Patent Application
20120176035
Light emitting diodes (“LEDs”) are widely used in a variety of sign, message board, and light source applications. The relatively high efficacy of LEDs (in lumens per watt) is typically the primary reason for their use. Large power savings are possible when LED signals are used to replace traditional incandescent signals of similar luminous output.
It is desirable to have uniform LED junction temperature on the LEDS along the light string, particularly for a relative long string (e.g., lengths over 3 meters or more) of LEDs. This can be advantageous for several reasons. First the life of an LED is inversely related to junction temperature. Secondly, light output degradation is related to junction temperature. For two LEDs driven at like power levels, the LED with the lower junction temperature will emit higher levels of light output measured in lumens.
LEDs being semi-conductor devices, contain a property know as forward voltage bias required to turn the LED on. These bias voltages sum for LEDs in series along the cable which dictates the drive voltage required to power the string. In order to maintain a reasonable operating voltage, 24 volts or less, the LEDs are arranged in series parallel groups along the length of the light string.
Optimum thermal and lumen output occurs when the voltage drop across each parallel group is equivalent. A flat cable, for example, having electrical conductors has inherent resistances which will result in parasitic voltage losses along the run of the LED string, with the LED groups at the end of the cable nearer to the power supply experiencing higher voltages and the LED groups at the far end of the LED string experiencing lower voltages. The result being that the earlier LEDs experience greater then the design intent voltages and thus heating and reduced life and lumen output, and the LEDs at the far end of the string experiencing lower then design intend voltage and resulting reduced lumen output.
In one aspect, the present disclosure describes a lighting assembly comprising:
Optionally, the first electrical group further comprises a second (one, two, three, four, five, sixth, seven, eight, nine, ten, or more) additional light emitting diode(s) electrically connected sequentially in series between the first light emitting diode and the control circuit of the first electrical group, wherein the second electrical group further comprises a second (one, two, three, four, five, sixth, seven, eight, nine, ten, or more) additional light emitting diode(s) electrically connected sequentially in series between the first light emitting diode and the control circuit of the second electrical group, and wherein when the light assembly is energized, the light emitting diodes exhibit draw the same level of power.
Optionally, the lighting assembly further comprises additional (i.e., one, two, three, four, five, sixth, seven, eight, nine, ten, or more) electrical groups as described for the second electrical group, which may include an additional light emitting diode(s) (i.e., one, two, three, four, five, sixth, seven, eight, nine, ten, or more) as described above.
In this application:
“Flexible” means the lighting assembly or cable, as applicable, can be wrapper around a 5 mm diameter rod without breaking or damaging the lighting function of the lighting assembly or cable, as applicable.
In some embodiments, and typically desirably, the light emitting diodes, when energized have a uniform lumens output. In some embodiments, lighting assemblies described herein have a total power usage of up to 1 watt, 0.75 watt, or even 0.5 watt, wherein lower wattages are typically more desirable.
Light assemblies described herein are useful, for example, in vehicles (e.g., automobile, trucks, etc.), as well as, task lighting accent lighting, merchandise display lighting, and back lighting applications. Useful embodiments of light assemblies described herein for vehicles include as a brake center light.
Referring to
Further,
Suitable flexible cables are known in the art, and include those marketed by Parlex USA, Methuen; Leoni AG, Nuremburg, Germany; and Axon' Cable S.A.S., Montmirail, France.
Exemplary widths of the electrical cable range from 10 mm to 30 mm. Exemplary thicknesses of the electrical cable range from 0.4 mm to 0.7 mm.
Suitable light emitting diodes are known in the art, and commercially available. LEDs are available in a variety of power usage ratings, including those ranging from less than 0.1 to 5 watts (e.g., power usage ratings up to 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 4, or even up to 5 watts) per LED. LEDs are available in colors ranging range from violet (about 410 nm) to deep red (about 700 nm). A variety of LED colors are available, including white, blue, green, red, amber, etc.
In some embodiments of light assemblies described herein, the distance between LEDs may be at least 50 mm, 100 mm, 150 mm, 200 mm, or even at least 250 mm or more.
In some embodiments of light assemblies described herein have at least 2, 3, 4, or even at least 5, light emitting diodes per length of, for example, 300 mm.
Suitable resistors are known in the art, and are typically current sense resistors, which generally less than 10 ohms.
A control circuit regulates the current to the LED(s) preceding it, and well as provides power to any subsequent LED(s) in the circuit. Typically, the control circuit(s) includes an associated sense resistor for current level selection. In some embodiments, the control circuit(s) include a temperature monitoring function (e.g., the control circuit(s) include an LED current regulator, a trim potentiometer, and a resistor to set the thermal monitor threshold where the output current starts to be reduced with increasing temperature. Control circuits can be made by one skilled in the art usually conventional circuitry components and techniques.
In some embodiments of light assemblies described herein have at least 3, 4, or even at least 5, light emitting diodes per length of, for example, 300 mm.
Suitable light assembly configurations can be designed and assembled using known techniques by one skilled in the art after reviewing the instant disclosure.
Preferably, the circuit board with control circuit and the flat flexible cable are electrically connected via an electrical connection protrusion(s) (e.g., a solder bump(s)), including an electrical connection protrusion made of a first metal composition having a first melting point, having an exposed outer surface, and being present on the circuit board, and a second metal composition having a second melting point, lower than the first melting point, being disposed around the remaining exposed outer surface of the protrusion, wherein there is a distinct line of demarcation between the protrusion and the second metal composition.
