LED matrix operation when the power supply voltage is less than the total forward voltage of the LEDs

Abstract

The lighting unit includes a power supply that provides a maximum voltage and multiple LED lighting circuits. Each of the LED lighting circuits includes an LED string, multiple switches, a switching sequencer, and a switch controller. The LED string includes multiple series-connected emitters with a total forward voltage that exceeds the maximum voltage of the power supply. Each of the switches is coupled in parallel with a respective LED of the LED string. The switching sequencer provides a sequence of switching patterns such that the total forward voltage of simultaneously active LEDs in each switching pattern does not exceed the maximum voltage of the power supply. The switch controller operates the switches according to each of the switching patterns in the sequence. The LED strings of each of the multiple LED lighting circuits are arranged in a two-dimensional array.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims the interests of U.S. Provisional Patent Application No. 63 / 025,638, filed on 15 May 2020, and European Patent Application No. 20187189.4, filed on 22 July 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] In light-emitting diode (LED) lighting circuits, a DC power supply can be used to drive a string of LEDs connected in series. The power supply may be implemented as a current source to supply a desired current. The voltage of the power supply may be regulated to the total forward voltage of the LEDs in the string. In other words, the power supply or current source may drive all the LEDs simultaneously. [Overview of the Initiative]

[0003] The lighting unit includes a power supply providing the maximum voltage and multiple LED lighting circuits. Each LED lighting circuit includes an LED string, multiple switches, a switching sequencer, and a switch controller. The LED string includes multiple series-connected emitters with a total forward voltage exceeding the maximum voltage of the power supply. Each switch is coupled in parallel with each LED in the LED string. The switching sequencer provides a sequence of switching patterns such that the total forward voltage of the simultaneously active LEDs in each switching pattern does not exceed the maximum voltage of the power supply. The switch controller acts on the switches according to each of the switching patterns in the sequence. The LED strings of each of the multiple LED lighting circuits are arranged in a two-dimensional array. [Brief explanation of the drawing]

[0004] A more detailed understanding can be obtained from the following explanation, which is provided as an example along with the attached drawings.

[0005] [Figure 1] This is a block diagram of an example LED lighting circuit.

[0006] [Figure 2] This is a timing diagram illustrating an exemplary pulse-width modulation (PWM) switching sequence.

[0007] [Figure 3] This is an illustrative graph showing the relative light intensity of the LEDs in the string in Figure 1 when driven using the sequence in Figure 2.

[0008] [Figure 4] Figure 1 is a block diagram of an exemplary lighting unit including several LED lighting circuits.

[0009] [Figure 5] Figures 1 and 4 are top views of an exemplary LED array that can be used in LED lighting circuits, such as the LED lighting circuits shown in Figures 1 and 4.

[0010] [Figure 6] This diagram shows an LED lighting circuit that does not include the elements of the embodiments in Figures 1-4 and requires all LEDs in the string to be turned on simultaneously.

[0011] [Figure 7] This is a flowchart illustrating an example method for operating an LED lighting circuit.

[0012] [Figure 8] This is a diagram illustrating an example vehicle headlamp system.

[0013] [Figure 9] This is a diagram illustrating another example of a vehicle headlamp system. [Modes for carrying out the invention]

[0014] Examples of different lighting systems and / or implementations of light-emitting diodes (“LEDs”) are described in more detail below with reference to the accompanying drawings. These examples are not mutually exclusive, and features found in one example can be combined with features found in one or more other examples to achieve additional implementations. Thus, it will be understood that the examples shown in the accompanying drawings are provided for illustrative purposes only and are not intended to limit the disclosure in any way. Like numbers refer to like elements throughout.

[0015] In this specification, terms such as first, second, third, etc. may be used to describe various elements, but it is understood that these elements should not be limited by these terms. These terms can be used to distinguish one element from another. For example, without departing from the scope of the present invention, a first element may be named a second element, and a second element may be named a first element. As used herein, the term “and / or” can include any and all combinations of one or more of the associated listed items.

[0016] When an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it is understood that it is either directly on the other element, or directly extends onto the other element, or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there may be no intervening elements. Also, when an element is referred to as being “connected to” or “coupled to” another element, it is understood that the element can be directly connected or coupled to the other element and / or connected or coupled to the other element through one or more intervening elements. In contrast, when an element is referred to as being “directly connected to” or “directly coupled to” another element, there are no intervening elements between the element and the other element. It is understood that these terms are intended to include different orientations of the element in addition to the orientation shown in the figures.

