METHOD FOR OPERATING AN LIGHT-LED DIODE MODULE AND LIGHT-LED DIODE MODULE

Description

[0001] The invention relates to a method for operating a light-emitting diode module and a light-emitting diode module.

[0002] During the manufacturing of light-emitting diodes (LEDs), variations in the parameters of the semiconductor structure of the LEDs lead to a distribution of their optical properties. This manifests itself particularly in the form of different emission spectra and different center wavelengths of the LEDs.

[0003] To generate a wide variety of color impressions, three LEDs are typically combined. The light emitted by a red, a green, and a blue LED spans a gamut. Through additive color mixing, all color points within the gamut can be achieved, and corresponding color impressions can be created. However, if the center wavelengths of the LEDs vary, the gamut provided by the LEDs also changes.

[0004] From DE 10 2008 025 865 A1, a method for operating a light-emitting diode module consisting of a number of different colored light-emitting diodes is known, which can be controlled by a control circuit via control signals, wherein the control circuit has at least one EPROM from which the control signals can be retrieved, wherein the parameters of a color space for the light control of the light-emitting diode module are stored in the EPROM, and that the data stored in the EPROM are read out by the electronics, all necessary color components of the individual light-emitting diodes are calculated and used to calculate the necessary color components.

[0005] DE 10 2011 014 440 A1 describes a method for adjusting the luminous color of a light source for a motor vehicle, comprising the following steps: a) specifying a set of target luminous colors; b) assigning a code to each target luminous color from the specified set of target luminous colors; c) assigning at least one control parameter to each code such that, when the code is selected via the at least one control parameter, the luminous color corresponding to the target luminous color is set on the light source; d) adjusting the luminous color by selecting the code, wherein in step a) the set of target luminous colors is specified in such a way that it completely covers a predefinable gamut, and that the color difference of the nearest adjacent target luminous colors on a predefined color chart is so small that the luminous colors corresponding to these target luminous colors are just barely distinguishable by the human eye.

[0006] From DE 10 2013 201 915 A1, a circuit for controlling several LED channels is known, each comprising at least one LED, for generating a mixed light from the light produced by the respective LED channels, wherein a look-up table is provided for each target color point achievable by the LED module, in which the operating current for each LED channel is stored.

[0007] From DE 10 2017 125 405 A1, a method for calibrating a light-emitting diode (LED), a red-green-blue (RGB) LED device, is known, wherein the RGB LED device is configured to set a pulse-width modulation (PWM) duty cycle and to supply the LED either with a current having a first value or with a current having a second value that is higher than the first value, wherein the method comprises the following steps: measuring a first group of tristimulus values ​​for the LED when the current having the first value is applied to the LED with a first PWM duty cycle; calculating parameters from the measured first group of tristimulus values ​​to express the color intensity as a function of the PWM duty cycle when the current having the first value is applied; measuring a second group of tristimulus values ​​for the LED when the current having the second value is applied.a second PWM duty cycle is applied, where the second PWM duty cycle is lower than the first PWM cycle, resulting in a current lower than the current obtained when the current with the first value is applied with the first PWM duty cycle; a third group of tristimulus values ​​for the LED is measured when the current with the second value is applied with a third PWM duty cycle, where the third PWM duty cycle is higher than the first PWM cycle, resulting in a current higher than the current obtained when the current with the first value is applied with the first PWM duty cycle; parameters are calculated from the measured second and third groups of tristimulus values ​​to express the color intensity as a function of the PWM duty cycle when the current with the second value is applied.

[0008] The invention is based on the objective of creating a method for operating a light-emitting diode module and a light-emitting diode module in which a predetermined gamut can be provided even with fluctuating emission properties of the light-emitting diodes.

[0009] The problem is solved according to the invention by a method with the features of claim 1 and a light-emitting diode module with the features of claim 6. Advantageous embodiments of the invention are set forth in the dependent claims.

[0010] In particular, a method for operating a light-emitting diode module is provided, wherein the light-emitting diode module comprises at least three different colored light-emitting diodes which together span a gamut of adjustable color points and which are controlled by means of a driver device via control signals, wherein current strengths with which the at least three different colored light-emitting diodes are each operated are adjusted to set predetermined corner points of the gamut, so that a predetermined gamut is provided.

[0011] Furthermore, a light-emitting diode module is created, comprising at least three different colored light-emitting diodes which together span a gamut of adjustable color points, and a driver device, wherein the driver device is designed to control the at least three light-emitting diodes via control signals, wherein current strengths with which the at least three different colored light-emitting diodes are each operated are adapted to set predetermined corner points of the gamut, so that a predetermined gamut is provided.

