Apparatus and method for controlling temperature

A temperature control apparatus is suitable for use in devices such as consumer electronics devices having different thermal characteristics. According to an exemplary embodiment, the temperature control apparatus includes a fan having a field winding (F3) and a speed controller for providing a speed control signal to the field winding (F3) responsive to a first control signal to control a rotating speed of the fan. First and second terminals of the fan enable operating power to be provided to the field winding (F3) and the speed controller. At least one of the first and second terminals is operatively coupled to a first voltage source. A third terminal of the fan provides the first control signal to the speed controller, and is operatively coupled to a second voltage source. The temperature control apparatus further includes a temperature measuring circuit operative to measure a temperature and provide a temperature indicating signal indicating the measured temperature, a processor operative to provide a second control signal responsive to the temperature indicating signal, and control circuitry operative to provide the first control signal to the third terminal of the fan responsive to the second control signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to temperature control, and more particularly, to a cost-effective temperature control apparatus including a variable-speed fan that is suitable for use in devices such as consumer electronics devices having different thermal characteristics, and a method for controlling temperature using such a device.

2. Background Information

Devices such as consumer electronic devices often require a temperature control mechanism such as a fan to prevent damage from excessive heat. At present, there are various different types of fans that may be used by such devices for temperature control. One such type of fan may be controlled by a thermistor. Thermistor-controlled fans can be a cost-effective option for temperature control in certain applications, but are disadvantageous in that the relationship between fan speed and temperature is fixed by the thermistor. Accordingly, thermistor-controlled fans may be unsuitable for certain applications. For example, thermistor-controlled fans may be unsuitable for applications in which the fan's orientation in a final device may vary (e.g., from model to model), and thereby require the relationship between fan speed and temperature to be modified in order to compensate for different thermal characteristics.

Another type of fan can be controlled by pulse width modulation (PWM). In short, PWM-controlled fans use the relative width of pulses in a train of on and off pulses to control the amount of power applied to the fan motor, and thereby control its rotating speed. Currently available PWM-controlled fans tend to be relatively expensive since they may utilize an expensive high-current transistor driven by the fan's operating power for receiving the pulses that control the fan's rotating speed. As a result, currently-available PWM-controlled fans may be unduly expensive for certain applications, particularly those applications where cost is a critical consideration.

Accordingly, there is a need for a cost-effective temperature control apparatus including a variable-speed fan that avoids the foregoing deficiencies, and is suitable for use in devices such as consumer electronics devices having different thermal characteristics. The present invention addresses these and/or other issues.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a temperature control apparatus is disclosed. According to an exemplary embodiment, the temperature control apparatus comprises a fan including a field winding, and a speed controller for providing a speed control signal to the field winding responsive to a first control signal to control a rotating speed of the fan. First and second terminals of the fan enable operating power to be provided to the field winding and the speed controller. At least one of the first and second terminals is operatively coupled to a first voltage source. A third terminal of the fan provides the first control signal to the speed controller. The third terminal is operatively coupled to a second voltage source. The temperature control apparatus further comprises temperature measurement means for measuring a temperature and providing a temperature indicating signal indicating the measured temperature, processing means for providing a second control signal responsive to the temperature indicating signal, and control means for providing the first control signal to the third terminal of the fan responsive to the second control signal.

In accordance with another aspect of the present invention, a method for controlling temperature is disclosed. According to an exemplary embodiment, the method comprises steps of providing a fan having a field winding, a speed controller for providing a speed control signal to the field winding responsive to a first control signal to control a rotating speed of the fan, first and second terminals for enabling operating power to be provided to the field winding and the speed controller, and a third terminal for providing the first control signal to the speed controller. At least one of the first and second terminals is operatively coupled to a first voltage source, and the third terminal is operatively coupled to a second voltage source. The method further comprises steps of measuring a temperature and providing a temperature indicating signal indicating the measured temperature, providing a second control signal responsive to the temperature indicating signal, and providing the first control signal to the third terminal of the fan responsive to the second control signal.

In accordance with yet another aspect of the present invention, a device having a temperature control apparatus is disclosed. According to an exemplary embodiment, the temperature control apparatus comprises a fan including a field winding, and a speed controller for providing a speed control signal to the field winding responsive to a first control signal to control a rotating speed of the fan. First and second terminals of the fan enable operating power to be provided to the field winding and the speed controller. At least one of the first and second terminals is operatively coupled to a first voltage source. A third terminal of the fan provides the first control signal to the speed controller. The third terminal is operatively coupled to a second voltage source. The temperature control apparatus further comprises a temperature measuring circuit operative to measure a temperature and provide a temperature indicating signal indicating the measured temperature, a processor operative to provide a second control signal responsive to the temperature indicating signal, and control circuitry operative to provide the first control signal to the third terminal of the fan responsive to the second control signal.

