|Publication number||US7069172 B2|
|Application number||US 10/843,199|
|Publication date||Jun 27, 2006|
|Filing date||May 11, 2004|
|Priority date||May 11, 2004|
|Also published as||US20050256670|
|Publication number||10843199, 843199, US 7069172 B2, US 7069172B2, US-B2-7069172, US7069172 B2, US7069172B2|
|Inventors||Leonid A. Bekker, Uri Segal|
|Original Assignee||Standard Microsystems Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (37), Non-Patent Citations (3), Referenced by (8), Classifications (9), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
This invention relates to cooling equipment for electronic systems, e.g., fans, and more particularly, to measuring the rotational speed of a fan.
2. Description of the Related Art
Fans are often used to evacuate warm air from enclosures in which electronic systems are contained. For example, most computer systems include one or more cooling fans to aid in circulating the air inside the enclosures and for maintaining the temperature inside the enclosures within an acceptable range. The increased airflow provided by fans typically aids in eliminating waste heat that may otherwise build up and adversely affect system operation. Employing cooling fans is especially helpful in ensuring proper operation for certain central processing units (CPUs) with relatively high operating temperatures.
Control of fans in a system typically involves a fan control unit executing a fan control algorithm. A fan control algorithm may determine the method for controlling one or more fans that are configured to evacuate warm air from a system enclosure. For example, the fan control algorithm may specify that a fan's speed should be increased or decreased dependent upon a detected temperature. Such control algorithms may also involve turning off a fan if the temperature is deemed cool enough to do so.
Fans often include a tachometer output that provides a signal indicative of the current speed of the fan. The tachometer signal may be used to determine whether the fan is operating properly. Often, fans used for CPU and/or computer system cooling have a three-wire interface with wires for power, ground, and the tachometer signal. Fan drive systems often use a signal generator that provides a Pulse Width Modulated (PWM) signal to drive an external circuit that connects and disconnects the fan to and from ground. In such systems, the fan is typically powered only for the duration of the pulse. Between pulses power to the fan is turned off, though typically the fan continues spinning even during the time period between applications of PWM pulses. The duty cycle of the PWM pulse train being provided to the fan determines the fan's speed.
One issue associated with employing PWM signal generators to power fan circuits that typically incorporate three-wire fans is that the tachometer circuitry associated with the fans does not receive power during the time the fans themselves are not powered, that is, between the PWM pulses. In general, this issue may pose a problem whenever the method to power the fan circuits involves use of a non-continuous power supply, that is, when power is not continuously provided to the fan, e.g., a PWM signal generator. As a result, the tachometer signal output by the fan may not represent the current fan speed during the time between pulses. Similarly, once the fan is turned off, the tachometer signal no longer indicates the speed of the fan. One technique that is currently used to measure fan speed in these situations involves using an analog filtering system to measure the back Electromotive Force (EMF) inserted into the fan tachometer signal by the rotating fan. One digital technique used for measuring fan speed includes stretching the PWM signal pulse to insure that a valid tachometer signal remains asserted until the speed of the fan has been determined in case the duty cycle of the PWM signal would not permit such a measurement. There are, however, disadvantages associated with such techniques, including low accuracy, especially at low PWM duty cycles, fan speed surges resulting directly from stretching the PWM pulse and unwanted fan noise resulting from the fan speed surges. Another drawback is that the stretching typically dominates at low PWM duty cycles. In other words, the fan's speed, which is measured in revolutions-per-minute (RPM), is effectively controlled by the stretching of the PWM pulse and not by the duty cycle itself of the PWM signal. Such techniques generally lead to complicated implementations with significant impact on die size, and are typically prone to electrical noise sensitivity.
Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.
