Abstract:
Disclosed is a compact inverter plug that can be used with LED lighting strings. The converter plug has a size and shape that is comparable to a standard wall plug and is capable of plugging into a standard wall socket. The converter plug is waterproof and can be easily assembled. A unique converter circuit is utilized that is compact and highly efficient. Monitoring is performed by a transformer coil that generates a monitoring signal. The converter is controlled by controlling the modulation frequency of a direct current signal using a controller.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of and priority to Chinese Application Serial No. 200920230903.3, filed Aug. 26, 2009, by Long Chen and Beijing Yu, and Chinese Application Serial No. 200920231361.1, filed Aug. 27, 2009, by Long Chen and Beijing Yu, the entire contents of which are specifically incorporated herein by reference for all that they disclose and teach. 
     BACKGROUND 
     Lighting using light emitting diodes is a practical and inexpensive way to provide illumination for various purposes. The advantages of LED lighting are that LEDs operate effectively at low direct current voltages and currents. Further, LED lights produce a large number of lumens for the energy that the LEDs consume. Moreover, LEDs do not generate a significant amount of heat, which renders LED lights a safer alternative to other forms of lighting. 
     SUMMARY 
     An embodiment of the present invention may therefore comprise a converter plug for an LED light string that plugs into a household alternating current socket that inverts alternating current household power to a low voltage direct current output in a small package that is watertight and has a shape similar to a wall plug comprising: plug blades that are molded into an enclosure that provides a watertight seal with the plug blades; a printed circuit board having converter circuitry mounted on at least one surface, the printed circuit board securely mounted in the enclosure; a connector having sockets that are adapted to connect to plugs on the LED light string, the connector having a watertight coupler that mates with the LED light string to provide a watertight connection between the connector and the light string, the connector being sealed to the enclosure so that the enclosure is watertight, the watertight coupler allowing the converter plug to be disconnected from and connected to the LED light string. 
     An embodiment of the present invention may further comprise a converter plug for use with an LED light string comprising: plug blades that fit in an alternating current wall socket; a housing having an end portion that is molded around the plug blades that provides a watertight seal between the housing and the plug blades and slots formed in edges of the housing; a printed circuit board having converter circuitry mounted thereon, the printed circuit board mounted and held securely in the slots in the housing, the printed circuit board having contacts at one end that abut against the plug blades so that the plug blades are electrically connected to the contacts on the printed circuit board, the printed circuit board having pins that provide direct current power from the printed circuit board; an end cap that attaches to the housing so that a watertight seal is created between the end cap and the housing; a connector molded to the end cap having sockets that are electrically connected to the pins on the printed circuit board, the connector having a watertight coupling for coupling the converter plug to the LED light string; a buffer disposed between the end cap and the printed circuit board that holds the printed circuit board in place in the housing and urges the printed circuit board against the plug blades so that the contacts on the printed circuit board maintain contact with the plug blades. 
     An embodiment of the present invention may further comprise a converter circuit for use in a converter plug for producing a direct current output for an LED light string comprising: a rectifier that rectifies a source of alternating current from a household socket; a low pass filter that provides a direct current signal; a filter absorber that protects the converter circuit from voltage spikes; a high speed switching transistor that modulates the direct current signal to produce a modulated direct current signal having a modulation frequency; a first coil in a transformer coupled to the modulated direct current signal that induces voltage charges in a second transformer coil and a third transformer coil; a high speed directional filter connected to the second transformer coil that produces the direct current output; a monitor circuit connected to the third transformer coil that produces a monitoring signal; a controller that controls the modulation frequency of the modulated direct current signal in response to the monitoring signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic view of a circuit layout employing embodiments of the present invention. 
         FIG. 2  is an embodiment illustrating an assembly procedure for a converter employed as a plug. 
         FIGS. 3-6  illustrate various configurations of a converter plug. 
         FIGS. 7-10  illustrate various assembly configurations for converter plugs. 
         FIGS. 11-13  illustrate various techniques for connecting conductors to a printed circuit board. 
         FIGS. 14 and 15  illustrate two embodiments of connectors for connecting a light string to a converter plug. 
         FIGS. 16 and 17  illustrate an assembly process for a converter plug. 
         FIG. 18  is a cross-sectional view of an another embodiment of a converter plug 
         FIG. 19  is a side view of an assembled converter plug of the embodiment of  FIG. 18 . 
         FIG. 20  is a schematic block diagram of an embodiment of an converter circuit. 