[0017] In this specification, relative terms such as "below", "above", "upper", "lower", "horizontal", or "vertical" may be used to describe the relationship between one element, layer, or region and another element, layer, or region as shown in the figures. It is understood that these terms are intended to include different orientations of the device in addition to the orientation shown in the figures.

[0018] Some lighting applications, such as automotive lighting applications, use LED strings for various purposes, such as adaptive front beams or matrix front beams. Due to safety standards, the maximum output voltage of the driver for such lighting circuits is typically limited to less than 60V with a margin defined by the vehicle manufacturer with respect to the vehicle ground. In such examples, the maximum available output voltage for the application may be 55V or lower. In the case of LED lighting applications, this limitation may impose constraints on the number of LEDs that can be included in the string, taking into account that the forward voltage of the LEDs can increase significantly at low temperatures. For example, if the total forward voltage of the LEDs is normally about 4V but rises to 4.5V in a low-temperature state, the total forward voltage of 12 such LEDs is already approaching the manufacturer's limit. If it is desired to use more than this number of LEDs, a second driver may be required, which can significantly increase the overall cost of the lighting application.

[0019] Embodiments described herein provide an LED lighting circuit including a power supply configured to provide a maximum voltage and an LED string including several series-connected LEDs. The total forward voltage of the LED string may exceed the maximum voltage of the power supply. The LED lighting circuit may also include a switch arrangement including several switches, each coupled in parallel with an LED in the LED string. The LED lighting circuit may also include a switching sequencer for providing a sequence of PWM switching patterns such that the total forward voltage of the simultaneously active LEDs in the switching pattern does not exceed the maximum voltage of the power supply. A switch controller may be configured to actuate the switches in the switch arrangement according to the switching pattern.

[0020] Accordingly, embodiments described herein may provide LED lighting circuits that enable a power supply to drive a larger number of LEDs. In other words, an LED lighting circuit may enable LEDs to have a total forward voltage exceeding the capacity of its driver. The LEDs can be driven so that not all LEDs in a string are ever turned on (lit) at the same time, and the total number of LEDs turned on at any one time does not exceed the maximum voltage of the power supply. Since the LEDs are switched so as not to exceed the capacity of the driver, an LED string can contain any number of LEDs. Furthermore, an LED string can also contain LEDs with higher maximum drive currents, for example.

[0021] Figure 1 is a block diagram of an exemplary LED lighting circuit 1. In the example shown in Figure 1, the LED lighting circuit 1 includes an LED string 1S having several LEDs 10 connected in series (for example, 14 LEDs 10 labeled #1 to #14 in the illustrated example). Each LED 10 has a forward voltage V f The LED lighting circuit 1 further applies a maximum voltage V across the entire LED string 1S. maxmay include a power supply 11 configured to provide. The power supply 11 may be, for example, a DC-DC converter. The number of LEDs 10 in the string 1S, if all the LEDs 10 are turned on simultaneously, the total forward voltage ΣV of the LEDs 10 in the string 1S f may be such a number that exceeds the maximum voltage V of the power supply max In the example shown in FIG. 1, assuming that the power supply 11 is configured to provide a maximum voltage V corresponding to 10·V f If all the LEDs 10 are turned on simultaneously, their total forward voltage 14·V max would exceed the maximum voltage V of the power supply 11 f The innermost two LEDs #7 and #8 may form the central group 1S_c. LEDs #1 to #6 may form the first outer LED group 1S_o1 starting from the string anode. LEDs #9 to #14 may form the second outer LED group 1S_o2 ending at the string cathode max would exceed.

[0022] In the example shown in FIG. 1, the LED lighting circuit 1 may further include several switches 10S, and each switch 10S may be electrically coupled in parallel with the LED 10 of the LED string 1S. Such a switch may sometimes be called a bypass switch as it serves to bypass the LEDs that are electrically coupled in parallel. However, those skilled in the art will recognize that other embodiments are possible without bypass switches such that these LEDs are always on when a particular LED is connected to the power supply

[0023] The switching sequencer 12 may provide a sequence of switching patterns P1,..., P14, which will be described in more detail below with reference to FIG. 2. The total forward voltage of the simultaneously active LEDs 10 in the switching patterns P1,..., P4 should not exceed the maximum voltage V of the power supply 11

[0024] max max should not exceed.

