Abstract:
A switching power supply includes: a coil; and a pedestal fixed to the coil, the pedestal includes a supporting member configured to support the coil in such a manner as to form a space through which air flows on a surface of the coil attached to the pedestal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from Japanese Patent Application No. 2008-202188 filed on Aug. 5, 2008, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a technology of cooling a coil. 
         [0004]    2. Related Art 
         [0005]    A switching power supply such as DC-converter uses a choke coil for smoothing current and boosting voltage. This choke coil is generally constituted by a toroidal coil which has windings wound around a doughnut-shaped toroidal core. The windings of the toroidal coil are exposed on the outer periphery of the coil. Therefore, when the toroidal coil is directly attached to a substrate, wiring pattern cannot be provided on a surface where the toroidal coil is mounted in the vicinity of the toroidal coil for securing sufficient insulation. For increasing the degree of freedom of the wiring pattern, the toroidal coil is attached to an insulating plate member (pedestal), and the coil attached to the pedestal (coil assembly) is mounted on the substrate (for example, see JP-A-6-44123, JP-A-2007-235054, JP-A-2007-234752, JP-A-2005-286066, JP-A-2001-326126, and JP-A-2000-228320). 
         [0006]    Since the choke coil included in the switching power supply is disposed on the source current path, a relatively high current flows in the choke coil. Thus, Joule heat is generated on the windings of the choke coil due to winding resistance, and the temperature of the choke coil rises. According to the known coil assembly which has the coil attached to the plate-like pedestal, however, efficiency of cooling the coil is not sufficiently high. This problem arises not only from the coil assembly containing the toroidal coil but also from various types of coil assembly included in the switching power supply and the like. 
       SUMMARY 
       [0007]    It is an advantage of some aspects of the invention to provide a technology of increasing efficiency of cooling a coil. 
         [0008]    A coil assembly according to an aspect of the invention includes a coil, and a pedestal fixed to the coil. The pedestal includes a supporting member configured to support the coil in such a manner as to form a space through which air flows on a surface of the coil attached to the pedestal. 
         [0009]    According to this structure, a space through which air can flow on the surface of the coil attached to the pedestal is produced by the supporting member provided on the pedestal. Thus, the surface of the coil attached to the pedestal is cooled as well, and efficiency of cooling the coil improves. 
         [0010]    It is preferable that the coil is a toroidal coil, and that the pedestal configured to support the coil such that the toroidal direction of the coil being substantially parallel with a substrate on which the coil assembly is provided. 
         [0011]    In this structure, the area of the coil surface facing the space increases by disposing the toroidal surface of the toroidal coil substantially parallel with the substrate. Thus, cooling of the coil can be further promoted by air passing through the space. 
         [0012]    It is preferable that the pedestal includes a plate-like portion contacting the substrate, and that the supporting member extends in the direction opposite to the substrate from the plate-like portion. 
         [0013]    According to this structure, the coil assembly can be more easily attached to the substrate by providing the plate-like portion on the pedestal. 
         [0014]    It is preferable that a through hole penetrated through the coil side and the substrate side is provided on each of the plate-like portion and the substrate in an area containing a position corresponding to a hole of the coil. 
         [0015]    According to this structure, a through hole penetrated through the coil side and the substrate side is provided on each of the plate-like portion and the substrate in an area containing a position corresponding to a hole of the coil Thus, air flowing through the through hole of the plate-like portion and the hole of the toroidal coil can be easily generated. Accordingly, efficiency of cooling the coil can increase. 
         [0016]    In this case, it is more preferable that a through hole is similarly formed on the substrate as well as on the plate-like portion. By providing the through hole on the substrate, air passing through the through hole of the substrate and the hole of the toroidal coil can be generated. Thus, efficiency of cooling the coil can further improves. 
         [0017]    It is preferable that the supporting member is made of heat conductive resin. 
         [0018]    According to this structure, the supporting member is formed by resin having high heat conductivity. Thus, heat generated by the coil can be released from the supporting member. Accordingly, efficiency of cooling the coil can further increases. 
         [0019]    The invention can be practiced in various forms such as a coil assembly and a method of mounting a coil, a power supply using the coil assembly and the method of mounting the coil, a discharge lamp driving device and a light source device including the power supply, and an image display apparatus including the light source device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0021]      FIG. 1  shows a general structure of a projector including a ballast unit according to a first embodiment of the invention. 
