Abstract:
Embodiments of the present invention provide an apparatus that reduces an audible noise produced in a power supply. The apparatus includes: (1) a housing; (2) an inductor coil formed from a coil of wire enclosed in the housing; (3) a set of wires that are coupled from the inductor coil to the outside of the housing through corresponding apertures in the housing, comprising electrical leads for the inductor coil; and (4) a predetermined amount of adhesive in the apertures that bonds the wires to the housing to reduce an audible noise produced when the current through the inductor coil is cycled quickly.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate to electronic circuits and power supplies. More specifically, embodiments of the present invention relate to techniques for reducing acoustic noise from power supply inductors. 
         [0003]    2. Related Art 
         [0004]    Many modem computer systems operate under strict power consumption limitations. In order to meet these limitations, some computer systems support one or more low-power modes in which some of the computer&#39;s components operate using less power or are disabled. For example, during a low-power power mode, the computer system&#39;s hard drives can be stopped, the display can be deactivated, and/or the CPU clock can be slowed down. 
         [0005]    When operating in full-power mode, the computer system draws current from a power supply according to the load on the computer system. For example,  FIG. 1A  presents a graph illustrating a current-flow pattern during full-power mode. As can be seen from  FIG. 1A , the computer system draws different levels of power for different loads. For example, when a user loads a program from disk into memory, the disk, the memory, and the CPU are all activated. Hence, power usage increases, which increases the current drawn from the power supply. When the computer system subsequently finishes loading the program from disk, there is a corresponding decrease in the current drawn from the power supply. 
         [0006]    When operating in low-power mode, the computer system can disable all but a minimal subset of computer system components. For example, the low-power mode may be a “sleep mode,” wherein all components are deactivated except a hardware monitor that is designed to wake the computer system upon receiving a communication from a peripheral (e.g., a keystroke or mouse movement). During the low-power mode, the computer system draws a small fraction of the power drawn during full-power mode. For example,  FIG. 1B  presents a graph illustrating a current-flow pattern during a low-power mode. 
         [0007]    Some computer systems support a hybrid mode, which limits power consumption by dynamically disabling and re-enabling computer system components and features as they are used. Although the components and features are sometimes disabled in the hybrid mode, the computer system appears to be fully functional. For example, in some hybrid modes, the computer system may slow down the CPU clock when a user is not performing operations that require the full CPU power. In some systems, during the hybrid mode the computer system cycles between a specialized low-power mode and full-power mode at every opportunity (e.g., between keystrokes). For example,  FIG. 1C  presents a graph illustrating a current-flow pattern during a hybrid low-power/full-power mode. As shown in  FIG. 1C , the computer system is subject to significant current swings during the hybrid mode (i.e., high dildt). 
         [0008]    Unfortunately, some computer systems include parts in the power supply that perform inadequately during such hybrid modes. For example, in some power supplies, an inductor will produce a clearly audible whine caused by the high dildt when cycling back and forth between low-power mode and full-power mode. Because there are often limitations on the noise that computer systems (particularly laptops) may emit, an audible whine from the power supply may be unacceptable. 
         [0009]    Hence, what is needed is a power supply for a computer system without the above-described problem. 
       SUMMARY 
       [0010]    Embodiments of the present invention provide an apparatus that reduces an audible noise produced in a power supply. The apparatus includes: (1) a casing; (2) an inductor coil formed from a coil of wire enclosed in the casing; (3) a set of wires that are coupled from the inductor coil to the outside of the casing through corresponding apertures in the casing comprising electrical leads for the inductor coil; and (4) a predetermined amount of adhesive in the apertures that bonds the wires to the casing to reduce an audible noise produced when the current through the inductor coil is cycled quickly. 
         [0011]    In some embodiments, the set of wires extend along the casing from the corresponding set of apertures and under the casing alongside an outside surface of the casing forming “J” leads for coupling the inductor coil to an electrical circuit. 
         [0012]    In some embodiments, a mechanical mount is coupled to the outside of the casing on an opposite side of the casing from the set of apertures. 
