Lighting device for a motor vehicle and method for operating a lighting device for a motor vehicle

Abstract

Lighting device (11) for a motor vehicle, comprising several light-emitting diode arrangements (19) with several light-emitting diodes (21), a voltage source (39) for generating an operating voltage (U) B ) for the at least one light-emitting diode arrangement (19) and at least one current source (41), wherein the current source (41) of the light-emitting diode arrangement (19) is assigned to generate an operating current (I1, I2, I3) of the light-emitting diode arrangement (19), wherein the lighting device (11) has a control arrangement (55) for controlling the operating voltage (U) B ) depending on a voltage (U1, U2, U3) applied to the power source (41), characterized in that controllable switching elements are provided in the light-emitting diode arrangements (19) with which individual light-emitting diodes (21) or individual series circuits of light-emitting diodes (21) of at least one light-emitting diode arrangement (19) can be switched on and off separately.

Description

Description

[0001] The invention relates to a lighting device for a motor vehicle according to the preamble of claim 1. Such a lighting device is known from DE 10 2006 037 342 A1.

[0002] A lighting device of the above-mentioned type is known from DE 100 27 478 A1. The lighting device has a plurality of light-emitting diode arrays, each light-emitting diode array comprising a plurality of light-emitting diodes. Each light-emitting diode array has a first and a second terminal for connecting a supply voltage. The first terminal of each light-emitting diode array is connected to a common voltage source designed as a pulse generator. Each light-emitting diode array is assigned a current source of the lighting device, the second terminal of each light-emitting diode array being connected to the current source assigned to that light-emitting diode array.

[0003] In order to guarantee reliable operation of the individual power sources in the known lighting device, it must be ensured that the voltage applied to the individual power sources does not fall below a minimum value. The voltage applied to the power sources depends essentially on the voltage applied to the corresponding LED array (chain voltage), which in turn depends on the temperature and component tolerances. In order to reliably prevent the voltage at the power sources from dropping below the minimum value, the operating voltage generated by the voltage source must be selected when designing the lighting device to be high enough that, even under unfavorable conditions, it never falls below the sum of the chain voltage of the LED array and the minimum value for the voltage at the power sources.Since these unfavorable conditions rarely occur during normal operation of the lighting system, the individual power sources often have a voltage significantly higher than the minimum value, resulting in relatively high power dissipation at the individual power sources. This results in the lighting system requiring relatively complex cooling, making it vulnerable and expensive to implement and requiring a lot of space.

[0004] Based on the described prior art, the object of the present invention is to create a possibility, on the one hand, to reduce the power loss of a lighting device of the type mentioned at the beginning and, on the other hand, to ensure simple and cost-effective production and a robust construction of the lighting device.

[0005] To achieve this object, based on the lighting device of the type mentioned above, it is proposed that controllable switching elements be provided in the LED arrays, with which individual LEDs or individual series circuits of LEDs of at least one LED array can be separately switched on and off. This ensures that, regardless of fluctuations in the chain voltage of the LED array and regardless of component tolerances, in particular of the LEDs, a voltage is always applied to the power source whose value is sufficiently high to ensure the function of the power source, while nevertheless not assuming excessively high values ​​that would lead to high power dissipation at the power source.An important aspect of the present invention is that the operating voltage generated by the voltage source is set as low as possible, but just high enough that the voltage applied to the power source has a sufficiently high value for the correct functioning of the power source.