In one set of embodiments, the invention comprises a system and method for obtaining accurate fan tachometer readings for fans with different speeds. The fans may be breakable-ground-controlled fans in an electrical system. As referred to herein, a breakable-ground-controlled fan is a fan which may have its power terminal uninterruptedly tied to a supply voltage, while on/off switching of the fan is achieved through connecting/disconnecting the fan's ground terminal to/from ground. In one embodiment, the duty cycle of a PWM signal provided by a signal generator output controls the speed of the fan, while a tachometer reading-unit monitors the revolutions per minute (RPM) of the fan. Instead of driving the fan directly; the PWM signal may switch a fan driver circuit, which may provide adequate power to spin the fan. In alternate embodiments, the fan may be powered and controlled by means other than a PWM signal generator. In one embodiment, the fan generates a tachometer signal comprising tachometer pulses (also referred to as a fan pulses) that are used by the tachometer reading-unit to measure the RPM of the fan.
Low duty-cycle very low frequency test (VLFT) pulses may be generated and provided through a test or sampling signal multiplexed with the PWM signal to sample the fan generated tachometer pulses. The VLFT pulses of the test or sampling signal may operate to determine if the tachometer signal reaching the tachometer reading-unit is high or low. In one set of embodiments, the VLFT pulses ensure that tachometer pulses that may be generated by the fan are available even when there is no power provided to the fan by the power source used to control the fan. In one embodiment, as described in the previous paragraph, power is provided to the fan in form of PWM signal generator pulses, where the fan does not receive power from the PWM signal generator between the PWM pulses.
The VLFT pulses may be used for sampling to determine stages of the tachometer pulses, which may essentially facilitate “recreating” the tachometer pulses. Recreated tachometer pulses may have variable width since the fan and VLFT pulses of the test signal may for the most part be asynchronous with respect to each other, although the number of tachometer pulses for a period of time will be commensurate with the actual fan rotation, if the frequency of the VLFT pulses is at least twice the frequency of the tachometer pulses. In one embodiment, the frequency of the test or sampling signal (which comprises the VLFT pulses) is selected to be at least twice the highest attainable frequency of the fan generated tachometer pulses, per Nyquist's sampling theorem. In some embodiments the speed of the fan may not increase, though it may decrease, due to causes other than the PWM signal generator. In such embodiments the highest attainable frequency of the fan generated tachometer pulses may be reached when the PWM duty cycle is 100%, and the frequency of the test or sampling signal may also be adjusted as a function of the PWM duty cycle value, still observing Nyquist's sampling theorem.
The frequency of the test or sampling signal may be determined based on the duty cycle value of the PWM signal used to power the fan. In one embodiment, the frequency of the test or sampling signal is obtained through dividing a base frequency by a divider coefficient that corresponds to a particular PWM duty cycle value. The duty cycle values may be selected in advance; for example duty cycle values of 9%, 12%, 25%, 50%, 75%, and 100% may be used. Furthermore, the frequencies may be automatically selected using the high bits of the duty cycle of the PWM signal, which may be stored in a duty cycle value register. In one embodiment, selected PWM duty cycle values are converted by a decoder to corresponding frequency divider coefficient values. In order to account for a possible variation—from fan to fan—of the different frequencies corresponding to various PWM duty cycle values, the base frequency may first be divided to obtain a maximum frequency for the test or sampling signal corresponding to a specific fan. The thus obtained maximum frequency corresponding to a specific fan may then be used as a scaled base frequency that may be divided using the frequency divider coefficient values obtained from the conversion of the selected PWM duty cycles values.
In one embodiment, the tachometer reading-unit includes a flip-flop with the sampling signal providing the VLFT pulses used as the clock input of the flip-flop, and the tachometer signal providing the tachometer pulses used as the data input of the flip-flop, where the output of the flip-flop is the recreated fan rotational pulses, (or recreated tachometer pulses). The recreated tachometer pulses may be the input to a counter that is gated (turned on) for a specific time, with the output of the counter providing the measured RPM of the fan.
Thus, various embodiments of the systems and methods described above may facilitate design of a system that uses a test or sampling signal to accurately measure the speed of a fan in an electrical system while minimizing audio noise and sensitivity to electrical noise, and maintaining smooth fan operation, where only a maximum frequency for the test or sampling signal specific to the fan needs to be programmed for each fan.
