection between the first fan and a power source to
power the first fan.
6. The system of claim 4, wherein the OR-logical element comprises
a transistor.
7. The system of claim 4, wherein the first pulsed width modulated
signal has a lower duty cycle than the second PWM signal.
8. The system of claim 4, wherein the first fan operates when the
controller is unpowered.
9. The system of claim 4, wherein the second PWM signal is provided
on a line of a multiline connection between the controller and the
power supply.
10. The system of claim 4, wherein the OR-logic is within the power
supply.
11. A method for controlling a power supply unit (PSU) fan, the
method comprising: providing a pulse width modulated (PWM) signal
via a power line to regulate a speed of the fan, wherein the PWM
signal is formed using a PWM signal from a power supply and a PWM
signal from a control board.
12. The method of claim 11, wherein the PWM signal from the control
board varies based on an input to a second fan.
13. The method of claim 11, wherein the PWM signal from the control
board is regulated so as to prevent backflow of air through the
power supply unit fan.
14. The method of claim 11, wherein the PWM signal from the control
board is provided on a channel of a multi-channel connector between
the control board and the power supply.
15. The method of claim 11, wherein the PWM signal is output by an
OR-logic element receiving the PWM signal from a power supply and
the PWM signal from a control board.
Description
BACKGROUND
[0001] One challenge in electronic devices is that the high
frequency operation can produce significant heating. Heat can
impact the performance and reduce the lifetime of electronic
components and devices. In order to mitigate the effects of heat,
some electronic devices include fans to circulate air over the
electronics. This reduces the temperature of the air over the
electronics, which increases the temperature differential between
the electronics and air. The temperature differential is one factor
in the transfer of heat between the electronics and air, with
larger differentials producing greater heat transfer. Thus, the
circulation of air by a fan allows more effective heat loss for the
electronic components
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The accompanying drawings illustrate various examples of the
principles described herein and are a part of the specification.
The illustrated examples are merely illustrative and do not limit
the scope of the claims. Like numerals denote like but not
necessarily identical elements.
[0003] FIGS. 1A-C show a structure consistent with one example of
the current specification with three different air flow patterns
produced by different fan control conditions.
[0004] FIGS. 2A-B show example structures consistent with the
current specification.
[0005] FIG. 3 shows examples of PWM signals and their possible
interactions using an OR-logic consistent with the current
specification.
[0006] FIGS. 4A-B are flowcharts showing example methods of
coordinating a power supply fan with other fans in a housing
consistent with the current specification.
[0007] FIG. 5 shows a structure consistent with one example of the
current specification.
DETAILED DESCRIPTION
[0008] Fans are often used to increase air circulation across
electronics in order to cool the electronics. Fans increase the air
pressure on one side of the fan and reduce the air pressure on the
other side of the fan. These air pressures then induce airflow,
with air flowing away from the high pressure area and towards low
pressure areas. However, when multiple fans exist in proximity to
each other, interaction between the pressures produced by the
individual fans may produce unstable, undesirable, and/or less
efficient airflow arrangements. In such circumstances, coordination
of the fans may allow better use of the fans or minimize the energy
consumed by the fans to achieve a desired airflow and cooling.
[0009] An electronic device typically includes a number of
electronic components in a housing. Examples include a desktop
tower, laptop case, tablet enclosure, phone, or similar enclosure.
Some components may be composed of a number of subcomponents,
including, in some cases, a fan for cooling the component. For
example, a power supply, which converts stored or received power to
desired voltages may include a dedicated fan. In many instances,
such a power supply is a commercially available design which lacks
available externally accessible controls in order to regulate the
included fan. This presents a challenge in trying to coordinate the
activity of a power supply fan with other fans that may be
installed in the housing of the electronic device, such as a fan
associated with the control panel.
