Parallel/series LED strip

An LED light engine includes a flexible electrical cable and a plurality of LEDs. The flexible electrical cable includes first, second and third electrical conductors and an electrically insulating covering for the electrical conductors. The conductors are arranged substantially parallel with one another having an insulating material therebetween. A first LED including a first lead electrically connects to the first electrical conductor and a second lead of the first LED electrically connects to the second conductor. A second LED includes a first lead electrically connected to the second electrical conductor and a second lead electrically connected to the third electrical conductor. A third LED includes first and second leads electrically connected to the second conductor. The third LED is interposed between the first LED and the second LED.

BACKGROUND OF THE INVENTION

Light emitting diodes (“LEDs”) are employed as a basic lighting structure in a variety of forms, such as outdoor signage and decorative lighting. LED-based light strings have been used in channel lettering systems, architectural border tube applications, under cabinet lighting applications and for general illumination. A known spoolable LED light string arranges the LEDs in parallel circuitry. This parallel arrangement requires a very low voltage output power supply (Voutapproximately 2.0 to 4.5 VDC) and a large amount of drive current capability. The large currents that must be delivered severely limits the distance that the power supply can be spaced from the LED strip as well as the length of the LED strip that can be driven by the power supply.

Known LED string lights also use parallel/series combinations of LEDs. These known systems require that the LEDs mount to a printed circuit board as well as some sort of current limiting device. These known systems require the printed circuit board to be environmentally isolated, which is expensive. Furthermore, the printed circuit board based systems are also difficult to spool, to mount and to cut to length in addition to requiring the expense of the printed circuit board itself.

Other known LED light strings employ a plurality of LEDs wired in a series/parallel block that are run directly off AC power. These known systems require complicated designs to account for the alternating current.

The present LED light engine contemplates an improved apparatus and method that overcomes the above-mentioned limitations and others.

SUMMARY OF THE INVENTION

An LED light engine includes a flexible electrical cable and a plurality of LEDs. The flexible electrical cable includes first, second and third electrical conductors and an electrically insulating covering for the electrical conductors. The conductors are arranged substantially parallel with one another having an insulating material therebetween. A first LED including a first lead electrically connects to the first electrical conductor and a second lead of the first LED electrically connects to the second conductor. A second LED includes a first lead electrically connected to the second electrical conductor and a second lead electrically connected to the third electrical conductor. A third LED includes first and second leads electrically connected to the second conductor. The third LED is interposed between the first LED and the second LED.

A method of manufacturing an LED light engine is disclosed. The method includes insulating first, second and third conductive elements to form an insulated conductor. The insulated conductor includes insulating material interposed between the conductive elements. The method further includes mechanically securing a plurality of LEDs spaced along the insulated conductor. The method further includes electrically contacting a first lead of a first LED of the plurality of LEDs to the first conductive element and a second lead of the first LED to the second conductive element. The method further includes electrically contacting a first lead and a second lead of a second LED of the plurality of LEDs to the second conductive element. The method further includes electrically separating the second conductive element between the first lead and the second lead of the second LED. The method further includes electrically contacting a first lead of a third LED of the plurality of LEDs to the second conductive element and a second lead of the third LED to the third conductive element. The second LED is interposed between the first LED and the third LED.

A light string includes a plurality of LEDs connected to one another in parallel, a predetermined number of LEDs electrically connected to one another in series, and conditioning electronics in electrical communication with the plurality of LEDs. The predetermined number of LEDs is electrically interposed between adjacent LEDs that are electrically connected to one another in parallel. The conditioning electronics convert AC power to DC power for driving the LEDs.

DETAILED DESCRIPTION

With reference toFIG. 1, a light engine10includes a flexible electrical conductor12having a socket housing14attached thereto. The socket housing14receives a light source, which in this embodiment is an LED16. The LED16is a pre-packaged LED of a type known to the art, e.g., an electroluminescent semi-conducting element arranged in a P4 (piranha) package with suitable epoxy or other encapsulant18. Other conventional light sources can be used with the light engine10including an incandescent light source. A plurality of socket housings14can attach to the insulated flexible electrical cord12at a plurality of locations along the cord, as seen inFIG. 5, to form a light strip or light string.

The light strip, in a preferred embodiment, is powered by AC power. In one embodiment, conditioning electronics20(FIG. 5) communicate through the insulated flexible electrical cord12with the LEDs16. The conditioning electronics convert building power (e.g., 120 VAC in the United States or 220 VAC in Europe) to power suitable for driving the LEDs16of the light strip10. In a preferred embodiment, the conditioning electronics include a class II power supply having output power limited to 5 amperes and 30 volts. Class II power supplies are relatively safe due to the low voltages and currents produced and typically are not required by electrical codes to be arranged in safety conduits.