         [0013]    In some embodiments, the casing is formed by press-fitting metal dust powder around the inductor coil. 
         [0014]    Embodiments of the present invention provide a method for manufacturing an inductor for reducing an audible noise in an electrical circuit. During the process, an inductor coil is first wound from a segment of wire. Next, the wound inductor coil is enclosed in metal dust powder. The metal dust powder is then press-fit into a casing for the inductor, wherein a set of wires are coupled from the inductor coil to the outside of the casing through a corresponding set of apertures in the casing (to serve as electrical leads for the inductor coil). Next, a predetermined amount of adhesive is placed in the apertures to bond the wires to the casing to reduce an audible noise produced when the current through the circuit element is cycled quickly. 
         [0015]    Embodiments of the present invention provide a computer system for reducing an audible noise produced in a power supply. The computer system includes a processor and a power supply that provides power to the processor. The power system includes: (1) a casing; (2) an inductor coil formed from a coil of wire enclosed in the casing; (3) a set of wires that are coupled from the inductor coil to the outside of the casing through corresponding apertures in the casing, wherein the wires form electrical leads for the inductor coil; and (4) a predetermined amount of adhesive in the apertures that bonds the wires to the casing to reduce an audible noise produced when the current through the inductor coil is cycled quickly. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0016]      FIG. 1A  presents a graph illustrating a current-flow pattern during a full-power mode in a computer system. 
           [0017]      FIG. 1B  presents a graph illustrating a current-flow pattern during a low-power mode in a computer system. 
           [0018]      FIG. 1C  presents a graph illustrating a current-flow pattern during a hybrid low-power/full-power mode. 
           [0019]      FIG. 2A  presents a block diagram of a computer system in accordance with embodiments of the present invention. 
           [0020]      FIG. 2B  presents a block diagram of a power supply in a computer system in accordance with embodiments of the present invention. 
           [0021]      FIG. 2C  presents a circuit diagram illustrating a buck converter circuit in accordance with embodiments of the present invention. 
           [0022]      FIG. 3A  presents a front view of an inductor in accordance with embodiments of the present invention. 
           [0023]      FIG. 3B  presents a side view of an inductor in accordance with embodiments of the present invention. 
           [0024]      FIG. 3C  presents an isometric view of an inductor in accordance with embodiments of the present invention. 
           [0025]      FIG. 4A  presents a front view of an inductor with a casing partially cut-away to reveal the inductor coil in accordance with embodiments of the present invention. 
           [0026]      FIG. 4B  presents a side view of an inductor with a casing partially cut-away to reveal the inductor coil in accordance with embodiments of the present invention. 
           [0027]      FIG. 4C  presents a top view of an inductor with a casing partially cut-away to reveal the inductor coil in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the claims. 
       Computer System 
       [0029]      FIG. 2A  presents a block diagram of a computer system  200  in accordance with embodiments of the present invention. Computer system  200  includes processor  202 , memory  204 , and mass-storage device  206 . Computer system  200  also includes power supply  208 , which supplies electrical power to processor  202 , memory  204 , mass-storage device  206 , and other components in computer system  200  (not shown) 
         [0030]    In some embodiments of the present invention, computer system  200  is a general-purpose computer system that supports low-power modes, including sleep, idle, and/or standby modes. During these low-power modes, some or all of the functions and/or components of computer system  200  are slowed down or disabled to conserve power. For example, when operating in a low-power mode, computer system  200  may slow down or disable processor  202 , memory  204 , mass-storage device  206 , and/or other devices such as monitors and peripheral devices (not shown). 
         [0031]    In embodiments of the present invention, computer system  200  also supports one or more “hybrid” modes in which computer system  200  appears to be in full-power mode, but instead dynamically switches from a full-power mode to one or more special low-power modes as conditions permit. For example, computer system  200  may slow down the CPU clock and/or other system clocks whenever the load on the CPU and other components is low, but may restore the CPU clock and/or other system clocks when the load increases. In some embodiments, computer system  200  can enter and exit a special low-power mode very rapidly, facilitating a nearly continuous switch between the modes. For example, when a user is editing a document, computer system  200  may generally operate in full-power mode, but as often as between keystrokes computer system  200  may enter the specialized low-power mode. 