           [0022]      FIG. 2  is a circuit diagram showing an example of the ballast unit. 
           [0023]      FIGS. 3A through 3D  show a condition of a mounted choke coil according to the first embodiment. 
           [0024]      FIGS. 4A through 4D  show a pedestal in related art and a pedestal according to the first embodiment disposed between the choke coil and a substrate. 
           [0025]      FIGS. 5A through 5D  show a condition of a mounted choke coil according to a second embodiment. 
           [0026]      FIGS. 6A through 6D  illustrate a pedestal according to a first modified example. 
           [0027]      FIGS. 7A and 7B  illustrate a pedestal according to a second modified example. 
           [0028]      FIGS. 8A through 8D  illustrate a pedestal according to a third modified example. 
           [0029]      FIGS. 9A and 9B  illustrate a pedestal according to a fourth modified example. 
           [0030]      FIG. 10  illustrates a choke coil mounted on a substrate according to a modified example. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A. First Embodiment 
     A1. Structure of Projector 
       [0031]      FIG. 1  illustrates a general structure of a projector  1000  including a ballast unit according to a first embodiment of the invention. The projector  1000  includes a power supply unit  100 , a ballast unit  200 , a control unit  300 , a light source lamp  400 , a liquid crystal panel  500 , and a projection lens  600 . 
         [0032]    The power supply unit  100  generates DC power to be supplied to the respective components of the projector  1000  from commercial power supply such as AC 100V. The power supply unit  100  has a not-shown boosting type converter (boost converter) to generate high tension DC power to be supplied to the ballast unit  200 . The boost converter has a not-shown power factor improvement circuit (PFC) so as not to send high-frequency noise generated by switching (chopper process) to the commercial power supply. However, the PFC circuit may be eliminated depending on the characteristics of noise filter or the like provided on the commercial power supply side of the power supply unit  100 . The boost converter which boosts voltage by chopper process is referred to as boost chopper as well. 
         [0033]    The ballast unit  200  generates light source driving power for driving the light source lamp  400  from the high tension DC power supplied from the power supply unit  100  in response to a switch control signal transmitted from the control unit  300 . The light source driving power thus generated is supplied to the light source lamp  400  from the ballast unit  200 . Generation of the light source driving power using the ballast unit  200  will be described later. 
         [0034]    The control unit  300  includes a CPU  310 , an image processing unit  320 , and a memory  330 . The CPU  310  performs various processes and controls under a computer program stored in the memory  330 . The image processing unit  320  applies image processing to image data received from an external device such as PC, DVD player, and external memory connected with an external connector (not shown), for example, and supplies the processed image data to the liquid crystal panel  500 . The control unit  300  operates by control unit driving power generated by the power supply unit  100 . 
         [0035]    The light source lamp  400  is a discharge lamp for supplying light to the liquid crystal panel  500 . The liquid crystal panel  500  is a transmission type liquid crystal panel which modulates light emitted from the light source lamp  400  according to image data given from the image processing unit  320 . The projection lens  600  projects the light modulated by the liquid crystal panel  500  onto a screen (not shown). By projecting the light modulated by the liquid crystal panel  500  to the screen, an image can be displayed on the screen. 
       A2. Structure of Ballast Unit 
       [0036]      FIG. 2  is a circuit diagram showing an example of the ballast unit  200  which supplies light source driving current to the light source lamp  400 . The ballast unit  200  in the first embodiment includes a down type converter (back converter)  210 , and an inverter  220 . 
         [0037]    The back converter  210  has a switching element Q 1 , a choke coil L 1 , a diode D 1 , and a capacitor C 1 . The switching element Q 1  switches between ON and OFF in response to a switch control signal transmitted from the control unit  300 . The high-tension DC power supplied from the power supply unit  100  ( FIG. 1 ) is decreased to voltage appropriate for the light source driving power according to chopper process by controlling the duty ratio of the ON condition of the switching element Q 1 . The power thus decreased is supplied to the inverter  220 . The back converter which decreases voltage by chopper process is referred to as back chopper as well. 
         [0038]    The inverter  220  is a full-bridge inverter having four full-bridge-connected switching elements Q 21  through Q 24 . The switching elements Q 21  through Q 24  also switch between ON and OFF in response to the switch control signal transmitted from the control unit  300 . The pair of the switching elements Q 21  and Q 24  and the pair of the switching elements Q 22  and Q 23  are alternately turned on to supply AC power having rectangular waves as the power supply driving power to the light source lamp  400  connected with two bridge intermediate points MP 1  and MP 2 . 
