Patent Publication Number: US-2007098374-A1

Title: Information processing apparatus and fan control method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2005-316380, filed Oct. 31, 2005, the entire contents of which are incorporated herein by reference.  
     BACKGROUND  
      1. Field  
      One embodiment of the invention relates to an information processing apparatus such as a personal computer, for example, having a fan.  
      2. Description of the Related Art  
      In recent years, various types of portable personal computers, such as laptop personal computers and notebook personal computers, have been developed. This type of personal computer includes heating devices such as a CPU, a display controller, a hard disk drive and a bus bridge device.  
      A fan is known as a cooling mechanism for cooling the heating devices. Recently, a fan (PWM fan), which is driven by a pulse width modulation signal (PWM signal), has begun to be used. The rotational speed of the fan is varied by a duty ratio of the PWM signal.  
      Jpn. Pat. Appln. KOKAI Publication No. 2003-195981 discloses an information processing apparatus which controls the driving of a fan by using a pulse signal PWM, thereby to cool the CPU.  
      Jpn. Pat. Appln. KOKAI Publication No. 2001-15972 discloses a computer system having a function of synchronizing the rotational speeds of a plurality of PWM fans.  
      In these KOKAI Publications Nos. 2003-195981 and 2001-15972, however, the fan is driven by a PWM signal of a fixed frequency.  
      In a system in which the fan is driven by the PWM signal of the fixed frequency, there is a tendency that the range of good linearity of variation of the fan rotation speed, relative to the variation of the duty ratio of the PWM signal, is limited to a relatively narrow range.  
      Thus, the precision in control of the fan rotation speed may deteriorate, depending on the value of a target rotation speed of the fan.  
      In addition, in order to avoid the deterioration of the control precision of the fan rotation speed, it becomes necessary to limit the range of usable fan rotation speeds to a narrow range.  
      Moreover, depending on the PWM signal frequency to be used, such a problem arises that a relatively large noise will occur even at the time of low-speed driving of the fan. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.  
       FIG. 1  is an exemplary perspective view showing a front-side external appearance of an information processing apparatus according to an embodiment of the invention;  
       FIG. 2  is an exemplary block diagram for describing a cooling control mechanism which is mounted in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 3  is an exemplary view for explaining a PWM signal for controlling a fan which is provided in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 4  is an exemplary view showing a plurality of kinds of PWM signals with different frequencies, which are used in order to control the fan provided in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 5  is an exemplary graph showing number-of-revolutions characteristics of the fan which is provided in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 6  is an exemplary graph showing noise characteristics of the fan which is provided in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 7  shows a table which defines an example of a relationship between target rotational speeds, PWM frequencies and duty ratios, which is used in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 8  shows a table which defines an example of a relationship between the temperatures of a heating device and target rotational speeds, which is used in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 9  is an exemplary diagram showing an example of specific connection between a fan control unit and a cooling fan, which are provided in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 10  is an exemplary block diagram that shows an example of the system configuration of the information processing apparatus shown in  FIG. 1 ;  
       FIG. 11  is an exemplary block diagram that shows an example of the structure of a cooling control mechanism which is applied to the system configuration shown in  FIG. 10 ;  
       FIG. 12  is an exemplary diagram showing an example of the structure of a temperature sensor which is provided in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 13  is an exemplary flowchart illustrating the procedure of a fan control process which is executed in the information processing apparatus shown in  FIG. 1 ;  
       FIG. 14  is an exemplary flowchart illustrating the procedure of a process which is executed by a system BIOS of the information processing apparatus shown in  FIG. 1 ; and  
       FIG. 15  is an exemplary flowchart illustrating the operation of the fan control unit which is provided in the information processing apparatus shown in  FIG. 1 . 
    
    
     DETAILED DESCRIPTION  
      Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, an information processing apparatus includes a main body, a fan which is provided in the main body and is driven by a pulse width modulation signal (PWM signal), and a fan control unit which varies a duty ratio of the pulse width modulation signal (PWM signal) and a frequency of the pulse width modulation signal (PWM signal) in accordance with a target rotational speed of the fan.  
