Patent Publication Number: US-9433043-B1

Title: Power supply for a plurality of light emitting diodes

Description:
FIELD OF THE INVENTION 
     This invention pertains to power supplies, in general, and to power supplies for providing current to a plurality of light emitting diodes, in particular. 
     BACKGROUND 
     It is highly desirable to provide a power supply for light emitting diode systems that can provide high power in a thin, compact package. 
     SUMMARY 
     An embodiment of a light emitting diode (LED) power supply for providing current to a plurality of LEDs is provided. The embodiment comprises a planar transformer. The planar transformer comprises a first multilayer printed circuit board comprising a first plurality of planar windings electrically connected in series to form a first primary portion. Each winding of the first plurality of planar windings is carried on a separate layer of the first multilayer printed circuit board. The transformer further comprises a second multilayer printed circuit board comprising a second plurality of planar windings electrically connected in series to form a second primary portion. Each winding of the second plurality of planar windings is carried on a separate layer of the second multilayer printed circuit board. The transformer additionally comprises a third multilayer printed circuit board comprising a third planar winding carried on one layer to provide a secondary. The third multilayer printed circuit board comprises a first aperture on one side of the third planar winding, a second aperture on an opposite side of the third planar winding, and a central aperture surrounded by the third planar winding. The third multilayer printed circuit board comprises a top surface carrying the first multilayer printed circuit board and a bottom surface carrying the second multilayer printed circuit board. The first and second multilayer printed circuit boards are disposed such that the first primary portion, the second primary portion and the secondary are in vertical alignment with each other to maximize electromagnetic coupling. 
     The transformer further comprises a first core consisting of a ferrite material and comprising first and second outer legs and a middle leg. The first core is carried on the first multilayer printed circuit board such that the middle leg extends therethrough in the middle of the first plurality of planar windings, and the first and second outer legs extend therethrough on opposite sides of the first plurality of planar windings. The transformer also comprises a second core consisting of the ferrite material and comprising first and second outer legs and a middle leg. The second core is carried on the second multilayer printed circuit board such that the middle leg extends therethrough in the middle of the second plurality of planar windings, and the first and second outer legs extend therethrough on opposite sides of the second plurality of planar windings. 
     The first and the second outer legs of the first core extend into the third multilayer printed circuit board. The first and the second outer legs of the second core extending into the third multilayer printed circuit board and in physical engagement with the first and the second outer legs of the first core, respectively. The middle leg of the first core and the middle leg of the second core are disposed proximate to each other in alignment with the central aperture such that a predetermined air gap is provided there between. 
     The embodiment further comprises a first rectifier circuit carried on the third multilayer printed circuit board for rectifying alternating current (ac) from a power source; a driver circuit carried on the third multilayer printed circuit board and disposed between the first rectifier circuit and the first and second primary portions; and a second rectifier circuit carried on the third multilayer printed circuit board and coupled to the secondary and coupled to output power terminals to provide direct current for powering the plurality of LEDs. 
     In accordance with one aspect of the embodiment, the third multilayer printed circuit board comprises a fourth planar winding carried on another layer to provide a bias winding, and the bias winding is coupled to the driver circuit. 
     In accordance with another aspect of the embodiment a plurality of terminals is carried by the third multilayer printed circuit board. The first primary portion is connected to first terminals of the plurality of terminals, the second primary portion is connected to second terminals of the plurality of terminals, and the first terminals and the second terminals are selectively connectable to connect the first primary portion in parallel with or in series with the second primary portion. 
     The embodiment may further comprise a first filter circuit disposed between the first rectifier circuit and the driver. 
     The embodiment may also further comprise a second filter circuit disposed between the second rectifier circuit and the output power terminals. 
     The embodiment may comprise a first insulating layer disposed between the first multilayer printed circuit board and the first core, a second insulating layer disposed between the first multilayer printed circuit board and the third multilayer printed circuit board, a third insulating layer disposed between the second multilayer printed circuit board and the second core, and a fourth insulating layer disposed between the second multilayer printed circuit board and the third multilayer printed circuit board. 
