Abstract:
Described herein are embodiments of an electronic device including a conductive noise shielding element. The noise shielding element may be connected to an electronic noise-generating element provided within a housing of the electronic device and may by connected to a source of direct current. The noise shielding element may be provided within the housing of the electronic device and may further be thermally connected to the housing.

Description:
RELATED APPLICATION 
       [0001]    This application is based on and claims benefit of U.S. Provisional Application No. 61/537,303, filed Sep. 21, 2011, entitled “Multi-Function Heat Sink Assembly.” A claim of priority to this prior application is hereby made, and the disclosure of this prior application is hereby incorporated by reference. 
     
    
     FIELD OF THE APPLICATION 
       [0002]    The present application relates generally to electronic devices. More specifically, the present application relates to electronic devices with high-power, high-frequency switching components capable of injecting electronic noise into input power lines. In particular, the present application relates to an electronic arc lamp ballast for a High Intensity Discharge (“HID”) lamp incorporating an internal noise shield configured to attenuate such noise. 
       BACKGROUND 
       [0003]    Electronic devices frequently produce electronic or electromagnetic interference (“EMI”), or noise, which can interrupt, obstruct, or otherwise degrade or limit the performance of other electronic devices. To control the propagation of this noise, the Federal Communications Commission (“FCC”) has placed strict limits on the amount of such noise that may be radiated by electronic devices. For example, with respect to arc lamp ballasts, the limits imposed by the FCC are particularly stringent for noise emitted in the AM and SW radio bands, which span from 450 KHz to 30 MHz. More specifically, the AM radio band spans from 450-1600 KHz. 
         [0004]    Continuing to use arc lamp ballasts as a representative example, the noise generated by an electronic arc lamp ballast and thereafter injected into the input power lines emerges primarily as the result of high-speed switching components within two circuits composing the ballast: (1) the power factor correction (“PFC”) circuit and (2) the lamp driver circuit. Transistors from these two circuits are frequently connected to an interior surface of the outer housing of the electronic arc lamp ballast so as to provide for the dissipation of heat. Unfortunately, because the outer housing of the modern electronic arc lamp ballast is typically grounded, an avenue thereby exists for noise generated by the aforementioned PFC and lamp driver circuits to propagate into the input power lines. 
         [0005]    To address this difficulty, numerous solutions have previously been proposed. Of most notoriety is the placement of large filter capacitors between the two input power lines and the ground line connected to the outer ballast housing. Such an arrangement allows the capacitors to collectively function as a low-pass filter for the input power lines, thereby shorting high-frequency noise to ground. However, this arrangement also creates a substantial risk of electric shock. Therefore, safety organizations such as Underwriters Laboratories (“UL”) place severe limits on the use of such capacitors, thus limiting their practical utility. In some applications, particularly with respect to medical equipment, these large filter capacitors may be entirely forbidden. As a second option, an in-line, common-mode filter, utilized to suppress differences between the currents carried by the two input power lines, may be utilized to block a portion of the noise transmitted via the two input power lines. However, even while using an in-line, common-mode filter, FCC guidelines remain difficult to satisfy. Thus, the ultimate solution is to block noise at its source, within the electronic device itself. 
       SUMMARY 
       [0006]    Therefore, described herein are electronic devices aimed at fulfilling the above criteria. In certain aspects, the electronic devices can include an electronic noise-generating element within a housing and a direct current source. The electronic noise-generating element and direct current course can be connected to a conductive shielding element. In certain aspects, the shielding element may be thermally connected to the housing and first and second electrical insulators may be provided. The first insulator may be fixed in the connection between the electronic noise-generating element and the shielding element, and the second insulator may be fixed in the connection between the housing and the shielding element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a perspective view of an exemplary electronic arc lamp ballast  1 . 
           [0008]      FIG. 2  shows a block circuit diagram of the exemplary electronic arc lamp ballast  1 . 
           [0009]      FIG. 3A  shows a circuit diagram of an exemplary noise filter circuit  20 . 
           [0010]      FIG. 3B  shows a circuit diagram of an exemplary power supply circuit  30 . 
           [0011]      FIG. 3C  shows a circuit diagram of an exemplary lamp driver circuit  40 . 