Throughout the drawings, like reference numbers represent the same or similar elements. The exemplifications set out herein illustrate preferred embodiments of the present invention, and such exemplifications are not to be construed as limiting the scope of the present invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly toFIG. 1, a diagram of a temperature control apparatus100according to an exemplary embodiment of the present invention is shown. As shown inFIG. 1, temperature control apparatus100comprises a fan10, a point of distribution (POD) card20, temperature measuring means such as temperature measuring circuit30, processing means such as processor40, memory means such as electrically-erasable programmable read-only memory (EEPROM)50, and control means such as control circuitry60. Some of the foregoing elements of temperature control apparatus100may be embodied using integrated circuits (ICs), and some elements may for example be included on one or more ICs. For clarity of description, certain conventional elements associated with temperature control apparatus100such as certain control signals, power signals and/or other elements may not be shown inFIG. 1. According to an exemplary embodiment, temperature control apparatus100may be included in a device such as a consumer electronic device for performing a temperature control function.

Fan10is operative to enable the aforementioned temperature control function. According to an exemplary embodiment, fan10comprises a rotor R, field windings F1to F4, a voltage to current converter12, a resistor Rf, and three input terminals1to3. Rotor R is rotated in response to an electrical field applied through field windings F1to F4which opposes a fixed magnet in rotor R. Voltage to current converter12controls the rotating speed of fan10based on a first control signal received via terminal3of fan10. As shown inFIG. 1, voltage to current converter12provides a speed control signal to field winding F3responsive to the first control signal received via terminal3to thereby control the rotating speed of fan10. Resistor Rf is operatively coupled between terminal3of fan10and a voltage source of 6V. According to an exemplary embodiment, resistor Rf has a value of 5 KΩ, although other values may be used.

Terminals1and2enable operating power to be provided to elements of fan10including field windings F1to F4and voltage to current converter12. As shown inFIG. 1, terminals1and2provide the operating power to fan10from a voltage source of 12V, which is the main power supply of fan10. According to the present invention, at least one of terminals1and2of fan10is operatively coupled to the 12V voltage source. As previously indicated herein, terminal3of fan10provides the first control signal to voltage to current converter12to thereby control the rotating speed of fan10, and is operatively coupled to the aforementioned 6V voltage source. According to an exemplary embodiment, fan10may be embodied using a Delta model AFB0812L-SX00 fan or an equivalent thereof.

POD card20is operative to generate and distribute heat. According to an exemplary embodiment, POD card is embodied using a “smart-card” or similar element. Temperature measuring circuit30is operative to measure an ambient temperature around POD card20. As will be described later herein, a temperature indicating signal indicating the temperature measured by temperature measuring circuit30is periodically read by processor40. According to an exemplary embodiment, temperature measuring circuit30may be embodied using a National Semiconductor model LM77 IC or an equivalent thereof.

Processor40is operative to perform various processing functions. According to an exemplary embodiment, processor40is operative to read the temperature indicating signal indicating the temperature measured by temperature measuring circuit30on a periodic basis, such as once every minute or other predetermined time period. Also according to an exemplary embodiment, processor40is operatively coupled to temperature measuring circuit30via an inter-integrated circuit (IIC) bus, which is generally known in the art.

Processor40compares the temperature indicated by the temperature indicating signal to a predetermined threshold temperature. If the measured temperature is greater than the predetermined threshold temperature, processor40provides a second control signal to control circuitry60using digital data (e.g., temperature versus voltage table) stored in EEPROM60. According to an exemplary embodiment, the second control signal indicates an address corresponding to a particular PWM duty cycle for the first control signal to be provided to terminal3of fan10. In other embodiments of the present invention that will be described later herein, processor40may also provide a third control signal that is used to turn fan10on and off.

EEPROM50is operative to store digital data including the digital data that is retrieved by processor40to enable the temperature control function of the present invention. According to an exemplary embodiment, EEPROM50is operatively coupled to processor40via an IIC bus.

Control circuitry60is operative to provide the first control signal to terminal3of fan10responsive to the second control signal provided from processor40. As shown inFIG. 1, control circuitry60comprises a field programmable gate array (FPGA)62, a diode D1, and a resistor R1. FPGA62comprises a 5-bit PWM unit64, a 5-bit register66, and a transistor Q1.