     Each of the first, second, third and fourth insulating layers may comprise polyimide. 
     A second embodiment of light emitting diode (LED) power supply for providing current to a plurality of LEDs comprises a transformer first primary portion comprising a plurality of serially connected planar first primary windings, a transformer second primary portion comprising a plurality of serially connected planar second primary windings, and a transformer secondary comprising a planar secondary winding. The second embodiment further comprises a multilayer printed circuit board comprising at least one layer having the planar secondary winding formed thereon. The second embodiment comprises a first multilayer printed circuit board carried on the multilayer printed circuit board. Each of the planar first primary windings is carried on a corresponding separate one layer of the first multilayer printed circuit boards. The second embodiment comprises a second multilayer printed circuit board carried on the multilayer printed circuit board. Each of the planar second primary windings is carried on a corresponding separate one layer of the second multilayer printed circuit board. The transformer first portion, the transformer second portion and the secondary are in axial alignment with each other to provide electromagnetic coupling there between. A transformer core is carried by the multilayer printed circuit board extending over the first primary portion and the second primary portion and extending through the multilayer printed circuit board. 
     The second embodiment comprises a first rectifier circuit carried on the multilayer printed circuit board for rectifying alternating current (ac) from a power source, a driver circuit carried on the multilayer printed circuit board and disposed between the first rectifier circuit and the first and second primary portions, and a second rectifier circuit carried on the multilayer printed circuit board and coupled to the secondary and coupled to output power terminals to provide direct current for powering the plurality of LEDs. 
     The multilayer printed circuit board comprises a fourth planar winding carried on another layer to provide a bias winding. The bias winding is coupled to the driver circuit. 
     The second embodiment may comprise a plurality of terminals carried by the multilayer printed circuit board. The first primary portion is connected to first terminals of the plurality of terminals. The second primary portion is connected to second terminals of the plurality of terminals. The first terminals and the second terminals are selectively connectable to connect the first primary portion in parallel with or in series with the second primary portion. 
     The second embodiment may comprise a first filter circuit disposed between the first rectifier circuit and the driver. 
     The second embodiment may further comprise a second filter circuit disposed between the second rectifier circuit and the output power terminals. 
     The second embodiment may comprise a first insulating layer disposed between the first multilayer printed circuit board and the first core, a second insulating layer disposed between the first multilayer printed circuit board and the multilayer printed circuit board, a third insulating layer disposed between the second multilayer printed circuit board and the second core, and a fourth insulating layer disposed between the second multilayer printed circuit board and the multilayer printed circuit board. 
     Each of the first, second, third and fourth insulating layers may comprise polyimide. 
     A third embodiment of a light emitting diode (LED) power supply for providing current to a plurality of LEDs, comprises a transformer first primary portion, a transformer second primary portion, a transformer secondary portion, and a multilayer printed circuit board. The multilayer printed circuit board comprises at least one layer having a planar secondary winding formed thereon, the transformer secondary portion comprising the planar secondary winding. The multilayer printed circuit board further comprises a plurality of first multilayer printed circuit boards carried on the multilayer printed circuit board. The transformer first primary portion comprises a plurality of serially connected planar first primary windings. Each of the planar first primary windings is carried on a corresponding separate one layer of the plurality of first multilayer printed circuit boards. The transformer second primary portion comprises a plurality of serially connected planar second primary windings. Each of the planar second primary windings is carried on a corresponding separate one layer of the plurality of second multilayer printed circuit boards. 
     The plurality of first multilayer printed circuit boards, the plurality of second multilayer printed circuit boards, and the planar secondary winding are in alignment with each other to provide electromagnetic coupling there between. 