[0010] In some examples, the power supply fan is oriented so as to
draw air from inside the housing, over the power supply, and blow
the air out a vent or opening in the housing. The fan includes an
electric motor which turns the fan and converts electricity into
mechanical work. The electrical motor may be capable of being
operated at more than one level of output, generally by varying the
voltage supplied to the electrical motor. Thus, higher voltages
applied to the motor cause the motor to turn the fan faster and
produce greater airflow. Adjusting the voltage that is applied to
the motor implies a way to control the fan.
[0011] While use of a variable transformer, rheostat, and other
solutions exist, one solution is to use a constant voltage signal
that is provided at controlled intervals. This is called pulse
width modulation (PWM). If the frequency of the pulse is selected
appropriately, the device receiving the PWM signal interprets the
PWM signal as a steady signal rather than reacting to the pulses.
For electric motors, this frequency is generally in excess of 1-10
kHz. When designed appropriately, an electric motor receiving PWM
signal with a duty cycle of X % at Y volts reacts as if it were
receiving a direct current (DC) of X % multiplied by Y volts. Thus,
for example, a 5-volt signal that is provided with a 40% duty cycle
powers the electric motor as if it received a 2-volt direct
current.
[0012] One advantage of PWM control is that it tends to have
relatively low losses. The use of PWM control also has the
advantage that the voltage source remains constant and the duty
cycle is adjusted to produce a range of effective voltages on the
electric motor. Part of the reason this works is the lag in the
elements powering the motor are significantly longer than the
switching time in the PWM signal. Thus, the motor and the fan
cannot react fast enough to respond to the variation in the PWM
signal and instead experiences the composite result of the PWM
signal. Accordingly, a PWM signal can be used to provide control as
well as power for an electric motor driving a fan.
[0013] In some examples, the PWM signal is provided as a control
signal that is used to control a switch or other connection between
a power source and the fan. In these cases, the PWN signal may have
an amplitude that is different from the maximum voltage applied
from the power source, for example, 1-volt vs. 5-volts. In other
examples, the PWM signal is provided as the power signal. In these
cases, the maximum amplitude of the PWM signal and the maximum
power applied may be the same. The use of a lower voltage control
signal may reduce power consumption in some designs. However,
generally speaking, PWM control signals tend to be fairly efficient
compared with other methods of scaling voltage.
[0014] Power Management Bus (PMBus) is an open standard
power-management protocol. For power supplies with a PMBus, an
interface exists to provide direct control over the fan from the
control panel. However, for non-PMBus power supplies, there may not
be available control access to directly control the power supply
fan. In this specification, a system and method are disclosed for
controlling the fan in a non-PMBus power supply by combining a
second PWM signal with the PWM signal from the power supply to the
fan. The second PWM signal is may be provided by the control panel
and allows the control panel to coordinate operation of the power
supply fan with other fans in the housing of the electronic
device.
[0015] FIG. 1A shows an example of a system (100) consistent with
the present specification. An enclosure (110) provides mounting
locations for a first fan (120) and a second fan (130). When both
the first fan (120) and the second fan (130) are powered at
similar, low voltages, the flow from both fans is to push air from
the inside of the enclosure (110) to the outside of the enclosure
(110). This is consistent with a low cooling demand condition.
[0016] However, as shown in FIG. 1B, when one of the fans, in this
case the first fan (120), is powered at a low level and the other
fan, in this case the second fan (130), is powered at a higher
level, the airflow of the second fan (130) dominates the airflow of
the first fan (120) and the airflow may reverse through the first
fan (120). If the first and second fans (120, 130) are located so
as to increase airflow over electronics or other components, this
inversion of the desired flow pattern results in less efficient
cooling as air warmed by passage near the first fan (120) is now
passed through the second fan (130) and used for cooling near the
second fan (130) rather than using unheated air. As the heat
transfer rate depends upon the temperature differential between the
heat source (e.g. electronics) and heat sink (surrounding air), the
use of warmer air results in less cooling. Accordingly,
coordination of the first and second fans in order to prevent
inversion of the airflow facilitates effective and efficient
cooling.
