Source: http://www.google.com/patents/US7327114?ie=ISO-8859-1&dq=7350717
Timestamp: 2014-10-22 16:16:06
Document Index: 61835108

Matched Legal Cases: ['ART) 57', 'ART 57', 'ART 57', 'ART 57', 'ART 66', 'ART 57']

Patent US7327114 - Fan control utilizing bi-directional communications - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA system and method for bi-directional communication between a system controller and a fan controller: The system operates in two modes and there are two communication paths between the system controller and the fan controller. The first communication path provides a PWM signal the frequency of which...http://www.google.com/patents/US7327114?utm_source=gb-gplus-sharePatent US7327114 - Fan control utilizing bi-directional communicationsAdvanced Patent SearchPublication numberUS7327114 B2Publication typeGrantApplication numberUS 11/559,599Publication dateFeb 5, 2008Filing dateNov 14, 2006Priority dateFeb 28, 2006Fee statusPaidAlso published asUS7141950, US20070200518Publication number11559599, 559599, US 7327114 B2, US 7327114B2, US-B2-7327114, US7327114 B2, US7327114B2InventorsGreg VergeOriginal AssigneeCypress Semiconductor Corp.Export CitationBiBTeX, EndNote, RefManPatent Citations (25), Non-Patent Citations (5), Referenced by (7), Classifications (7), Legal Events (1) External Links: USPTO, USPTO Assignment, EspacenetFan control utilizing bi-directional communicationsUS 7327114 B2Abstract A system and method for bi-directional communication between a system controller and a fan controller: The system operates in two modes and there are two communication paths between the system controller and the fan controller. The first communication path provides a PWM signal the frequency of which indicates the mode in which the system is operating. During the first mode, the duty cycle of the PWM signal on the first signal path indicates the desired fan speed. In the first mode, the second communication path carries a conventional tachometer signal. In the second mode the second communication path operates as a bi-directional communications signal path between said system controller and said fan controller.
RELATED APPLICATION This application is a continuation of patent application Ser. No. 11/365,066 filed Feb. 28, 2006 now U.S. Pat. No. 7,141,950. Priority to application Ser. No. 11/365,066 field Feb. 28, 2006 is hereby claimed. The entire content of application Ser. No. 11/365,066 filed Feb. 28, 2006 is hereby incorporated herein by reference.
FIELD OF THE INVENTION The present invention relates to the cooling fans for computer systems and more particularly to a system and method for controlling the speed of a cooling fan.
BACKGROUND Many computer systems include a fan which moves air over the system's components in order to prevent excessive heating of the components. Many such fans are single speed fans that operate constantly while the computer is in operation.
Some more modern systems utilize variable speed cooling fans. The speed of such fans is increased when more cooling is desired. One such prior art system has a configuration such as that shown in FIG. 1. The system shown in FIG. 1 includes a system controller 1, a fan 2, and a fan controller 3. The connections between the system controller 1 and the fan controller 3 include a power line 1 a, a ground line 1 b, a Pulse Width Modulated (PWM) signal line 1 c and a tachometer signal line 1 d. A transistor switch 4 controls the voltage on tachometer line 1 d. The fan controller 3 is physically attached to the fan motor (not shown in FIG. 1) and it drives the coils in the fan motor causing the fan 2 to rotate. Both the system controller 1 and the fan controller 3 include microprocessors that perform various calculations digitally.
It is noted that with the system shown in FIG. 1, only one parameter is communicated in each direction. Desired speed is communicated from system controller 1 to fan controller 3 on line 1 c. Measured fan speed is communicated from fan controller 3 to system controller 1 on line 1 d. It is also noted that two signal conversions are required in the system described above. The PWM signal is converted to a digital signal in the fan controller 3 and the frequency signal on line 1 d is converted into a digital signal indicating fan speed at the system controller 1. Such conversions are inherently somewhat inaccurate, especially in low cost devices.