         [0039]    The light source lamp  400  is a reflection type light source lamp including a high-pressure discharge lamp such as high-pressure mercury lamp and metal halide lamp. The light source lamp  400  has an arc tube  410  fixed to the central portion of a reflection mirror  420  by heat resistance cement. As described above, electrodes  412  and  414  of the arc tube  410  are connected with the two bridge intermediate points MP 1  and MP 2  included in the inverter  220 . 
       A3. Mounting Choke Coil 
       [0040]      FIGS. 3A through 3D  illustrate mounting conditions of a choke coil L 1  included in the ballast unit  200  in the first embodiment.  FIGS. 3A and 3B  show a pedestal  700  on which the choke coil L 1  is mounted.  FIGS. 3C and 3D  illustrate the choke coil L 1  disposed on a substrate  900 . According to the first embodiment, the choke coil L 1  is constituted by a toroidal coil which has windings  820  around a doughnut-shaped toroidal core  810  as shown in  FIGS. 3C and 3D .  FIGS. 3A and 3C  illustrate the pedestal  700  and the choke coil L 1  as viewed from the surface (upper surface) on which the choke coil L 1  is mounted.  FIGS. 3B and 3D  illustrate the pedestal  700  and the choke coil L 1  as viewed from the side. 
         [0041]    As shown in  FIGS. 3A and 3B , the pedestal  700  has a disk  710  having approximately the same outside diameter as that of the toroidal core  810 , cylindrical pins  720  extended toward the upper surface from the disk  710 , and lead holding portions  730  extended in the direction of the outer circumference of the disk  710  from the disk  710 . Each of the lead holding portions  730  has a notch  732  extending from the outer circumference toward the center. The pedestal  700  can be integrally formed by injection molding using thermoplastic resin, for example. However, the pedestal  700  is not required to be integrally formed but may be produced by inserting the pins  720  formed separately from the disk  710  and the lead holding portions  730  into the disk  710 . Each diameter, length, shape, number, position, and the like of the pins  720  may be varied, and the shape of the plate-shaped disk  710  may be changed to an arbitrary shape such as rectangular shape. 
         [0042]    As illustrated in  FIGS. 3C and 3D , the choke coil L 1  is placed on the pedestal  700  such that the toroidal direction of the toroidal core (i.e., direction of magnetic flux) being parallel with the substrate  900  in the first embodiment. Leads  822  at both ends of the windings  820  are attached to the lead holding portions  730  under the condition of contact between the choke coil L 1  and the pins  720 . By this arrangement, the choke coil L 1  is fixed to the pedestal  700  such that position shift caused by vibration can be prevented. Moreover, the choke coil L 1  and the pedestal  700  (collectively referred to as “coil assembly” as well) can be handled more easily by fixing the choke coil L 1  to the pedestal  700 . 
         [0043]    The leads  822  extended from the lead holding portions  730  toward the lower surface project toward the lower surface of the substrate  900  via through holes (not shown) formed on the substrate  900 . The leads  822  projecting toward the lower surface are connected with a wiring pattern (not shown) provided on the substrate  900  by soldering or by other methods. According to the first embodiment, the distance between the choke coil L 1  and the substrate  900  can be increased by providing the pins  720  on the pedestal  700 . Thus, transmission of noise to the wiring pattern disposed close to the choke coil L 1  can be prevented. 
         [0044]      FIGS. 4A through 4D  illustrate a pedestal  700   x  in related art and the pedestal  700  in the first embodiment disposed between the choke coil L 1  and the substrate  900 .  FIGS. 4A and 4B  show the related-art pedestal  700   x  for insulating the choke coil L 1  from the wiring pattern on the upper surface of the substrate  900  as a comparison example.  FIGS. 4C and 4D  show the condition of the pedestal  700  in the first embodiment.  FIGS. 4A and 4C  show the pedestals  700   x  and  700  and the choke coil L 1  as viewed from the mounting surface (upper surface) of the choke coil L 1 .  FIGS. 4B and 4D  show the pedestals  700   x  and  700  and the choke coil L 1  as viewed from the side. 