[0017] FIG. 1C shows the first fan (120) and the second fan (130)
being operated in a coordinated fashion. Accordingly, even though
the airflow from the second fan (130) has been increased, the first
fan (120) continues to expel air though an opening in the housing
(110). This shows a high cooling demand condition being efficiently
managed by coordinating the behavior of the two cooling fans (120,
130).
[0018] Accordingly, the present specification describes, among
other examples, a system for coordinating the performance of fans
in a housing, the system including: a first fan, wherein the first
fan is a power supply fan; a second fan; a power supply; a control
board to provide a first pulsed wave modulated (PWM) signal to the
second fan; and a logic element to provide a control signal to the
first fan by combining a second PWM signal from the power supply
and a third PWM signal from the control board.
[0019] In another example, a system for enabling control panel
regulation of a fan, the system including a first fan; an OR-logic
element that outputs a control signal to the first fan; a power
supply to provide a first pulsed wave modulated (PWM) signal to the
OR-logic; and a controller to provide a second PWM signal to the
OR-logic. The second PWM signal is used to increase a duty cycle
applied to the first fan so as to prevent backflow in air
circulation when a second fan is operated.
[0020] These examples are illustrated and described as follows.
[0021] FIG. 2A shows a control arrangement a system for
coordinating the performance of fans in a housing, the system (200)
including: a first fan (120) for cooling a power supply (250); a
second fan (130); a control board (240) to provide a first pulsed
wave modulated (PWM) signal to the second fan (130); and a logic
element (265) to provide a control signal to the first fan (120)
based on a second PWM signal from the power supply (250) and a
third PWM signal from the control board (240).
[0022] FIG. 2B shows a control arrangement (201) for integrating
PWM control signals for the first fan (120). By providing the
controller (240) managing the second fan (130) the ability to
increase the effective voltage on the first fan motor, the
controller (240) can increase the duty cycle applied to the first
fan (120) when increasing the flow to the second fan (130) in order
to prevent inversion of airflow through the first fan (120). Also
shown in FIG. 2 is the equipment (250) cooled by the first fan
(120), the equipment (250) cooled by the first fan (120) may be
electronics and/or a power supply. Control lines from the
controller (240) and equipment (250) are provided to a logic
element (260) for example, an OR-logic element. A control line is
output from the OR-logic (260) to the first fan (120). This allows
the equipment (250) to provide operational control over the first
fan (120) without relying on the controller (240) being operative.
The OR-logic (260) and/or the first fan (120) may be external to
the equipment (250). Alternately, the OR-logic (260) and the first
fan may be internal to the equipment (250). For example, the
equipment (250) may be a power supply with an internal fan (120)
and an internal OR-logic (260). In one example, the equipment (250)
is a non-PMBus power supply module (PSM).
[0023] The controller (240) provides a pulsed width modulation
(PWM) signal to the OR-logic (260). The controller also provides a
control signal to the second fan (130). The control signal to the
second fan may be a PWM signal. The control signal to the second
fan may be a non-PWM signal. The controller (240) may have a look
up table, either internally or accessible. The lookup table
considers the control signal provided by the controller (240) to
the second fan (120) and determines the PWM signal for the
controller (240) to output to the OR-logic (260) based on the
signal provided to the second fan (130). This allows the look up
table to compensate for the fan curves of the first fan (120) and
second fan (130), especially any differences in the two curves. In
one example the signal provided to the second fan (130) is also
provided to the OR-logic (260). In other examples, the signal
provided to the second fan (120) by the controller (240) is
different from the signal provided to the OR-logic (240). The
controller (240) may be mounted on a control board and/or may be
part of a control board. The controller (240) may be a dedicated
fan controller or may be a general purpose processor that performs
a variety of tasks in addition to controlling the fan outputs.
[0024] As stated, the equipment (250) cooled by the first fan (120)
may be electronics and/or a power supply. The equipment (250) is
mounted such that airflow produced by the first fan (120) passes
over the equipment (250) to improve heat transfer from the
equipment (250) to the air. The fan (120) may be internal to the
equipment (250). In some examples, the equipment (250) is a power
supply with an internal fan, specifically, the equipment (250) is a
non-PMBus power supply module (PSM).