[0025] In the example shown in Figure 1, the LED lighting circuit 1 also includes a switch controller 13, which may be configured to actuate switches 10S selected according to switching patterns P1, ..., P14 by generating appropriate switch control signals. The switches 10S can be provided in the form of one or more integrated circuits (ICs), each containing a switch and a level shifter in a single package that can be mounted together with the LEDs on a common carrier or PCB. Such switching ICs may be commercially available, as is known to those skilled in the art.

[0026] In another example not shown in Figure 1, the LED string may have 20 LEDs #1 to #20 in series in anode-to-cathode order. In this example, LEDs #9 to #12 may form a central group, LEDs #1 to #8 may form a first outer LED group, and LEDs #13 to #20 may form a second outer LED group. In this embodiment, the central LED group may have up to 1 / 4 of the total number of LEDs in the LED string. The LEDs in the central group may always be on or almost always on, while the LEDs in the outer groups may be driven so that they are never all on at the same time.

[0027] In some embodiments, the position of the central LED group may be dynamic. For example, a constantly illuminated hotspot or group of LEDs may shift its position within the string. Such dynamic hotspots may be useful in adaptive front lighting applications to direct light towards a curve in response to steering input when turning a corner or in a pre-emptive approach.

[0028] In the embodiment, hot spots, or groups of LEDs that are always on, can be driven on a 100% duty cycle or a smaller duty cycle, such as 90%, to conserve energy or protect the LEDs from overheating.

[0029] Figure 2 is a timing diagram showing an exemplary pulse-width modulation (PWM) switching sequence. In the example shown in Figure 2, the sequence includes a set of 14 patterns P1-P14, and the sequence can be repeated indefinitely. However, those skilled in the art will recognize that the sequence can include any number of patterns, and that patterns P1-P14 shown in Figure 2 are merely examples. Each row in the timing diagram corresponds to an LED in the string in Figure 1 and shows how the corresponding LED switches between on and off states. Each pattern P1, ..., P14 in the exemplary sequence can define the on / off state of the LEDs in the string. For example, in pattern P1, LEDs #1-#6 are off and all other LEDs are on. In pattern P3, LEDs #1-#10 are on and all other LEDs are off.

[0030] The timing diagram in Figure 2 also shows how the two innermost LEDs, #7 and #8, are always on. The different duty cycles of the LEDs in the outer LED groups 1S_o1 and 1S_o2 are also clearly shown in Figure 2. For example, LEDs #1 and #14 may each have only a 30% duty cycle, while LEDs #6 and #9 may each have a 90% duty cycle. As a result, the total forward voltage of the active LEDs in string 1S never exceeds the maximum value of the driver. For example, the total forward voltage of pattern P1_ΣV f is 8·V f On the other hand, the total forward voltage of pattern P9 is P9_ΣV f is 10·V f That is the case.

[0031] In some embodiments, the switching sequencer 12 in Figure 1 may be configured to compile a sequence of switching patterns in which the duty cycle of the LEDs in the outer LED group is shorter than the duty cycle of the LEDs in the central LED group. The LEDs in the outer LED group may all have, for example, a 50% duty cycle, and complementary pairs of LEDs in the outer LED group may be switched alternately such that only one LED in each such pair is on at a time. Alternatively, the switching sequencer 12 may be configured to compile a sequence of switching patterns in which the duty cycle of the outermost LED in the outer LED group is shorter than the duty cycle of the innermost LED in that outer LED group. In other words, the duty cycle of an LED may decrease as the distance from the center of the string increases. In some embodiments, the duty cycle of the outermost LED in the outer LED group may be up to 30%. In other embodiments, the duty cycle of the innermost LED in the outer LED group may be up to 90%. The duty cycle of the LEDs in the central LED group can be 100%, meaning that the central LED of the string can be on whenever the string is connected to a power source.

[0032] Figure 3 is an illustrative graph showing the relative light intensity of LED 10 in string 1S of Figure 1 when driven using the sequence of Figure 2. In the graph of Figure 3, each column corresponds to an LED in string 1S of Figure 1, as indicated by labels #1 through #14. If we consider the intensity of the two central LEDs #7 and #8 to be 1 or 100%, the relative intensity of the outermost LEDs #1 and #14 may be as low as 0.3 or 30%.