         FIG. 21  is a schematic circuit diagram of the embodiment of the converter circuit of  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic diagram of one embodiment of an LED string  100  utilizing a compact converter plug  102 . The compact converter plug  102  has plug blades  104  for plugging the compact converter plug  112  into a wall socket, such as a standard 117 volt rms alternating current power source. The miniature converter plug  102  has a small size which is similar to the size of a standard wall plug with a slightly extended length. The LED light string  110  is connected to the compact converter plug  102  using an extendable power plug  106 . The extendable power plug  106  can be easily inserted and removed from the compact converter plug  102 , while maintaining a watertight seal. Alternatively, the LED light string  110  can be permanently connected to the miniature converter plug  102 . At the other end of the LED light string  110 , an extendable power socket can be employed, which allows the LED light string  110  to be connected to additional light strings with extendable power plugs, such as extendable power plug  106 . In accordance with the embodiments in which the extendable power plug  106  can be disconnected from the miniature converter plug  102 , the compact converter plug  102  can be sold separately from the LED light strings  110 , which allows the consumer greater options and greater savings in employing multiple or single light strings, such as LED light string  110  in various applications, as desired. 
       FIG. 2  illustrates the manner in which the converter plug  102  can be assembled. As illustrated in  FIG. 2 , wall plug blades  104  are mounted in an end piece  200 . This process can be achieved by molding the end piece  200  around the wall plug blades  104 , using injection molding, such that the wall plug blades  104  are securely mounted and sealed in the front cover  200 . Front cover  200  also includes a notch  210 , which engages with housing  202  to provide a secure, watertight seal between the front cover  200  and housing  202 . A conductor  208  connects the wall plug blades  104  to the printed circuit board  204 . Wires  212  connect the printed circuit board  204  to the connector  214 . The mating of the housing  202  with the front cover  200  can be by way of a friction fit, ultrasonic welding, or other standard processes for creating a watertight fit. In this manner, the converter plug  102  can be used in outdoor environments while maintaining a watertight seal for the electrical components  206  mounted on the printed circuit board  204  inside housing  202 . 
       FIG. 3  is a side view of one embodiment of an converter plug  300 . As shown in  FIG. 3 , plug blades  302  extend from a first end of the converter plug  300  while connector  304  extends from an opposite end of the converter plug  300 . Housing  306  can provide watertight encapsulation of the electrical components within the converter plug  300 . 
       FIG. 4  is a side view of another embodiment of an converter plug  400 . As illustrated in  FIG. 4 , housing  408  encloses the electronic components. Plug blades  402  extend from one end of the housing  408  while connectors  404 ,  406  extend from the opposite end of the housing  408 . In the embodiment illustrated in  FIG. 4 , two connectors  404 ,  406  are provided, which are capable of supplying direct current power to two separate LED light strings. Circuitry can be provided for producing direct current outputs to each of the connectors  404 ,  406 . 
       FIG. 5  discloses another embodiment of an converter plug  500 . As illustrated in  FIG. 5 , plug blades  502  extend laterally from the housing  506  at one end of the converter plug  500 . Connector  504  extends in a longitudinal direction at the other end of the housing  506 . The configuration illustrated in the embodiment of  FIG. 5  is useful in situations where there is limited space adjacent the wall socket. 
       FIG. 6  illustrates another embodiment of an converter plug  600 . As disclosed in  FIG. 6 , plug blades  602  extend laterally from the housing  606 . Multiple connectors  604  are provided at an opposite end of the housing  606 . 
       FIGS. 7-10  illustrate four different ways of assembling converter plugs. As illustrated in  FIG. 7 , a cover  704 , which has plug blades  708  mounted therein, can be assembled in housing  702  during initial fabrication. Connector  706  is mounted to the housing  702  during initial fabrication of the plug blade  700 . 
       FIG. 8  illustrates an alternative method of assembling an converter plug  800 . As illustrated in  FIG. 8 , plug blades  808  are connected to the housing  802  during initial fabrication. Similarly, connector  806  is connected to cover  804  during initial fabrication. Then, after the electronic circuits are inserted into the housing  802 , the cover  804  can be assembled with the housing  802  in accordance with any of the methods described above. 
       FIG. 9  illustrates another embodiment of a process for assembling an converter plug  900 . As shown in  FIG. 9 , the housing  902  and connectors  906  are assembled in the initial fabrication process. Similarly, plug blades  908  and cover  904  are assembled in the initial fabrication process. After a circuit board is inserted in housing  902 , the cover  904  can be assembled and sealed to the housing  902  in accordance with any of the desired methods disclosed above, including ultrasonic welding, heat curing, friction fit assembly and other methods, to create a watertight seal between the cover  904  and housing  902 . 