           [0012]      FIG. 3D  shows a circuit diagram of an exemplary current control circuit  50 , an exemplary ignition circuit  60 , and an exemplary lamp  70 . 
           [0013]      FIG. 4  shows a portion of the interior of a typical embodiment of the exemplary electronic arc lamp ballast  1  that lacks noise shield  100 . 
           [0014]      FIG. 5A  shows a portion of the interior of an embodiment of the exemplary electronic arc lamp ballast  1  with noise shield  100 . 
           [0015]      FIG. 5B  shows a portion of the interior of another embodiment of the exemplary electronic arc lamp ballast  1  with noise shield  100 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0016]    Hereinafter, embodiments of an exemplary electronic arc lamp ballast  1  will be explained in more detail with reference to the provided drawings. It is to be understood that, in the description that follows, like elements are marked throughout the specification with like reference numerals. It is to be further understood that the electronic arc lamp ballast  1  described hereinafter is merely exemplary of the electronic devices covered by the instant application and that the scope of the instant application is thus not limited by the disclosed embodiments. 
         [0017]      FIG. 1  provides a perspective view of an exemplary embodiment of the electronic arc lamp ballast  1  for a high power arc lamp such as a High Intensity Discharge (“HID”) lamp. As can be seen, the electronic arc lamp ballast  1  can include a housing  2  configured to house and protect various electrical circuits within. As can further be seen from  FIG. 1 , two input power lines can protrude from the housing  2  toward a source of electrical power, and a ground line, connected to the housing  2 , can similarly protrude. Additionally, two output lines can protrude so as to connect the electronic arc lamp ballast  1  to the arc lamp. 
         [0018]      FIG. 2  provides an exemplary block circuit diagram of the electronic arc lamp ballast  1 . As can be seen in  FIG. 2 , the electronic arc lamp ballast  1  can include a noise filter circuit  20 , a power supply circuit  30 , a lamp driver circuit  40 , a current control circuit  50 , and an ignition circuit  60 . An AC power source  10  can be electrically connected to the noise filter circuit  20 , and a lamp  70  can be electrically connected to the ignition circuit  60 . In certain aspects, the noise filter circuit  20  is omitted from the electronic arc lamp ballast  1 . In certain aspects, the power supply circuit  30  is supplemented with a power factor correction (“PFC”) circuit. 
         [0019]    The AC power source  10  is archetypal of that found in many developed countries. In certain aspects, the AC power source  10  operates between 100V and 300V and at frequencies ranging from 50 Hz-60 Hz. More specifically, regions transmitting at 60 Hz, such as the Americas, typically utilize voltages of 120V, 20$V, 240V, or 278V in the non-residential locations where HID lamps are most often employed, and regions transmitting at 50 Hz, such as most of Europe, typically utilize voltages ranging from 220V-240V. Certain locations may run higher wattage lamps at 440V. 
         [0020]    The noise filter circuit  20  helps ensure compliance with FCC requirements and, to some extent, maintains stable operation of the electronic arc lamp ballast  1  by separating the AC power source  10  from the latter circuits  30 ,  40 ,  50 ,  60  of the electronic arc lamp ballast  1 . To do so, the noise filter circuit  20  may perform two primary functions. First, the noise filter circuit  20  may have the primary function of preventing noise generated by the high-speed switching of inductive circuits internal to the electronic arc lamp ballast  1  from propagating to the two input power lines and thereafter to the AC power source  10 . Additionally, the noise filter circuit  20  may have the secondary function of preventing noise transmitted from the AC power source  10 , such as that accompanying a supplied over-voltage, from propagating into the electronic arc lamp ballast  1 . 
         [0021]      FIG. 3A  provides a circuit diagram of an exemplary noise filter circuit  20 . As can be seen, the exemplary noise filter circuit  20  includes one or two common-mode inductors L 22  and capacitors C 21 , C 23 , C 24 , and C 25 . In certain aspects, capacitors C 21  or C 23  may, be omitted from the noise filter circuit  20 . In certain aspects, other elements such as a thermistor may be employed. In certain aspects, capacitors C 24  and C 25  may have very small values or may be omitted entirely. 