         [0032]    In  FIG. 2A , processor  202  is a central processing unit (CPU) that processes instructions for computer system  200 . For example, processor  202  can be a microprocessor, a device controller, or other type of computational engine. Memory  204  is volatile memory that stores instructions and data for processor  202  during operation of computer system  200 . For example, memory  204  can include DRAM, SDRAM, or another form of volatile memory. Mass-storage device  206  is a non-volatile storage device that stores instructions and data for processor  202 . For example, mass-storage device  206  can be a hard disk drive, a flash memory, an optical drive, or another non-volatile storage device. 
         [0033]    Note that although we describe embodiments of the present invention using computer system  200 , alternative embodiments can be used within other types of computing systems. Moreover, embodiments of the present invention are operable in any type of electronic device wherein a circuit element produces an audible noise caused by significant dildt. 
       Power Supply 
       [0034]      FIG. 2B  presents a block diagram of a power supply in computer system  200  in accordance with embodiments of the present invention. The power supply includes adaptor  210 , charger  212 , and a set of DC/DC converters  214  and  216  (i.e., voltage regulators). 
         [0035]    Adapter  210  converts an AC signal from a power source (e.g., a common 120 VAC electrical outlet) to a 16.5 VDC signal which is in turn converted by charger  212  into a 12.6 VDC signal. The 12.6 VDC signal is then used as an input for DC/DC converters  214 . The 12.6 VDC signal can also be used to charge a battery (not shown) if there is a battery present in the system. 
         [0036]      FIG. 2C  presents a circuit diagram illustrating a buck converter circuit  220  in accordance with embodiments of the present invention. Buck converter circuit  220  is a switched-mode step-down DC-to-DC converter. Note that charger  212  includes a buck converter circuit  220 . 
         [0037]    Buck converter circuit includes inductor  222 , capacitors  224  and  230 , and switching elements  226  and  228 . The operation of the circuit elements in the buck circuit is known in the art, hence a more detailed description is not provided. Note that in some embodiments of the present invention, both switching element  226  and  228  are transistors. However, in alternative embodiments, switching element  226  is a transistor while switching element  228  is a diode or another such circuit element. 
       Inductor 
       [0038]      FIG. 3A-3C  present front, side, and isometric external views of an inductor  222  in accordance with embodiments of the present invention. Inductor  222  includes casing  302 , electrical leads  306 , and mechanical mount  304 . 
         [0039]    In some embodiments of the present invention, casing  302  is formed from press-fit metal dust powder. In these embodiments, inductor coil  400  (see  FIG. 4 ) is formed from a segment of wire. Inductor coil  400  is then enclosed in metal dust powder, which is pressed into the final shape of casing  302 . When pressing the metal dust powder around inductor coil  400 , a pressure of several tons of force per square inch is used. Although there are multiple forms of metal dust powder that may be used to form casing  302 , forming an inductor casing from metal dust powder is known in the art and is therefore not described in more detail. Note that although we describe embodiments of the present invention that use press-fitting to form the casing, alternative embodiments use sintering or other techniques to form the casing from the metal dust powder. 
         [0040]    In some embodiments, casing  302  is a small-outline j-lead (SOJ) package for surface-mounting inductor  222 . Hence, as shown in  FIGS. 3A-3C , electrical leads  306  extend out of an aperture in the side of casing  302 , then run alongside casing  302 , and under casing  302  as shown in  FIG. 3B  (i.e., the leads appear as a “J”). In addition, mechanical mount  304  is bonded to the outside of casing  302  on the opposite side of casing  302  from electrical leads  306 . Mechanical mount  304  runs alongside casing  302 , and under casing  302  as shown in  FIG. 3B  (i.e., also appearing as a “J”). Note that although we describe embodiments of the present invention using the SOJ package, in alternative embodiments, casing  302  is in another packaging format. 