     A transformer core is carried by the multilayer printed circuit board extends over the first primary portion and the second primary portion and extends through the multilayer printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be better understood from a reading of the following detailed description of preferred embodiments of the invention in which like reference designators identify like elements: 
         FIG. 1  is a block diagram of an embodiment of the invention; 
         FIG. 2  illustrates a top layer of a multilayer printed circuit board; 
         FIG. 3  illustrates a second layer of the multilayer printed circuit board of  FIG. 2 ; 
         FIG. 4  illustrates a third layer of the multilayer printed circuit board of  FIG. 2 ; 
         FIG. 5  illustrates a fourth layer of the multilayer printed circuit board of  FIG. 2 ; 
         FIGS. 6 through 9  illustrates layers of a second multilayer printed circuit; 
         FIG. 10  is a side view of a planar transformer portion of an assembled LED power supply; 
         FIG. 11  is a cross-section of the planar transformer portion of  FIG. 11 ; 
         FIG. 12  illustrates an insulating layer; and 
         FIG. 13  illustrates two ferromagnetic cores. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to  FIG. 1  a power supply  100  for powering a plurality of LEDs from an alternating current (ac) power source is shown. Power supply  100  comprises multilayer printed circuit board  101 . Contact pads  103  are carried on a top surface of multilayer printed circuit board  101 . Contact pads  103  are connectable to an ac power line. A rectifier circuit  105  is coupled to contact pads  103 . In the embodiment, rectifier circuit  105  is a commercially available bridge rectifier module. Direct current (dc) outputs from rectifier circuit  105  are filtered by filter circuit  107  to provide a filtered dc output. The filtered dc output from filter circuit  107  is provided to driver circuit  109 . Driver circuit  109  comprises a commercially available integrated circuit such as a “non-isolated, phase dimmable, buck power factor controller LED driver” TPS92075 available from Texas Instruments. Driver circuit  109  is connected to the primary of a planar transformer  111 . The primary of this embodiment comprises a first portion  117  and a second portion  119 . In the embodiment shown, primary first portion  117  is connected in series with primary second portion  119 . Transformer  111  further comprises a bias winding  123  connected to driver circuit  109 . Transformer  111  comprises a secondary winding  121  that is connected to a second rectifier circuit  113 . Second rectifier circuit  113  is a commercially available circuit and its dc output is connected to a second filter circuit  115  that provides filtered dc current for LEDs at terminals  105 . 
     Primary first portion  117  is connected to terminals  117   a ,  117   b . Primary second portion  119  is connected to terminals  119   a ,  119   b . In the embodiment shown in  FIGS. 1  terminals  117   b  and  119   a  are connected so that primary first portion  117  is connected in series with primary second portion  119 . This connection arrangement is utilized when the ac source to be connected to terminals  103  is 220-277 volts. Primary first portion  117  and primary second portion  119  are connected in parallel when the ac source at terminals  103  is 100-130 volts. 
     Advantageously, the entirety of power supply  100  is on a single multilayer circuit board  101 . Still further, power supply  100  carries transformer  111  with secondary winding  121  and bias winding  123  integrated into multilayer circuit board  101  and primary first portion  117  and primary second portion  119  formed as planar transformer windings on first and second multilayer printed circuit boards carried on multilayer printed circuit board  101 . 
     Turning now to  FIGS. 2 through 5 , several different layers  201 ,  301 ,  401 ,  501  of multilayer printed circuit board  101  are shown. It will be apparent to those skilled in the art that although four layers are shown in the drawing figures that there may be more or less than four layers in other embodiments.  FIG. 2  shows a top layer  201  of multilayer printed circuit board  101 . Top layer  201  carries printed conductive traces  203  only one of which is identified for clarity. Top layer  201  also carries ac input contacts  103  for connection to an ac line voltage source and dc output contacts  105  for connection to LEDs. Top layer  201  additionally carries a planar bias winding  205 . It should also be apparent to those skilled in the art that planar bias winding  205  may be carried on another layer rather than the top layer  201 . Planar bias winding  205  comprises a conductive trace formed onto layer  201 . 
     In each of the layers  201 ,  203 ,  204 ,  205  are three elongate apertures  207 ,  209 ,  211  that are disposed such that the two outer apertures  209 ,  211  are disposed on opposite sides of central aperture  207 . Central aperture  207  is positioned to be centered in one end portion of multilayer circuit board  101  such that bias winding  205  is centered around central aperture  207  and contained within outer apertures  209 ,  211 . 