       FIG. 10  illustrates another embodiment of a process for assembling an converter plug  1000 . As shown in  FIG. 10 , both the plug blades  1008  and connectors  1006  are initially fabricated and secured to the housing  1002 . A printed circuit board and accompanying circuitry is then mounted in the housing  1002 , and the electrical connections are made to the plug blades  1008  and connectors  1006 . Cover  1004  is then sealed to the housing  1002  using any of the methods disclosed above. 
       FIGS. 11-13  disclose various processes for connecting a printed circuit board to the plug blades. As disclosed in  FIG. 11 , a bent metal conductor  1102  is used to connect the printed circuit board  1104  to the plug blades  1108 . In addition, conductors  1106  are used to connect the printed circuit board  1104  to the connector  1110 . 
     As illustrated in  FIG. 12 , wire conductors  1202  are used to connect the printed circuit board  1204  to the plug blades  1208 . Conductors  1206 , such as wires, are used to connect the printed circuit board  1204  to the connector  1210 . 
     As illustrated in  FIG. 13 , a socket bracket  1302  is used to connect the plug blades  1308  to the printed circuit board  1304 . Conductors  1306  are used to connect the printed circuit board  1304  to the connector  1310 . 
       FIGS. 14 and 15  disclose two different embodiments for connecting an extendable power plug to an converter plug. As illustrated in  FIG. 14 , converter plug  1400  has a pair of sockets  1404  disposed in a threaded connector  1402 . Plugs  1406  disposed in an extendable power plug  1412  can be inserted in the sockets  1404  and electrically connected to the sockets  1404 . A cap  1408  is threaded on the threaded connector  1402  and seals the extendable power plug  1412  against the sealing stop  1410 . 
       FIG. 15  is an illustration of another embodiment of an converter plug  1500  and an extendable power plug  1506 . The extendable power plug  1506  has a sleeve  1502  that slides over an extended portion  1504  of the converter plug  1500 , as illustrated by the dotted lines in  FIG. 15 . Sleeve  1502  creates a friction fit with the extended portion  1504  to create a watertight seal between the sleeve  1502  and the extended portion  1504 . Also, a tight slide fit can be created between sleeve  1502  and extended portion  1504  and a locking mechanism provided. Alternatively, sleeve  1502  can be permanently attached to the extended portion  1504 , using ultrasonic welding, adhesives, or other methods. The disadvantage in permanently attaching the sleeve  1502  to the extended portion  1504  is that the converter plug  1500  cannot be used with other light strings. For example, the LED light string attached to the extendable power plug  1506  may be damaged and unrepairable. In that case, the converter plug  1500  will have to be discarded with the light string. Of course, the removable extended power plug  1412 , illustrated in  FIG. 14 , allows the converter plug  1400  of  FIG. 14  to be used with other light strings. 
       FIGS. 16 and 17  illustrate one method of assembling an converter plug. As illustrated in  FIG. 16 , plug blades  1604  are molded into an end piece  1602  that encapsulates and surrounds the plug blades  1604 . A watertight seal is created between the plug blades  1604  and the end piece  1602 . End piece  1602  can be part of the housing  1600  or can be attached to the housing  1600  by various means, including ultrasonic welding, etc. Housing  1600  has ends  1606 ,  1608  that extend on the open end of housing  1600 . 
       FIG. 17  is a schematic illustration of an assembled converter plug. As illustrated in  FIG. 17 , plug blades  1604  are secured in the end piece  1602 . The printed circuit board  1614  is connected to the plug blades  1604  by conductor  1616 . Conductor  1616  may be a bent piece of metal that has a sufficient amount of elasticity so that, when the printed circuit board  1614  is mounted in the housing  1600 , an electrical contact is made between the plug blades  1064  and the printed circuit board  1614 . In that regard, housing  1600  may include various mounting devices for mounting the printed circuit board  1614  in the housing  1600 . As also illustrated in  FIG. 17 , connector end piece  1612  is attached at ends  1606 ,  1608  to housing  1600 . Attachment can be performed by various methods, including ultrasonic welding and other techniques disclosed herein. 