One skilled in the art can select the appropriate first and second metal compositions (typically solders) having the desired melting and flow characteristics.
The circuit board with control circuit and the flat flexible cable can be electrically connected via electrical connection protrusion (s) (e.g., solder bump(s)), for example, by providing a circuit board having an electrical connection protrusion(s) made of a first metal composition having a first melting point and an exposed outer surface; providing a flat flex cable with an electrical contact; placing the electrical contact in direct contact with a portion of the outer exposed surface of the protrusion(s), leaving a remaining outer exposed surface of the protrusion(s); providing a second solder composition having a second melting point, lower than the first melting point; heating the second solder composition to provide a melt that is disposed around the remaining exposed outer surface of the protrusion(s) without melting the first metal composition; and cooling the melt disposed around the remaining exposed outer surface of the protrusion(s).
It may be desirable for some applications to linearly connect, in electrically series, 2, 3, 4, 5, or more light assemblies as described herein to provide light over long distances.
Light assemblies described herein are useful, for example, in vehicles (e.g., automobile, trucks, etc.), as well as, task lighting accent lighting, merchandise display lighting, and back lighting applications. Useful embodiments of light assemblies described herein for vehicles include as a brake center light.
Advantages and embodiments of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated.
A lighting assembly was constructed as generally shown in
A Class IV CO2 laser was used to make cut-outs and remove insulation from the flat flexible cable, and thereby facilitating proper electrical contact for the resistors, LEDs and control circuits. A series of three electrically parallel groups of LEDs and control circuits were surface mounted onto the cable and electrically connected to the conductor below via the cut-outs. Each group consisted of four LED's (obtained under the trade designation “LCW W5AM” from Osram-Sylvania, Danvers, Mass.) followed by a control circuit. The control circuit consisted of the following components: an LED current regulator (obtained under the trade designation “A6260” from Allegro Microsystems, Worcester, Mass.), an associated sense resistor (obtained under the trade designation “0805”) for current level selection, a trim potentiometer, and a resistor to set the thermal monitor threshold where the output current starts to be reduced with increasing temperature.
The components were mounted onto a FR4 copper circuit board with 2 ounce copper. A maximum copper etch was utilized. The LEDs and control circuits were hand soldered to the cable using a conventional tin-lead solder paste. The circuit board with the control circuits and the flat flexible cable were electrically connected via solder bumps. Four tin-silver-copper solder bumps (1.3 mm (0.05 inch) diameter, 0.64 mm (0.025 inch) height) made of solder obtained under the trade designation “NC254” from Aim Solder, Cranston, R.I.) were provided on the control circuits. These solder bumps had exposed outer surfaces. The electrical contacts of the flat flex cable were placed in direct contact with a portion of the respective outer exposed surfaces of the solder bumps, leaving a remaining outer exposed surface of the solder bump. A second, bismuth-tin solder (made of solder obtained under the trade designation “INDALLOY #281” from Indium Corporation of America, Utica, N.Y.) was heated to provide a melt that was disposed around the remaining exposed outer surface of the solder bump without melting the first solder, and then cooled.
The first group was constructed with a schottky diode (obtained under the trade designation “MBRS360T3G” from ON Semiconductor, Phoenix, Ariz.) positioned to bridge the outer conductor (power supply) and the center conductor of the cable. The first LED within a group was positioned with its anode electrically connected to the schottky diode. The second, third and fourth LEDs were positioned with their anodes biased to the higher potential. The control circuit was positioned on the cable such that it was electrically connected to the cathode of the fourth LED. The control circuit regulates the current in a group and provides the power connection (bridge) from the power conductor to the anode of the first LED in the next group via the center conductor, and bridged from the center conductor and the outer conductor (ground potential).
The spacing between the first resistor and first LED in the first group was about 100 mm. The spacing between each LED within a group was about 110 mm. The spacing between the last LED in the group and the control circuit was about 60 mm. The spacing between the control circuit and the first LED in the next group was about 100 mm. An additional cut-out was made through the center conductor using a conventional punch tool in a hand operated press, in between each group to interrupt electrical current flow and provide series-parallel electrical circuits in the flat flexible cable. To provide power to the lighting assembly, one of the outer conductors was connected to a positive power supply potential and the other outer conductor being connected to a ground potential.
The lighting assembly was tested for power uniformity. A 15 volt laboratory power supply was connected to the light assembly. The lighting assembly was allowed to stabilize for 30 minutes after start-up. A copper (22 AWG) wire, about 70 mm in length, was used to jump from the control circuit board cathode connection to the cathodes of the fourth LED in the groups. The jumper wire was constructed so as to provide a separable connection via wire terminals. A multi-meter (obtained from Fluke, Everett, Wash.) was connected in series between the cathode of the fourth LED and the control circuit board in the first group to measure current flow. The current reading was 306 milliamperes. The jumper for the first group was re-connected and the multi-meter was then connected in series between the cathode of the fourth LED and the control circuit board in the second group to measure current flow. The current reading was 310 milliamperes. The jumper for the second group was re-connected and the multi-meter was then connected in series between the cathode of the fourth LED and the control circuit board in the third group to measure current flow. The current reading was 307 milliamperes. The percentile difference between the high and low current readings was 1.3% indicating a high level of current uniformity which directly leads to more uniform LED power, which resulted in more uniform lumen output among all the LEDs in the example lighting assembly.
Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2010/049970 | 9/23/2010 | WO | 00 | 3/21/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61245026 | Sep 2009 | US |