[0012] The process and the LED module enable the compensation of fluctuations in the manufacturing process and the resulting variations in the emission characteristics of the LEDs. This is achieved by changing or adjusting the current with which an LED is operated. Changing the current alters the emitted spectrum and, in particular, a center wavelength, which can also be referred to as the dominant wavelength. For example, if the current is tripled from the usual 20 mA to 60 mA, a center wavelength changes by approximately 5 nm. This effect is used to adjust the gamut spanned by the at least three LEDs. The current is individually selected or adjusted for each of the at least three LEDs so that a center wavelength necessary to reproduce a predefined gamut is set.

[0013] Due to the manufacturing process, the aforementioned variations in emission characteristics always occur. Therefore, LED manufacturers typically measure the LEDs after production and classify them according to a specific wavelength range (or "bins") based on their respective center wavelength. The LEDs are then marketed according to these wavelength ranges. The described method and LED module thus make it possible to utilize a larger number of these wavelength ranges, thereby increasing the available options and reducing costs.

[0014] In particular, three light-emitting diodes are used, whereby a red light-emitting diode (wavelength range of 580-650 nm), a green light-emitting diode (wavelength range of 500-560 nm) and a blue light-emitting diode (wavelength range of 430-480 nm) are combined together to form a light-emitting diode module.

[0015] A gamut refers to a range in the color space that can be reproduced by the LED module through additive color mixing. This range can be illustrated, for example, using the CIE chromaticity diagram (CIE 1931).

[0016] The dependence of the emission characteristics of LEDs, particularly the center wavelength, on the current intensity can be determined empirically, for example. Alternatively or additionally, the dependence can also be calculated using a simulation.

[0017] The LEDs are controlled using pulse-width modulation (PWM). The PWM pulses are generated by the driver unit. The pulse current, i.e., the amplitude, determines or adjusts the center wavelength of each LED. The pulse width, in turn, controls the intensity of the emitted light via the driver unit, enabling additive color mixing to achieve a desired color point within the gamut.

[0018] The driver setup can be designed as a combination of hardware and software, for example as program code that runs on a microcontroller or microprocessor.

[0019] In one embodiment, the current is adjusted using a series resistor. This is a particularly simple implementation of the method and the LED module in terms of complexity, since only the series resistor needs to be adjusted, while the rest of the control circuitry remains unchanged. This keeps costs and effort to a minimum. Depending on a target wavelength for the center wavelength, a current is calculated that is necessary to achieve the target wavelength. Subsequently, a suitable series resistor for the respective LED is selected based on the available operating voltage and installed in the LED module.

[0020] In one embodiment, the current levels are adjusted by means of the driver unit, which adjusts the control signals accordingly. Specifically, the driver unit adjusts the amplitude of the pulse-width modulated pulses. This allows for flexible adjustment. Readjustment at a later time is also possible without significant effort, as only the relevant parameters in the driver unit need to be changed.

[0021] It may be stipulated that the adjustment takes place before the LED module is first put into operation, but that no further or subsequent adjustments are made. However, it may also be stipulated that the adjustment takes place while the LED module is operating.

[0022] In one embodiment, it is provided that any change in intensity caused by adjusting the current is compensated for by adjusting the drive signals. This allows the overall intensity to be kept constant. In particular, the pulse width of the pulse-width modulated pulses is adjusted accordingly. Simply put, the pulse width is reduced when the intensity increases and increased when the intensity decreases. It can be specifically provided that the pulse width is adjusted in such a way that the effective current is kept constant when driving a light-emitting diode.

[0023] In one embodiment, at least one emission characteristic is detected and / or obtained for each of the at least three LEDs, with a value for the adjusted current being determined based on the detected and / or obtained emission characteristic. This allows the LED module to be set to a predetermined gamut before use. For example, a manufacturer of LEDs from which an LED module is to be assembled may provide emission characteristics, in particular a center wavelength, for each of the LEDs, for example in the form of a datasheet or an electronic file. These emission characteristics, in particular the center wavelength, are then used in the execution of the method to calculate and adjust the currents with which the respective LEDs are operated.Once the current levels are adjusted, the LED module can be installed at its final location. For example, the driver unit may include a memory where the emission characteristics are stored before the LED module is positioned at or within its final location. Based on these stored emission characteristics, the driver unit calculates the adjusted current levels and saves them in the memory. The driver unit then makes the calculated current levels available.

[0024] Features for the design of the LED module are derived from the description of embodiments of the method. The advantages of the LED module are the same in each embodiment as in the embodiments of the method.