[0006] Because the operating voltage is regulated as a function of the voltage applied to the power source, it is ensured that fluctuations in the chain voltage applied to the LED array, which can be caused by temperature fluctuations, for example, are compensated for by appropriate readjustment of the operating voltage. If the chain voltage increases, the operating voltage is increased accordingly so that a sufficiently high voltage is applied to the power source even at a high chain voltage. If the chain voltage drops, the control arrangement sets a relatively low operating voltage. This ensures that the voltage at the power source remains relatively low even at a low chain voltage. Consequently, regardless of the current value of the chain voltage, there is low power loss at the power source.This allows the use of cost-effective and compact power sources that do not require particularly complex measures for dissipating the power source's power loss, such as bulky and heavy heat sinks. Thermal stress on components of the lighting system is relatively low. The low power loss also results in low energy consumption of the lighting system and thus also in low load on the vehicle's electrical system. The invention can be used in conjunction with any lighting function of the lighting system—such as indicator lights, side marker lights, low beams, high beams, cornering lights, fog lights, or tail lights.

[0007] By means of the control or regulating arrangement provided in the lighting device according to the invention, not only can fluctuations that occur during operation of the lighting device be compensated, but also component tolerances, in particular of the LEDs in the LED array, can be compensated. Calibration of the operating voltage depending on the properties of the LEDs is not required. Such component tolerances can occur between individual LEDs within a manufactured lighting device; they can also result from changes in the LED production process, so that LED arrays manufactured at different times differ in their properties.

[0008] Depending on the design of the lighting device according to the invention, the light-emitting diode arrangement can form a light source of a motor vehicle lamp, in particular a daytime running lamp or a motor vehicle headlight. Particularly in the case where the lighting device comprises a daytime running lamp, the low energy consumption of the lighting device is particularly advantageous, since the daytime running lamp has a relatively high duty cycle compared to, for example, headlights or taillights.

[0009] The voltage source is expediently designed as an adjustable voltage source, wherein the operating voltage for the light-emitting diode arrangement can be adjusted by means of a control signal that characterizes a control variable.

[0010] It is particularly preferred that the lighting device comprises a plurality of LED arrays, each LED array being assigned a current source, and the control arrangement comprising a minimum value generator for forming a minimum value signal that characterizes a minimum value of the voltages applied to the individual current sources. Each LED array can have the same number of LEDs. However, it can also be provided that the LED arrays differ in the number of LEDs they contain.

[0011] The individual LED arrays and the power sources connected in series with them are thus connected in parallel. This parallel connection allows the lighting array to operate at a significantly lower operating voltage than would be the case with a series connection of the LED arrays. This allows a lighting array with a large number of LEDs or LED arrays to be implemented without the need for expensive components, especially connectors, for high voltages, which, for safety reasons, require protective measures to protect against contact.

[0012] The minimum value generator ensures that the lowest voltage applied to the individual power sources is always used to regulate the operating voltage. This ensures that, at various chain voltages, the operating voltage is sufficiently high that, on the one hand, no voltage applied to the individual power sources is too low for proper function of the power source, and, on the other hand, the operating voltage is not set to an unnecessarily high value.

[0013] Although preferably several LED arrays are provided, it is sufficient for the lighting device to have a common voltage source for all LED arrays. The lighting device according to the invention is thus particularly cost-effective.

[0014] In a preferred embodiment of the invention, the control arrangement comprises a subtractor for forming a control difference signal that characterizes a control difference between a predetermined minimum value and the voltage applied to the current source or the minimum value of the voltages applied to the individual current sources. This minimum value preferably corresponds to a minimum voltage for which the function of the current source is just still guaranteed.

[0015] If multiple LED arrays and thus multiple power sources are provided, and the individual LED arrays exhibit different chain voltages during operation of the lighting device, a voltage corresponding to the minimum value will be applied to the power source associated with the LED array exhibiting the highest chain voltage. Higher voltages will then be applied to the other power sources.

[0016] To achieve good control behavior of the control arrangement, it can be provided that the control arrangement has a control element, for example, a proportional controller, for determining a control signal for adjusting the operating voltage. In this case, it can be expediently provided that the control element has an output for outputting the control signal and the voltage source has an input for the control signal, with the output of the control element being connected to the input of the voltage source.

