Optoelectronic module and method for operating optoelectronic module

Abstract

The invention relates to an optoelectronic module, comprising:-at least one light-emitting diode (2), which emits light having a light intensity (Iv) during operation; -an integrated circuit (3) which, during operation, regulates an operating current (I) of the light emitting diode (2) and measures a value of a forward voltage (Vf) of the light emitting diode (2), the integrated circuit (3) determining degradation of the light emitting diode (2) by measuring the value of the forward voltage (Vf) and increasing or decreasing the operating current (I) as a function of the measured value of the forward voltage (Vf), in this way, a change in the light intensity (Iv) due to the degradation is at least partially compensated. The invention further relates to a method for operating an optoelectronic module.

Description

[0001] A photoelectronic module and a method for operating a photoelectronic module are provided.

[0002] A photoelectronic module with improved stability against changes in light intensity related to aging should be provided. This object is achieved by a product having the features of independent claim 1.

[0003] Furthermore, a method for operating a photoelectronic module with improved stability against changes in light intensity related to aging should be provided. This object is achieved by a method having the features of independent claim 6.

[0004] Advantageous embodiments and improvements of the photoelectronic module and the method for operating the photoelectronic module are provided in the dependent claims.

[0005] According to one embodiment, the photoelectronic module has at least one light-emitting diode that emits light with a light intensity during operation. For example, the light-emitting diode emits electromagnetic radiation during operation. In particular, the light-emitting diode emits light in the spectral range between infrared light and ultraviolet light. Preferably, the light-emitting diode emits light in the visible spectral range during operation. In particular, the light-emitting diode converts the operating current into light.

[0006] Herein and hereinafter, the light intensity refers to the luminous flux generated by the light-emitting diode in a unit solid angle and is particularly provided in units of "candela". Here, the luminous flux corresponds to the radiation power of the light-emitting diode, and this radiation power is weighted using the wavelength-dependent sensitivity of the human eye. The radiation power represents the energy transmitted by the light emitted per unit time.

[0007] In particular, the light-emitting diode includes an epitaxial semiconductor layer stack having an active layer for converting the operating current into electromagnetic radiation. For example, the active layer has a pn junction that can be configured as a quantum well structure or a multiple quantum well structure.

[0008] According to another embodiment, the photoelectronic module has an integrated circuit that regulates the operating current of the light-emitting diode and measures the value of the forward voltage of the light-emitting diode during operation. For example, the integrated circuit is an application-specific integrated circuit (abbreviation: ASIC).

[0009] In particular, the integrated circuit has a circuit for regulating the operating current of the light-emitting diode. For example, the circuit includes an adjustable current source.

[0010] In addition, the integrated circuit has a circuit for measuring the forward voltage of the light-emitting diode. Herein and hereinafter, the forward voltage particularly refers to the voltage dropped across the semiconductor layer stack of the light-emitting diode when a constant operating current flows through the light-emitting diode in the forward direction. In other words, the forward voltage corresponds to the voltage drop between the anode and the cathode of the light-emitting diode operating in the forward direction.

[0011] According to another embodiment of the optoelectronic module, the integrated circuit determines the degradation of the light-emitting diode by measuring the value of the forward voltage. Herein and hereinafter, degradation refers to the change in the light intensity related to aging of the light-emitting diode at a predetermined operating current.

[0012] For example, during the operation of the light-emitting diode, defects are formed in the active layer. In addition, defects already present in the semiconductor layer stack may migrate into or out of the active layer during the operation of the light-emitting diode. These defects are, for example, defects or dislocations in the crystal arrangement of the semiconductor layer stack. An increase in the defect density in the active layer due to the aging of the light-emitting diode, for example, leads to a decrease in the internal quantum efficiency of the light-emitting diode. Therefore, as the lifetime of the light-emitting diode increases, the light intensity of the light emitted by the light-emitting diode at a predetermined operating current particularly decreases. As the lifetime of the light-emitting diode increases, the defect density in the active layer may also decrease, thereby increasing, for example, the light intensity of the light-emitting diode.

[0013] At a predetermined operating parameter (in particular a predetermined operating current and a predetermined temperature), the forward voltage of the light-emitting diode can change, for example, according to the defect density in the active layer. In particular, the degradation of the light-emitting diode is related to the change in the forward voltage related to aging at a predetermined operating parameter. Therefore, the change in the forward voltage of the light-emitting diode at a predetermined operating parameter can be used as a measure of the degradation of the light-emitting diode. For example, when the degradation of the light-emitting diode reduces the light intensity, the forward voltage decreases, and vice versa.

[0014] According to another embodiment of the optoelectronic module, the integrated circuit increases or decreases the operating current of the light-emitting diode according to the measured value of the forward voltage, such that the change in the light intensity due to degradation is at least partially compensated. For example, the integrated circuit increases or decreases a temporally constant operating current. For example, if the light intensity of the light-emitting diode is adjusted by pulse-width modulation of the operating current, the integrated circuit can also increase or decrease the time average value of the operating current.

[0015] Compensation is particularly carried out such that by increasing or decreasing the operating current and the resulting change in the light intensity, the change in the light intensity due to degradation is at least partially compensated. In other words, when the light intensity of the light-emitting diode decreases due to degradation, the operating current is increased, and vice versa.

