Patent number 8648537 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates generally to LED-based lighting units, and more particularly to methods and apparatus for driving a plurality of LED-based lighting units in a combination of series or parallel connection.
"Light emitting diodes (LEDs) are semiconductor-based light sources often employed in low-power instrumentation and appliance applications for indication purposes. The application of LEDs in various lighting units has become more and more popular. For example, high brightness LEDs have been widely used for traffic lights, vehicle indicating lights, and braking lights.
"An LED has an I-V characteristic curve similar to an ordinary diode. When the voltage applied to the LED is less than a forward voltage, only very small current flows through the LED. When the voltage exceeds the forward voltage, the current increases sharply. The output luminous intensity of an LED light is approximately proportional to the LED current for most operating values of the LED current except for the high current value. A typical driving device for an LED light is designed to provide a constant current for stabilizing light emitted from the LED and extending the life of the LED.
"In order to increase the brightness of an LED light, a number of LEDs are usually connected in series to form an LED-based lighting unit and a number of LED-based lighting units may further be connected in series to form a lighting apparatus. For example, U.S. Pat. No. 6,777,891 discloses a plurality of LED-based lighting units as a computer-controllable light string with each lighting unit forming an individually-controllable node of the light string.
"The operating voltage required by each lighting unit typically is related to the forward voltage of the LEDs in each lighting unit, how many LEDs are employed for each of the lighting unit and how they are interconnected, and how the respective lighting units are organized to receive power from a power source. Accordingly, in many applications, some type of voltage conversion device is required in order to provide a generally lower operating voltage to one or more LED-based lighting units from more commonly available higher power supply voltages. The need of a voltage conversion device reduces the efficiency, costs more and also makes it difficult to miniaturize an LED-based lighting device.
"U.S. Pat. No. 7,781,979 provides an apparatus for controlling series-connected LEDs. Two or more LEDs are connected in series. A series current flows through the LEDs when an operating voltage is applied. One or more controllable current paths are connected in parallel with at least an LED for partially diverting the series current around the LED. The apparatus permits the use of operating voltages such as 120V AC or 240V AC without requiring a voltage conversion device.
"As more and more LED-based lighting units are used in high brightness lighting equipment, there is a strong need to design methods and apparatus that can drive and connect the LED-based lighting units intelligently and efficiently to increase the utilization of the LEDs and provide stable and high brightness by using the readily available AC source from a wall power unit. In addition, it is also highly desirable to provide many different lighting modes for the connected LED-based lighting units so that the brightness can be controlled properly according to different lighting requirements or the variation of the voltage level of the AC source."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "The present invention has been made to meet the above mentioned needs in the application of LED-based lighting units. A primary object of the present invention is to provide an apparatus that can flexibly connect a plurality of LED-based lighting units in such a way that each of the LED-based lighting units may be connected in series or in parallel with its neighboring LED-based lighting unit, or by-passed.
"Accordingly, the apparatus of the present invention comprises a plurality of LED-based lighting units interleaved with a plurality of switching units controlled by a controller. Each switching unit is connected with a leading LED-based lighting unit and a trailing LED-based lighting unit. The switching unit can be configured to connect the two LED-based lighting units in parallel or in series, or to bypass the leading LED-based lighting unit. An input voltage supply is connected to the first LED-based lighting unit to supply power to the apparatus and a current control device connects the last LED-based lighting unit to ground.
"In a preferred embodiment of the present invention, each switching unit comprises a first parallel connection switch for connecting two respective positive terminals of the leading and trailing LED-based lighting units, and a second parallel connection switch for connecting two respective negative terminals of the leading and trailing LED-based lighting units. In addition, each switching unit further comprises a series connection switch for connecting the negative terminal of the leading lighting unit to the positive terminal of the trailing lighting unit.
"Another object of the present invention is to provide an apparatus for controlling the connection of the plurality of LED-based lighting units according to the voltage level of the input voltage supply or the voltage level across the current control device, or the voltage levels of both of them. In the preferred embodiments of the present invention, the current control device may be a current sensing resistor or a variable current source.
"According to one preferred embodiment of the invention, all the plurality of LED-based lighting units are connected in series when the input voltage supply is at a maximum voltage level, and all the plurality of LED-based lighting units are connected in parallel when the input voltage supply is at a minimum voltage level. As the voltage level of the input voltage supply decreases, the number of LED-based lighting units connected in parallel increases, and vice versa.
"It is also an object of the present invention to provide various methods for driving the LED-based lighting units in order to provide multiple lighting modes by connecting some of the LED-based lighting units in series and some of the LED-based lighting units in parallel or by-passing some of the LED-based lighting units. Five examples of driving methods each providing multiple lighting modes in a different way are provided for the controller to control the plurality of switching units."
URL and more information on this patent, see: Chu, Hung-Chi. Methods and Apparatus for Driving LED-Based Lighting Units. U.S. Patent Number 8648537, filed
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