The insulated flexible electric cord12includes a first conductor22, a second conductor24and a third conductor26. Each of the conductors22,24and26is preferably sized to be about 18 gauge. Additionally, each conductor is preferably stranded and includes a plurality of strands (e.g., seven strands). With a current running through the flexible electrical cord12, the first conductor22can be referred to as the positive (+) conductor, the third conductor can be referred to as the negative (−) conductor, and the second conductor24can be referred to as the series conductor. Each of the conductors is situated generally parallel to one another and an insulating material28(e.g., rubber, PVC, silicone and/or EPDM), is situated between the conductors.

The electrical cord12can include an alignment mechanism to facilitate alignment of the socket housing14on the electrical cord. In a preferred embodiment, the alignment mechanism is two grooves30, which have a V-shaped configuration, into which a portion of the socket housing14can be received. Alignment of the socket housing14with the grooves30aligns the internal components located in the socket housing, which will be described in more detail below, with the electrical conductors22,24and26in the cord12to promote a good electrical connection. In alternative embodiments, the alignment mechanism can include a line drawn or made on the cord, or any conventional indicia to facilitate location of the socket housing14on the electrical cord.

The socket housing14attaches to the insulated flexible electrical cord12. In a preferred embodiment, the socket housing is a molded body of a plastic or other suitable electrically insulating material. With reference toFIG. 2, the socket housing14includes two sections: a hollow socket body32and a socket cover34. The socket body32is generally box-shaped and defines an LED seat36on an upper surface thereof. The LED seat36is dimensioned to receive a correspondingly sized LED16. The seat36includes a platform38upon which the LED16rests. The socket body32is hollow so that it can receive prongs42inside the socket body and below the LED platform38.

The prongs42include insulation-piercing members that are arranged in a substantially fixed manner in slots or openings (not shown) in the socket body32. The prongs42are formed from sheet metal or another suitably electrically conductive material. With reference toFIG. 3, each prong42is substantially planar and includes fingers44that extend towards the LED platform38to define slots46that receive corresponding LED leads48to effectuate electrical contact of the positive and negative terminals (anode and cathode) of the LED16with the corresponding positive or negative prong. The LED platform38includes openings52(only one is visible inFIG. 2) through which the terminals48protrude before entry into the slots46of the prongs42. Receiving of the LED leads48into the slots46does not include a soldering step. Hence, the LED16is optionally detachable from the prong42and the socket body32, for example to facilitate replacement of a failed LED.

With continued reference toFIGS. 2 and 3, each prong42includes a bifurcated portion56that extends out of the socket body32toward the socket cover34such that when the socket body32is fastened to the socket cover34with the cable12sandwiched therebetween the bifurcated portion56of the prongs42punctures the cable insulation28and contacts a respective conductor22,24or26. Points58are formed at the end of the bifurcated portion to facilitate puncturing of the insulating material28. Each bifurcated portion56defines a gap62dimensioned to receive a respective conductor22,24or26. With reference toFIG. 4, each conductor22,24or26compressively squeezes into the gap62of one of the prongs42when the socket body32is connected to the socket cover34. The compression preferably does not break or fracture the individual strands of the conductors, but does ensure a reliable electrical contact between the prongs42and a respective conductor22,24or26.

The snapping connection of the socket body32and the socket cover34about the cable12effectuates both a mechanical connection of the LED16to the cable12as well as a simultaneous electrical connection of the positive and negative (anode and cathode) terminals of the LED12via the prongs42to the conductors22,24or26that supply electrical power. With reference back toFIG. 2, the socket cover34is generally L-shaped and includes a base70that closes off the bottom of the socket body32and an upwardly extending wall72that covers the opposite side of the electrical cord12as the socket body32. The base70includes a first channel74located on one side of the base and a second channel76located on an opposite side of the base the channels74and76receive tongues (not visible inFIG. 2) that fit into the channels when the socket body32is fastened to the socket cover34.

The upwardly extending wall72includes a knurl82positioned above the electrical cord12when the socket body32attaches to the socket cover34. The knurl82engages an opening84located on the socket body32. The knurl and opening provide a selective engagement between the socket body32and the socket cover34; however, the socket body and the socket cover can secure to one another in any conventional manner. The wall72also includes alignment members86that are received in the grooves30of the electrical cord12. The alignment members86further align the socket housing14in a direction generally perpendicular to the length of the electrical cord12. With reference back toFIG. 2, an insulating member88is positioned between the prongs42to puncture the insulating material28and separate (e.g. cut) the series conductor24upon connection of the socket body32to the socket cover34. The insulating member88mounts inside the socket body32in a similar manner to the prongs42. The insulating member88includes a blade90to cut through the insulating material28and the series conductor24. The insulating member88is flat, similar to the prongs42, however, the insulating member88includes a dielectric material92positioned to prohibit the flow of electricity through the deflective material92when the socket housing14is affixed to the electrical cord12.