      To begin with, referring to  FIG. 1 , the structure of an information processing apparatus according to an embodiment of the invention is described. The information processing apparatus is realized, for example, as a battery-powerable portable notebook personal computer  10 .  
       FIG. 1  is a front-side perspective view of the computer  10  in the state in which a display unit of the personal computer  10  is opened.  
      The computer  10  comprises a computer main body  11  and a display unit  12 . A display device that is composed of an LCD (Liquid Crystal Display)  17  is built in the display unit  12 . The display screen of the LCD  17  is positioned at an approximately central part of the display unit  12 .  
      The display unit  12  is supported on the computer main body  11  such that the display unit  12  is freely rotatable, relative to the computer main body  11 , between an open position in which the top surface of the computer main body  11  is exposed and a closed position in which the top surface of the computer main body  11  is covered. The computer main body  11  has a thin box-shaped casing. Various heating devices, such as a CPU, a display controller, a hard disk drive and a bus bridge device, are mounted in the computer main body  11 .  
      A keyboard  13 , a power button  14  for powering on/off the computer main body  11 , an input operation panel  15  and a touch pad  16  are disposed on the top surface of the computer main body  11 .  
      The input operation panel  15  is an input device that inputs an event corresponding to a pressed button. The input operation panel  15  has a plurality of buttons for activating a plurality of functions. The buttons include buttons  15 A and  15 B for starting specific application programs.  
       FIG. 2  shows an example of a cooling control mechanism which is provided in the computer main body  11 . As is shown in  FIG. 2 , a heating device  21 , a fan  22 , a fan control unit  23  and a temperature sensor  24  are provided in the computer main body  11 .  
      The heating device  21  is a device such as a CPU, a display controller, a hard disk drive or a bus bridge device.  
      The fan  22  is a cooling fan for cooing the heating device  21 , or for lowering the temperature within the computer main body  11 . The fan  22  is realized by a so-called PWM fan which is configured to be driven by a pulse width modulation signal (PWM signal). The rotational speed of the fan  22  is varied in accordance with the duty ratio of the PWM signal (also referred to as “PWM clock signal”) which is supplied from the fan control unit  23 .  FIG. 3  shows an example of the PWM signal. The PWM signal shown in  FIG. 3  is a PWM signal having a duty ratio=50%. The duty ratio is a ratio (also referred to as “on-duty ratio”) of an on-state pulse width (on-duty width) to a cycle T of the PWM signal.  
      The fan  22  is disposed, for example, in the vicinity of the heating device  21 . For example, the fan  22  cools a heat sink, which is thermally connected to the heating device  21  via a heat receiver, etc., thereby cooling the heating device  21 . In addition, the fan  22  exhausts heated air around the heating device  21  to the outside, thereby cooling the heating device  21  and devices around the heating device  21 . A structure disclosed in Japanese Patent No. 3 637 304, for instance, is usable as an attachment structure for the fan  22 .  
      The temperature sensor  24  is a sensor for detecting the temperature of the heating device  21 . The temperature sensor  24  is provided, for example, on the heating device  21 .  
      The fan control unit  23  controls the fan  22 . The fan control unit  23  supplies a PWM signal to the fan  22  as a control signal for controlling the rotational speed (i.e. the number of revolutions) of the fan  22 . In addition, the fan control unit  23  receives a number-of-revolutions signal (pulse signal) which is fed back from the fan  22 , and monitors the rotational speed of the fan  22  by using the received number-of-revolutions signal. The fan  22  outputs, for example, two pulse signals per single revolution of the fan  22 , as the number-of-revolutions signal.  
      The fan control unit  23  executes a process for varying the duty ratio of the PWM signal in accordance with a target rotational speed of the fan  22 . The target rotational speed is determined in accordance with the temperature of the heating device  21 , which is detected by the temperature sensor  24 .  