[0017] The voltage applied to the current sources can be detected or determined by any suitable means. However, it is preferred that a first terminal of the current source is connected to the light-emitting diode arrangement to which the current source is assigned, a potential common to at least some of the current sources, preferably a ground potential, is applied to a second terminal of the current source, and the control arrangement has at least one measuring element assigned to the current source for detecting an electrical potential applied to the first terminal of the current source. Since the current sources are connected to a common potential, in order to determine the voltage applied to the current sources, only the potential at the first terminal relative to the common potential needs to be measured.To determine the voltage applied to the current sources, only one measurement at a single point is required, namely at the first terminal of each current source. This allows for a simple and cost-effective design of the measuring elements. The shared potential also makes it comparatively easy to implement the minimum value generator, as it only needs to compare the potentials at the first terminal of each current source. Furthermore, the control arrangement can thus be easily implemented as a digital control arrangement, with an analog-to-digital converter arranged in the measuring element. Overall, this results in a particularly simple lighting device that can be implemented cost-effectively.

[0018] It can be provided that at least one of the current sources is an adjustable current source. If the operating current of at least one LED array changes by adjusting the adjustable current source, the lighting device according to the invention adjusts the operating voltage accordingly.

[0019] Furthermore, it can be provided that individual LEDs or individual series circuits of LEDs of at least one LED array can be switched on and off separately. This enables a gradual change in the luminous intensity of the light emitted by the lighting device.

[0020] As a further solution to the problem, a method for operating a lighting device for a motor vehicle is proposed, wherein the lighting device comprises at least one light-emitting diode arrangement with a plurality of light-emitting diodes, a voltage source for generating an operating voltage for the at least one light-emitting diode arrangement and at least one current source, and wherein the current source is assigned to the light-emitting diode arrangement for generating an operating current of the light-emitting diode arrangement, which is characterized in that the method comprises the following steps: detecting a voltage applied to the at least one current source and setting the operating voltage as a function of the voltage applied to the current source.When the method according to the invention is implemented, it is achieved that, regardless of fluctuations in the chain voltage of the light-emitting diode arrangement and regardless of component tolerances, in particular of the light-emitting diodes, a voltage is always applied to the current source whose value is sufficiently high to ensure the function of the current source, and yet does not assume excessively high values ​​that would lead to high power loss at the current source.

[0021] In this case, it can be provided that the lighting device has a plurality of LED arrays, each LED array being assigned a current source, and that a minimum value of the voltage applied to the current sources is determined, and the operating voltage is adjusted depending on the minimum value. This ensures safe and low-loss operation of a lighting device with a plurality of LED arrays, whereby no high voltages need to be generated and thus high-voltage components, in particular high-voltage connectors, can be avoided.

[0022] Preferably, a control difference is formed between a predetermined minimum value and the voltage applied to the power source or the minimum value of the voltages applied to the power sources. This ensures that the operating voltage is adjusted depending on the voltage applied to the power sources with the lowest value. This ensures that each power source operates reliably, even with different chain voltages of the individual LED arrays.

[0023] In order to provide a simple and reliable control, it is preferred that a manipulated variable for adjusting the operating voltage is formed as a function of the control difference, for example by multiplying the control difference by a constant control coefficient.

[0024] It can be provided that the operating current of at least one LED array is adjusted depending on a current setpoint. The current setpoint can be a variable value, for example, specified by a control device.

[0025] Furthermore, it can be provided that, in order to gradually change the luminous intensity of light emitted by the lighting device, at least one individual light-emitting diode of at least one light-emitting diode arrangement and / or at least one individual series connection of light-emitting diodes of at least one light-emitting diode arrangement are separately switched on or off.

[0026] As yet another solution to the problem, a control or regulating device for a lighting device for a motor vehicle is provided, which comprises at least one light-emitting diode arrangement with a plurality of light-emitting diodes, a voltage source for generating an operating voltage for the at least one light-emitting diode arrangement, and at least one current source, wherein the current source is assigned to the light-emitting diode arrangement for generating an operating current for the light-emitting diode arrangement, which is characterized in that the control or regulating device is programmed to execute a method according to the invention. The control or regulating device according to the invention has the advantages of the lighting arrangement according to the invention and the method according to the invention.