The foregoing, as well as other objects, features, and advantages of this invention may be more completely understood by reference to the following detailed description when read together with the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims. Furthermore, note that the word “may” is used throughout this application in a permissive sense (i.e., having the potential to, being able to), not a mandatory sense (i.e., must). The term “include”, and derivations thereof, mean “including, but not limited to”. The term “coupled” means “directly or indirectly connected”.
As used herein, a “trigger” signal is defined as a signal that is used to initiate, or “trigger”, an event or a sequence of events in a digital system. A trigger signal is said to be in a “triggering state” at a time when it initiates a desired event, or sequence of events. A periodic trigger signal may commonly be referred to as a “clock”. In a “synchronous” digital system, generally a clock, commonly referred to as a “system clock”, may be used for initiating most events, or sequences of events. An example of a triggering state may be, but is not limited to, a rising edge of a pulse of a clock in a synchronous digital system. A “frequency” of pulses refers to a number of pulses that may appear within a selected unit period of time. For example, if twenty pulses appear within duration of one second, then the frequency of the pulses is 20 Hz.
When an event, or a sequence of events, is said to be initiated “in response to” receiving a stimulus signal, it may be implied that the event, or the sequence of events, is initiated as a result of a combination of a trigger signal, used in triggering the event or sequence of events, being in a triggering state at a time when the stimulus signal is asserted. In one set of embodiments, the sending of a pulse through an output port may indicate a point in time at which a leading edge of the pulse occurs at the output port, and the receiving of a pulse through an input port may indicate a point in time at which a leading edge of the pulse occurs at the input port. As used herein, “setting” a device refers to setting an output of the device to a high logic level, whereas “resetting” a device refers to setting an output of the device to a low logic level. It will be evident to those skilled in the art that a high logic level may be physically represented by either a high voltage or a low voltage, and similarly a low logic level may be physically represented by either a low voltage or a high voltage.
When referencing a pulse of a signal, a “leading edge” of the pulse is a first edge of the pulse, resulting from the value of the signal changing from a default value, and a “trailing edge” is a second edge of the pulse, resulting from the value of the signal returning to the default value. When data is said to be “registered” or “latched” “using” a signal, the signal acts as a trigger signal that controls the storing of the data into the register or latch. In other words, when a signal “used” for registering or latching data is in its triggering state, the data residing at respective input ports of the register or latch is stored into the register or latch. Similarly, when data is latched “on the leading edge” or “on the trailing edge” of a pulse of a clock, the data residing at respective input ports of a register or latch is stored into the register or latch, respectively, when a leading edge or a trailing edge of a pulse of the clock occurs, respectively.
A user programmable PWM duty cycle value 140 for PWM signal 152 may be programmed into PWM value register 122. The value of the duty cycle may be provided by register 122 to PWM generation circuit 124, which will correspondingly adjust the duty cycle of PWM signal 152, which in turn will result in the speed of fan 128 being adjusted accordingly. For example, at a PWM duty cycle value of 100%, fan 128 may reach a maximum RPM value, while a PWM duty cycle value of 50% would lower the speed of fan 128 from the maximum RPM value. PWM value register 122 may also provide the currently programmed PWM duty cycle value to a lookup table 120. In one embodiment, lookup table 120 holds divider coefficient values, which are provided to a down counter (or frequency counter) 116 for generating sampling signal 150 based on a base frequency 118 provided to down counter 116.
The divider coefficients for a particular fan may be determined from empirical data for various selected PWM duty cycle values for the fan. In order to obtain the divider coefficients for the fan, a set of PWM duty cycle values may first be selected, and rotational speed of the fan (revolutions per second) may be measured using an optical tachometer. A frequency for the tachometer signal that comprises the tachometer pulses generated by the fan may thus be determined, since the fan will generate a pre-determined number of tachometer pulses per revolution. A minimum frequency for the sampling signal may be selected such that quantization of the sampling may be equal or higher than quantization of the tested asynchronous sequence (that is, quantization of the tachometer pulses generated by the fan). Furthermore, Nyquist's sampling theorem may be applied, and the frequency for the sampling signal may be selected to be at least twice the tachometer signal frequency that corresponds to the selected PWM duty cycle value. Note that this analysis may be performed for any fan, including fan 128, which may be selected from a variety of available fans. Some fans may generate more tachometer pulses per revolution than others.