      Further, the fan control unit  23  executes a process for varying the frequency of the PWM signal in accordance with the target rotational speed, in addition to the process for varying the duty ratio. Specifically, the fan control unit  23  selectively uses one of a plurality of PWM signal frequencies, on the basis of the value of the target rotational speed. The control range of the fan rotation speed is divided into a plurality of fan speed ranges, and the frequencies of PWM signals, which are to be used, are preset for the respective fan speed ranges. The fan control unit  23  generates a PWM signal of a frequency corresponding to the fan speed range within which the target rotational speed falls.  
      As described above, the PWM signal frequency is dynamically altered in accordance with the target rotational speed. Thereby, it is possible to use an optimal PWM signal frequency for each fan speed range, from the standpoint of the control precision of the rotational speed and the reduction in noise. Hence, no matter which speed range the target rotational speed falls within, it is possible to satisfactorily maintain the linearity of variation of the fan rotational speed relative to the duty ratio of the PWM signal. Therefore, without limiting the range of usable fan rotation speeds to a narrow range, the fan rotation speed can be controlled with sufficient precision. Moreover, noise can be reduced, for example, at the time of low-speed rotation of the fan.  
      The fan control unit  23  includes a duty ratio setting unit  231  and a PWM frequency setting unit  232 .  
      The duty ratio setting unit  231  executes a process of varying the duty ratio of the PWM signal in accordance with the target rotational speed of the fan  22 . The value of the rotational speed of the fan  22  is controlled, for example, by using the following four levels:  
      First rotational speed (Low),  
      Second rotational speed (Middle),  
      Third rotational speed (High), and  
      Fourth rotational speed (Max).  
      The rotational speed of the fan  22  increases in the order of Low, Middle, High and Max. Temperature ranges are assigned to Low, Middle, High and Max. The temperature ranges, which correspond to Low, Middle, High and Max, rise in the order of Low, Middle, High and Max. In addition, the values of the duty ratio are assigned to Low, Middle, High and Max. The duty ratios, which correspond to Low, Middle, High and Max, increase in the order of Low, Middle, High and Max.  
      The duty ratio setting unit  231  determines whether the current target rotational speed of the fan  22  is Low, Middle, High or Max, and sets the duty ratio of the PWM signal at a value corresponding to the current target rotational speed.  
      The PWM frequency setting unit  232  executes a process for varying the frequency of the PWM signal in accordance with the target rotational speed of the fan  22 . As described above, the PWM frequencies are specified for the respective fan speed ranges. Thus, the PWM frequency setting unit  232  sets the frequency of the PWM signal at the frequency corresponding to the fan speed range to which the target rotational speed belongs.  
       FIG. 4  shows examples of three kinds of PWM signals with different frequencies (a low-frequency PWM signal, an intermediate-frequency PWM signal and a high-frequency PWM signal). Each of the PWM signals shown in  FIG. 4  has a duty ratio=50%. In accordance with the target rotational speed of the fan  22 , the PWM frequency setting unit  232  sets the frequency of the PWM signal at one of a low frequency, an intermediate frequency and a high frequency. Needless to say, the number of kinds of frequencies to be used is not limited to three. For example, in accordance with the target rotational speed of the fan  22 , one of two kinds of frequencies, that is, a low frequency and a high frequency, may be selectively used. Further, four or more frequencies may selectively used in accordance with the target rotational speed of the fan  22 .  
      Next, the method of determining the PWM frequency to be used is described.  
       FIG. 5  shows number-of-revolutions characteristics of the fan  22 .  
      The number-of-revolutions characteristics show the variations of the fan rotation speed (number of revolutions (rpm)) in relation to the duty ratio (on-duty %) with respect to a plurality of frequencies (10 KHz, 20 KHz, 30 KHz, 40 KHz and 50 KHz).  
      As is understood from  FIG. 5 , in the case of high PWM frequencies exceeding 30 KHz, the linearity of the variation of the rotational speed, relative to the duty ratio, deteriorates as the duty ratio approaches 100% and the rotational speed increases. The characteristic curves vary from fan to fan. However, basically, in any type of fan, such a phenomenon commonly occurs that the linearity in the region of high rotational speeds deteriorates as the frequency of the PWM signal becomes higher.  