[0027] Further features and advantages of the invention will become apparent from the following description, in which exemplary embodiments are explained in more detail with reference to the drawings. In this schematic representation: Fig. 1 a lighting device for a motor vehicle; Fig. 2 a control or regulating device of the lighting device Fig. 1; and Fig. 3 a flowchart of a method for operating the lighting device from Fig. 1.

[0028] In Fig. 1, a lighting device for a motor vehicle is designated in its entirety by the reference numeral 11. It can be seen that the lighting device 11 has a control or regulating device 13 and a light source 15. In the embodiment shown, the light source 15 is arranged in a daytime running light 17. In addition to the light source 15, the daytime running light 17 has components for influencing the light emitted by the light source 15 during its operation, such as reflectors, prisms, or lenses (not shown). The light source 15 and the components for influencing the light emitted by the light source interact in such a way that the daytime running light 17 generates a light beam that complies with the legal requirements for daytime running lights, particularly with regard to contour and illuminance distribution and maxima.

[0029] In the embodiment shown, the light source 15 comprises three light-emitting diode arrays 19; however, in other embodiments of the invention, a different number of light-emitting diode arrays 19 can be provided. Although the invention is also applicable in connection with a light source 15 having only one light-emitting diode array 19, it is preferred that the light source 15 has a plurality of light-emitting diode arrays 19. Each light-emitting diode array 19 comprises a series circuit of three light-emitting diodes 21. Alternatively, a different number of light-emitting diodes 21 per light-emitting diode array 19 or a different interconnection of the light-emitting diodes 21 within the light-emitting diode array 19 can also be provided.In the embodiment shown, the LED arrays 19 of the light source 15 each have the same structure, in particular the same number of LEDs 21 and the same serial connection of the LEDs 21 to one another. However, light sources 15 can also be provided that comprise LED arrays 19 that differ from one another in their structure, in particular in the number of LEDs. Each LED array 19 has an anode terminal 23 that is connected to an anode of a first LED 21 (in . Fig. 1 the upper LED 21 of the LED array 19) of the series circuit of the LED array 19. In addition, each LED array 19 has a cathode terminal 25, which is connected to a cathode of a last LED 21 (in Fig. 1 the lower LED 21 of the LED array 19) of the series circuit is connected.

[0030] The anode terminals 23 of the individual LED arrays 19 of the light source 15 are interconnected and connected to an operating voltage output 27 of the control or regulating device 13. The control or regulating device 13 has a current source terminal 29 for each LED array 19, and the cathode terminal 25 of each LED array 19 is connected to exactly one current source terminal 29. This means that each LED array 19 is assigned to exactly one current source terminal 29.

[0031] The control or regulating device 13 also has a first vehicle electrical system connection 31 and a second vehicle electrical system connection 33. The first vehicle electrical system connection 31 is connected to a vehicle electrical system line 35 of a vehicle electrical system, and the second vehicle electrical system connection 33 is connected to a ground potential 37 of the vehicle electrical system.

[0032] The Fig. Figure 2 shows the control or regulating device 13 in more detail. It can be seen that the two on-board power supply connections 31, 33 of the control or regulating device 13 are connected to a voltage source 39 for generating an operating voltage U B, which can be adjusted by means of a control signal x. In the embodiment shown, the voltage source 39 is a switching regulator. However, the voltage source can also be implemented in a different way. An output of the voltage source 39 is connected to the operating voltage output 27 of the control or regulating device 13. A current source 41 is arranged between each current source connection 29 of the control or regulating device 13 and the second vehicle electrical system connection 33. The number of current sources 41 thus corresponds to the number of LED arrays 19, with exactly one current source 41 being assigned to each LED array 19. A first connection 43 of each current source 41 is connected to a measuring element 46 of a minimum value generator 47, and a second connection 45 of each current source 41 is connected to the second vehicle electrical system connection 33.The minimum value generator 47 is also connected to the second vehicle electrical system connection 33 and has an output for outputting a minimum value signal m, which is connected to a subtrahend input of a subtractor 49. A setpoint generator 51 for generating a setpoint signal s is connected to a minuend input of the subtractor 49. An output of the subtractor 49 is connected to an input for a control difference signal d of a control element 53, which can be designed, for example, as a proportional controller. An output of the control element 53 is connected to a control input of the voltage source 39. The minimum value generator 47, the subtractor 49, the setpoint generator 51, and the control element 53 form a control arrangement 55 of the control or regulating device 13.