         [0022]    The power supply circuit  30  outputs a regulated DC voltage to the lamp driver circuit  40 . To do so, the power supply circuit  30  may have the primary function of converting the filtered AC power transmitted by the AC power source  10  through the noise filter circuit  20  into DC power via full-wave rectification. However, although the process of full-wave rectification can deliver unidirectional current, this uni-directional current is not produced at a constant voltage. Therefore, in certain aspects, an output filter capacitor is provided so as to function as a smoothing element and thereby produce a largely-steady DC voltage. In certain aspects, a regulator circuit is provided so as to control the voltage. In certain aspects, the power supply circuit  30  also includes a power factor correction circuit. The power factor of a circuit is defined as the ratio of active, real power P transmitted to the load of a circuit to the apparent power S (P/S) in the circuit. In purely resistive circuits, voltage and current waveforms are in phase; however, when reactive loads are present, such as with capacitors and inductors, energy stored in the loads creates a time difference between the current and voltage waveforms, thus rendering the waveforms out of phase and resulting in a lower power factor. A load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. Thus, it is often desirable to increase the power factor of an electrical system. In certain aspects, the addition of a power factor correction circuit to the power supply circuit  30  can increase the power factor of the electronic arc lamp ballast  1  from approximately 80% to approximately 99%. 
         [0023]      FIG. 3B  provides a circuit diagram of an exemplary power supply circuit  30  incorporating the above-described circuits. Integrated circuit controller U 34  performs all the logic functions required to keep the output voltage stable and to maintain the power factor near unity. Diode bridge B 31  rectifies the AC input and outputs a raw DC voltage to the capacitor C 32 . Transistor Q 36 , inductor L 33 , and diode D 35  together form the power factor correction circuit. Resistors R 37  and R 38  detect the output voltage and send a sample to the controller U 34 , thereby allowing the controller U 34  to exert control over the output voltage. Finally, capacitor C 39  functions as the aforementioned smoothing capacitor, producing a largely-steady DC voltage from the ripple voltage output by the diode bridge B 31 . 
         [0024]    The lamp driver circuit  40  outputs a lamp driving signal to the current control circuit  50 . To do so, the lamp driver circuit  40  may have the primary function of generating a high-frequency square wave oscillating at a frequency of from 50 KHz-200 KHz. The frequency output from the lamp driver circuit  40  can vary depending on the running state of the lamp  70 . For example, during the ignition operation of the lamp  70 , the lamp driver circuit  40  outputs a very high-frequency drive signal, which it then lowers during the running operation of the lamp  70  after ignition. In certain aspects, the lamp driver circuit  40  is configured to raise the output drive frequency so as to dim the lamp  70 . 
         [0025]      FIG. 3C  provides a circuit diagram of an exemplary lamp driver circuit  40  performing the above-described functions. Integrated circuit controller U 41  generates the aforementioned drive frequency. In certain aspects, the controller U 41  is combined with the controller U 34  of the power supply circuit  30 , leaving the electronic arc lamp ballast  1  with but one controller, thereby gaining somewhat-improved functionality and decreased size. Power transistors Q 44  and Q 45 , shown to be oriented in a half-bridge configuration, provide the high-frequency driving signal. Assembly A 43  contains those circuits necessary to convert the controller outputs to proper gate driving signals. Resistor R 47  functions so as to monitor the current in power transistors Q 44  and Q 45  and to discontinue operation of the controller U 41  if the detected current exceeds a predetermined threshold. Capacitor C 46  removes the DC part of the output from the lamp driver circuit  40 . Such an operation is necessary because, in certain aspects, the lamp  70  requires a pure AC drive signal to operate. Finally, dimmer circuit  48  detects inputs from a dimmer switch and relays such information to the assembly A 42 . 
         [0026]    The current control circuit  50  may have the primary function of limiting the current transmitted to the lamp  70 . Moreover, the current control circuit  50  may have the secondary function of resonating with the ignition circuit  60  at the ignition frequency, thereby generating a very high voltage adequate to ignite the lamp  70 . In certain aspects, such as that presented in  FIG. 31 ), the current control circuit  50  is a discrete inductor with a non variable inductance value that is selected for use in a particular lighting application. In certain aspects, the current control circuit  50  is a programmable inductor including a plurality of selectable inductance values. In certain aspects, the current control circuit  50  is a plurality of inductors, each having a different inductance value to be paired with a corresponding lamp  70 . In certain aspects, the ignition circuit  60  is simply a capacitor. With reference to  FIG. 3D , inductor L 51  serves as the current control circuit  50  and capacitor C 61  serves as the ignition circuit  60 . 