SUMMARY OF THE INVENTION The present invention provides a system and method for bi-directional communication between a system controller and a fan controller. The system includes two communication paths between the system controller and the fan controller. The first path provides a PWM signal the frequency of which indicates the mode in which the system is operating. During said first mode of operation, the duty cycle of the PWM signal on said first path indicates the desired fan speed. The second communication path serves one function in a first mode of operation and a second function in a second mode of operation. In the first mode, the second communication path carries a conventional tachometer signal. In the second mode, the second communication path operates as a bi-directional communications link between the system controller and the fan controller.
BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows a prior art system.
Box �p� indicates a conventional preamble or sync signal that is used to synchronize the transmission operation in the system controller 21 with the reception in fan controller 23. Box �c� indicates the transmission of a command that is to be performed by the microprocessor in fan controller 23. Box �a� indicates the address of data that is to be accessed by the microprocessor in fan controller 23. Box �d1� indicates data byte 1 of �n� data bytes. Box �d2� indicates data byte 2 of �n� data bytes. (There can be any number of such data bytes) Box �cs� indicates a conventional checksum to insure that the previous bytes are valid. The system controller 21 can transmit both commands and data to the fan controller 23. The commands that can be transmitted are conventional microprocessor commands. Examples of the types of data and commands that can be transmitted from the system controller 21 to the fan controller 23 are:
a) The default fan speed that fan controller 23 uses during the start up phase of operation, prior to receiving and interpreting a speed signal on line 21 c. b) A parameter that specifies a delay time period before the fan starts at system power up time. c) Default parameters that specify how the fan should operate if the bi-directional communication with the controller 21 is for some reason lost. d) A command indicating that the fan controller 23 should transmit certain data to the system controller 21. Waveform 34 shows an example of the signal that the fan controller applies to the transistor 24 in order to transmit fan speed to the system controller. It is noted that when the fan controller 23 detects a switch to communication mode, that is, when data is being transmitted on line 21 d, the transistor 24 is held in the open state so that the system controller 21 can modulate the signal on line 21 d. It is noted that the wave form 34 represents the control signal to the base of transistor 24. The signal applied to the base of transistor 24 is a signal that is generated by a tachometer in the fan controller. As shown in FIG. 8, this signal is generated by a hall sensor in a conventional manner.
FIG. 4 shows examples of the waveforms that occur when data is transferred from the fan controller 23 to the system controller 21. Note that in waveform 43, a point 43 b, the system controller 21 sends a command to the fan controller 23. This command tells the fan controller 23 to begin transmitting data and this happens at point 43 c. Waveform 41 illustrates a change in PWM frequency which indicates a shift to bi-directional communication mode.
Waveform 43 indicates the signal on line 21 d. At point 43 a, there is a conventional tachometer pulse. At point 43 b, the system controller sends information by modulating line 21 d. At point 43 c, the fan controller sends information by modulating line 21 d. Waveform 44 indicates how the fan controller 23 controls the base control line of transistor 24. At point 44 a, the transistor 24 is closed to transmit a tachometer pulse. At point 44 b, the transistor control line is modulated to transmit data.
a) A parameter indicating the actual speed of the fan 22. b) A parameter indicating the actual temperature of the air flowing through the fan. c) A parameter indicating the amount of current in the fan coil at a particular time. d) A parameter indicating the number of locked rotor events that have occurred. e) A parameter indicating some type of abnormal fan operation which may predict future fan failure. Thus, during the second mode of operation, the system controller 21 sends digital data to the fan controller 23 that can for example indicate the desired speed at which the fan can operate. It can also send other data such as the speed at which the fan should operate under default conditions. During the second mode of operation the fan controller 23 can send data to the system controller indicating the speed and data concerning other operating conditions of the fan.
System controller 21 also includes registers 52 and 55, a counter 53, a comparator 54, a line driver 56, a conventional �Universal Asynchronous Receiver Transmitter� (UART) 57 and a conventional tachometer signal digitizer 58.
UART 57 is a conventional �Universal Asynchronous Receiver Transmitter� device. A UART is a computer component that handles asynchronous serial communication on a signal line. For example, many computers contain UARTs to manage their serial ports. UART 57 and a corresponding UART in fan controller 23 control the transmission of data on tach line 21 d. This occurs when the PWM pulses on line 21 c have a relatively high frequency.