[0016] For example, during calibration, a light-emitting diode has a specific light intensity at a predetermined first operating current and a specific forward voltage at a predetermined second operating current. Here, the first operating current and the second operating current may be the same or different. For example, after calibration, after a certain operating time of the light-emitting diode, due to the degradation of the light-emitting diode, the light intensity at the first operating current and the forward voltage at the second operating current change. At this time, the integrated circuit particularly determines the value of the changed forward voltage at the second operating current as a measure of the degradation of the light-emitting diode. Thereafter, for example, the first operating current is increased or decreased according to the measured value of the forward voltage, so that the light intensity of the degraded light-emitting diode at the first operating current corresponds to the light intensity at the first operating current during calibration, or has as little deviation as possible therefrom.

[0017] According to a preferred embodiment, the optoelectronic module comprises:

[0018] - at least one light-emitting diode that emits light with a light intensity during operation;

[0019] - an integrated circuit that regulates the operating current of the light-emitting diode and measures the value of the forward voltage of the light-emitting diode during operation, wherein,

[0020] - the integrated circuit determines the degradation of the light-emitting diode by measuring the value of the forward voltage and increases or decreases the operating current according to the measured value of the forward voltage, so that the change in light intensity due to degradation is at least partially compensated.

[0021] The optoelectronic module described herein is particularly based on the idea of electronically controlling and, if necessary, compensating for changes in the light intensity of a light-emitting diode due to aging-related degradation. Here, advantageously, the degradation is determined by measuring the forward voltage of the light-emitting diode using an integrated circuit, which can also control the operating current of the light-emitting diode.

[0022] Particularly at relatively low operating currents, the forward voltage is related, for example, to the defect density in the active layer of the light-emitting diode and thus to the degradation of the light-emitting diode. Therefore, the measured value of the forward voltage can be used to adapt the operating current of the light-emitting diode so that the change in light intensity due to aging is at least partially compensated.

[0023] For example, in the optoelectronic module described herein, in the context of manufacturing the optoelectronic module, an expensive aging process (Einbrennen) of the light-emitting diode can advantageously be omitted. In the aging process, particularly before optical calibration of the light intensity, the light-emitting diode is operated at the maximum operating current for a long time to prevent rapid initial degradation during operation after calibration. Compared with aging, the optoelectronic module described herein advantageously allows monitoring of degradation during operation.

[0024] Furthermore, in the optoelectronic module described herein, there is no need to expensively record the operating time and / or the temperature change during operation in order to at least partially compensate for the change in light intensity associated with aging. In particular, in the optoelectronic module described herein, the measured value of the forward voltage is advantageously directly related to the degradation of the light-emitting diode. In contrast, for example, the operating time or the temperature change is only an indirect measure of the degradation of the light-emitting diode. The operating time or the temperature change in particular does not have information about the individual degradation state of the light-emitting diode in the optoelectronic module. In contrast, in the optoelectronic module described herein, the degradation can be compensated according to the individual state of the light-emitting diode. Therefore, the compensation can be advantageously carried out with higher precision.

[0025] In the optoelectronic module described herein, an optical light intensity sensor for monitoring the degradation of the light-emitting diode can also be omitted. Therefore, the optoelectronic module described herein can be advantageously manufactured cost-effectively.

[0026] According to another embodiment of the optoelectronic module, the integrated circuit has an analog-to-digital converter that measures the value of the forward voltage during operation. In particular, the analog-to-digital converter measures and digitizes the forward voltage at a predetermined time point. For example, the analog-to-digital converter measures a voltage of up to 1 V to 3 V (including the boundary values) with an accuracy of 0.1 mV to 10 mV (including the boundary values). Correspondingly, the resolution of the analog-to-digital converter is, for example, 7 bits to 15 bits.

[0027] According to another embodiment of the optoelectronic module, the integrated circuit or the measurement control unit for controlling the integrated circuit has a memory in which the measured value of the forward voltage is stored. The measurement control unit is arranged, for example, outside the optoelectronic module and is designed to control the integrated circuit to measure the value of the forward voltage of the light-emitting diode. Furthermore, the integrated circuit or the measurement control unit can calculate the change in the operating current based on the stored value of the forward voltage in order to at least partially compensate for the change in light intensity associated with aging of the light-emitting diode.

[0028] Furthermore, the calibration data of the optoelectronic module can be stored in the memory. The calibration data in particular includes the relationship between the light intensity of the light-emitting diode and the operating current. Furthermore, the calibration data preferably includes the value of the forward voltage of the light-emitting diode as a reference value for determining the degradation. The calibration data can also include the relationship between the light intensity of the light-emitting diode and the operating temperature of the light-emitting diode. For example, after the optoelectronic module is calibrated, the calibration data is stored in the memory.

[0029] According to another embodiment of the optoelectronic module, the integrated circuit has a pulse width modulator, wherein the pulse width modulator modulates the operating current of the light-emitting diode to control the light intensity. In particular, the pulse width modulator periodically changes the operating current over time. During one period, the operating current can, for example, assume two different values within two corresponding time intervals of different durations. Preferably, one value of the operating current corresponds to the operating current value of the maximum operating current of the light-emitting diode, while the other value corresponds to a minimal operating current. In other words, when the operating current is one value, the light-emitting diode emits light with maximum light intensity, and when the operating current is the other value, the light-emitting diode does not emit light. For example, the period is less than 20 milliseconds to avoid perceptible and disturbing flicker of the optoelectronic module.