       FIG. 6  shows noise characteristics of the fan  22 .  
      These noise characteristics show variations of noise values (dBA) relative to the fan rotation speed. Normally, as the fan rotation speed (rpm) decreases, wind noise decreases and accordingly the noise value sufficiently decreases in the region of low fan rotation speeds (rpm). However, when low PWM frequencies of 20 KHz or less are used, even if the fan rotation speed (rpm) decreases, the noise value does not sufficiently decrease. The reason for this is as follows. In the case of using low PWM frequencies of 20 KHz or less, the frequency of sound, which is produced from the motor of the fan, falls within the range of audio frequencies. Thus, even if the fan rotation speed (rpm) decreases, the total noise value does not greatly decrease due to the effect of the sound produced from the motor of the fan. While the PWM signal is in an on-period, a power supply voltage Vcc is supplied to the motor of the fan, and while the PWM signal is in an off-period, the power supply voltage Vcc is not supplied to the motor. Thus, a sound of a frequency corresponding to the PWM frequency is produced from the motor of the fan.  
      In the present embodiment, frequencies, which do not affect the noise value and realize good linearity of variation of the rotational speed relative to the duty ratio, are preselected from usable PWM frequency ranges with respect to respective target rotational speeds, and the fan control unit  23  executes a control to automatically vary the frequency of the PWM signal in accordance with the target rotational speed.  
      Thereby, the fan  22  can be driven with an optimal PWM frequency for each target rotational speed.  
       FIG. 7  shows an example of a table which defines a relationship between target rotational speeds (fan rotation speeds), PWM frequencies and duty ratios.  
      The control of the PWM signal by the fan control unit  23  is executed according to the table shown in  FIG. 7 . If the target rotational speed falls within a fan rotation range between 4000 rpm and 5000 rpm, the fan control unit  23  sets the frequency of the PWM signal at a first value (e.g. 30 KHz) and varies the duty ratio in a range between 50% and 70% in accordance with the target rotational speed. If the target rotational speed falls within a fan rotation range between more than 5000 rpm and 6000 rpm, the fan control unit  23  sets the frequency of the PWM signal at a second value (e.g. 20 KHz), which is lower than the first value, and varies the duty ratio in a range between 70% and 100% in accordance with the target rotational speed. If the target rotational speed falls within a fan rotation range between less than 4000 rpm and 2000 rpm, the fan control unit  23  sets the frequency of the PWM signal at a third value (e.g. 40 KHz), which is higher than the first value, and varies the duty ratio in a range between 25% and 50% in accordance with the target rotational speed.  
      Preferably the third value of the frequency should be set at a value higher than the audio frequency range.  
       FIG. 8  shows an example of a table which defines a relationship between the temperatures of the heating device  21  and target rotational speeds (fan rotation speeds).  
      The temperature of the heating device  21  is managed with four temperature ranges of levels 1 to 4. The temperatures of levels 1 to  4  rise in the order of level 1, level 2, level 3 and level 4. When the temperature of the heating device  21  falls within the temperature range of level 1, the target rotational speed of the fan  22  is set at Low (e.g. 2000 rpm). When the temperature of the heating device  21  falls within the temperature range of level 2, the target rotational speed of the fan  22  is set at Middle (e.g. 4000 rpm). When the temperature of the heating device  21  falls within the temperature range of level 3, the target rotational speed of the fan  22  is set at High (e.g. 5000 rpm). When the temperature of the heating device  21  falls within the temperature range of level 4, the target rotational speed of the fan  22  is set at Max (e.g. 6000 rpm).  
       FIG. 9  shows an example of a specific connection between the fan control unit  23  and fan  22 .  
      The fan  22  is connected to a power supply voltage Vcc of a fixed value. Only when the PWM signal is in the on-period, the power supply voltage Vcc is supplied to the motor of the fan  22 .  