     Layer  401  carries a planar secondary winding portion  405  that is also positioned to be centered around central aperture  207  and contained within outer apertures  209 ,  211 . Similarly layer  501  carries a planar secondary winding portion  505  that is positioned to be centered around central aperture  207 . Planar secondary winding portions  405 ,  505  each comprise conductive traces formed on the respective layers  401 ,  501 . It will be apparent to those skilled in the art that although two secondary winding portions  401 ,  501  are shown in the embodiment, other embodiments may comprise only one winding portion or more than two winding portions on different layers. The two secondary winding portions may be connected in series or in parallel utilizing through vias in multilayer printed circuit board  101 . 
     Two primary winding portions  117 ,  119  are carried on top and bottom surfaces  101   a ,  101   b  of multilayer printed circuit board  101  as shown in  FIG. 10 . 
     Primary winding portions  117 ,  119  are identical and comprise a plurality of layers of corresponding multilayer printed circuit boards  1001 ,  1003 , respectively. 
       FIGS. 6-9  show layers  601 ,  701 ,  801 ,  901  of multilayer printed circuit board  1001 . Layer  601  is a top layer and includes spiral conductive trace  603  forming one section of a planar primary winding. One end  607  of spiral conductive trace  603  is connected to through terminal via  601   a  and the other end  605  of spiral conductive trace  603  is connected to a through via  601   b . Layer  701  is an intermediate layer and includes spiral conductive trace  703  forming one section of a planar primary winding. One end  705  of spiral conductive trace  703  is connected with end  605  of spiral trace  603  through via  605 . The other end  707  of spiral conductive trace  703  is connected to a through via that is not shown. Layer  801  is an intermediate layer and includes spiral conductive trace  803  forming one section of a planar primary winding. One end  807  of spiral conductive trace  803  is connected with end  707  of spiral trace  703  by a through via that is not shown. Layer  901  is a bottom layer and includes spiral conductive trace  903  forming one section of a planar primary winding. One end  905  of spiral conductive trace  903  is connected to end  805  of spiral conductive trace  803  by a through via  905 . The other end  907  or spiral conductive trace  903  is connected to terminal  901   a . Spiral conductive traces  603 ,  703 ,  803 ,  903  are connected in series to form a planar first primary portion  117 . Planar second primary portion  119  is constructed in the same manner. 
     It will be appreciated by those skilled in the art that each of planar first primary portion  117  and planar second primary portion  119  may comprise more or less layers of a multilayer printed circuit board. The number of layers and the number of turns of the spiral trace on each layer is determined in accordance with well-known transformer design principles and algorithms. 
     Planar transformer  111  is shown in end view in  FIG. 10  and in cross-section view in  FIG. 11 . Planar transformer  111  comprises multilayer printed circuit board  101  that in turn comprises planar bias winding  123  that in turn comprises spiral trace  205  formed on layer  201 . Multilayer printed circuit board  101  further comprises and planar secondary winding  121  that in turn comprises spiral traces  405 ,  505  formed on layers  401 ,  401 . 
     Planar transformer  111  further comprises first multilayer printed circuit board  1001   a  comprising layers  601 ,  701 ,  801 ,  901  carried above top surface  101   a  of multilayer printed circuit board  101  and a second multilayer printed circuit board  1001   b  comprising layers  601 ,  701 ,  801 ,  901  is carried below bottom surface  101   b  of multilayer printed circuit board  101 . Insulating layers  1009  are provided between multilayer printed circuit board  101  and each of first and second multilayer printed circuit boards. In addition, insulating layers are also provided to cover first and second multilayer printed board outer surfaces  1009   a ,  1009   b.    
     Each insulating layer  1009  comprises a polyimide material and is shaped as shown in  FIG. 12 . Each insulating layer  1009  includes a central aperture  1207  that is disposed to be in alignment with central aperture  207  of multilayer printed circuit board  101  and first and second multilayer printed circuit boards  1001   a ,  1001   b . Each insulating layer  1009  also comprises a pair of side channels  1209 ,  1211  that are disposed to be in alignment with apertures  209 ,  211  of multilayer printed circuit board  101  and first and second multilayer printed circuit boards  1001   a ,  1001   b  when planar transformer  111  is assembled. 