[0030] By adjusting the duty cycle between the two values of the operating current, the pulse width modulator can in particular provide any average operating current time value between 0 amperes and the maximum operating current. The duty cycle represents the time ratio between the two time intervals during which the operating current assumes two different values. The duty cycle is preferably given as a percentage. For example, when the duty cycle is 0%, the light-emitting diode does not emit light in terms of the average value over time, and when the duty cycle is 100%, the light-emitting diode emits light with maximum light intensity in terms of the average value over time. Compared with adjusting a corresponding time-constant operating current, by using the pulse width modulator to adjust the average operating current time value, the color shift of the light emitted by the light-emitting diode can be advantageously reduced or avoided. In addition, the light intensity of the light emitted by the light-emitting diode is proportional to the duty cycle.

[0031] According to another embodiment, the optoelectronic module has three light-emitting diodes that emit electromagnetic radiation in the red, green, or blue spectral range during operation. In particular, the first light-emitting diode emits red light, the second light-emitting diode emits blue light, and the third light-emitting diode emits green light. For example, the optoelectronic module can emit light of any mixed color by correspondingly adjusting the relative light intensities of the three light-emitting diodes.

[0032] According to another embodiment of the optoelectronic module, the integrated circuit controls the operating currents of the three light-emitting diodes separately from each other and measures the values of the forward voltages of the three light-emitting diodes independently of each other to determine degradation. Thus, the degradation of each of the three light-emitting diodes is determined independently of each other in particular.

[0033] According to another embodiment of the optoelectronic module, the integrated circuit at least partially compensates for the change in light intensity due to degradation of each of the three light-emitting diodes. Thus, when the degradations of the three light-emitting diodes are different, the color stability of the optoelectronic module can be advantageously improved. By compensating for the aging-related changes in the respective light intensities of the three light-emitting diodes, the integrated circuit at least partially compensates for the aging-related changes in the color coordinates of the mixed light emitted by the optoelectronic module in particular.

[0034] Furthermore, a method for operating an optoelectronic module is provided. In particular, the optoelectronic module described herein can be operated using this method. All features of the optoelectronic module are also disclosed for the method of operating the optoelectronic module, and vice versa.

[0035] According to one embodiment of the method for operating an optoelectronic module, first, at least one light intensity of at least one light-emitting diode is adjusted by controlling the operating current using the integrated circuit. Preferably, pulse width modulation is performed on the operating current. For example, the light intensity is adjusted by the time average value or duty cycle of the operating current with a predetermined pulse width modulation.

[0036] According to another embodiment of the method, the degradation of the light-emitting diode is determined by measuring the value of the forward voltage using the integrated circuit. Preferably, the forward voltage is measured under predetermined operating parameters of the light-emitting diode (for example, at a predetermined operating current and / or a predetermined temperature). For example, in addition to being related to degradation, the forward voltage is also related to the temperature of the light-emitting diode. By measuring the forward voltage under the same operating parameters, in particular, the influence of degradation on the forward voltage can be distinguished from other effects. For example, the compensation accuracy of the aging-related change in light intensity can be improved thereby.

[0037] According to another embodiment of the method, when adjusting the light intensity, the change in light intensity due to degradation is compensated by increasing or decreasing the operating current according to the measured value of the forward voltage. In particular, the operating current is changed by increasing or decreasing. For example, the operating current of the light-emitting diode is changed according to the measured value of the forward voltage such that the light intensity of the light emitted by the degraded light-emitting diode at least approximately corresponds to the light intensity of the light-emitting diode at a constant operating current during calibration.

[0038] According to a preferred embodiment, the method for operating an optoelectronic module includes the following steps:

[0039] - Adjusting the light intensity of at least one light-emitting diode by controlling the operating current using the integrated circuit;

[0040] - Determining the degradation of the light-emitting diode by measuring the value of the forward voltage using the integrated circuit, wherein,

[0041] - When adjusting the light intensity, the operating current is increased or decreased according to the measured value of the forward voltage to compensate for the change in light intensity due to degradation.

[0042] Preferably, the steps of the method are performed in the above order. The above steps of the method can be performed at any time.

[0043] According to another embodiment of the method, the degradation of the light-emitting diode is determined when the light-emitting diode is turned on and / or at a predetermined time point. For example, the value of the forward voltage is determined when each optoelectronic module is put into operation and / or after a determined service interval.

[0044] In addition, the value of the forward voltage can also be measured continuously, for example, during the operation of the optoelectronic module. For example, during pulse width modulation, one of the two values of the operating current can be designed to measure the forward voltage. This can be done especially when the predetermined value of the operating current for measuring the forward voltage is small such that the light-emitting diode does not emit light or does not emit perceivable light. In this case, the forward voltage of the light-emitting diode is measured within a sub-cycle of the pulse width modulation, within which the light-emitting diode does not emit perceivable light.

[0045] According to another embodiment of the method, the forward voltage is measured at a predetermined value of the operating current. Preferably, the forward voltage is measured at multiple time points, where the predetermined value of the operating current has the same value each time the forward voltage is measured. For example, this can improve the compensation accuracy for the change in light intensity related to aging. The predetermined operating current for measuring the forward voltage is especially selected such that the change in the forward voltage due to degradation is particularly sensitive to the degradation of the light-emitting diode.