      In a case where the value of the power supply voltage of the fan control unit  23  differs from the value of the power supply voltage of the fan  22 , the PWM signal, which is output from the fan control unit  23 , is supplied to the fan  22  via a level conversion circuit  25 . The level conversion circuit  25  converts the amplitude of the PWM signal from the value of the power supply voltage of the fan control unit  23  to the value of the power supply voltage of the fan  22 . For example, if the power supply voltage of the fan control unit  23  is 3.3V and the power supply voltage of the fan  22  is 5V, the level conversion circuit  25  converts the amplitude of the PWM signal from 3.3V to 5V.  
      Next, referring to  FIG. 10 , the system configuration of the computer  10  is described.  
      The computer  10  comprises a CPU  111 , a north bridge  112 , a main memory  113 , a display controller  114 , a south bridge  115 , a hard disk drive (HDD)  116 , a network controller  117 , a flash BIOS-ROM  118 , an embedded controller/keyboard controller IC (EC/KBC)  119 , and a power supply circuit  120 .  
      The CPU  111  is a processor that controls the operation of the components of the computer  10 . The CPU  111  executes an operating system and various application programs/utility programs, which are loaded from the HDD  116  into the main memory  113 . The CPU  111  also executes a system BIOS (Basic Input/Output System) that is stored in the flash BIOS-ROM  118 . The system BIOS is a program for hardware control.  
      The north bridge  112  is a bridge device that connects a local bus of the CPU  111  and the south bridge  115 . In addition, the north bridge  112  has a function of executing communication with the display controller  114  via, e.g. an AGP (Accelerated Graphics Port) bus. Further, the north bridge  112  includes a memory controller that controls the main memory  113 .  
      The display controller  114  controls an LCD  17  that is used as a display monitor of the computer  10 . The display controller  114  has a function of 2D/3D image rendering arithmetic function, and functions as a graphics accelerator. The south bridge  115  is connected to a PCI (Peripheral Component Interconnect) bus and an LPC (Low Pin Count) bus.  
      The embedded controller/keyboard controller IC (EC/KBC)  119  is a 1-chip microcomputer in which an embedded controller for power management and a keyboard controller for controlling the keyboard (KB)  13  and touch pad  16  are integrated. The embedded controller/keyboard controller IC  119  cooperates with the power supply circuit  120  to power on/off the computer  10  in response to the user&#39;s operation of the power button switch  14 . The power supply circuit  120  generates system power, which is to be supplied to the components of the computer  10 , using power from a battery  121  or external power supplied from an AC adapter  122 .  
      In the system shown in  FIG. 10 , for example, the CPU  111 , display controller  114 , north bridge  112  and HDD  116  are heating devices.  
      Next, referring to  FIG. 11 , an example of the cooling control mechanism, which is applied to the system of  FIG. 10 , is described. It is assumed that the CPU  111  and display controller  114  are cooled by two fans (FAN # 0 , FAN # 1 ).  
      In  FIG. 11 , a fan (FAN # 0 )  22 - 1  is a fan which cools the CPU  111 , and a fan (FAN # 1 )  22 - 2  is a fan which cools the display controller  114 . Needless to say, it is not necessary that the fan and the device to be cooled are associated in one-to-one correspondency.  
      These fans  22 - 1  and  22 - 2  are realized by PWM fans. The temperature of the CPU  111  and the temperature of the display controller  114  are detected by temperature sensors  24 - 1  and  24 - 2 .  
      The above-described fan control unit  23  is provided, for example, within the EC/KBC  119 . The fan control unit  23  is configured to control the two fans  22 - 1  and  22 - 2 . Specifically, the fan control unit  23  controls the rotational speed of the fan  22 - 1  by a first PWM signal (PWM # 1 ), and receives a number-of-revolutions signal # 1  from the fan  22 - 1 . Further, the fan control unit  23  controls the rotational speed of the fan  22 - 2  by a second PWM signal (PWM # 2 ), and receives a number-of-revolutions signal # 2  from the fan  22 - 2 .  