[0033] When the lighting device 11 is in operation, a vehicle electrical system voltage U is present between the first vehicle electrical system connection 31 and the second vehicle electrical system connection 33. Bordof the vehicle's electrical system. The electrical system voltage U Bord is usually about 9 V to 18 V, typically 12 V. The voltage source 39 of the control or regulating device 13 generates the operating voltage U depending on the control signal x B between the operating voltage output 27 of the control or regulating device and the second vehicle electrical system connection 33, which is largely independent of fluctuations in the vehicle electrical system voltage U Bord The operating voltage U Bis applied to series circuits comprising the light-emitting diode array 19 and the current source 41 assigned to this light-emitting diode array. This results in an operating current I1, I2, I3 within each of these series circuits. The current sources 41 adjust the voltages U1, U2, U3 applied between their two terminals 43 and 45 such that the operating current I1, I2, I3 flowing through the light-emitting diode array 19 has a predetermined, constant value. The current sources 41 thereby compensate, in particular, for temperature-dependent fluctuations in the properties of the light-emitting diodes 21 of the light-emitting diode arrays 19 as well as for manufacturing tolerances of the light-emitting diodes 21.

[0034] The fluctuations or manufacturing tolerances lead to the fact that a chain voltage between the anode terminal 23 and the cathode terminal 25 of each light-emitting diode arrangement 19 at the predetermined constant current I1, I2, I3 is not constant or the same for all manufactured light-emitting diode arrangements 19, but depends on ambient conditions, such as the temperature or fluctuations in the manufacturing process of the light-emitting diodes 21.

[0035] The control arrangement 55 of the control or regulating device 13 provides the operating voltage U Bas low as possible in order to keep the power loss of the individual current sources 41 to a minimum. At the same time, the control arrangement 55 ensures that the voltages U1, U2, U3 applied to the individual current sources 41 between the first terminal 43 and the second terminal 45 do not fall below a minimum value required for the reliable operation of the current sources 41. For this purpose, the minimum value generator 47 detects the voltages U1, U2, U3 applied to the individual current sources 41 and determines a minimum value signal m, which characterizes a minimum value of the voltage U1, U2, U3 applied to the individual current sources 41.Since both the second terminal 45 of all current sources 41 and the minimum value generator 47 are connected to a common potential, namely the ground potential 37 present at the second vehicle electrical system terminal 33, it is sufficient to measure the potential at the first terminal 43 of each current source 41 using the measuring elements 46 and determine the minimum potential. Therefore, the potential at the second terminal 45 of each current source 41 does not need to be measured.

[0036] From the minimum value signal m, a control difference signal d is formed by means of the subtractor 49, in which the minimum value signal m is subtracted from the setpoint signal s generated by the setpoint generator 51. The setpoint signal s thus characterizes the minimum value for the voltages U1, U2, U3, and the control difference signal d characterizes the difference between the minimum value and the minimum value. The control difference signal d is fed to the control element 53, which determines the control signal x from the control difference signal d by multiplying the control difference signal d by a constant control coefficient (proportional control). Control element 53 can also perform other calculations to determine the control signal. The control signal x is fed to the voltage source 39. This provides the operating voltage U B depending on the control signal x, whereby a small value of the control signal x corresponds to a relatively small operating voltage U Band a large value of the control signal x of a relatively large operating voltage U B corresponds.