[0046] According to another embodiment of the method, the predetermined value of the operating current for measuring the forward voltage is selected such that after a predetermined operating time, the statistical correlation between the change in the forward voltage due to the degradation of the light-emitting diode and the change in light intensity is maximized. For example, in multiple identical optoelectronic modules, the forward voltage and light intensity are measured at the start and end of a predetermined operating time for multiple different operating currents. The change in the forward voltage is determined, for example, as the ratio of the values of the forward voltage measured at the start and end of the predetermined operating time at the predetermined operating current. Similarly, the change in light intensity is determined, for example, as the ratio of the values of the light intensity measured at the start and end of the predetermined operating time at the predetermined operating current. Based on the measured change in the forward voltage and the measured change in light intensity for each of the multiple optoelectronic modules, a measure of their statistical correlation for different operating currents can be calculated. The predetermined operating time is, for example, from 1 hour to 48 hours (including the boundary values).

[0047] For calculating the statistical correlation, the change in forward voltage and the change in light intensity are in particular regarded as two statistically random variables. For example, the Pearson correlation coefficient between the measured change in light intensity and the measured change in forward voltage can be calculated as a measure of their statistical correlation. The Pearson correlation coefficient in particular corresponds to the covariance between two random variables divided by the standard deviations of these two random variables. Here, the covariance corresponds to the expected value of the product of the difference between the first random variable and its mean and the difference between the second random variable and its mean.

[0048] The statistical correlation between the change in forward voltage and the change in light intensity is in particular a function of the operating current of the light-emitting diode. Preferably, when measuring the value of the forward voltage to determine degradation, the operating current with the greatest statistical correlation between the change in forward voltage and the change in light intensity is selected.

[0049] According to another embodiment of the method, the predetermined operating current for measuring the forward voltage is from 50 microamperes to 5 milliamperes (including the boundary values).

[0050] According to another embodiment of the method, when adjusting the light intensity of the light-emitting diode, the operating current is corrected using a compensation factor that is linearly correlated with the measured value of the forward voltage. For example, in order to compensate for degradation, the value of the operating current that is constant over time is changed by the compensation factor. In order to compensate for degradation, the duty cycle of the pulse-width modulation of the operating current can also be changed by the compensation factor. For example, the duty cycle is increased or decreased inversely proportional to the compensation factor. The duty cycle can also be increased or decreased directly proportional to the compensation factor.

[0051] The compensation factor is in particular a linear function of the measured value of the forward voltage. The compensation factor can also be any function of the value of the forward voltage. For example, the compensation factor is a polynomial, i.e., the sum of multiples of powers of the measured value of the forward voltage.

[0052] According to another embodiment of the method, the compensation factor depends on predetermined compensation parameters. The compensation parameters are, for example, the coefficients in a polynomial formed by powers of the measured value of the forward voltage. In the case where the measured value of the forward voltage and the compensation factor are linearly related, the compensation factor includes, for example, two compensation parameters.

[0053] According to another embodiment of the method, the compensation parameter is determined by measuring the change in light intensity due to degradation in a plurality of identical light-emitting diodes and performing subsequent statistical evaluation. For example, for a plurality of identical light-emitting diodes, after a predetermined operating time, the change in light intensity and the change in the value of the forward voltage are measured. Subsequently, the relationship between the change in light intensity and the change in forward voltage is determined by means of regression analysis. In particular, a polynomial relationship, such as a linear relationship, between the change in light intensity and the change in forward voltage is adopted, and the coefficients of the polynomial, i.e., the compensation parameter, are determined by regression analysis. For example, the compensation parameter is determined by minimizing the mean square deviation between the measured change in light intensity and the change in forward voltage and the adopted polynomial relationship.

[0054] According to another embodiment of the method, the temperature of the light-emitting diode is measured immediately before or after measuring the value of the forward voltage used to determine degradation. For example, the temperature of the light-emitting diode is measured using a temperature sensor.

[0055] According to another embodiment of the method, the temperature of the light-emitting diode is determined by measuring the value of the forward voltage at a predetermined operating current greater than the operating current used to determine degradation. At a predetermined operating current, the forward voltage of the light-emitting diode depends in particular on the temperature of the active layer. Therefore, by measuring the forward voltage at a predetermined operating current, the temperature of the light-emitting diode can be determined in particular. For example, the temperature of the light-emitting diode is measured while the light-emitting diode is continuously operating at the recommended value of the operating current. For example, the greater the predetermined operating current, the greater the change in the forward voltage due to the change in temperature. Therefore, the accuracy of temperature measurement can be advantageously improved.

[0056] According to another embodiment of the method, if the temperature at the time of determining the degradation of the light-emitting diode is different from a predetermined temperature, the measured value of the forward voltage is corrected. In particular, the measured value of the forward voltage used to determine degradation is corrected such that the corrected value at least approximately corresponds to the value of the forward voltage at the predetermined temperature. Therefore, the temperature difference in different measurements of the forward voltage used to determine degradation can be at least partially compensated. Thereby, the compensation accuracy of degradation is advantageously improved.

[0057] According to another embodiment of the method, the measured value of the forward voltage is corrected according to the known relationship between the forward voltage and the temperature of the light-emitting diode at a predetermined operating current. For example, when the temperature of the light-emitting diode increases by one degree Celsius, the forward voltage drops or rises by a known amount. By multiplying the temperature deviation (i.e., the difference between the measured temperature of the light-emitting diode and the predetermined temperature) by the known amount of increase or decrease in the forward voltage per degree Celsius, the corrected value of the forward voltage can be determined in particular.

[0058] According to another embodiment of the method, the optoelectronic module is calibrated before the first operation. In particular, the optoelectronic module is optically calibrated before the first operation. The calibration can also be performed at a plurality of time points after a specific operating time of the optoelectronic module or after different operating times. During the calibration process, for example, the light intensity of the emitted light and / or the color coordinates of the optoelectronic module are measured under predetermined operating parameters (such as operating current and temperature). The measured values ​​are stored in particular in a memory of the integrated circuit.