     Planar transformer  111  comprises two transformer cores  1005 ,  1007  each having an E-shaped cross section as most clearly seen in  FIG. 13 . Transformer cores  1005 ,  1007  each comprise a ferrite material and are commercially available. Transformer core  1005  comprises outer legs  1105   a ,  1105   c  and middle or center leg  1105   b . Transformer core  1007  comprises outer legs  1107   a ,  1107   c  and middle or center leg  1107   b . Outer legs  1105   a ,  1105   c  engage outer legs  1107   a ,  1107   c , respectively, when transformer cores  1005 ,  1007  are assembled into apertures  209 ,  211 . Center legs  1105   b ,  1107   b  have a length such that a predetermined air gap  1101  is provided there between. It will be apparent to those skilled in the art that although cores of E-shaped cross section are utilized in this embodiment, other embodiments may use other core shapes such as, by way of non-limiting example, rectangular modulus (RM) shaped cores. 
     The embodiment of a light emitting diode (LED) power supply  100  for providing current to a plurality of LEDs shown in the drawing figures comprises a planar transformer  111 . Planar transformer  111  comprises a first multilayer printed circuit board  1001   a  comprising a first plurality of planar windings  603 ,  703 ,  803 ,  903  electrically connected in series to form a first primary portion  117 . Each planar winding  603 ,  703 ,  803 ,  903  of the first plurality of planar windings is carried on a separate layer  601 ,  701 ,  801 ,  901  of the first multilayer printed circuit board  1001 . Transformer  111  further comprises a second multilayer printed circuit board  1003  comprising a second plurality of planar windings  603 ,  703 ,  803 ,  903  electrically connected in series to form a second primary portion  119 . Each winding  603 ,  703 ,  803 ,  903  of the second plurality of planar windings is carried on a separate layer  601 ,  701 ,  801 ,  901  of the second multilayer printed circuit board  1003 . Transformer  111  additionally comprises a third multilayer printed circuit board  101  comprising a third planar winding  405  carried on one layer  401  to provide a secondary  121 . Third multilayer printed circuit board  101  comprises a first aperture  209  on one side of third planar winding  405 , a second aperture  211  on an opposite side of the third planar winding  405 , and a central aperture  207  surrounded by third planar winding  405 . Third multilayer printed circuit board  101  comprises a top surface  101   a  carrying first multilayer printed circuit board  1001   a  and a bottom surface  101   b  carrying second multilayer printed circuit board  1001   b . First and second multilayer printed circuit boards  1001   a ,  1001   b  are disposed such that first primary portion  117 , second primary portion  119  and secondary  121  are in vertical alignment with each other to maximize electromagnetic transformer coupling. 
     Transformer  111  further comprises a first core  1005  of E-shaped cross-section consisting of a ferrite material and comprising first and second outer legs  1105   a ,  1105   c  and a middle leg  1105   b . First core  1005  is carried on first multilayer printed circuit board  1001   a  such that the middle leg  1105   b  extends therethrough in the middle of the first plurality of planar windings  603 ,  703 ,  803 ,  903 , and the first and second outer legs  1105   a ,  1105   c  extend therethrough on opposite sides of the first plurality of planar windings  603 ,  703 ,  803 ,  903 . Transformer  111  also comprises a second core  1007  of E-shaped cross-section consisting of the ferrite material and comprising first and second outer legs  1107   a ,  1107   c  and a middle leg  1107   b . Second core  1107  is carried on second multilayer printed circuit board  1003  such that middle leg  1107   b  extends therethrough in the middle of the second plurality of planar windings  603 ,  703 ,  803 ,  903 , and the first and second outer legs  1107   a ,  1107   c  extend therethrough on opposite sides of the second plurality of planar windings  603 ,  703 ,  803 ,  903 . 