In one embodiment, lookup table 120 holds a set of divider coefficients corresponding to respective PWM duty cycle values for fan 128, such that an appropriate frequency for sampling signal 150 may be generated from base frequency 118. In alternate embodiments, lookup table 120 may hold multiple sets of frequency divider coefficient values, each set of frequency divider coefficient values corresponding to a particular fan and to the set of PWM duty cycle values associated with the particular fan. The PWM duty cycle values may be selected based on what expected PWM duty cycle values might be programmed into register 122 during system operation. In a preferred embodiment, every time a new PWM duty cycle value is programmed into register 122, a corresponding divider coefficient is selected from lookup table 120 and provided to down counter 116, resulting in sampling signal 150 being generated at a frequency corresponding to the currently used PWM duty cycle.
Table 300 in
It should also be noted that an embodiment such as shown in
In one embodiment, sampling signal 150 operates to obtain tachometer pulses from fan 128 even during time periods when PWM signal 152 might be unasserted. By multiplexing sampling signal 150 with PWM signal 152 using OR gate 126, and using the resultant output from OR gate 126 as PWM output 156 provided to FU 108, tachometer pulses may be obtained every time a pulse is present in sampling signal 150, provided that there is in fact a tachometer pulse present at the time of a pulse being present in sampling signal 150. By selecting the frequency of sampling signal 150 as previously described, all necessary tachometer pulses—of the appropriate width—may be recreated. This in turn may allow counting the tachometer pulses for a determined period of time, thus obtaining the RPM of fan 128.
The count may be achieved by using tachometer signal 154 as the data input into flip-flop 112 and clocking flip-flop 112 using sampling signal 150, which results in flip-flop 112 outputting recreated tachometer pulses via a recreated tachometer signal 158. The recreated tachometer pulses may then be provided to pulse counter 114, and the output of counter 114 will be fan RPM value 138. In some systems, fan RPM value 138 may be used as a feedback signal to determine if the speed of fan 128 needs to be altered, which may be accomplished by reprogramming PWM register 122 with an appropriate PWM duty cycle value as warranted by the current status of the system.
In one set of embodiments, a solution that may consume substantially less die area and does not feature a table that has to be programmed for each fan may be substituted for lookup table 120 (
F Tach=(RPM/60 sec)*(number of pulses per revolution), (1)
and may be plotted on the Y-axis of the graph vs. the PWM duty cycle plotted on the X-axis of the graph. It may be observed upon comparison of individual graphs thus obtained for a variety of fans that such graphs are substantially similar in shape and differ only in vertical scale, or, in other words, in the maximum tachometer frequency value (maximum RPM) associated with each fan.
Based on the relationship between VLFT frequency and PWM duty cycle value obtained from
Selecting X1 to represent scale factor coefficient 340, and X2 to represent divider coefficient 342, the frequency of the VLFT pulses (comprised, for example, in sampling signal 150 in
F VLFT =F base/(X 1*(X 2+1)),
where Fbase represents the base frequency 318 as shown in
F VLFT=(F base /M*X 1)*(M/X 2+1), (3)
where M represents a constant that corresponds to a lowest possible value of X2+1, in other words, (X2+1)≧M. Establishing X2≦1, a maximum value of FVLFT may be obtained by setting M=X2+1, resulting in:
F VLFT =F base/(M*X 1). (4)
Based on equations (3) and (4), X1 (that is, scale factor coefficient 340) may be programmed by the user such that FVLFT≧2*FTach. Furthermore, X1 may only need to be programmed once for the currently controlled fan. X2 (divider coefficient 342) may be derived solely from the PWM duty cycle value (stored in register 122 in the system of
As an example, if Fbase is selected to be 90 kHz, and M is selected to be 16, and the maximum FTach of the currently controlled fan is 200 Hz, then keeping with Nyquist's sampling theorem the value for the maximum frequency of the VLFT pulses may be written as FVLFT
Thus, various embodiments of the systems and methods described above may facilitate design of a system that uses a test or sampling signal to accurately measure the speed of a rotating device, for example a fan in an electrical system, while minimizing audio noise and sensitivity to electrical noise, and maintaining smooth fan operation, where only a maximum frequency for the test or sampling signal specific to the currently controlled fan needs to be programmed for each fan.