[0033] Figure 4 is a block diagram of an exemplary lighting unit including several LED lighting circuits 1 from Figure 1. In the example in Figure 4, five LED strings 1S of the lighting circuit are arranged in a two-dimensional array 40, and each string 1S contains 16 series-connected LEDs (shown as pixel squares in the array 40). The driver module 41 includes one driver 11 for each LED string 1S. Each driver operates under a limited voltage V max This can be supplied, which may be lower than the total forward voltage of string 1S, as shown in the drawing. Lighting unit 4 may have an advantage in that it can have a larger array size (i.e., more image pixels in the array) as long as the total number of LEDs in the string that are on at any given time does not exceed the maximum number that can be driven by the corresponding power supply.

[0034] The driver module 41 may include a single switching sequencer similar to the one described in Figure 1, but it can be configured to provide a switching pattern sequence to each of the LED strings 1S. The driver module 41 may also include a switch controller that can generate control signals for switching the LED strings 1S according to the switching pattern.

[0035] Increasing image size without changing driver size can be a crucial aspect for compact applications such as automotive signaling lamps. For example, modern vehicles are equipped with lighting units that can convey information to the vehicle owner and / or other road users. Increasing image size can improve the quality of the information that can be displayed. In some embodiments, the lighting unit may be an automotive adaptive front beam, an automotive daytime running light, or a non-automotive application such as an interior lighting application or a dynamic spot lighting application where dynamic control of LEDs is desired.

[0036] In some embodiments, the lighting unit may include multiple LED lighting circuits, and the LED string may be arranged in a two-dimensional array. Such embodiments can be used as a matrix light, where each LED functions as a pixel or emitter.

[0037] Figure 5 is a top view of an exemplary LED array 510 that may be used in LED lighting circuits, such as the LED lighting circuits in Figures 1 and 4. In the example shown in Figure 5, the LED array 510 is an array or matrix of emitters 511. LED arrays can be used in a variety of applications, including those requiring precise control of the LED array emitters. The emitters 511 of the LED array 510 may be individually addressable or may be addressable in groups / subsets.

[0038] An exploded view of a 3x3 section of the LED array 510 is also shown in Figure 5. As shown in the exploded view of the 3x3 section, the LED array 510 may include emitters 511, each having a width w1. In embodiments, the width w1 may be about 100 μm or less (e.g., 40 μm). The lanes 513 between the emitters 511 may have a width w2, and a width w2. In embodiments, the width w2 may be about 20 μm or less (e.g., 5 μm). The lanes 513 may provide an air gap between adjacent emitters or may include other materials. The distance d1 from the center of one emitter 511 to the center of an adjacent emitter 511 may be about 120 μm or less (e.g., 45 μm). It will be understood that the widths and distances provided herein are merely examples and actual widths and / or dimensions may vary.

[0039] While a rectangular emitter arranged in a symmetric matrix is ​​shown in Figure 5, it will be understood that emitters of any shape and arrangement can be applied to the embodiments described herein. For example, the LED array 510 in Figure 5 may include more than 20,000 emitters in any applicable arrangement, such as a 200 × 100 matrix, a symmetric matrix, or an asymmetric matrix. It will also be understood that multiple sets of emitters, matrices, and / or boards can be arranged in any applicable form to implement the embodiments described herein.

[0040] As mentioned above, LED arrays such as the LED Array 510 can contain up to 20,000 or more emitters. Such arrays are 90 mm². 2 They may have a surface area greater than or equal to that and may require considerable power to supply them, such as 60 watts or more. Such LED arrays may be called micro-LED arrays or simply micro-LEDs. A micro-LED may consist of an array of individual emitters provided on a substrate, or it may be a single silicon wafer or die divided into segments that form the emitters. The latter type of micro-LED may be called a monolithic LED.

[0041] Figure 6 is a diagram of an LED lighting circuit that does not include the elements of the embodiments in Figures 1-4 and requires that all LEDs in the string be turned on simultaneously. As described above, the usual method of controlling a string of series-connected LEDs generally involves a mode in which all LEDs in the string are turned on simultaneously. However, the maximum voltage of the driver cannot exceed a threshold defined by the manufacturer. In automotive applications that must function even in very cold conditions, the total forward voltage of 12 4V LEDs already approaches the upper limit of the 60V supply (after deducting the manufacturer's safety margin). Therefore, to drive the same number of LEDs as the LED lighting circuit in Figure 1, the LED lighting circuit shown in Figure 6 requires two drivers 11A and 11B, each capable of driving a string segment. Here, the circuit uses the first driver 11A for the first string 1SA with 12 LEDs #1-#12, and the second driver 11B for the second string 1SB with two additional LEDs #13 and #14. The elements of the switching circuit are connected accordingly, for example, with additional ICs for switching LEDs #13 and #14.