According to an exemplary embodiment, the second control signal provided from processor40indicates an address of 5-bit register66that contains data indicating a particular PWM duty cycle for the first control signal to be provided to terminal3of fan10. In response to the second control signal, 5-bit register66provides the data indicating the particular PWM duty cycle for the first control signal to 5-bit PWM unit64which in turn outputs pulses in accordance with the particular PWM duty cycle. According to an exemplary embodiment, the pulses output from 5-bit PWM unit64range from 0 to 3.3V and control the duty cycle that transistor Q1is turned on. Transistor Q1may be embodied as an open-drain, N-channel metal oxide semiconductor field effect transistor (MOSFET), or other type of switching means. When transistor Q1is turned on, drain to source current flows through transistor Q1and resistor R1is connected to ground. According to an exemplary embodiment, resistor R1has a value of 10 KΩ, although other values may be used.

By controlling the time that resistor R1is grounded, the average current of the first control signal on terminal3of fan10can be varied. To control the rotating speed of fan10, 5-bit PWM unit64may be run from a maximum duty cycle of 31 out of 32 steps (i.e., 5-bits) at the gate of transistor Q1to roughly 16 out of 32 steps (i.e., 50% duty cycle). Since the maximum duty cycle results in transistor Q1being turned on almost 100% of the time, resistor R1appears to be grounded almost continuously in this state. In this manner, varying the duty cycle of 5-bit PWM unit64from 50% to 100% varies the rotating speed of fan10from minimum to maximum speed. The use of 5-bit data for controlling duty cycle is exemplary only, and other numbers of bits may also be used.

According to an exemplary embodiment, the minimum PWM value may need to be controlled to prevent the peak voltage on the drain of transistor Q1from exceeding the 3.9V rating on FPGA62. With fan10, terminal3floats to 6V when open-circuited. To prevent an over-voltage problem, Schottky diode D1is connected from the drain of transistor Q1to the 3.3V supply of FPGA62. In this manner, diode D1limits the peak voltage on the drain of transistor Q1to 0.4V above the 3.3V supply of FPGA62.

Referring toFIG. 2, a diagram of a temperature control apparatus200according to another exemplary embodiment of the present invention is shown. Temperature control apparatus200ofFIG. 2is substantially identical to temperature control apparatus100ofFIG. 1, except that temperature control apparatus200ofFIG. 2further includes resistor R2and eliminates diode D1. Resistor R2allows a minimum current to be set up which limits the maximum voltage seen by the drain of transistor Q1. Resistor R1then just controls the additional current needed to run fan10from minimum to maximum speed. According to an exemplary embodiment, resistors R1and R2are both 5.1 KΩ, although other values may be used. With temperature control apparatus200ofFIG. 2, the voltage present on terminal3of fan10ranges from 2.9V to 1.9V. Voltage to current converter12of fan10uses this voltage variation to vary the rotating speed of fan10from a minimum speed of 800 RPM to a maximum speed of 2000 RPM. In addition to eliminating the potential voltage problem on the drain of transistor Q1, temperature control apparatus200ofFIG. 2also eliminates the need to limit the PWM range since the full range is useable. That is, resistors R1and R2enable the current in terminal3of fan10to be linearly controlled from a 0% duty cycle to a 100% duty cycle. To minimize noise with temperature control apparatuses100and200ofFIGS. 1 and 2, respectively, it may be desirable to keep the PWM period above 20 kHz.

Referring toFIG. 3, a diagram of a temperature control apparatus300according to yet another exemplary embodiment of the present invention is shown. Temperature control apparatus300ofFIG. 3is substantially identical to temperature control apparatus200ofFIG. 2, except that temperature control apparatus300ofFIG. 3further includes a capacitor C1in parallel with resistor R2. According to an exemplary embodiment, capacitor C1is operative to integrate the average current through resistor R1in parallel with resistor R2to thereby eliminate a time-varying signal input to terminal3of fan10. One primary advantage to the addition of capacitor C1is the elimination of any frequency dependence on 5-bit PWM unit64. In particular, 5-bit PWM unit64may operate at a frequency as low as a few kilohertz without creating any audible noise. Also according to an exemplary embodiment, capacitor C1has a value of 10 μF, although other values may be used.

Referring toFIG. 4, a diagram of a temperature control apparatus400according to still yet another exemplary embodiment of the present invention is shown. Temperature control apparatus400ofFIG. 4is substantially identical to temperature control apparatus300ofFIG. 3, except that temperature control apparatus400ofFIG. 4further includes a transistor Q2, a resistor Rb, and diode D1. According to an exemplary embodiment, transistor Q2is embodied as an NPN-type transistor, but may be embodied as any type of switching mechanism. The addition of transistor Q2inFIG. 4enables fan10to be selectively turned on and off responsive to a control signal from processor40that is applied to the base terminal of transistor Q2. As indicated inFIG. 4, the collector of transistor Q2is operatively coupled to terminal3of fan10, and the emitter thereof is operatively coupled to ground. According to an exemplary embodiment, resistor Rb has a value of 10 KΩ, although other values may be used.