[0025] The invention is explained in more detail below with reference to preferred embodiments and the figures. These show: Fig. 1 a schematic representation of an embodiment of the light-emitting diode module; Fig. 2 a schematic representation of an embodiment of the method for operating a light-emitting diode module.

[0026] In Fig. 1 Figure 1 shows a schematic representation of an embodiment of the LED module 1. The LED module 1 comprises three differently colored LEDs 2, 3, 4 and a driver unit 5.

[0027] The differently colored LEDs 2, 3, and 4 each have center wavelengths that provide red, green, and blue light, respectively. LED 2 emits in the red wavelength range, meaning its center wavelength lies in the range of 580–650 nm; LED 3 emits in the green wavelength range, meaning its center wavelength lies in the range of 500–560 nm; and LED 4 emits in the blue wavelength range, meaning its center wavelength lies in the range of 430–480 nm. Together, LEDs 2, 3, and 4, or rather their respective center wavelengths, span a gamut.

[0028] The driver unit 5 is designed to control the LEDs 2, 3, 4 via control signals 6. The control signals 6 comprise pulse-width modulated pulses, which are defined by an amplitude and a pulse width.

[0029] The currents used to operate LEDs 2, 3, and 4 are adjusted to set predefined gamut points, thus providing a specified gamut. For example, it may be necessary to shift the center wavelength of LED 2 by 3 nm to achieve the specified gamut. Accordingly, the current used to drive LED 2, or the amplitude of the pulse-width modulated pulses, is increased accordingly. Furthermore, the example may require that the center wavelength of LED 3 be decreased by 2 nm. Accordingly, the current used to drive LED 3, or the amplitude of the pulse-width modulated pulses, is decreased accordingly, and so on.By shifting the center-of-mass wavelengths, the corner points of the spanned gamut also shift, so that the gamut changes accordingly and can thus be approximated to a given gamut.

[0030] After the specified gamut has been provided, a specific or desired color point within the gamut is set by adjusting the pulse width of the pulses used to drive the LEDs 2, 3, and 4. The specified or desired color point is communicated to the driver unit 5, for example, via a color point signal 8. This allows the intensity emitted by the LEDs 2, 3, and 4 to be adjusted. The required intensity is calculated by the driver unit 5 and determined via the pulse widths of the pulse-width modulated control signals 6. The desired color point is achieved through additive color mixing of the electromagnetic radiation emitted by the LEDs 2, 3, and 4.

[0031] It can be provided that the current strengths are adjusted by means of a series resistor 7. The respective series resistors 7 are selected and arranged such that, starting from a supply voltage or signal voltage, the respective specified current strength or the respective specified pulse amplitude is achieved. In the Fig. 1 In the embodiment shown, the series resistors 7 are connected in series in the respective signal path between the driver device 5 and the light-emitting diodes 2, 3, 4.

[0032] Alternatively, it can be provided that the current strengths are adjusted by means of the driver device 5 (active), wherein the driver device 5 adjusts the control signals 6 accordingly, in particular an amplitude of the pulse width modulated pulses.

[0033] It can also be provided that any change in intensity caused by adjusting the current is compensated for by adjusting the control signals. In particular, the pulse width of the pulse-width modulated pulses is adjusted for this purpose. For example, it can be provided that the pulse widths are adjusted by the driver device in such a way that the effective current remains constant.

[0034] It can further be provided that at least one emission property 9 is detected and / or received for each of the three LEDs 2, 3, 4, whereby a value of the adjusted current is determined in each case based on the detected and / or received at least one emission property 9. In particular, the driver device 5 can receive, in particular by receiving, a center wavelength of the respective LEDs 2, 3, 4 as an emission property 9. The center wavelengths are measured, for example, by a manufacturer of the LEDs 2, 3, 4 and provided in the form of a data sheet. Based on the received emission properties 9, the driver device 5 determines the adjusted currents, for example, by comparing them with wavelengths of corner points of the specified gamut.

[0035] In Fig. 2 Figure 1 shows a schematic representation of an embodiment of the method for operating a light-emitting diode module.

[0036] In process step 100, a predefined gamut or its three endpoints is provided. This is done by receiving wavelengths corresponding to the three endpoints of the gamut, for example using the driver device.

[0037] In process step 101, the emission properties of three light-emitting diodes (LEDs) are obtained. These three LEDs cover the three colors red, green, and blue, which are intended to define the gamut. The obtained emission properties are taken, for example, from the technical data sheets of an LED manufacturer and include, in particular, the respective center wavelength or dominant wavelength of the electromagnetic radiation emitted by the LEDs.