[0025] The OR-logic (260) merges the control signals provided by
the equipment (250) and the controller (240) to form a control
signal provided to the first fan (120). In one example, the
OR-logic (260) provides a control signal to both the first fan
(120) and the second fan (130). In a second example, the OR-logic
(260) provides a control signal to just the first fan (120) and not
the second fan (130). The control signals received and provided by
the OR-logic (260) may be PWM signals. The control signals may be
power signals, where the peak voltage applied to the first fan
(120) is also the peak voltage of the signal provided by the
OR-logic (260). Alternately, the control signal provided by the
OR-logic (260) to the first fan (120) may have a lower voltage than
the peak voltage applied to the first fan (120). In this approach,
the signal provided to the first fan (120) may be used to regulate
connection between the first fan (120) and a power source.
[0026] The OR-logic (260) may output the control signal to the
first fan (120) by synchronizing the received control signals from
the controller (240) and the equipment (250). Synchronization may
be performed using a separate clock signal, by extracting a clock
signal from a control signal, and/or by other suitable methods. In
one example, the synchronization is performed by delaying one
signal until a level change by the other signal.
[0027] As discussed below with respect to FIG. 3, the control
signal from the equipment (250) and the controller (240) may
operate of different frequencies. In some examples, the one control
signal may have a frequency of at least 10 times the frequency of
the other control signal. In some examples, the one control signal
may have a frequency of at least 100 times the frequency of the
other control signal. In some examples, the one control signal may
have a frequency of at least 1000 times the frequency of the other
control signal. For example, the control signal from the equipment
(250) to the OR-logic (260) may operate in the kHz range while the
control signal from the controller (240) to the OR-logic may
operate in the MHz range (or vice versa).
[0028] The OR-logic (260) may be an electrical connection between
the conductor carrying the signal from the equipment (250) to the
first fan (120) and the conductor carrying the signal from the
controller (240) to the first fan (120). The electrical connection
may be internal to the first fan (120), for example having a
conductor from the equipment connected to an electric motor
powering the first fan (120) and a conductor from the controller
connected to the electric motor powering the first fan (120). In
one example, the electrical connection is a simple splice between
two conductors carrying the respective signals.
[0029] The OR-logic (260) may include components to prevent one
control signal from being detected by the source of the other
control signal. For example, the OR-logic (260) may include
transistors (e.g. a field effect transistor or FET) to isolate the
two signals. Alternately, the OR-logic (260) may allow propagation
of the signal from the equipment (250) to the controller (240) and
vice versa. In one example, the controller samples the line between
the controller (240) and the OR-logic (260) and may determine the
duty cycle provided by the equipment (250) to the OR-logic (260)
based on this sampling. Similarly, the equipment (250) may sample
the line between the equipment (250) and the OR-logic (260) and may
determine the duty cycle provided by the controller (240) to the
OR-logic (260) based on this sampling. The controller (240) or the
equipment (250) may embeds signal information in the PWM signal
provided to the OR-logic (260) that is detected by the equipment
(250) or controller (240) respectively.
[0030] The OR-logic may receive PWM signals from the equipment
(240) and the controller (240) and output a steady voltage DC
signal to the first fan (120). In this approach, the OR-logic
includes a component with a relatively high latency (which is to
say, the component does not respond in the time frame of the
individual pulses of the PWM input signals) between each of the
lines from the controller (240) and the equipment (250) and the
connection between the two input signal lines. In one example, the
component is an electric motor of the first fan (120). In another
example, the component is an inductor coil.
[0031] FIG. 3 shows one challenge with using a simple electrical
connection to provide the OR functionality. Namely, coordinating
the PWM signals to control the composite signal provided to the
first fan (120). One solution to this is also shown. By combining a
high frequency PWM signal with a lower frequency PWM signal, the
two signals do not need to be synchronized in order to assure a
predictable output. However, the output is not a simple maximum
relationship between the two inputs but rather uses the slightly
more complex formula below.