         [0045]    As illustrated in  FIG. 4B , the choke coil L 1  contacts the flat upper surface of the pedestal  700   x  in the related art. Thus, air passing through the center of the choke coil L 1  is not generated, achieving substantially no cooling of the choke coil L 1  by natural convection. When airflow for cooling the choke coil L 1  is supplied from the side, only the upper surface of the choke coil L 1  is cooled. Thus, cooling efficiency cannot be easily raised. 
         [0046]    According to the first embodiment, however, a space is produced between the choke coil L 1  and the disk  710  by the presence of the pins  720  on the pedestal  700 . By providing this space, air flowing from the outer circumference toward the center on the lower surface side of the choke coil L 1  and flowing upward at the center is generated as indicated by arrows in  FIGS. 4C and 4D . Thus, the choke coil L 1  in the first embodiment can be sufficiently cooled by natural convection. When airflow for cooling the choke coil L 1  is supplied from the side, the air passes along both of the upper surface and the lower surface of the choke coil L 1 . Thus, both the upper surface and the lower surface of the choke coil L 1  are cooled, and cooling efficiency becomes higher than that in case of the comparison example. 
         [0047]    According to the first embodiment, therefore, the choke coil L 1  can be sufficiently cooled by natural convection. Thus, the degree of freedom for positioning the choke coil L 1  within the housing can be increased. Even in case of forced air cooling, efficiency of cooling the choke coil L 1  can be similarly raised. Thus, the degree of freedom for disposing the choke coil L 1  within the housing can be further improved, and the air flow amount from a cooling fan required for supplying airflow decreases. Accordingly, the entire size of the ballast unit  200  can be reduced by miniaturization of the cooling fan, and power consumption can be decreased by reduction of the power for driving the cooling fan. 
         [0048]    The heat generated from the choke coil L 1  provided with the toroidal core  810  is chiefly constituted by Joule heat from the windings  820 . Thus, rated current of the choke coil L 1  is determined by the diameter of the windings  820 . Since the cooling of the choke coil L 1  is promoted in the first embodiment, the diameter of the windings  820  of the choke coil L 1  for the same rated current can be reduced. By reducing the diameter of the windings  820 , inductance of the choke coil L 1  can be raised with an increased number of windings, and the size of the choke coil L 1  can be reduced with miniaturization of the toroidal core  810 . 
       B. Second Embodiment 
       [0049]      FIGS. 5A through 5D  illustrate conditions of the mounted choke coil L 1  according to a second embodiment.  FIGS. 5A and 5B  show a pedestal  700   a  on which the choke coil L 1  is placed in the second embodiment.  FIGS. 5C and 5D  show the condition of the choke coil L 1  disposed on a substrate  900   a.    
         [0050]    As shown in  FIGS. 5A and 5B , the pedestal  700   a  in the second embodiment is different from the pedestal  700  in the first embodiment shown in  FIGS. 3A and 3B  in that a through hole  740  is formed at the center of the pedestal  700   a  at a position corresponding to the hole of the choke coil L 1 . Moreover, as shown in  FIGS. 5C and 5D , a through hole  940  corresponding to the through hole  740  formed on the pedestal  700   a  is formed on the substrate  900   a . Other parts are similar to those in the first embodiment. 
         [0051]    According to the second embodiment, air flowing from the lower surface toward the upper surface of the substrate  900   a  is generated as indicated by arrows by providing the through holes  740  and  940  on the pedestal  700   a  and the substrate  900   a . Thus, efficiency of cooling the choke coil L 1  by natural convection further improves. Moreover, by providing projection or the like at a position corresponding to the through hole  940  on the lower part of the substrate  900   a , airflow for forced air cooling can be guided from the lower surface toward the upper surface of the substrate  900   a  through the through hole  940 . In this case, efficiency of cooling the choke coil L 1  by forced air cooling further improves. 
         [0052]    In the second embodiment, the through holes  740  and  940  having substantially the same diameters as that of the hole of the choke coil L 1  are formed. However, the diameters of the through holes  740  and  940  may be larger. Generally, each of the through holes  740  and  940  is only required to penetrate through the upper surface and the lower surface in an area containing the position corresponding to the hole of the choke coil L 1 . 
