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.

Description

BACKGROUND

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

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.

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.

FIGS. 2A-B show example structures consistent with the current specification.

FIG. 3 shows examples of PWM signals and their possible interactions using an OR-logic consistent with the current specification.

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.

FIG. 5 shows a structure consistent with one example of the current specification.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

These examples are illustrated and described as follows.

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).

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).

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.

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).

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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).

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.

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.