[0042] Figure 7 is a flowchart 700 of an exemplary method for operating a lighting unit, such as the lighting unit of Figure 4. In the example of Figure 7, a lighting unit may be provided (702). The lighting unit may be any of the lighting units described herein. For example, the lighting unit may include at least one power supply configured to provide a maximum voltage, a two-dimensional matrix of emitters, at least one group of two-dimensional emitters having a total forward voltage exceeding the maximum voltage of at least one power supply, a plurality of switches, each of which is coupled in parallel with each of the emitters, a switching sequencer, and at least one switch controller.

[0043] This method may also include obtaining a sequence of at least one switching pattern from at least one switching sequencer (704). In embodiments, the sequence of at least one switching pattern is such that the total forward voltage of the simultaneously active LEDs in each switching pattern does not exceed the maximum voltage of at least one power supply.

[0044] This method may also include applying a sequence of switching patterns to a switch controller (706). In an embodiment, the switch controller may actuate the switches according to each of the switching patterns in the sequence.

[0045] Figure 8 is a diagram of an exemplary vehicle headlamp system 800 that may incorporate one or more embodiments and examples described herein. The exemplary vehicle headlamp system 800 shown in Figure 8 includes a power line 802, a data bus 804, an input filter and protection module 806, a bus transceiver 808, a sensor module 810, an LED DC-DC (DC / DC) module 812, a logic low-dropout (LDO) module 814, a microcontroller 816, and an active headlamp 818. In embodiments, the active headlamp 818 may also be a signal lamp, which may be configured to implement multiple lighting functions simultaneously or at different times in combination with other components of the vehicle headlamp system 800 and / or external automotive components of the vehicle headlamp system 800, and in some embodiments may be used to ensure that various safety regulations can be met.

[0046] The power line 802 may have an input that receives power from the vehicle, and the data bus 804 may have inputs and outputs through which data can be exchanged between the vehicle and the vehicle headlamp system 800. For example, the vehicle headlamp system 800 may receive instructions from other locations within the vehicle, such as instructions to turn on the turn signaling or to turn on the headlamps, and may send feedback to other locations within the vehicle as needed. In embodiments, the active headlamp 818 may include one or more LED lighting circuits or lighting units, as described above with respect to Figures 1-4.

[0047] The sensor module 810 may be communicatively coupled to the data bus 804 and may provide additional data to the vehicle headlamp system 800 or other locations within the vehicle regarding, for example, environmental conditions (e.g., time of day, rain, fog, or ambient light level), vehicle status (e.g., parked, moving, speed, or direction of movement), and the presence / location of other objects (e.g., vehicles or pedestrians). The vehicle headlamp system 800 may include a headlamp controller separate from the vehicle controller communicatively coupled to the vehicle data bus. In Figure 8, the headlamp controller may be a microcontroller such as a microcontroller (μc) 816. The microcontroller 816 may be communicatively coupled to the data bus 804.

[0048] The input filter and protection module 806 may be electrically coupled to the power line 802 and may support various filters, for example, to reduce conducted emissions and provide power immunity. Additionally, the input filter and protection module 806 may provide electrostatic discharge (ESD) protection, load dump protection, alternator field decay protection, and / or reverse polarity protection.

[0049] The LED DC / DC module 812 may be coupled between the input filter and protection module 806 and the active headlamp 818 to receive filtered power and supply drive current to power the LEDs in the LED array of the active headlamp 718. The LED DC / DC module 812 may have an input voltage between 7 and 18 volts with a nominal voltage of about 13.2 volts and an output voltage slightly higher (e.g., 0.3 volts) than the maximum voltage of the LED array (determined, e.g., by coefficient or local calibration and adjustment of operating conditions due to load, temperature or other factors).

[0050] The logic LDO module 814 may be coupled to the input filter and protection module 806 to receive filtered power. The logic LDO module 814 may also be coupled to the microcontroller 816 and / or active headlamp 818 to power electronics within the microcontroller 816 and / or active headlamp 818, such as CMOS logic.