[0038] In a process step 102, differences between the wavelengths of the corner points of the specified gamut and the respective corresponding center wavelengths of the light-emitting diodes are determined.

[0039] In process step 103, the respective current strengths or amplitudes for driving the light-emitting diodes are determined based on the determined differences.

[0040] In process step 104, the specified current values ​​are provided in one alternative by selecting and connecting series resistors. In another alternative, the values ​​for the specified current values ​​for each of the LEDs are stored in the driver unit. The driver unit then controls the respective LEDs with current values ​​or amplitudes according to the stored values.

[0041] In a process step 105, pulse widths of control signals for driving the individual LEDs are then calculated, whereby the pulse widths are chosen in such a way that a specified or desired color point within the spanned gamut is achieved.

[0042] In process step 105, it may be provided that any change in intensity caused by adjusting the current strengths is compensated for by adjusting the control signals. In particular, the pulse width of the pulse-width modulated pulses is adjusted for this purpose.

[0043] The advantage of the LED module and the process is that a uniform color impression can be achieved even with fluctuating emission properties of the LEDs used, due to manufacturing tolerances. In particular, this allows for consistent color impressions in applications such as motor vehicles, regardless of the specific batch of LEDs used. Uniform color impressions can also be achieved across all LED modules when using multiple modules. Since the emission properties, especially the center wavelength, can be adjusted within the process, costs can be reduced due to a wider range of usable LEDs. Reference symbol list

[0044] 1 LED module 2 LED 3 LED 4 LED 5 Driver unit 6 Control signal 7 Series resistor 8 Color position signal 9 Emission characteristic 100-105 Process steps

Claims

1. Method for operating a light-emitting diode module (1), the light-emitting diode module (1) comprising at least three different colored light-emitting diodes (2,3,4) which together span a gamut of settable spectrum loci and which are controlled by means of a driver device (5) via pulse width modulation control signals (6), in order to manage the intensity of the light emitted by the relevant light-emitting diode (2,3,4), characterized in that current strengths, with which the at least three different colored light-emitting diodes (2,3,4) are each operated, are individually adjusted for each of the at least three different colored light-emitting diodes (2,3,4) so that the centroid wavelength of the respective at least three different colored light-emitting diodes (2,3,4) necessary in each case to replicate a given gamut or its at least three corner points is set.

2. Method according to claim 1, wherein the current strengths are each adjusted by means of a ballast resistor (7).

3. Method according to claim 1, wherein the current strengths are adjusted by means of the driver device (5), wherein the driver device (5) adjusts the control signals (6) accordingly for this purpose.

4. Method according to any of the preceding claims, wherein any change in intensity caused by adjusting the current strengths is compensated for in each case by adjusting the control signals (6).

5. Method according to any of the preceding claims, wherein at least one emission property (9) is detected and / or obtained for each of the at least three light-emitting diodes (2,3,4), wherein a value of the adjusted current strength is determined in each case on the basis of the at least one emission property (9) detected and / or obtained.

6. Light-emitting diode module (1), comprising: at least three different colored light-emitting diodes (2,3,4) which together span a gamut of settable spectrum loci, and a driver device (5), the driver device (5) being configured to control the at least three light-emitting diodes (2,3,4) via pulse width modulation control signals (6), in order to manage the intensity of the light emitted by the relevant light-emitting diode (2,3,4), characterized in that current strengths, with which each of the at least three different colored light-emitting diodes (2,3,4) are operated, are individually adjusted for each of the at least three different colored light-emitting diodes (2,3,4) so that the centroid wavelength of the respective at least three different colored light-emitting diodes (2,3,4) necessary in each case to replicate a given gamut or its at least three corner points is set.

7. Light-emitting diode module (1) according to claim 6, further comprising ballast resistors (7), wherein the ballast resistors (7) are selected and arranged such that the adjusted current strengths are used when controlling the light-emitting diodes (2,3,4).

8. Light-emitting diode module (1) according to claim 6, wherein the driver device (5) is further configured to adjust the respective current strengths.

9. Light-emitting diode module (1) according to any of claims 6 to 8, wherein the driver device (5) is further configured to compensate for any change in intensity caused by adjusting the current strengths in each case by adjusting the control signals (6).

10. Light-emitting diode module (5) according to any of claims 6 to 8, wherein the driver device (5) is configured to obtain at least one emission property (9) for each of the at least three light-emitting diodes (2,3,4) and to determine a value of the adjusted current strength in each case on the basis of the relevant at least one emission property (9) obtained.