In an alternative embodiment, the wall72can also include an insulation barrier (not shown) that is aligned to fit between the prongs42and separate the series conductor24between the prongs42when the socket body32attaches to the socket cover34. The insulation barrier can comprise a dielectric material that can puncture through the insulating material28of the electrical cord12and also cut through the series conductor24thus electrically separating the series conductor between two adjacent prongs42. In an alternative embodiment, the series conductor24can be cut by a feature integral to the socket body32and this feature can also electrically separate the series conductor24between two adjacent prongs42. In yet another alternative embodiment, a secondary component can be inserted into the socket housing14, i.e., through an opening (not shown) in the socket cover34.

A mounting portion94also attaches to the socket housing14. The mounting portion in the light engine depicted inFIG. 2includes an opening96that is adapted to receive a fastener. The mounting portion allows the socket housing14and thus the light engine10to attach to an associated surface such as a portion of outdoor signage, channel lettering systems, architectural border tube applications, under cabinet lighting applications and any surface to which one may want to mount a light engine. The light engine10can mount to the associated surface in other conventional manners including tape, hook and loop fasteners, as well as having a mounting portion that takes other configurations that the hook has shown.

The mechanical connection between the socket housing14and the electrical cord12facilitates placement of the light engine10in a channel letter100. As seen inFIG. 1, the LED16is generally perpendicular a plane that intersects the conductors22,24and26. Such a configuration allows for easy manipulation of the light string10on a mounting surface into a variety of configurations while emitting light away from the mounting surface. With reference toFIG. 7, the light engine10mounts inside a channel letter100. A protective translucent cover (not shown) encloses the light engine10in the channel letter100. With reference toFIG. 8, the light engine10mounts to the channel letter100by fasteners102received in the slots94of the mounting portion92and in openings104formed in the channel letter100. In addition to using fasteners, the light engine10can mount to the channel letter, or another mounting surface, in any conventional manner including clips, hook and loop fasteners, tape, glue and the like.

The electrical connection between the components of the light engine10need not include auxiliary electrical components, such as resistors and the like, and need not include soldering. Preferably, the conductors22,24and26, the prongs42and the LED leads48are formed from substantially similar metals to reduce galvanic corrosion at the electrically contacting interfaces, or are coated with a conductive coating that reduces galvanic corrosion at the interfaces.

The orientation of the prongs42inside the socket body32is dependent upon the location of the socket housing14along the electrical cord12. As best shown inFIGS. 5 and 6, the location of each bifurcated portion56of the prongs42is dependent upon the location of LED on the electrical cord12. As shown inFIG. 5, the left-most LED16is electrically connected to the positive conductor22and the series conductor24. The right-most LED16is electrically connected to the negative conductor26and the series conductor24. The left-most LED and the right-most LED each have their prongs42offset from one another along the electrical cord12and the conductors22,24and26running within. The prongs42are also offset perpendicular to the length of the electrical cord12so that each prong contacts a different conductor. The central LEDs, which are interposed between the left-most and right-most LEDs, have leads48that attach to prongs42to the second or series conductor24. The central LEDs have their prongs offset only along the length of the series conductor24. Also, the insulating member88cuts through the series conductor22between each pair of prongs42for each LED16.

With reference toFIG. 9, a cord12′ can include additional wires or conductors. The cord12′ includes a positive conductor22′, a series conductor24′ and a negative conductor26′. The cord12′ also includes additional wires110and112. These wires can also communicate with an LED16′ housed in a socket body14′ which is attached to the cord. Information can be passed along the additional wires110and112. In such a case the wires110and112would also communicate with a control center. The additional wires can allow for dimming an LED in the string separately from other LEDs, perhaps due to a higher current draw. Other control examples that can be run through the additional wiring include sequencing LED's to create active effects, probing the LED socket for lifetime information, passing diagnostic information back and forth, reading temperature data from the socket (via electronics, thermocouples, or current and voltage characteristics), real time feedback to a power supply of voltage and current usage to allow for immediate modification of drive current or voltage, and addressing a resistive load at the module to allow for slight modifications to affect drive current. Furthermore, even though only two additional wires are depicted inFIG. 6, it is contemplated that many more wires can be added to allow for the communication of information between the LEDs and the wires.

A light engine10that has a parallel and series electrical configuration has been described. The conditioning electronics20allow DC power to run the LEDs14, allowing for a less complicated design. Furthermore, due to the electrical configuration, current limiting resistors are not required in the light engine. Also, by connecting some of the LEDs in series, the amount of current required to drive the light engine can be lessened.

The light engine has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. As just one example, the light engine was described with particular reference to LEDs; however, as indicated above, the light source can be any conventional light source, including incandescent bulbs. It is intended that the light engine be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.