     First and the second outer legs  1105   a ,  1105   c  of first core  1005  extend into the third multilayer printed circuit board  101 . First and the second outer legs  1107   a ,  1107   c  of second core  1007  extend into third multilayer printed circuit board  101  and are in physical engagement with the first and the second outer legs  1105   a ,  1105   c  of first core  1005 , respectively. Middle leg  1105   b  of first core  1005  and middle leg  1107   b  of second core  1007  are disposed proximate to each other in alignment with the central aperture such that a predetermined air gap  1101  is provided there between. 
     The embodiment further comprises a first rectifier circuit  105  carried on third multilayer printed circuit board  101  for rectifying alternating current (ac) from a power source coupled to terminals  103 ; a driver circuit  109  carried on third multilayer printed circuit board  101  and disposed between first rectifier circuit  105  and first and second primary portions  117 ,  119 ; and a second rectifier circuit  113  carried on third multilayer printed circuit board  101  and coupled to secondary  121  and coupled to output power terminals  105  to provide direct current for powering the plurality of LEDs. 
     In accordance with one aspect of the embodiment, third multilayer printed circuit board  101  comprises a fourth planar winding  205  carried on another layer  201  to provide a bias winding  123 , and bias winding  123  is coupled to driver circuit  109 . 
     In accordance with another aspect of the embodiment, a plurality of terminals  117   a ,  117   b ,  119   a ,  119   b  is carried by third multilayer printed circuit board  101 . First primary portion  117  is connected to first terminals  117   a ,  117   b  of the plurality of terminals, second primary portion  119  is connected to second terminals  119   a ,  119   b  of the plurality of terminals. The first terminals  117   a ,  117   b  and second terminals  119   a ,  119   b  are selectively connectable to connect first primary portion  117  in parallel with or in series with second primary portion  119 . 
     The embodiment may further comprise a first filter circuit  107  disposed between first rectifier circuit  105  and driver  109 . 
     The embodiment may also further comprise a second filter circuit  115  disposed between second rectifier circuit  113  and output power terminals  105 . 
     The embodiment may comprise a first insulating layer  1009  disposed between first multilayer printed circuit board  1001  and first core  1005 , a second insulating layer  1009  disposed between first multilayer printed circuit board  1001  and third multilayer printed circuit board  101 , a third insulating layer  1009  disposed between second multilayer printed circuit board  1003  and second core  1007 , and a fourth insulating layer  1009  disposed between second multilayer printed circuit board  1003  and third multilayer printed circuit board  101 . 
     Each of the first, second, third and fourth insulating layers  1009  may comprise polyimide. 
     A second embodiment of light emitting diode (LED) power supply  100  for providing current to a plurality of LEDs comprises a transformer first primary portion  117  comprising a plurality of serially connected planar first primary windings  603 ,  703 ,  803 ,  903 , a transformer second primary portion  121  comprising a plurality of serially connected planar second primary windings  603 ,  703 ,  803 ,  903  and a transformer secondary  121  comprising a planar secondary winding  405 . The second embodiment further comprises a multilayer printed circuit board  101  comprising at least one layer  401 ,  501  having the planar secondary winding  405 ,  505  formed thereon. The second embodiment comprises a first multilayer printed circuit board  1001  carried on multilayer printed circuit board  101 . Each of planar first primary windings  603 ,  703 ,  803 ,  903  is carried on a corresponding separate one layer  601 ,  701 ,  801 ,  901  of the first multilayer printed circuit board  1001 . The second embodiment comprises a second multilayer printed circuit board  1003  carried on multilayer printed circuit board  101 . Each of planar second primary windings  603 ,  703 ,  803 ,  903  carried on a corresponding separate one layer  601 ,  701 ,  801 ,  901  of multilayer second printed circuit board  1003 . First primary portion  117  carried by first multilayer printed circuit board  1001 , second primary portion  119  carried by second multilayer printed circuit board  1003 , and planar secondary winding  121  are in axial alignment with each other to provide electromagnetic transformer coupling there between. A transformer core  1005 ,  1007  is carried by multilayer printed circuit board  101  extending over the first primary portion  117  and second primary portion  119  and extends through the multilayer printed circuit board  101 . 