       FIG. 18  is a schematic cutaway view of another embodiment of an converter plug  1800 . As illustrated in  FIG. 18 , the converter plug  1800  includes a connector  1802  and a body  1804 . Plug blades  1816  are molded into the end portion  1808  and extend into an interior portion of the converter plug  1800 . Printed circuit board  1812  is mounted in housing  1810  by sliding the printed circuit board  1812  into slots  1811 , along the sides of housing  1810 . Plug blades  1816  abut against contacts  1830 ,  1832  to make electrical contact with the printed circuit board  1812 . Alternatively, wires can be used to connect PCB  1812  to plug blades  1816 . Electrical components  1814  are mounted on the printed circuit board  1812  and comprise the converter circuitry necessary to invert the alternating current from a standard household plug, such as a 117 volt RMS alternating current signal, to a low voltage direct current signal that is less than 10 volts. 
     As further shown in  FIG. 18 , the printed circuit board has a pair of pins  1834 ,  1836  that provide the output direct current voltage from the printed circuit board  1812 . Pins  1834 ,  1836  are connected to sockets  1820 ,  1822 , which interface with plugs, such as plugs  1406 , illustrated in  FIG. 14 . End cap  1806 , as illustrated in  FIG. 18 , attaches to housing  1810 . As illustrated in the embodiment of  FIG. 18 , a ridge on the housing  1810  interfaces with a detent  1828  on the end cap  1806  to provide a watertight seal between housing  1810  and end cap  1806 . Of course, other methods of attaching the end cap  1806  to the housing  1810  can be used. For example, end cap  1806  may be permanently attached to housing  1810  using ultrasonic welding, melting or other techniques. Buffer  1824  is disposed between the end cap  1806  and the printed circuit board  1812 . Buffer  1824  assists in holding the printed circuit board  1812  in place and urging contacts  1830 ,  1832  against the ends of plug blades  1816  to make an electrical connection between the printed circuit board  1812  and plug blades  1816 . The buffer  1824  can be constructed of acrylonitrile butadiene styrene (ABS) or other type of suitable thermoplastic material. Pins  1834 ,  1836  can be pressed against sockets  1820 ,  1822 , respectively, or otherwise electrically connected using wires (not shown). Connector  1802  also includes a threaded connector end  1818  that allows a watertight connection between an LED string and the converter plug  1800 . 
       FIG. 19  is a side view of the assembled converter plug  1800 . As illustrated in  FIG. 19 , the converter plug  1800  has a general shape and size that corresponds to a standard electric plug to be inserted into an electrical wall socket. As such, the converter plug  1800  is a convenient device for providing direct current power to an LED array because of its size and high efficiency. Threaded connector  1818  allows light strings to be attached and detached from the converter plug  1800 , while providing a watertight seal between the converter plug  1800  and an LED light string. End cap  1806  provides a convenient device for attaching the threaded connector  1818  to the housing  1810 . As illustrated in various embodiments disclosed above, plug blades  1816  can extend from the end or sides of the converter plug  1800 . 
       FIG. 20  is a schematic block diagram of an embodiment of an converter circuit  2000  that can be utilized with any of the embodiments of the converter plug disclosed herein. As illustrated in  FIG. 20 , an alternating current input  2002  is applied to a safety resistor  2004 . Safety resistor  2004  may be a resistive fuse that blows when an excessive amount of current is applied to the converter circuit  2000 . The alternating current signal is then applied to a full wave rectifier  2006 , which rectifies the alternating current input into a fully rectified signal. Low pass filter  2008  filters out higher frequencies, so that a direct current signal is produced at the input to filter absorber  2010 . Filter absorber  2010  absorbs current spikes that protects the microchip controller  2016 , energy converter  2012  and other components in the converter circuit  2000 . The direct current signal is then applied via connector  2020  to microchip controller  2016 . Startup circuit  2014  assists in starting the microchip controller  2016  and providing a source of direct current power to operate the microchip controller  2016 . Energy converter  2012  includes a high speed switching circuit and a transformer that reduces the voltage level of the direct current voltage signal. High speed filter  2022  creates the direct current output  2024 . This circuit is more fully disclosed in  FIG. 21 . 