      Two control registers  233  and  234  are provided in the fan control unit  23 . Parameters for controlling the fan  22 - 1  are set in the control register  233  by the system BIOS. In addition, parameters for controlling the fan  22 - 2  are set in the control register  234  by the system BIOS.  
       FIG. 12  shows an example of the temperature sensor  24 - 1 .  
      The temperature sensor  24 - 1  comprises a diode (thermal diode)  51  and a temperature detection IC  52 . The diode  51  is mounted on the CPU  111  or built in the CPU  111 . The value of current flowing through the diode  51  varies depending on the temperature of the CPU  111 . The temperature detection IC  52  converts the value of the current into data indicative of the temperature of the CPU  111 .  
      Next, referring to  FIG. 13 , a fan control process, which is executed by the fan control unit  23 , is described.  
      Assume now that the fan  22 - 1  is to be controlled. Also assume that a control table, for example, as shown in  FIG. 7 , which stores information indicative of PWM frequencies and duty ratios to be used for respective target rotational speed ranges, is preset in the fan control unit  23 .  
      The system BIOS determines a target rotational speed in accordance with the CPU temperature that is detected by the temperature sensor  24 - 1 , and sets the determined target rotational speed as a control parameter in the control register  233  of the fan control unit  23 .  
      The fan control unit  23  checks the value of the set target rotational speed (block S 11 ), and determines the duty ratio of the PWM signal corresponding to the target rotational speed by referring to the above-described control table (block S 12 ).  
      Subsequently, referring to the control table, the fan control unit  23  determines the frequency of the PWM signal corresponding to the target rotational speed (blocks S 13  to S 16 ). In this case, if the target rotational speed is Low, the fan control unit  23  sets the frequency of the PWM signal at a high frequency (e.g. 40 KHz) (block S 14 ). If the target rotational speed is Middle or High, the fan control unit  23  sets the frequency of the PWM signal at an intermediate frequency (e.g. 30 KHz) (block S 15 ). If the target rotational speed is Max, the fan control unit  23  sets the frequency of the PWM signal at a low frequency (e.g. 20 KHz) (block S 16 ).  
      The fan control unit  23  outputs the PWM signal having the set frequency and duty ratio (block S 17 ).  
      The system BIOS may determine the value of the PWM frequency to be used, and may set the determined value of the PWM frequency as a control parameter in the fan control unit  23 .  
      In this case, the system BIOS executes a process as illustrated in a flowchart of  FIG. 14 .  
      The system BIOS manages a control table which stores information that is indicative of PWM frequencies and duty ratios to be used for respective target rotational speeds. The system BIOS determines a target rotational speed which corresponds to the CPU temperature that is detected by the temperature sensor  24 - 1  (block S 21 ). Then, referring to the control table, the system BIOS determines the PWM frequency corresponding to the determined target rotational speed (block S 22 ). The system BIOS sets the determined target rotational speed and PWM frequency as control parameters in the control register  233  of the fan control unit  23  (block S 23 ).  
      A flowchart of  FIG. 15  illustrates the operation of the fan control unit  23 .  
      The fan control unit  23  includes a table indicative of duty ratios for respective target rotational speeds. The fan control unit  23  sets the duty ratio of the PWM signal at a value corresponding to the target rotational speed which is designated by the control parameter (block S 31 ). Then, the fan control unit  23  sets the frequency of the PWM signal at a value that is designated by the control parameter (block S 32 ).  
      The system BIOS may determine PWM frequencies and duty ratios in accordance with the target rotational speed, and may set control parameters, which are indicative of the PWM frequencies and duty ratios, in the control register  233 .  
      As has been described above, in the fan control process of the present embodiment, a relatively high PWM frequency, which is out of the audio frequency range, is used in a region of low target FAN rotational speeds, and a relatively low PWM frequency with good linearity of variation of the number of revolutions relative to the duty ratio, is used in a region of high target FAN rotational speeds. Since both the duty ratio and PWM frequency are varied in accordance with the target FAN rotation speed, both the high-precision control of the fan rotation speed and the reduction in noise can be realized.  
      While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.