     The second embodiment comprises a first rectifier circuit  105  carried on multilayer printed circuit board  101  for rectifying alternating current (ac) from a power source connected to terminals  103 , a driver circuit  109  carried on multilayer printed circuit board  101  and disposed between first rectifier circuit  105  and the first and second primary portions  117 ,  119  and a second rectifier circuit  113  carried on multilayer printed circuit board  101  and coupled to secondary  123  and coupled to output power terminals  105  to provide direct current for powering the plurality of LEDs. 
     Multilayer printed circuit board  101  comprises a fourth planar winding  205  carried on another layer to provide a bias winding  123 . Bias winding  123  is coupled to driver circuit  109 . 
     The second embodiment may comprise a plurality of terminals  117   a ,  117   b ,  119   a ,  119   b  carried by multilayer printed circuit board  101 . First primary portion  117  is connected to first terminals  117   a ,  117   b  of the plurality of terminals. Second primary portion is connected to second terminals  119   a ,  119   b  of the plurality of terminals. First terminals  117   a ,  117   b  and second terminals  119   a ,  119   b  are selectively connectable to connect first primary portion  117  in parallel with or in series with second primary portion  119 . 
     The second embodiment may comprise a first filter circuit  107  disposed between first rectifier circuit  105  and driver  109 . 
     The second embodiment may further comprise a second filter circuit  115  disposed between second rectifier circuit  113  and output power terminals  105 . 
     The second embodiment may comprise a first insulating layer  1009  disposed between first multilayer printed circuit board  1001   a  and a first core portion  1005 , a second insulating layer  1009  disposed between first multilayer printed circuit board  1001   a  and multilayer printed circuit board  101 , a third insulating layer  1008  disposed between second multilayer printed circuit board  1001   b  and second core portion  1007 , and a fourth insulating layer disposed between second multilayer printed circuit board  1001   b  and multilayer printed circuit board  101 . 
     Each of the first, second, third and fourth insulating layers  1009  may comprise polyimide. 
     A third embodiment of a light emitting diode (LED) power supply  100  for providing current to a plurality of LEDs, comprises a transformer first primary portion  117 , a transformer second primary portion  119 , a transformer secondary portion  123 , and a multilayer printed circuit board  101 . Multilayer printed circuit board  101  comprises at least one layer  401 ,  501  having a planar secondary winding  405 ,  505  formed thereon. Transformer secondary portion comprises planar secondary winding  405 ,  505 . Multilayer printed circuit board  101  further comprises a plurality of first multilayer printed circuit boards  1001   a  carried on multilayer printed circuit board  101 . Transformer first primary portion  117  comprises a plurality of serially connected planar first primary windings  603 ,  703 ,  803 ,  903 . Each of planar first primary windings  603 ,  703 ,  803 ,  903  is carried on a corresponding separate one layer  601 ,  701 ,  801 ,  901  of the plurality of first multilayer printed circuit boards  1001   a . Transformer second primary portion  119  also comprises a plurality of serially connected planar first primary windings  603 ,  703 ,  803 ,  903 . Each of planar first primary windings  603 ,  703 ,  803 ,  903  is carried on a corresponding separate one layer  601 ,  701 ,  801 ,  901  of the plurality of second multilayer printed circuit boards  1001   a.    
     The plurality of first multilayer printed circuit boards, the plurality of second multilayer printed circuit boards, and the planar secondary winding are in alignment with each other to provide electromagnetic coupling there between. 
     It will be understood by those skilled in the art that the dimensions shown in the various drawing figures are not intended to in any way limit the invention and that the various sizes and shapes of the various elements are intended only to be representative of those elements and are likewise not intended to limit the invention. 
     The invention has been described in conjunction with various embodiments. It will be understood by those skilled in the art that the invention is not limited by the various embodiments shown and described herein. Various modifications may be made without departing from the scope of the invention. It is intended that the invention shall be limited in scope only by the claims appended hereto.