Although the embodiments above have been described in considerable detail, other versions are possible. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications. Note the section headings used herein are for organizational purposes only and are not meant to limit the description provided herein or the claims attached hereto.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4722669||Aug 29, 1985||Feb 2, 1988||Control Resources, Inc.||Fan speed controller|
|US4727468||Mar 6, 1987||Feb 23, 1988||Kabushiki Kaisha Toshiba||Digital PWM control circuit|
|US5249741||May 4, 1992||Oct 5, 1993||International Business Machines Corporation||Automatic fan speed control|
|US5307439||Feb 6, 1992||Apr 26, 1994||Nec Corporation||Driving circuit for controlling the speed of a motor in PWM and linear modes|
|US5687079||Jun 1, 1995||Nov 11, 1997||Sun Microsystems, Inc.||Method and apparatus for improved control of computer cooling fan speed|
|US5727928||Dec 14, 1995||Mar 17, 1998||Dell Usa L.P.||Fan speed monitoring system for determining the speed of a PWM fan|
|US5825972||Jun 13, 1997||Oct 20, 1998||Dell Usa, L.P.||Direct current fan motor speed controller|
|US5942866||Jan 20, 1998||Aug 24, 1999||Hsieh; Hsin-Mao||PWM control circuit for a DC brushless fan|
|US5962933||Oct 1, 1997||Oct 5, 1999||Micron Electronics, Inc.||Computer fan speed control method|
|US5990582||Oct 1, 1997||Nov 23, 1999||Micron Electronics, Inc.||Computer fan speed control device|
|US6029119||Jan 16, 1996||Feb 22, 2000||Compaq Computer Corporation||Thermal management of computers|
|US6182902||Jul 22, 1999||Feb 6, 2001||Mitac Technology Corp.||Device and method for automatically controlling rotating speed of fan cooler|
|US6188189||Dec 23, 1999||Feb 13, 2001||Analog Devices, Inc.||Fan speed control system|
|US6208538||Jun 1, 2000||Mar 27, 2001||Semiconductor Components Industries, Llc||PWM control apparatus|
|US6226324||Dec 17, 1997||May 1, 2001||The Foxboro Company||Methods and systems for trimming a PWM signal|
|US6247898||Oct 1, 1997||Jun 19, 2001||Micron Electronics, Inc.||Computer fan speed control system|
|US6262549||Jun 29, 2000||Jul 17, 2001||System General Corp.||Fan speed pulse filter for a PWM fan|
|US6519167||Dec 27, 2001||Feb 11, 2003||Tranh To Nguyen||PWM controller with single-cycle response|
|US6526333||Oct 1, 1997||Feb 25, 2003||Micron Technology, Inc.||Computer fan speed control system method|
|US6528987||Jun 19, 2000||Mar 4, 2003||Analog Devices, Inc.||Method and apparatus for determining fan speed|
|US6563284||Nov 21, 2001||May 13, 2003||Texas Instruments Incorporated||Single wire digital width modulation for fan control with tachometer feedback|
|US6601168||Nov 19, 1999||Jul 29, 2003||Hewlett-Packard Development Company, L.P.||Computer fan speed system to reduce audible perceptibility of fan speed changes|
|US6617815||Apr 14, 1999||Sep 9, 2003||Hewlett-Packard Development Company, L.P.||Fan control circuit|
|US6650074||Oct 15, 2002||Nov 18, 2003||Dell Products, L.P.||Fan speed controller with conditioned tachometer signal|
|US6661679||Oct 28, 2002||Dec 9, 2003||System General Corporation||PWM controller having adaptive off-time modulation for power saving|
|US6674369||Aug 14, 1998||Jan 6, 2004||Minebea Co., Ltd.||Fan control circuit|