         [0027]    The lamp  70  may be a high power arc lamp in which light is produced by means of an electrical arc between electrodes housed within an arc tube. The tube of the arc lamp may be filled with both a gas that facilitates the arcs initial strike as well as metal salts which, once the arc is ignited, evaporate and thereby form a plasma. The lamp  70  can be rated for a certain wattage in the range of SOW to 2000 W, the certain wattage of the lamp  70  matching that provided by the current control circuit  50 . In certain aspects, the lamp  70  possesses a rating in the most common range of 250 W-400 W. In certain aspects, the lamp  70  possesses a less common rating of 150 W, 175 W or 320 W. In certain aspects, the electrodes of the lamp  70  are formed of tungsten. In certain aspects, the tube of the lamp  70  is formed of fused quartz. In certain aspects, the tube of the lamp  70  is formed of fused alumina. In certain aspects, the lamp  70  is a High Intensity Discharge (“HID”) lamp. In certain aspects, the HID lamp  70  is a mercury vapor lamp. In certain aspects, the HID lamp  70  is a metal halide lamp. In certain aspects, the HID lamp  70  is a low-pressure sodium vapor lamp. In certain aspects, the HID lamp  70  is a high-pressure sodium vapor lamp. 
         [0028]      FIG. 4  provides a typical embodiment of a portion of the interior of the electronic arc lamp ballast  1 . As with  FIGS. 5A and 5B  discussed below, elements of the electronic arc lamp ballast  1  not necessary to understand the disclosed embodiment are not illustrated in  FIG. 4 . As can be seen from  FIG. 4 , a circuit card assembly  130  can be provided within the interior space formed by the housing  2 . The circuit card assembly  130  may include any combination of the following: the noise filter circuit  20 , the power supply circuit  30 , the lamp driver circuit  40 , the current control circuit  50 , and the ignition control circuit  60 . In the embodiment illustrated in  FIG. 4 , the circuit card assembly  130  includes at least the power supply circuit  30  and the lamp driver circuit  40 . From the circuit card assembly  130 , the second lamp driver transistor Q 45 , the power supply transistor Q 36 , and the first lamp driver transistor Q 44  can each be connected to the housing  2  via a metallic backing connected to an electrode of each transistor. Finally, with further reference to  FIG. 4 , transistor insulators  180 , composed of a polyimide plastic such as Kapton® in certain aspects, can be positioned between each of the transistors Q 45 , Q 36 , and Q 44  and the housing  2 , thereby electrically isolating the transistors from the housing  2  as well as from each other. 
         [0029]    Such connections are necessary to shunt heat generated by the transistors Q 45 , Q 36 , and Q 44  toward the metallic housing  2  and thereafter into the surrounding environment. However, such connections also ensure that any signal generated by the transistors Q 45 , Q 36 , and Q 44  on the aforementioned electrode of each transistor connected to the metallic backing is capacitively coupled directly to the housing  2 . Moreover, as previously explained, since the housing  2  of the modern electronic arc lamp ballast  1  is connected to the ground line, the signals generated by the transistors Q 45 , Q 36 , and Q 44  become noise on the ground line, bypassing any common-mode filter fixed between the two input power lines. 
         [0030]    Thus,  FIG. 5A  provides an exemplary embodiment of a portion of the interior of the electronic arc lamp ballast  1  directed at solving such noise transmission problems. As can be seen, in this embodiment, a noise shield  100  can be provided within the interior space formed by the housing  2 . The structure and composition of the noise shield  100  is not particularly limited. In certain aspects, the noise shield  100  may be formed out of aluminum, which is a desirable material because it is a quality conductor of both heat and electricity and is easily machined. 
         [0031]    With further reference to  FIG. 5A , the circuit card assembly  130  can once again be provided within the interior space aimed by the housing  2 . However, in this embodiment, the second lamp driver transistor Q 45 , being a problematic noise-generating element primarily due to its drain being connected to the driver assembly A 43 , and the power supply transistor Q 36 , also being a problematic noise-generating element, can each be connected to the noise shield  100 . In certain aspects, the leads  150  and  160 , respectively connecting the circuit card assembly  130  to the transistors Q 45  and Q 36 , are sufficiently substantial so as to support the circuit card assembly  130 . Thus, in certain aspects, the circuit card assembly  130  may be supported solely by the noise shield  100 . In certain other aspects, the circuit card  130  may be supported at other locations by various mechanical mounts. Furthermore, transistor insulators  140 , composed of a polyimide plastic such as Kapton® in certain aspects, can be positioned between the transistor Q 45  and the noise shield  100  as well as between the transistor Q 36  and the noise shield  100 , thereby electrically isolating the transistors Q 45  and Q 36  from the noise shield  100 . 
