Patent Application
20060181232
N/A
N/A
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In the presently disclosed embodiment, if the sensed die temperature (Tdiode) is greater than a predetermined minimum level (Tmin) and Tdiode is less than or equal to the predetermined control level (Tcontrol), 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 Tdiode to increase such that it gradually approaches the level of Tcontrol. If Tdiode rises to a level greater than Tcontrol, 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 Tdiode to decrease such that it again gradually approaches the level of Tcontrol. If Tdiode falls to a level less than Tmin, then the fan control system is deactivated. If Tdiode subsequently rises to a level greater than Tmin and greater than or equal to Tcontrol, 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 Tdiode as close as possible to Tcontrol.
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.
Other features, functions, and aspects of the invention will be evident from the Detailed Description of the Invention that follows.
The invention will be more fully understood with reference to the following Detailed Description of the Invention in conjunction with the drawings of which:
a 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;
b 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;
c 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
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.
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.
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.
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 (Tdiode,analog) of the computer device 114 to the ADC 120, which converts the analog temperature representation to digital form (Tdiode). As shown in
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 Tdiode 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”.
More specifically, the control logic 118 receives the sensed temperature Tdiode from the ADC 120, and compares the temperature Tdiode to a predetermined minimum level Tmin. In the event Tdiode is less than Tmin, 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 Tdiode 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.
As shown in
At time T1, the PWM controller 102 provides about a 50% PWM duty cycle (DC %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.
From time T1 to time T2, the PWM controller 102 provides PWM duty cycles (DC %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
From time T2 to time T3, the PWM controller 102 provides the 100% PWM duty cycles (DC %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.
From time T3 to time T4, the PWM controller 102 provides PWM duty cycles (DC %1) ranging from about 100% to 75% to the power converter 110. As shown in
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.
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.
A method of performing the presently disclosed fan spin up procedure is illustrated by reference to
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 Tcontrol. 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.
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.
The temperature control procedure performed by the PWM controller 104 will be better understood with reference to
b depicts the plot 402 and a second plot 404 of the maximum case temperature of the computer device 114 (see
c depicts a plot 406 of the thermal diode temperature Tdiode of the computer device 114 (see
The PWM controller 104 is operative to perform the temperature control procedure to maintain the thermal diode temperature Tdiode of the computer device 114 at about the predetermined control level Tcontrol within the power level range 0 to Pint2. Because Tcontrol is less than Tmax, the fan 111 may be run at speeds that are less than its maximum speed within the range 0 to Pint2. For example, within the range 0 to Pint2, the fan 111 can be run at speeds greater than its minimum speed but less than its maximum speed, and within the range Pint2 to TDP, the fan 111 can be run at its maximum speed.
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 Tdiode, as close as possible to the predetermined control level Tcontrol. In the event the sensed temperature is below Tcontrol, the fan speed is decreased. In the event the sensed temperature is above Tcontrol, the fan speed is increased. In this way, the temperature of the computer device 114 is prevented from significantly exceeding the predetermined control level Tcontrol 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 Tmax and remains as close as possible to the control level Tcontrol. 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.
A method of performing the temperature control procedure is illustrated by reference to
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
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.
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.
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.