         [0041]    When placed in an electrical circuit, inductor  222  is mounted by bonding (e.g., soldering) electrical leads  306  and mechanical mount  304  to a mounting surface. In some embodiments of the present invention, mechanical mount  304  has no electrical function and serves only as a third mounting point for inductor  222  in order to provide mechanical stability. 
         [0042]    Inductor  222  also includes adhesive  308  on electrical leads  306 . During manufacture, adhesive  308 , initially liquid, is placed in aperture  402  (see  FIG. 4B ) from which electrical leads  306  extend out of casing  302 . Adhesive  308  then sets, bonding the electrical leads  306  to one or more walls of aperture  402 . By bonding electrical leads  306  to casing  302  in this way, a significant reduction in acoustic noise is achieved. 
         [0043]    Adhesive  308  can be any adhesive used to bond electrical parts to one another. Such adhesives are known in the art. In some embodiments of the present invention, the adhesive is Chemiseal E-1358B from the Chemitech Inc. of Tokyo, Japan. 
         [0044]      FIGS. 4A-4C  present front, side, and top partially cut-away views of inductor  222  in accordance with embodiments of the present invention. In the front view in  FIG. 4A , inductor coil  400  can be seen within casing  302  (although inductor coil  400  is partially obscured by electrical leads  306 ). 
         [0045]    In the side view in  FIG. 4B , an electrical lead  306  can be seen extending from inductor coil  400  out of aperture  402  in casing  302  and around casing  302  in the “J”-shape described above. Adhesive  308  bonds electrical lead  306  to one or more walls of aperture  402  in casing  302 . Bonding electrical leads  306  to the walls of aperture  402  stabilizes electrical leads  306 , which minimizes the movement of electrical leads  306  when inductor  222  experiences high dildt during the hybrid mode. Minimizing the movement of electrical leads  306  reduces the acoustic noise that might otherwise be produced by inductor  222 . 
         [0046]    In the top view in  FIG. 4C , inductor coil  400 &#39;s circular shape is visible with electrical leads extending from inductor coil out of aperture  402  in casing  302 . Also shown is adhesive  308 , which bonds electrical leads  306  within aperture  402 . 
         [0047]    Note that in some embodiments of the present invention, casing  302  may not include aperture  402 . In these embodiments, electrical leads  306  extend directly out of the side of casing  302  and adhesive  308  can be a drop on the surface of casing  302  that surrounds electrical lead  306  (and bonds electrical lead  306  to casing  302 ). 
       Manufacturing Process 
       [0048]      FIG. 5  presents a flowchart illustrating a method of manufacturing an inductor in accordance with embodiments of the present invention. The process starts when inductor coil  400  is wound from a segment of wire (step  500 ). Inductor coil  400  is then enclosed by metal dust powder, which is press-fit into the final shape of casing  302  (step  502 ). When step  502  is complete, electrical leads  306  extend from inductor coil  400  within casing  302  out of aperture  402  and around casing  302  in the “J”-shape described above. 
         [0049]    Next, adhesive  308  is placed in aperture  402  in order to bond electrical leads  306  to casing  302  (step  504 ). 
       Alternative Embodiments 
       [0050]    In some embodiments of the present invention, inductor  222  is entirely covered with adhesive  308 . In these embodiments, as with embodiments where the adhesive is only placed in aperture  402 , adhesive  308  bonds electrical leads  306  to casing  302  (as described above). These embodiments incur the cost of the additional adhesive to avoid the manufacturing step of precisely placing the correct amount of adhesive directly in apertures  402 . 
         [0051]    In some embodiments, inductor  222  is mounted by adhesively bonding the center of casing  302  to a mounting surface along with soldering or otherwise bonding electrical leads  306  and mechanical mount  304  to the mounting surface. By adhesively bonding the center of casing  302 , acoustic noise is further reduced. 
         [0052]    The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.