[0059] According to another embodiment of the method, the relationship between the operating current and the light intensity of the light emitting diode is determined during the calibration process. In particular, the light intensity of the emitted light is measured for a plurality of predetermined operating current values. In addition, the relationship between temperature and light intensity can be measured at a predetermined operating current.

[0060] According to another embodiment of the method, during the calibration process, the value of the forward voltage of the light emitting diode is measured at a subsequent time point under the same conditions as when the degradation was determined. The measured value of the forward voltage is then stored. In particular, the value of the forward voltage measured during the calibration process is stored in a memory of the integrated circuit or in a memory of an external measurement control unit.

[0061] The value of the forward voltage measured during the calibration is in particular a reference value for determining the degradation of the light emitting diode. For example, the value of the forward voltage is measured after a certain operating time and compared with the reference value to determine the degradation of the light emitting diode. The change in the forward voltage is, for example, proportional to the degradation of the light emitting diode.

[0062] Further advantageous embodiments and developments of the optoelectronic module and of the method for operating an optoelectronic module are apparent from the exemplary embodiments described below in conjunction with the figures.

[0063] Figure 1 A schematic diagram of an optoelectronic module according to one embodiment is shown.

[0064] Figure 2 and Figure 3 Schematic block circuit diagrams of optoelectronic modules according to various embodiments are shown.

[0065] Figure 4 and Figure 5 FIG. 4 shows a schematic circuit diagram of an optoelectronic module according to further embodiments.

[0066] Figure 6 A schematic flow chart of a method for operating an optoelectronic module according to one embodiment is shown.

[0067] Figure 7 A schematic diagram showing the internal quantum efficiency of a light-emitting diode as a function of the operating current is shown by way of example.

[0068] Figure 8 A diagram showing by way of example the statistical correlation between the degradation-related change in the forward voltage and the degradation-related change in the light intensity as a function of the operating current of the light-emitting diode is shown.

[0069] Figure 9 A diagram showing by way of example the degradation-related change in the light intensity over the degradation-related change in the forward voltage of a light-emitting diode is shown.

[0070] Figure 10 Graphs of compensated degradation versus uncompensated degradation for a number of optoelectronic modules are shown by way of example.

[0071] Figure 11 , Figure 12 and Figure 13 Graphs showing degradation of compensation of an optoelectronic module over the operating time of the optoelectronic module according to various embodiments.

[0072] In the drawings, identical, similar or functionally identical elements are provided with the same reference numerals. The shapes and size ratios of the elements shown in the drawings should not be considered to be to scale. On the contrary, individual elements may be shown exaggeratedly for better illustration and / or better understanding.

[0073] according to Figure 1 The optoelectronic module 1 of the embodiment of the embodiment has a light-emitting diode 2 and an integrated circuit 3, which are arranged on a main surface of a common carrier 8. The carrier 8 has an electrical contact surface, via which the light-emitting diode 2 and the integrated circuit 3 are electrically contacted. In addition, the carrier 8 has electrical connection contacts on the surface opposite to the main surface for external electrical contact of the optoelectronic module 1. The carrier 8 has, for example, plastic, ceramic and / or metal, or consists of one of these materials. In particular, the optoelectronic module 1 is surface-mountable.

[0074] The light emitting diode 2 comprises a semiconductor layer stack having an active layer for converting an operating current I into electromagnetic radiation. In particular, the light emitting diode 2 emits light in the visible spectral range during operation. The light intensity Iv of the light emitted by the light emitting diode 2 can be adjusted via the operating current I.

[0075] The integrated circuit 3 includes a circuit for regulating the operating current I of the light-emitting diode 2 and a circuit for measuring the forward voltage Vf of the light-emitting diode 2. The integrated circuit 3 is designed to determine the aging-related degradation of the light-emitting diode 2 by measuring the value of the forward voltage Vf. In particular, in order to measure the forward voltage Vf, a predetermined constant operating current I is applied to the light-emitting diode 2, where the forward voltage Vf is particularly sensitive to the degradation of the light-emitting diode 2. In other words, at the predetermined operating current I, there is a high statistical correlation between the aging-related change in the light intensity Iv of the light-emitting diode 2 and the aging-related change in the forward voltage Vf.

[0076] Furthermore, the integrated circuit 3 is designed to at least partially compensate for the aging-related change in the light intensity Iv of the light emitted by the light-emitting diode 2 based on the measured value of the forward voltage Vf. To this end, the integrated circuit 3 increases or decreases the operating current I of the light-emitting diode 2 according to the measured value of the forward voltage Vf. In particular, the operating current I is changed such that the light intensity Iv of the light emitted by the light-emitting diode 2 at least approximately corresponds to the light intensity Iv during the optical calibration of the light-emitting diode 2 at a constant operating current I.

[0077] Figure 2 Shows a schematic block circuit diagram of the optoelectronic module 1 according to the embodiment described in conjunction with Figure 1 The anode of the light-emitting diode 2 is connected to the supply voltage VLED, while the cathode of the light-emitting diode 2 is connected to the reference potential GND via a current source 10 in the integrated circuit 3. The current source 10 is in particular designed to provide the operating current I of the light-emitting diode 2.