To facilitate a better understanding of the present invention, an example will now be provided. Referring toFIG. 5, a flowchart500illustrating steps for controlling temperature according to an exemplary embodiment of the present invention is shown. For purposes of example and explanation, the steps ofFIG. 5will be described with reference to temperature control apparatus400ofFIG. 4. The steps ofFIG. 5are exemplary only, and are not intended to limit the present invention in any manner.

At step505, fan10is turned off. According to an exemplary embodiment, processor40provides a logic low signal to the base of transistor Q2and thereby causes fan10to be turned off at step505. At step510, a temperature reading is performed. According to an exemplary embodiment, processor40initiates the temperature reading at step510by providing a control signal to temperature measuring circuit30via the IIC bus that connects processor40and temperature measuring circuit30. In response to the control signal, temperature measuring circuit30provides a temperature indicating signal indicating the measured ambient temperature around POD card20to processor40via the IIC bus. According to an exemplary embodiment, processor40reads the temperature indicating signal from temperature measuring circuit30on a periodic basis, such as once every minute or other predetermined time period.

At step515, a determination is made as to whether the temperature read at step510is greater than a predetermined threshold temperature for X number of consecutive readings. According to an exemplary embodiment, processor40is programmed to make the determination at step515, and X is equal to 5 although other values may also be used. If the determination at step515is negative, process flow loops back to step510where processor40performs another temperature reading in accordance with the predetermined time period (e.g., once every minute). Alternatively, if the determination at step515is positive, process flow advances to step520where fan10is tuned on to its minimum speed. According to an exemplary embodiment, processor40provides a logic high signal to the base of transistor Q2and thereby causes fan10to be turned on at step520. Processor40also provides the second control signal to FPGA62which enables generation of the first control signal on terminal3of fan10at a duty cycle corresponding to minimum fan speed.

At step525, another temperature reading is performed in the manner previously described above at step510. At step530, a determination is made as to whether the read temperature is greater than the predetermined threshold temperature for Y number of consecutive readings. According to an exemplary embodiment, processor40is programmed to make the determination at step530, and Y is equal to 2 although other values may also be used. If the determination at step530is negative, process flow advances to step535where a determination is made as to whether fan10is running at its minimum speed and the read temperature is less than the threshold temperature by a predetermined temperature limit. According to an exemplary embodiment, processor40is programmed to make the determination at step535and the predetermined temperature limit used at step535is a matter of design choice.

If the determination at step535is positive, process flow loops back to step505where fan10is tuned off by processor40providing a logic low signal to the base of transistor Q2. Alternatively, if the determination at step535is negative, process flow advances to step545where another temperature reading is performed in the manner previously described above at step510. If the determination at step530is positive, process flow advances to step540where the speed of fan10is increased by one step. According to an exemplary embodiment, processor40provides the second control signal to FPGA62which in turn increases the duty cycle of the first control signal on terminal3of fan10by one step, and thereby increases the speed of fan10by one step at step540. From step540, process flow advances to step545where another temperature reading is performed in the manner previously described above at step510.

At step550, a determination is made as to whether the temperature read at step545has decreased for Z number of consecutive readings. According to an exemplary embodiment, processor40is programmed to make the determination at step550, and Z is equal to 4 although other values may also be used. If the determination at step550is negative, process flow loops back to step530previously described herein. Alternatively, if the determination at step550is positive, process flow advances to step555where the speed of fan10is decreased by one step. According to an exemplary embodiment, processor40provides the second control signal to FPGA62which in turn decreases the duty cycle of the first control signal on terminal3of fan10by one step, and thereby decreases the speed of fan10by one step at step555. From step555, process flow advances to step560where another temperature reading is performed in the manner previously described above at step510. From step560, process flow loops back to step530previously described herein. The steps ofFIG. 5may be repeated in the indicated manner. The steps ofFIG. 5may be used to maintain temperature below a given threshold (e.g., less than 65° C., etc.).

As described herein, the present invention provides a cost-effective temperature control apparatus including a variable-speed fan that is suitable for use in devices such as consumer electronics devices having different thermal characteristics, and a method for controlling temperature using such a device. The present invention may be applicable to various devices, either with or without an integrated display element. Accordingly, the phrase “consumer electronics device” as used herein may refer to systems or devices including, but not limited to, television sets, computers or monitors that include an integrated display element, and systems or devices such as set-top boxes, video cassette recorders (VCRs), digital versatile disk (DVD) players, video game boxes, personal video recorders (PVRs), computers or other devices that may not include an integrated display element.