[0032] Sig. A (Signal A) shows a PWM signal with a 50% duty cycle.
Sig. B (Signal B) shows a second PWM signal with a 50% duty cycle
at is the inverse of Sig. A. Combining Sig. A and Sig. B (Sig. A v
B) can produce a PWM signal with a duty cycle anywhere from 50% to
100% depending on the degree to which the phases are synchronized.
Thus, to the degree that it is desired to combine the two different
PWM signals to produce a composite control signal, synchronization
may be needed in order to achieve a predictable output.
[0033] Sig. C (Signal C) shows a higher frequency 50% duty cycle
signal. This produces the same output as either Sig. A or Sig. B
when applied to an electric motor as both have the same peak
voltage and duty cycle. However, signal C can be combined with Sig.
A and always produces the same duty cycle without having to
synchronize the signals (Sig. A v C). The duty cycle of the
combined signals is 1-((1-DutyCycleA)(1-DutyCycleC)). So combining
two 50% duty cycles produces 1-(1-0.5)*(1-0.5) or a duty cycle of
75%. Accordingly, while the output duty PWM signal is not the same
as either input PWM signal, the duty cycle of the combined signal
is easily calculable. Accordingly, a PWM signal provided with a
higher frequency can reliably produce predictable fan behavior.
[0034] While a 1 to 10 kHz frequency is generally sufficient for a
PWM signal to be interpreted by an electric fan motor as a DC
voltage, modern processors operate at much higher frequencies and
can readily produce megahertz frequency control signals without
additional hardware.
[0035] Other options include synchronizing the PWM signals between
the two different signal inputs. This avoids the uncertainty in the
output signal. Synchronizing the input signals may be accomplished
using a common clock and/or introducing a delay into one line.
Synchronizing the input signals may also be accomplished by
converting the signals to a DC voltage before joining the two input
signals. For example, by placing a relatively high latency element
between the signal sources and the junction between the signal
lines. This allows a simple junction to provide the desired OR
functionality.
[0036] An example method consistent with this specification is
illustrated in FIG. 4A. In FIG. 4A, a method (450) for controlling
a power supply unit (PSU) fan, the method includes providing (460)
a pulse width modulated (PWM) signal via a power line to regulate a
speed of the fan, wherein the PWM signal is formed using a PWM
signal from a power supply and a PWM signal from a control
board.
[0037] FIG. 4B shows a method (400) consistent with the present
specification. Operation 410 is providing a pulse width modulated
(PWM) signal from a power supply. Operation 420 is providing a PWM
signal from a control panel. Operation 430 is combining the two PWM
signals using an OR operation. Operation 440 is using the combined
PWM signal to control power application to a fan in a housing.
[0038] Operation 410 includes providing a pulse width modulated
signal from power supply. A pulse width modulated signal uses
pulses of on and off to that switch between two voltages to produce
an effective voltage in a component or device with a longer
response time that the pulse frequency. The amount of time the
pulse is on is referred to as the duty cycle and is often expressed
as a percentage. For example, a PWM signal with a frequency of 100
Hz and a pulse length of 3 mS would have a duty cycle of 30%. PWM
is an energy and equipment efficient method of providing tuned
voltages to devices with longer response times.
[0039] Operation 420 includes providing a PWM signal from a control
panel. The frequency of the PWM signal from the control panel and
the power supply may be the same. Alternately, the frequencies of
the two signals may have different frequencies. In one example, the
frequency of one signal is at least ten times the frequency of the
other signal. In one example, the frequency of one signal is at
least a hundred times the frequency of the other signal. In one
example, the frequency of one signal is at least a thousand times
the frequency of the other signal.
[0040] Operation 430 includes combining the two PWM signals using
an OR operation. The use of the OR operation allows either signal
to independently increase the duty cycle in the output provided to
the fan. In one example, the duty cycle of the output is equal to
the larger of the two inputs signals such that, Duty cycle of the
output=max(dutycycleA, dutycycleB). In another example, the duty
cycle of the output is 1-((1-dutycycleA)*(1-dutycycleB)). Other
variations are possible, especially by applying the two duty cycles
in an asynchronous manner.