|US6747424||Oct 2, 2000||Jun 8, 2004||International Business Machines Corporation||Integrated fan speed control and fault detection circuitry|
|US6757592||Sep 30, 2002||Jun 29, 2004||National Semiconductor Corporation||Nonlinear fan control|
|US6765422||Jun 5, 2003||Jul 20, 2004||National Semiconductor Corporation||High resolution fan control at high PWM frequency with a low clock frequency input|
|US6778938||Aug 2, 2002||Aug 17, 2004||National Semiconductor Corporation||Fan speed detection in the presence of PWM speed control|
|US6812737||Jun 28, 2002||Nov 2, 2004||Semiconductor Technology Academic Research Center||Programmable logic circuit device having look up table enabling to reduce implementation area|
|US20020197424||Apr 9, 2002||Dec 26, 2002||Bayer Robert T.||Four edge sealed sterilization wrap and method for sterilizing an article|
|US20030011332||May 13, 2002||Jan 16, 2003||Mays Ford Chapman||Brushless DC fan module incorporating integral fan control circuit with a communication port for receiving digital commands to control fan|
|US20030137267||Dec 18, 2000||Jul 24, 2003||John Blake||Fan speed control system|
|US20030234630||Jun 24, 2002||Dec 25, 2003||John Blake||Fan speed control system|
|US20040001542||Jul 1, 2002||Jan 1, 2004||Miller Wayne A.||Method and apparatus for measuring the rotational speed of a fan|
|US20040027763||Aug 6, 2002||Feb 12, 2004||Dhuey Michael J.||Quiet fan speed control|
|1||"Accurate Remote Diode Digital Temperature Sensor with Integrated Fan Control", LM63, National Semiconductor, 2003.|
|2||"dBCOOL(TM) Remote Thermal Controller and Voltage Monitor", Analog Devices, ADM1027, 2003.|
|3||Stephen Ohr, "Analog IC Vendors Find 'Intel Inside' a Safe Bet", EETimes, http://www.eetimes.com/story/OEG20020912S0026 Sep. 12, 2002.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7190142 *||Mar 30, 2004||Mar 13, 2007||Lg Electronics Inc.||Apparatus and method for controlling fan drive in computer system|
|US7863849||Feb 29, 2008||Jan 4, 2011||Standard Microsystems Corporation||Delta-sigma modulator for a fan driver|
|US8241008||Feb 26, 2009||Aug 14, 2012||Standard Microsystems Corporation||RPM controller using drive profiles|
|US8606429 *||Dec 28, 2010||Dec 10, 2013||Hon Hai Precision Industry Co., Ltd.||System and method for controlling an electronic device fan|
|US9212664||Jul 16, 2012||Dec 15, 2015||Standard Microsystems Corporation||RPM controller using drive profiles|
|US20050013114 *||Mar 30, 2004||Jan 20, 2005||Lg Electronics Inc.||Apparatus and method for controlling fan drive in computer system|
|US20100215510 *||Feb 26, 2009||Aug 26, 2010||Chao-Ming Tsai||RPM Controller Using Drive Profiles|
|US20120035769 *||Dec 28, 2010||Feb 9, 2012||Hon Hai Precision Industry Co., Ltd.||System and method for controlling an electronic device fan|
|U.S. Classification||702/145, 388/804, 318/599|
|International Classification||G01P3/00, H02P7/06, G06F15/00, G01P3/48|
|May 11, 2004||AS||Assignment|
Owner name: STANDARD MICROSYSTEMS CORPORATION, NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BEKKER, LEONID A.;SEGAL, URI;REEL/FRAME:015322/0730
Effective date: 20040506
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Year of fee payment: 4
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