         [0032]    With yet further reference to  FIG. 5A , the first lamp driver transistor Q 44 , having its drain directly connected to the highly-filtered DC output of the power supply circuit  30  and thereby carrying very little signal or noise, can be directly connected to the noise shield  100 . In certain aspects, the leads  170  of the transistor Q 44  are sufficiently substantial to aid in the support of the circuit card assembly  130 . Alternatively, in certain aspects, a conductive wire  190  (illustrated in  FIG. 5B ) may connect the DC output node of the lamp driver circuit  40  to the noise shield  100 . In certain other aspects, the conductive wire  190  may connect the ground node of the lamp driver circuit  40  to the noise shield  100 . As one can surmise from the foregoing discussion, the origin of the DC signal input to the noise shield  100  is not particularly limited and may be obtained from locations other than the circuit card assembly  130 . Accordingly, it is to be understood that the above embodiments are merely exemplary and are not intended to limit the scope of this application. 
         [0033]    With final reference to  FIG. 5A , the noise shield  100  can be fixed to an interior surface of the housing  2  via lips  102 . Insulators  110 , composed of a polyimide plastic such as Kapton® in certain aspects, can be provided in the connection between the lips  102  and the housing  2  so as to electrically isolate the source of DC signal, the transistor Q 44  in  FIG. 5A , from the housing  2 . In certain aspects, a cut-out region  101  can be formed in the noise shield  100 , thus reducing the contact area between the noise shield  100  and the housing  2  and thereby preventing the introduction of other noise sources onto the ground line connected to the housing  2 . In certain aspects, non-conductive fasteners  120  such as nylon screws can be utilized to secure the noise shield  100  to the housing  2 , thereby further electrically isolating the noise shield  100  and the elements connected thereto from the housing  2 . Thus, by connecting the noise shield  100  to the housing  2 , the noise shield  100  is able to effectively serve as part of the heat sinking mechanism for the transistors Q 36 , Q 44  and Q 45  by siphoning heat generated by these elements toward the metallic housing  2  so as to thereafter be radiated into the surrounding environment. Furthermore, because of the incorporation of the DC signal from the transistor Q 44 , very little noise from the transistors Q 36  and Q 45  is coupled to the housing  2 , thereby solving the noise problem of the typical embodiment illustrated in  FIG. 4 . 
         [0034]      FIG. 5B  provides another exemplary embodiment of a portion of the interior of the electronic arc lamp ballast  1 . The noise shield  100 , formed as a thin metal plate in this embodiment, can once again be provided within the interior space formed by the housing  2 . Furthermore, the second lamp driver transistor Q 45  and the power supply transistor Q 36  can once again each be connected to the noise shield  100 , and insulators  140  can once again be positioned between the transistor Q 45  and the noise shield  100  and between the transistor Q 36  and the noise shield  100 , thereby electrically isolating the transistors Q 45  and Q 36  from the noise shield  100 . 
         [0035]    However, in this embodiment, the conductive wire  190  can be employed so as to provide a DC signal to the noise shield  100 , thereby allowing the area of the surface of the noise shield  100  facing the reader to be substantially reduced. In certain aspects, the surface of the noise shield  100  facing the reader possesses an area substantially equivalent to the combined areas of the insulators  140 . Additionally, as may also be seen in  FIG. 5B , the insulator  110 , once again composed of a polyimide plastic such as Kapton® in certain aspects, can be provided between the noise shield  100  and the housing  2 , thereby electrically isolating the source of DC signal, the wire  190  in  FIG. 5B , from the housing  2 . Furthermore, the first lamp driver transistor Q 44  can be fixed to the housing  2 , thereby allowing heat to be shunted away from the transistor Q 44  and toward the housing  2 . Finally, insulator  180  can be provided between the transistor Q 44  and the housing  2 , thereby electrically isolating the transistor Q 44  from the housing  2 . 
         [0036]    By placing the noise shield  100  in close contact with the housing  2 , the noise shield  100  is able to effectively conduct heat generated by the transistors Q 45  and Q 36  to the housing  2 , thus allowing the housing  2  to serve effectively as a heat sink. Furthermore, because of the incorporation of the DC signal from the wire  190 , very little noise from the transistors Q 36  and Q 45  is coupled to the housing  2 , thereby once again solving the noise problem of the typical embodiment illustrated in  FIG. 4 . In summation, by arranging the described elements in a manner such as that of the previously-discussed embodiments illustrated in  FIGS. 5A and 5B , heat generated by the transistors Q 36 , Q 44  and Q 45  may be effectively disposed of while simultaneously preventing the propagation of noise generated by the transistors Q 36  and Q 45  to the ground line connected to the housing  2 . 
         [0000]    
       