[0037] The control arrangement 55 is designed to carry out a Fig. 3 for operating the lighting device 11. In this method 61, after a start 63 of the method 61, a step 65 is carried out in which the voltages U1, U2, U3 present at the individual current sources 41 are recorded. Subsequently, in a step 67, a minimum value is formed from these voltages U1, U2, U3. The minimum value signal m characterizes this minimum value. In a step 69 following step 67, a control difference between a predetermined minimum value and the minimum value determined in step 67 is formed. The control difference signal d characterizes this minimum value. Subsequently, in a step 71, a manipulated variable, which is characterized by the control signal x, is used to adjust the operating voltage U BThe manipulated variable can be calculated by multiplying the control difference by a constant control coefficient (proportional control). However, other control methods can also be used. Subsequently, in step 73, the operating voltage U B depending on the manipulated variable. The procedure can be as described in Fig. 3, are executed in an endless loop, so that a change in a chain voltage or a resulting change in the voltage U1, U2, U3 at the current sources 41 leads to a suitable adjustment of the operating voltage U B leads.

[0038] In an embodiment of the lighting device (not shown), the current sources 41 are adjustable depending on a variable current setpoint. The current setpoint can be specified, for example, by a control device of a motor vehicle. If the current setpoint of one of the current sources is changed during operation of the lighting device, then, as a rule, the chain voltage at the corresponding LED arrangement 19 or the minimum value of the chain voltages changes, and the control arrangement 55 controls the operating voltage U B If necessary, adjust accordingly. By changing the current setpoint of at least one of the current sources 41, it is possible, for example—if the lighting device 11 is a rear light—to switch between a rear light function and a brake light function.

[0039] In a further embodiment not shown, individual LEDs 21 or individual series circuits of LEDs 21 can be switched on and off. For this purpose, controllable switching elements are provided in the LED arrays 19. During operation of the lighting device 11, the switching elements are controlled depending on a desired operating state of the lighting device 11, for example by the control device of the motor vehicle, to switch the individual LEDs 21 or series circuits on or off. This allows a step-by-step change in the luminous intensity of the light emitted by the lighting device 11, for example, a change between position and parking light. The control arrangement 55 supplies the operating voltage U B if necessary, when LEDs 21 or series circuits of LEDs 21 are switched on or off and the chain voltages or their minimum value change as a result.

[0040] During operation of the lighting device 11, it is thus ensured that the voltage U1, U2, U3 present between the first terminal 43 and the second terminal 45 of each current source 41 corresponds to or is greater than the minimum value. The control arrangement 55 thereby provides the operating voltage U B to the lowest possible value, resulting in minimal power loss at current sources 41. The lowest voltage of the voltages U1, U2, U3 is present at the current source 41 associated with the LED array 19 that has a maximum chain voltage between its two terminals 23, 25. This lowest voltage corresponds precisely to the minimum value required for reliable operation of current source 41. If the chain voltages at the individual LED arrays 19 are different, higher voltages U1, U2, U3 result at the other current sources 41.