[0051] The bus transceiver 808 may have, for example, a Universal Asynchronous Receiver Transmitter (UART) or Serial Peripheral Interface (SPI) interface and may be coupled to the microcontroller 816. The microcontroller 816 may convert vehicle inputs based on, or including, data from the sensor module 810. The converted vehicle inputs may include video signals that can be transferred to an image buffer in the active headlamp 818. Furthermore, the microcontroller 816 may load a default image frame and test open / short pixels during startup. In embodiments, the SPI interface may load a CMOS image buffer. The image frame may be a full frame, a differential frame, or a partial frame. Other functions of the microcontroller 816 may include control interface monitoring of CMOS conditions, including die temperature, as well as logic LDO outputs. In embodiments, LED DC / DC outputs may be dynamically controlled to minimize headroom. In addition to providing image frame data, other headlamp functions may also be controlled, such as complementary use in combination with side markers or turn signal lights, and / or activation of daytime running lights.

[0052] Figure 9 shows another exemplary vehicle headlamp system 900. The exemplary vehicle headlamp system 900 shown in Figure 9 includes an application platform 902, two LED lighting systems 906 and 908, and secondary optics 910 and 912.

[0053] The LED lighting system 908 may emit a light beam 914 (shown between arrows 914a and 914b in Figure 9). The LED lighting system 906 may emit a light beam 916 (shown between arrows 916a and 916b in Figure 9). In the embodiment shown in Figure 9, a secondary optical system 910 is adjacent to the LED lighting system 908, and light emitted from the LED lighting system 908 passes through the secondary optical system 910. Similarly, a secondary optical system 912 is adjacent to the LED lighting system 906, and light emitted from the LED lighting system 906 passes through the secondary optical system 912. In an alternative embodiment, the vehicle's headlamp system does not have secondary optical systems 910 / 912.

[0054] The application platform 902 may provide power and / or data to the LED lighting systems 906 and / or 908 via line 904, which may include one or more of the power line 802 and data bus 804 in Figure 8. One or more sensors (sensors in the vehicle headlamp system 900 or other additional sensors) may be located inside or outside the housing of the application platform 902. Alternatively or additionally, as shown in the exemplary vehicle headlamp system 800 in Figure 8, each LED lighting system 908 and 906 may include its own sensor module, connection and control module, power module, and / or LED array.

[0055] In an embodiment, the vehicle headlamp system 900 may represent an automobile with a steerable light beam that can selectively activate LEDs to provide steerable light. For example, an array of LEDs or emitters may be used to define or project a shape or pattern or to illuminate only a selected section of a road. In one exemplary embodiment, infrared cameras or detector pixels in the LED lighting systems 906 and 908 may be sensors (for example, similar to the sensors in sensor module 810 in Figure 8) that identify the portion of a scene (e.g., a road or crosswalk) that requires illumination.

[0056] Although embodiments have been described in detail, those skilled in the art will understand, in consideration of this description, that modifications can be made to the embodiments described herein without departing from the spirit of the concept of the present invention. Therefore, the scope of the present invention is not intended to be limited to the specific embodiments illustrated and described.

Claims

1. Multiple LED lighting circuits, where each LED lighting circuit is: A power supply configured to provide the maximum voltage; An LED string having a plurality of series-connected LEDs having a total forward voltage exceeding the maximum voltage of the power supply; A plurality of switches, each of which is connected in parallel to each LED of the LED string; A switching sequencer configured to provide a sequence of switching patterns such that the total forward voltage of the simultaneously active LEDs of each switching pattern does not exceed the maximum voltage of the power supply; A switch controller configured to operate the switches according to each of the switching patterns in the sequence; It has multiple LED lighting circuits, Each of the LED strings in the plurality of LED lighting circuits is arranged in a two-dimensional array. Each of the plurality of series-connected LEDs in the LED string includes a central LED group between two outer LED groups, the number of LEDs in the central LED group is less than the number of LEDs in each of the two outer LED groups, the LEDs in the central LED group are always on, and the position of the central LED group can be shifted within the LED string. Lighting unit.

2. Each of the plurality of LED lighting circuits has its own driver, each driver has the power supply, the switching sequencer, and the switch controller, the power supply is configured to supply a maximum voltage to the corresponding LED lighting circuit, the switching sequencer is configured to provide a sequence of switching patterns for the corresponding LED lighting circuit, and the switch controller is configured to activate the switches of the corresponding LED lighting circuit based on the provided sequence of switching patterns. The lighting unit according to claim 1.

3. The outer LED group has equal length. The lighting unit according to claim 1.

4. One of the outer LED groups begins at the anode of the LED string, and the other of the outer LED group ends at the cathode of the LED string. The lighting unit according to claim 1.