         
               
               
             
               
               
             
           
               
                   
               
               
                 Numeral 
                 Element 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Electronic Arc Lamp Ballast 
               
               
                 2 
                 Ballast Housing 
               
               
                 10 
                 AC Power Source 
               
               
                 20 
                 Noise Filter Circuit 
               
               
                 21 
                 1 st  Noise Filter Capacitor 
               
               
                 22 
                 Noise Filter Inductor 
               
               
                 23 
                 2 nd  Noise Filter Capacitor 
               
               
                 24 
                 3 rd  Noise Filter Capacitor 
               
               
                 25 
                 4 th  Noise Filter Capacitor 
               
               
                 30 
                 Power Supply Circuit 
               
               
                 31 
                 Power Supply Diode Bridge 
               
               
                 32 
                 1 st  Power Supply Capacitor 
               
               
                 33 
                 Power Supply Inductor 
               
               
                 34 
                 Power Supply Circuit Controller 
               
               
                 35 
                 Power Supply Diode 
               
               
                 36 
                 Power Supply Transistor 
               
               
                 37 
                 1 st  Power Supply Resister 
               
               
                 38 
                 2 nd  Power Supply Resister 
               
               
                 39 
                 2 nd  Power Supply Capacitor 
               
               
                 40 
                 Lamp Driver Circuit 
               
               
                 41 
                 Lamp Driver Circuit Controller 
               
               
                 42 
                 1 st  Lamp Driver Assembly 
               
               
                 43 
                 2 nd  Lamp Driver Assembly 
               
               
                 44 
                 1 st  Lamp Driver Transistor 
               
               
                 45 
                 2 nd  Lamp Driver Transistor 
               
               
                 46 
                 Lamp Driver Capacitor 
               
               
                 47 
                 Lamp Driver Resister 
               
               
                 48 
                 Dimmer Circuit 
               
               
                 50 
                 Current Control Circuit 
               
               
                 51 
                 Current Control Inductor 
               
               
                 60 
                 Ignition Circuit 
               
               
                 61 
                 Ignition Capacitor 
               
               
                 70 
                 Lamp 
               
               
                 100 
                 Noise Shield 
               
               
                 101 
                 Noise Shield Cut-Out 
               
               
                 102 
                 Noise Shield Lip 
               
               
                 110 
                 Shield-Housing Insulator 
               
               
                 120 
                 Non-Conductive Fastener 
               
               
                 130 
                 Circuit Card Assembly 
               
               
                 140 
                 Transistor-Shield Insulator 
               
               
                 150 
                 Q45 Leads 
               
               
                 160 
                 Q36 Leads 
               
               
                 170 
                 Q44 Leads 
               
               
                 180 
                 Transistor-Housing Insulator 
               
               
                 190 
                 Conductive Wire