Tachometer signal digitizer 58 is a conventional device that takes the tachometer pulses on line 21 d, and provides a digital number to microprocessor 51 indicating the frequency of the pulses and hence the actual frequency of fan 22. The tachometer pulses appear on line 21 d when there are relatively low frequency PWM pulses on line 21 c. FIG. 6 is a block diagram of the major components in fan controller 23. Fan controller 23 contains a conventional microprocessor 61. Microprocessor 61 controls and interacts with the various components shown in FIG. 6 as explained below. Microprocessor 61 also performs a number of conventional operations not explained herein.
The microprocessor 61 calculates the PWM frequency from the time period that elapses between two raising edges as measured by timer 63. At system start-up the timers 63 and 64 are initially started at the same time (that is, in synchronization). One timer is reset by the raising pulse edge and the other by the falling pulse edge. This allows the system to calculate pulse width by measuring the time period between a rising edge as measured by time 63 and a falling edge as measured by time 64. The PWM duty cycle is calculated by dividing the PWM pulse width by the PWM period. It is noted that in an alternate embodiment a single timer is used to perform the function of timers 63 and 64. In such an embodiment, the single timer performs the function of timer 63 during a first pulse on line 21 c and the function of timer 64 during a second pulse on line 21 c. The UART 57 in the system controller communicates with the UART 66 in the fan controller 23 allowing the system controller 21 and the fan controller 23 to exchange data. This type of communication between two UARTs is conventional.
A temperature sensor 71 provides a temperature input to the system controller 21 and to the microprocessor 61 in a conventional manner. A voltage supply 75 provides power to the system. Resistors 72, 73 and 74 provide conventional current limiting functions. It is noted that there are two connections from the system controller 21 to communication line 21 d. One output is from the UART 57 and it controls the base of transistor 25 which drives line 21 d low. The second connection to line 21 d is a tachometer and UART input line. The PWM output is connected to line 21 c. The connections to the fan controller 23 are shown in FIG. 8. The output of the fan controller 23 drives the fan motor coil 86 in a conventional manner. Current in the fan motor coil 86 is controlled by transistors 87 a, 87 b, 87 c and 87 d which are connected in a bridge circuit in a conventional manner. Outputs 88 directly control transistors 87 c and 87 d and transistors 87 a and 87 b are controlled through inverters 85 a and 85 b. The bridge circuit controlling the fan motor coil 86 is conventional.
At block 96, a determination is made as to whether the PWM signals are in legacy mode or in bi-directional communication mode. If the PWM signals are at the slow frequency, the system proceeds to block 97. The signal on line 21 d continues to be the legacy tachometer signal. As indicated by blocks 98 and 99, the fan is made to operate at the speed specified by the PWM signal that was received. As indicated by block 100, the fan speed is outputted on line 21 d. If, at block 96, it is determined that the PWM signal is at a high frequency, the system switches to bi-directional communication mode. It is noted that such a switch would be initiated by the system controller 21 in response to the detection of some conditions pre-programmed into the system controller. If a high frequency PWM signal is detected, first a check is made by block 102 to insure that the PWM frequency is in fact the bi-direction communication mode frequency. If it is not, the fan is set to a default error speed and the system returns to block 93.
An alternate embodiment is shown in FIGS. 10A and 10B. The alternate embodiment includes a system controller 121 and a fan controller 123 that are connected by signal lines 121 c and 121 d. The power and ground lines are not shown in FIGS. 10A and 10B. This alternate embodiment utilizes the type of communication protocol known as Inter-IC or I2C. The I2C protocol is a multi-master bus type of communication. This means that the units at either end of the bus can act as a master and initiate communication; however, in this embodiment the I2C module in the system controller acts as the master. In this second embodiment, during the first or legacy mode of communication, the system operates as previously described. That is, line 121 c operates as a first communication path that carries PWM signals and line 121 d operates as a second communication path that carries a tachometer signal. However, during a second mode of operation, line 121 d provides a second communication path, but line 121 c provides a clock signal for the communication that occurs on line 121 d. As is well know in the art I2C communication requires two signal lines. One signal line transmits a clock signal and a second signal line carries bi-directional modulated communication signals.
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