5. The central LED group includes up to 25% of the total number of LEDs in the LED string. The lighting unit according to claim 1.

6. The switching sequencer is configured to store a sequence of switching patterns in which the duty cycle of the LEDs in the outer LED group is shorter than the duty cycle of the LEDs in the central LED group. The lighting unit according to claim 1.

7. The switching sequencer is configured to accumulate a sequence of switching patterns in which the duty cycle of the outermost LED in the outer LED group is shorter than the duty cycle of the innermost LED in the outer LED group. The lighting unit according to claim 1.

8. A method for operating a lighting unit, the method being: A step of providing a lighting unit, wherein the lighting unit is: At least one power supply configured to supply the maximum voltage; A two-dimensional matrix of emitters having multiple emitter strings, each of which has multiple series-connected emitters having a total forward voltage exceeding the maximum voltage of at least one power supply; A plurality of switches, each of which is coupled in parallel to one of the emitters; With at least one switching sequencer; Having at least one switch controller; Step and; A step of obtaining a sequence of at least one switching pattern from the at least one switching sequencer, wherein the sequence of at least one switching pattern is such that the sum of the forward voltages of the simultaneous active emitters of each switching pattern does not exceed the maximum voltage of the at least one power supply; The steps include: applying the sequence of switching patterns to the switch controller so as to actuate the switch according to each of the switching patterns in the sequence of at least one switching pattern; Each of the emitter strings of the plurality of series-connected emitters includes a central emitter group between two outer emitter groups, the number of emitters in the central emitter group is less than the number of emitters in each of the two outer emitter groups, the emitters in the central emitter group are always on, and the position of the central emitter group can be shifted within the emitter string. method.

9. The step described above involves ensuring that the duty cycle of the emitters in the outer emitter group is shorter than the duty cycle of the emitters in the central emitter group. The method according to claim 8.

10. The duty cycle of the outermost emitter in the outer emitter group is shorter than the duty cycle of the innermost emitter in the outer emitter group. The method according to claim 8.

11. The duty cycle of the outermost emitter in the aforementioned outer emitter group is a maximum of 30%. The method according to claim 8.

12. The duty cycle of the innermost emitter in the outer emitter group is at least 60%. The method according to claim 8.

13. The duty cycle of the emitter decreases as the distance from the center of the emitter string increases. The method according to claim 8.

14. A power supply configured to provide the maximum voltage; A two-dimensional matrix of emitters having a plurality of emitters connected in series having a total forward voltage exceeding the maximum voltage of the power supply; A plurality of switches, each of which is coupled in parallel to each emitter or each group of emitters in the two-dimensional matrix of emitters; A switching sequencer configured to provide a sequence of switching patterns such that the sum of the forward voltages of the simultaneous active emitters of each switching pattern does not exceed the maximum voltage of the power supply; A switch controller configured to operate the switches according to each of the switching patterns in the sequence; The emitters in the two-dimensional matrix of emitters include at least one central emitter group between two outer emitter groups, the number of emitters in the central emitter group is less than the number of emitters in each of the two outer emitter groups, the emitters in the central emitter group are always on, and the position of the central emitter group can be shifted within the two-dimensional matrix of emitters. Lighting unit.

15. The lighting unit further has a driver, the driver having a single switching sequencer for all of the emitters in a two-dimensional matrix of emitters and a single switch controller, The lighting unit according to claim 14.

16. The lighting unit further has one driver for each of the multiple series emitter strings in the two-dimensional matrix of emitters, and each driver has a switching sequencer and a switch controller for the corresponding series emitter string. The lighting unit according to claim 14.

17. The outer emitter groups are of equal length. The lighting unit according to claim 14.

18. The switching sequencer is configured to accumulate a sequence of switching patterns in which the duty cycle of the emitters in the outer emitter group is shorter than the duty cycle of the emitters in at least one central emitter group. The lighting unit according to claim 14.

19. The switching sequencer is configured to accumulate a sequence of switching patterns in which the duty cycle of the outermost emitter in the outer emitter group is shorter than the duty cycle of the innermost emitter in the outer emitter group. The lighting unit according to claim 14.

20. At least one of the duty cycles of the outermost emitter in the outer emitter group is at most 30%, or the duty cycle of the innermost emitter in the outer emitter group is at least 60%. The lighting unit according to claim 14.