Claims

[1] Lighting device (11) for a motor vehicle, comprising a plurality of light-emitting diode arrangements (19) with a plurality of light-emitting diodes (21), a voltage source (39) for generating an operating voltage (U B ) for the at least one light-emitting diode arrangement (19) and at least one current source (41), wherein the current source (41) is assigned to the light-emitting diode arrangement (19) for generating an operating current (I1, I2, I3) of the light-emitting diode arrangement (19), wherein the lighting device (11) has a control arrangement (55) for controlling the operating voltage (U B ) depending on a voltage (U1, U2, U3) applied to the current source (41), characterized by that controllable switching elements are provided in the light-emitting diode arrangements (19), with which individual light-emitting diodes (21) or individual series circuits of light-emitting diodes (21) of at least one light-emitting diode arrangement (19) can be separately switched on and off. [2] Lighting arrangement (11) according to claim 1, characterized by that the lighting device (11) has a plurality of light-emitting diode arrangements (19), each light-emitting diode arrangement (19) being assigned a current source (41) and the control arrangement (55) has a minimum value generator (47) for forming a minimum value signal (m) which characterizes a minimum value of the voltages (U1, U2, U3) applied to the individual current sources (41). [3] Lighting device (11) according to claim 1 or 2, characterized by that the control arrangement (55) has a subtractor (49) for forming a control difference signal (d) which characterizes a control difference between a predetermined minimum value and the voltage (U1, U2, U3) applied to the current source (41) or the minimum value of the voltages (U1, U2, U3) applied to the individual current sources. [4] Lighting arrangement (11) according to one of the preceding claims, characterized bythat the control arrangement (55) has a control element (53) for determining a control signal (x) for setting the operating voltage. [5] Lighting device (11) according to one of the preceding claims, characterized by that a first terminal (43) of the current source (41) is connected to the light-emitting diode arrangement (19) to which the current source (41) is assigned, a potential (33) common to at least some of the current sources (41), preferably a ground potential (37), is applied to a second terminal (45) of the current source, and the control arrangement (55) has at least one measuring element (46) assigned to the current source (41) for detecting an electrical potential applied to the first terminal of the current source (41). [6] Lighting device according to one of the preceding claims, characterized by that at least one of the current sources (41) is an adjustable current source. [7] Method (61) for operating a lighting device (11) for a motor vehicle, which comprises at least one light-emitting diode arrangement (19) with a plurality of light-emitting diodes (21), a voltage source (39) for generating an operating voltage (U B ) for the at least one light-emitting diode arrangement (19) and at least one current source (41), wherein the current source (41) is assigned to the light-emitting diode arrangement (19) for generating an operating current (I1, I2, I3) of the light-emitting diode arrangement (19), wherein the method comprises the following steps: detecting (65) a voltage (U1, U2, U3) applied to the at least one current source (41) and setting (73) the operating voltage (U B ) depending on the voltage applied to the power source (U1, U2, U3), characterized byin that, in order to gradually change the luminous intensity of light emitted by the lighting device (11), at least one individual light-emitting diode (21) of at least one light-emitting diode arrangement (19) and / or at least one individual series connection of light-emitting diodes (21) of at least one light-emitting diode arrangement (19) are separately switched on or off by means of controllable switching elements arranged in the light-emitting diode arrangements (19). [8] Method (61) according to claim 7, characterized by that the lighting device (11) has a plurality of light-emitting diode arrangements (19), each light-emitting diode arrangement (19) being assigned a current source (41), and that a minimum value of the voltages (U1, U2, U3) applied to the current sources is determined (67) and the operating voltage (U B ) is set depending on the minimum value (73). [9] Method (61) according to claim 8, characterized bythat a control difference is formed between a predetermined minimum value and the voltage applied to the current source or the minimum value of the voltages applied to the current sources (69). [10] Method (61) according to claim 9, characterized by that a control variable for setting the operating voltage (U B ) is formed depending on the control difference (71). [11] Method (61) according to one of claims 7 to 10, characterized by that the operating current (I1, I2, I3) of at least one light-emitting diode arrangement (19) is set as a function of a current setpoint. [12] Control or regulating device (13) for a lighting device (11) for a motor vehicle, which comprises at least one light-emitting diode arrangement (19) with a plurality of light-emitting diodes (21), a voltage source (39) for generating an operating voltage (U B) for the at least one light-emitting diode arrangement (19) and at least one current source (41), wherein the current source (41) is assigned to the light-emitting diode arrangement (19) for generating an operating current (I1, I2, I3) of the light-emitting diode arrangement (19), characterized by that the control or regulating device (55) is programmed to carry out a method (61) according to one of claims 7 to 11.

Images