[0041] Operation 440 includes using the combined PWM signal to
control power application to a fan in a housing. In one example,
the combined PWM signal is use as the power source. In another
example, the combined PWM signal is used to regulate the on/off
behavior of a power source.
[0042] In some examples, the signal from the control panel is
provided to the power supply as part of a multi-channel connection
between the control panel and the power supply. The signal is then
combined with the power supply provided signal within the power
supply with the output being provided to a power supply fan that
cools the power supply. One notable advantage of this approach is
that in many instances, there is already a multichannel connection
between the control panel and the power supply and one of the
channels can be used to provide this communication without
additional equipment costs. In some examples the signal is provided
from the control panel to the power supply with another signal
being carried on the same line. This provides another way to
provide the signal as the response time needed for the fan may be
much slower than the response time needed for other components in
the system. Accordingly, in some approaches the ability to control
the power supply fan using the controller can be added to an
existing design without additional equipment or component costs.
Because the OR-logic (260) can be implemented in a variety of ways,
the examples described in this specification can provide
significantly increased cooling control without increased
costs.
[0043] FIG. 5 shows a control arrangement for integrating PWM
control signals for the first fan (120). By providing the
controller (240) managing the second fan (130) the ability to
increase the effective voltage on the first fan motor, the
controller (240) can increase the duty cycle applied to the first
fan (120) when increasing the flow to the second fan (130) in order
to prevent inversion of airflow through the first fan (120). FIG. 5
is the equipment (250) cooled by the first fan (120), the equipment
(250) cooled by the first fan (120) may be electronics and/or a
power supply. Control lines from the controller (240) and equipment
(250) are provided to an OR-logic (260). A control line is output
from the OR-logic (260) to the first fan (120). This allows the
equipment (250) to provide operational control over the first fan
(120) without relying on the controller (240) being operative. In
this example, the first fan (120) and the OR-logic (260) are
located within the equipment (250). The equipment (250) includes a
signal source (570) which generates one of the pulse width
modulated signals provided to the OR-logic.
[0044] FIG. 5 also shows the lines carrying four pulse width
modulated signals used to coordinate the first fan (120) and the
second fan (130). The first line (580) from the controller (240) to
the second fan (130) carries a first PWM signal. The second line
(582) carries a second PWM signal from the signal source (570) in
the equipment (250) to the OR-logic (260). The third line (584)
carries a third PWM signal from the controller (240) to the
OR-logic (260). The fourth line (586) carries a fourth PWM signal
from the OR-logic (260) to the first fan (120). The fourth PWM
signal is formed by the OR-logic (260) based on the second and
third PWM signals carried by the second line (582) and third line
(584) respectively. The controller (240) coordinates the first PWM
signal and the third PWM signal carried by the first line (580) and
the third line (584) in order to coordinate the output of the
second fan (130) and the first fan (120).
[0045] The equipment (250) may be a power supply. More
specifically, the equipment (250) may be a non-PMBus power supply
unit. Such power supply units may be more economical than power
supplies with a PMBus but their lack of a bus may make system
control over the power supply fan (120) may make it challenging to
coordinate the internal power supply fan (120) with other fans
(130). The method and system described in this specification
provide an economical and effective method of providing this
control.
[0046] The signal source (570) may be a processor and/or other
component of the equipment (250). In some examples, the signal
source (570) outputs the same signal when the equipment (250) is
powered. That is to say, the duty cycle output by the signal source
(570) is not dependent on factors other than the power state of the
equipment (250). In other examples, the signal source (570) varies
the duty cycle of the signal based on circumstances. For example,
the signal source (570) may have access to temperature information
and may adjust the duty cycle of the output signal based on the
temperature of the equipment (250).
[0047] It will be understood that, within the principles described
by this specification, a vast number of variations exist. It should
also be understood that the examples described are just examples,
and are not intended to limit the scope, applicability, or
construction of the claims in any way.
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