[0078] The integrated circuit 3 further includes a circuit for measuring the forward voltage Vf of the light-emitting diode 2 (in particular an analog-to-digital converter 4) and a pulse width modulator 7, a control unit 9 and a memory 6. The analog-to-digital converter 4 for measuring the forward voltage Vf is electrically connected to the anode and cathode of the light-emitting diode 2 and transmits the measured value of the forward voltage Vf to the control unit 9, which stores the value in the memory 6.

[0079] The control unit 9 controls the pulse width modulator 7, which pulse-width modulates the operating current I of the light-emitting diode 2. In particular, the control unit 9 sets the duty cycle of the pulse-width modulated operating current I to regulate the light intensity Iv of the light-emitting diode 2.

[0080] Furthermore, the control unit 9 calculates a compensation factor F based on the measured value of the forward voltage Vf and predetermined compensation parameters A, B. In particular, the duty cycle of the pulse-width modulated operating current I changes inversely with the compensation factor F so as to at least partially compensate for the degradation-related change in the light intensity Iv of the light-emitting diode 2. The compensation parameters A, B are stored, for example, in the memory 6 during the manufacturing process of the optoelectronic module 1.

[0081] Figure 3 FIG. shows a schematic block circuit diagram of an optoelectronic module 1 according to another embodiment. Compared with the embodiment Figure 2 described, the optoelectronic module 1 additionally has an external measurement control unit 5. For example, the external measurement control unit 5 is not arranged on the common carrier 8, but is spatially separated from the integrated circuit 3 and the light-emitting diode 2. Furthermore, the external measurement control unit 5 can control, for example, a plurality of integrated circuits 3 and associated light-emitting diodes 2. In particular, the memory 6 is part of the measurement control unit 5 rather than part of the integrated circuit 3. The measurement control unit has a control unit 9 that receives the measured value of the forward voltage Vf from the control unit 9 of the integrated circuit 3 and stores it in the memory 6. In this embodiment, in particular, the control unit 9 of the measurement control unit 5 calculates the compensation factor F based on the compensation parameters A, B and the measured value of the forward voltage Vf and sends it to the control unit 9 of the integrated circuit to change the duty cycle of the pulse-width modulator 7. In addition, the measurement control unit 5 controls the time point at which the integrated circuit 3 measures the value of the forward voltage Vf.

[0082] According to Figure 4 the embodiment of, the optoelectronic module 1 has an integrated circuit 3 and three light-emitting diodes 21, 22, 23, and the integrated circuit and these light-emitting diodes are arranged on a common carrier 8. The anodes of the three light-emitting diodes 21, 22, 23 are connected to a common supply voltage VLED, and the cathodes of the three light-emitting diodes 21, 22, 23 are electrically connected to corresponding terminals of the integrated circuit 3. During operation, the first light-emitting diode 21 emits light in the red spectral range, the second light-emitting diode 22 emits light in the green spectral range, and the third light-emitting diode 23 emits light in the blue spectral range.

[0083] The integrated circuit 3 independently controls the operating currents I of the three light-emitting diodes 21, 22, 23 such that the relative light intensity Iv of the light emitted by the three light-emitting diodes 21, 22, 23 can be adjusted. In particular, the optoelectronic module 1 can emit mixed light of any color during operation.

[0084] In addition, the integrated circuit 3 independently determines the degradation of each of the three light-emitting diodes 21, 22, 23 by measuring the corresponding forward voltage Vf. Based on the measured forward voltage Vf, the integrated circuit compensates for the change in the light intensity Iv related to aging of the three light-emitting diodes 21, 22, 23. In particular, the color shift related to aging of the optoelectronic module 1 is advantageously compensated for at least in part thereby.

[0085] The optoelectronic module 1 has connection contacts 11 for connecting the integrated circuit 3 to a serial bus. Via the serial bus, the integrated circuit 3 exchanges data with an external measurement control unit 5 (not shown here, see for example Figure 3 ).

[0086] Compared with the embodiment of Figure 4 , the optoelectronic module 1 according to the embodiment of Figure 5 has an integrated circuit 3 which is not arranged on the carrier 8 together with the three light-emitting diodes 21, 22, 23, but is spatially separated from them. For example, in this way, the light-emitting diodes 21, 22, 23 of a plurality of optoelectronic modules 1 can be arranged particularly compactly adjacent to each other, while the associated integrated circuits 3 are arranged beside the light-emitting diodes 21, 22, 23.

[0087] Figure 6 Different steps 101, 102, 103, 104 of a method of operating an optoelectronic module 1 according to the embodiment of Figure 2 are shown. In a first step 101, the optoelectronic module 1 is calibrated. In particular, at a constant temperature, the light intensity Iv of the light emitted by the light-emitting diode 2 is measured according to the operating current I and stored as a reference value Iv0 of the light intensity. In addition, the forward voltage Vf of the light-emitting diode is measured and stored at a predetermined operating current I and a constant temperature. Here, the predetermined operating current I is selected such that the change in the forward voltage Vf is particularly sensitive to the degradation of the light-emitting diode 2. For example, the selection of the predetermined operating current I is described in conjunction with Figure 8 . The measured value of the forward voltage Vf is stored as a reference value Vf0 in the memory 6 of the integrated circuit 3.

[0088] In a second step 102, the optoelectronic module 1 is in operation and the light-emitting diode 2 emits light with an adjustable light intensity Iv. The light intensity Iv is adjusted here by the integrated circuit 3 by pulse-width modulation of the operating current I. In particular, the light intensity Iv is proportional to the duty cycle of the pulse-width modulated operating current I.