       C. Modified Example of Pedestal 
       [0053]    The pedestal on which the choke coil L 1  is mounted is not limited to those in the respective embodiments, but may be various types. For example, the supporting members for supporting the choke coil L 1  such as the pedestal  700  and the pins  720  may be made of heat conductive resin to conduct heat generated by the choke coil L 1  to the pedestal  700  or the pins  720  and thereby improve cooling efficiency. Moreover, the shape of the pedestal may be various shapes as long as a space through which air can pass toward the surface of the choke coil L 1  facing the substrates  900  and  900   a , that is, the surface on the pedestal side can be produced. The shapes of the pedestal are shown in  FIGS. 6A through 9B  as modified examples. 
       C1. Pedestal in First Modified Example 
       [0054]      FIGS. 6A through 6D  illustrate a pedestal according to a first modified example. A pedestal  700   b  shown in  FIGS. 6A and 6B  according to the first modified example is different from the pedestal  700  in the first embodiment in that plate-like fins  720   b  are provided on the disk  710  in place of the cylindrical pins  720 . Other parts are similar to those of the pedestal  700  in the first embodiment shown in  FIGS. 3A and 3B . Airflow in the direction along the fins  720   b  can be generated by using the plate-like fins  720   b  shown in  FIGS. 6A and 6B . In forced air cooling, airflow can be produced on the lower surface side of the choke coil L 1  by adjusting the direction of the fins  720   b  to the cooling airflow direction, and thus efficiency of cooling the choke coil L 1  can be sufficiently increased. While the pedestal  700   b  in the first modified example shown in  FIGS. 6A through 6D  does not have a through hole, a through hole may be formed at the center of the pedestal  700   b  similarly to the second embodiment. 
       C2. Pedestal in Second Modified Example 
       [0055]      FIGS. 7A and 7B  show a pedestal in a second modified example. According to this example shown in  FIGS. 7A and 7B , a choke coil L 1   c  having substantially circular cross section is used.  FIGS. 7A and 7B  do not show a toroidal core and windings of the choke coil L 1   c . As shown in  FIG. 7A , the shapes of pins  720   c  are varied according to the shape of the choke coil L 1   c  depending on the positions of the pins  720   c . By changing the shapes of the pins  720 C according to the shape of the choke coil L 1   c , the choke coil L 1   c  can be fixed to a more accurate position on a pedestal  700   c , and position shift of the choke coil L 1   c  can be more securely prevented. It is possible to form a through hole at the center of the pedestal  700   c  in the second modified example shown in  FIGS. 7A and 7B  similarly to the second embodiment. 
       C3. Pedestal in Third Modified Example 
       [0056]      FIGS. 8A through 8D  show a pedestal in a third modified example. A pedestal  700   d  in the third modified example shown in  FIGS. 8A and 8B  is different from the pedestal  700  in the first embodiment shown in  FIGS. 3A and 3B  in that lead holding portions  730   d  extend toward the upper surface and that pins  720  are removed. According to the third modified example, the choke coil L 1  is supported by the lead holding portions  730   d  extended toward the upper surface as shown in  FIGS. 8C and 8D . In the third modified example, a space through which air can pass is produced on the lower surface of the choke coil L 1  similarly to the first embodiment. Thus, cooling the choke coil L 1  can be promoted similarly to the first embodiment. It is possible to form a through hole at the center of the pedestal  700   d  in the third modified example shown in  FIGS. 8A through 8D  similarly to the second embodiment. 
         [0057]    According to the third modified example, the choke coil L 1  is supported by the lead holding portions  730   d  extended toward the upper surface. However, the choke coil L 1  may be supported by members similar to the lead holding portions  730  in the first embodiment and members similar to the lead holding members  730   d  in the third modified example. For example, the choke coil L 1  can be supported by supporting members  750  similar to the lead holding portions  730   d  indicated by alternate long and two short dashes lines in  FIG. 8A . It is preferable that the choke coil L 1  is supported in a direction different from the direction of extracting leads  822  as in this case in view of avoiding bending stress applied to the leads  822 . In this structure, the choke coil L 1  is fixed to the supporting members  750  by adhesive or the like. It is possible to use both the lead supporting portions  730   d  in the third modified example and the supporting members  750  at the same time. 
       C4. Pedestal in Fourth Modified Example 
       [0058]      FIGS. 9A and 9B  show a pedestal in a fourth modified example. As shown in  FIG. 9A , a pedestal  700   e  in the fourth modified example includes pins  722  and  724  having different heights at positions close to the two lead holding portions  730 . Thus, the choke coil L 1  attached to the upper side of the pedestal  700   e  is fixed with inclination to the disk  710  and the substrate  900  as shown in  FIG. 9B . The description “the toroidal direction of the choke coil L 1  is substantially parallel with the substrate” includes the condition in which the choke coil L 1  is obliquely attached as shown in  FIGS. 9A and 9B . 