       FIG. 21  illustrates the converter circuit  2000 , shown in the block diagram of  FIG. 20 . As illustrated in  FIG. 21 , an alternating current signal  2002  is applied to leads  2026 ,  2028 . Fuse (safety resistor)  2004  is a 10 ohm winding resistor installed in the alternating current power input on lead  2026 . If a short circuit, or other abnormal condition occurs, fuse  2004  produces an open circuit and prevents the application of the alternating current input power to the converter circuit  2000 . Fuse  2004  also limits the current fluctuation during on and off transitions. Full wave rectifier  2006  rectifies the alternating current input  2002  to produce a pulsed direct current voltage. Low pass filter  2008 , which comprises capacitors  2030 ,  2034  and inductor  2032 , generates a direct current voltage at node  2035 . Lead  2038  applies the direct current voltage to resistor  2040  and to the base of switching transistor  2050 . Direct current voltage at node  2035  is also applied to a filter absorber  2010 , which comprises capacitor  2042 , resistor  2044 , resistor  2046 , and diode  2048 . Filter absorber  2010  protects the switching transistor  2050  from voltage spikes that may occur during operation of the transformer  2058 . 
     The switching transistor  2050 , of  FIG. 21 , is controlled by controller  2016 . A suitable controller for use as controller  216  for low power converters, comprises part #FT831B, FT881 from Fremont Micro Devices (SZ) Ltd., #5-8, 10-F, Changhong Science and Technology Building, Ke-Ji Nan 12 Road, Nanshan District, Shenzhen, Guangdong. For higher power converters, part # ACT361, ACT355 is available from Active-Semi, Inc., 2728 Orchard Parkway, San Jose, Calif., 95134, or from iWatt, Inc., 101 Albright Way, Los Gatos, Calif., 95032. Switching transistor  2050  is turned on and off by pins  2090 ,  2092  of controller  2086 , which modulates the direct current voltage at node  2035 . Since the direct current voltage at node  2035  is modulated, the voltage transitions are transmitted from the primary coil  2052  of transformer  2058  to secondary coils  2054 ,  2056  via transformer core  2060 . The transitioning voltage across coil  2052  induces a voltage in secondary coil  2054 . The voltage transitions occur in both a positive and negative direction on coil  2052 . This causes both positive going and negative going voltage transitions to be induced in secondary coils  2054 ,  2056 . 
     Diode  2062  only allows the current to pass in the direction of the diode  2062 . The high speed filter  2022 , which comprises capacitor  2064  and resistor  2066  filters and stores the positive direct current voltage on node  2068  and the negative output direct current voltage on node  2070  of direct current output voltage  2004 . 
     As also illustrated in  FIG. 21 , the transitioning voltages on primary coil  2052  also create transitioning voltages on secondary coil  2056  that are applied to the startup circuit  2014  and the voltage dividing circuit comprising resistors  2080 ,  2082 . With regard to the startup circuit  2014 , diode  2072  only allows passage of current in the direction of the diode  2072 . Resistors  2074 ,  2078  and capacitor  2076  provide a voltage at pin  2075 , which is the VDD voltage that operates the controller  2086 . The voltage dividing circuit that comprises  2080 ,  2082  provides a voltage at node  2084 , which is the induced voltage on secondary coil  2056  divided between resistors  2080 ,  2082 . The voltage on node  2084  is applied to the feedback pin  2085  of controller  2086 . The voltage at feedback pin  2085  of controller  2086  controls the frequency of switching on nodes  2090 ,  2092  of controller  2086 . When there is no load at the direct current output  2004 , the frequency is reduced to achieve energy savings. When a load is present at the direct current output  2004 , the frequency of the switching transistor  2050  is increased, which delivers more energy across the transformer  2058  from primary coil  2052  to secondary coil  2056  to support the energy requirements of the load at the direct current output  2004 . Secondary coil  2056  has a proportional amount of energy transferred from the primary coil  2052  as the secondary coil  2054 , depending upon the number of windings in secondary coil  2054  and secondary coil  2056 . Hence, secondary coil  2056  has the same, or a proportional, amount of energy delivered to the secondary coil  2056  as the secondary coil  2054 . In other words, the secondary coil  2054  has a certain amount of energy delivered across the transformer  2058  and secondary coil  2056  has the same, or a proportional, amount of energy delivered to it. Hence, the voltage at node  2084 , which is applied to the feedback pin  2085 , is proportional to the voltage produced at the direct current output  2004 . In this manner, the controller  2086  can monitor the voltage that is produced at the direct current output  2004  without any feedback from the direct current output  2004 . Optic couplers have been used to provide a feedback loop from an output voltage, such as the direct current output voltage  2004 , which provides isolation between a direct current output and a controller, such as direct current output  2004  and controller  2086 . Opto-couplers are expensive and bulky. In order to maintain a small package that has a size that is consistent with a wall plug, opto-couplers provide an inconvenient solution that does not meet the size requirements for the miniature converter  102 , illustrated in  FIG. 1 . 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.