[0089] In the third step 103, after a predetermined operating time of the optoelectronic module 1, for example, after a service interval, the value of the forward voltage Vf of the light-emitting diode 2 is measured under the same operating conditions as during calibration. In particular, Vf is measured at the same predetermined operating current I as during calibration and at the same temperature of the optoelectronic module 1. The degradation of the light-emitting diode 2 is determined by measuring the value of the forward voltage Vf. For example, the degradation-related change Iv / Iv0 of the light intensity of the light emitted by the light-emitting diode 2 is at least approximately proportional to the change Vf / Vf0 of the value of the forward voltage, where the changes are determined relative to the calibration reference values Iv0, Vf0.

[0090] In the fourth step 104, the integrated circuit 3 at least partially compensates for the change in the light intensity Iv due to the degradation of the light-emitting diode 2 during the subsequent operation of the optoelectronic module 1. To this end, the integrated circuit 3 calculates a compensation factor F, which depends on the value of the forward voltage Vf measured in step 103, the reference value measured in step 101, and the compensation parameters A, B. In particular, the compensation factor F has the form:

[0091]

[0092] where A and B are compensation parameters, Vf represents the value of the forward voltage measured in step 103, and Vf0 represents the reference value of the forward voltage measured in step 101. The compensation factor F in particular describes the change in the light intensity Iv of the light emitted by the degraded light-emitting diode 2 relative to the light intensity Iv when the optoelectronic module 1 is calibrated. For example, the determination of the compensation parameters A, B is described in Figure 9 In particular, the compensation parameters A, B are stored in the memory 6 of the integrated circuit 3 during the manufacturing process of the optoelectronic module 1.

[0093] During the subsequent operation of the optoelectronic module 1, the duty cycle PWM of the pulse-width-modulated operating current I is corrected using the compensation factor F:

[0094]

[0095] Here, PWM c represents the corrected duty cycle, and PWM represents the original duty cycle. By pulse-width modulating the operating current I of the light-emitting diode 2 using the corrected duty cycle PWM c at least partially compensates for the degradation-related change in the light intensity Iv of the light-emitting diode 2. In particular, the light intensity Iv of the light generated using the corrected duty cycle PWM c is at least approximately the same as the light intensity Iv of the light generated using the duty cycle PWM during calibration. Since the time-averaged light intensity Iv of the light emitted by the light-emitting diode 2 is proportional to the duty cycle PWM of the pulse-width-modulated operating current I, the above correction of the duty cycle PWMc Calibration can at least partially compensate for degradation in a simple manner.

[0096] Steps 101 to 104 are preferably executed in this order. Steps 103 and 104 can be repeated multiple times during the operation of the optoelectronic module 1. Advantageously, the degradation of the light-emitting diode 2 can thus be determined more precisely during the operation of the optoelectronic module 1, and compensation can be performed with higher precision.

[0097] Figure 7 Schematically shows the internal quantum efficiency IQE of the light-emitting diode 2 as a function of the operating current I. The internal quantum efficiency IQE corresponds to the number of photons emitted by the active layer of the light-emitting diode 2 per unit number of carriers injected into the active layer. Here, the internal quantum efficiency IQE is limited, for example, by non-radiative recombination processes of carriers in the active layer. At low operating currents I, for example, non-radiative Shockley-Read-Hall (SRH) recombination dominates, while at high operating currents, non-radiative Auger (AUG) recombination dominates. In Shockley-Read-Hall recombination, carriers recombine, for example, at defects in the lattice of the active layer.

[0098] Due to degradation, the internal quantum efficiency IQE of the light-emitting diode 2 changes. Here, in particular, at low operating currents I (see the arrows and dashed lines in Figure 7 ), where Shockley-Read-Hall recombination dominates, the internal quantum efficiency IQE decreases particularly strongly. At these low operating currents I, the forward voltage Vf of the light-emitting diode 2 is particularly sensitive to the defect density in the active layer and thus to the degradation of the light-emitting diode 2. The operating current I used to measure the forward voltage Vf should not be chosen too small so that the measured value of the forward voltage Vf is not affected by noise or is affected by noise as little as possible. In addition, the operating current I used to measure the forward voltage Vf should not be too large so that the degradation has as large an impact as possible on the measured value of the forward voltage Vf. Figure 7 The preferred range 12 of the operating current I is marked in

[0099] Figure 8 Shows the Pearson correlation coefficient PC between the relative change in forward voltage Vf / Vf0 and the relative change in light intensity Iv / Iv0. The Pearson correlation coefficient PC is calculated based on the changes Vf / Vf0 in the measured forward voltage and the changes Iv / Iv0 in light intensity as a function of the operating current I for multiple identical light-emitting diodes 2 after 24 hours of operation. For example, the Pearson correlation coefficient PC is calculated based on the measured values of the changes Vf / Vf0 in the forward voltage and the changes Iv / Iv0 in light intensity for at least one hundred identical light-emitting diodes 2. In particular, Figure 8The Pearson correlation coefficient PC of three different types of light-emitting diodes 21, 22, and 23 is shown. The first light-emitting diode 21 emits red light, the second light-emitting diode 22 emits green light, and the third light-emitting diode 23 emits blue light.