         [0059]    According to the fourth modified example, the choke coil L 1  is fixed with inclination to the disk  710 . In this case, air from the right in the figure passes the center of the toroidal core  810  and flows from the lower surface toward the upper surface as indicated by an arrow in  FIG. 9B . Thus, cooling efficiency in forced air cooling can be sufficiently increased. 
         [0060]    In the example shown in  FIGS. 9A and 9B , the pins  722  and  724  are provided at positions close to the lead holding portions  730 , and the leads  822  are extracted in the arrangement direction of the pins  722  and  724 . It is more preferable, however, that the extracting direction of the leads  822  is different from the arrangement direction of the pins  722  and  724  in view of prevention of bending stress applied to the leads  822 . 
       D. Mounting in Modified Example 
       [0061]      FIG. 10  shows a condition of the choke coil L 1  mounted on the substrate  900  according to a modified example. The choke coil L 1  and the pedestal  700  (coil assembly) according to the mounting in this modified example shown in  FIG. 10  are similar to those in the first embodiment. In the example shown in  FIG. 10 , however, a heat conductive sheet  980  and a heat sink  990  fixed to the substrate  900  are attached to the upper surface of the choke coil L 1 . The heat sink  990  is fixed to the substrate  900  by screw (not shown) or the like. 
         [0062]    In the example shown in  FIG. 10 , a space is similarly produced on the lower surface side of the choke coil L 1 . Thus, the choke coil L 1  is cooled by air flowing on the lower surface of the choke coil L 1  as well as heat conduction by the heat conductive sheet  980  and the heat sink  990 . Accordingly, cooling of the choke coil L 1  can be further promoted. In the example shown in  FIG. 10 , it is similarly preferable that the pedestal  700  and the pins  720  are formed by heat conductive resin in view of achieving higher cooling efficiency. 
         [0063]    Moreover, the distance between the choke coil L 1  and the substrate  900  (mounting height) can be more easily changed by adequately adjusting the length of the pins  720  on the pedestal  700 . For adjusting the mounting height, a spacer may be additionally provided between the pedestal  700  and the substrate  900 . According to the example shown in  FIG. 10 , the choke coil L 1  can be sufficiently cooled by the heat conduction from the heat conductive sheet  980  and the heat sink  990  and the air passing the lower surface of the choke coil L 1  even when the spacer is added between the pedestal  700  and the substrate  900 . 
       E. Other Modified Examples 
       [0064]    The invention is not limited to the embodiments and examples described herein, but may be practiced otherwise without departing from the scope and spirit of the invention. For example, the following modifications may be made. 
       E1. Modified Example 1 
       [0065]    While the invention has been applied to a toroidal coil in the embodiments, the invention is applicable to various types of coil other than the toroidal coil. For example, the invention can be applied to a coil having windings wound around a bar-shaped or E-shaped core. Generally, heat generated on the coil is chiefly constituted by Joule heat on the windings. Thus, by mounting the coil on the pedestal, the windings producing a large volume of heat can be efficiently cooled, and efficiency of cooling the coil can be further increased. 
       E2. Modified Example 2 
       [0066]    While the invention is applied to the choke coil L 1  of the back converter ( FIG. 2 ), the invention is applicable to coils included in various switching power supplies. More specifically, the invention is applicable to a choke coil included in a boost converter, a choke coil included in a back-boost converter, a flyback transformer included in a flyback type converter, an insulation transformer included in an insulation type converter, or other coils included in various switching power supplies. In these switching power supplies, the choke coil and transformer are disposed on the flow path of source current, and relatively high current flows in these transformer units. By disposing these coils on the pedestal to promote cooling of the coils, miniaturization of coils, increase in inductance, higher degree of freedom for disposition, and reduction of power for cooling can be achieved. Also, the invention is applicable to various types of coil generating a large volume of heat such as common mode transformer and choke coil included in noise filter or the like. 
       E3. Modified Example 3 
       [0067]    While the projector  1000  ( FIG. 1 ) includes the liquid crystal panel  500  as the light modulation unit in the respective embodiments, the light modulation unit may be other modulation units such as DMD (digital micromirror device: trademark of Texas Instruments Co.).