[0100] In the first light-emitting diode 21 and the second light-emitting diode 22, the Pearson correlation coefficient PC is maximum when the operating current I is about 100 μA, while in the third light-emitting diode 23, the Pearson correlation coefficient PC is maximum when the operating current I is about 3 mA. Advantageously, a predetermined operating current I for determining the degradation of the light-emitting diodes 21, 22, 23 is selected based on the measured value of the forward voltage Vf such that the Pearson correlation coefficient PC is maximum at this predetermined operating current I. Thereby, by measuring the forward voltage Vf, the degradation-related changes in the light intensity Iv of the light-emitting diodes 21, 22, 23 can be compensated with high precision.

[0101] Figure 9 The measured values of the relative change Iv / Iv0 of the light intensity with respect to the relative change Vf / Vf0 of the forward voltage value at a predetermined operating current I after 24 hours of operation of the light-emitting diode 2 are shown. In particular, the measured values of a plurality of first, second, and third light-emitting diodes 21, 22, 23 that are part of the optoelectronic module 1 are shown, where no degradation compensation is performed. As described in connection with Figure 8 the predetermined operating current I for measuring the value of the forward voltage Vf is selected.

[0102] In particular, Figure 9 The linear relationship between the relative change Vf / Vf0 of the forward voltage and the relative change Iv / Iv0 of the light intensity is shown, which is obtained by performing linear regression on the respective measured values of the first, second, and third light-emitting diodes 21, 22, 23. The linear relationship is parameterized by the following formula:

[0103]

[0104] where A and B are compensation parameters, and the right side of formula (G3) corresponds to the compensation factor of formula (G1) described in connection with Figure 6 The compensation parameters A and B can be determined in particular by linear regression, and these compensation parameters are used to compensate for degradation in the method of operating the optoelectronic module.

[0105] Figure 9The linear relationship shown particularly deviates from the point (Iv / Iv0, Vf / Vf0) = (1, 1). In other words, even if the forward voltage Vf of the light-emitting diode 2 does not change, there may be variations in the measured light intensity Iv in the statistical average. Such deviations may be caused, for example, by aging-related changes in the absorption coefficient of the carrier 8 or other parts of the optoelectronic module 1, which affects the measured light intensity Iv.

[0106] Figure 10 shows the relative change Iv c / Iv0 of the light intensity of a plurality of optoelectronic modules 1 according to an embodiment, where the degradation is compensated according to the method described herein. In particular, the measured values are centered along the vertical axis around Iv c / Iv0 = 1. This shows that the degradation can be at least partially compensated by the method described herein.

[0107] Figure 11 、 Figure 12 and Figure 13 shows the relative change Iv c / Iv0 of the light intensity of the light-emitting diode 2 in the optoelectronic module 1 according to an embodiment, where the degradation is at least partially compensated over the operating time. Here, Figure 11 shows according to Figure 4 the change in the light intensity Iv of the first light-emitting diode 21 according to the embodiment of Figure 12 shows according to Figure 4 the change in the light intensity Iv of the second light-emitting diode 22 according to the embodiment of Figure 13 shows according to Figure 4 the change in the light intensity Iv of the third light-emitting diode 23 according to the embodiment of. The compensation is carried out as described in connection with the embodiment of Figure 6 . As a comparison, the dashed line represents the relative change Iv / Iv0 of the light intensity in the case where the degradation of the light-emitting diode 2 is not compensated. In particular, Figure 11 、 Figure 12 and Figure 13 show the average value of the relative change Iv c / Iv0, where the light intensity Iv is averaged over 280 identical light-emitting diodes 2. In addition, the three times standard deviation (±3σ) of the relative change of the light intensity Iv of a plurality of identical light-emitting diodes 2 is also shown. In particular, Figure 11 、 Figure 12 and Figure 13 show that the degradation compensation carried out according to the method described herein is particularly effective at longer operating times.

[0108] This patent application claims the priority of German Patent Application DE 102022129162.6, the disclosure of which is incorporated herein by reference.

[0109] The present invention is not limited to the description based on the embodiments. On the contrary, the present invention includes any new feature and any combination of features, which in particular includes any combination of features in the claims, even if such feature or combination is not explicitly stated in the claims or embodiments.

[0110] List of reference numerals

[0111] 1 Optoelectronic module

[0112] 2 Light-emitting diode

[0113] 21 First light-emitting diode

[0114] 22 Second light-emitting diode

[0115] 23 Third light-emitting diode

[0116] 3 Integrated circuit

[0117] 4 Analog-to-digital converter

[0118] 5 Measurement control unit

[0119] 6 Memory

[0120] 7 Pulse width modulator

[0121] 8 Carrier

[0122] 9 Control unit

[0123] 10 Current source

[0124] 11 Connection contact

[0125] 12 Range

[0126] 101 First step

[0127] 102 Second step

[0128] 103 Third step

[0129] 104 Fourth step

[0130] A, B Compensation parameters

[0131] AUG Auger recombination

[0132] I Operating current

[0133] IQE Internal quantum efficiency

[0134] Iv Light intensity

[0135] Reference value of Iv0 light intensity

[0136] Iv c Compensated light intensity

[0137] PC Pearson correlation coefficient

[0138] SRH Shockley-Read-Hall recombination

[0139] t Time

[0140] Vf Forward voltage

[0141] Reference value of Vf0 forward voltage

[0142] VLED Power supply voltage

[0143] GND Reference potential

Claims

1. An optoelectronic module (1), comprising: - at least one light-emitting diode (2) that emits light with a light intensity (Iv) during operation; - an integrated circuit (3) that regulates the operating current (I) of the light-emitting diode (2) and measures the value of the forward voltage (Vf) of the light-emitting diode (2) during operation, wherein - the integrated circuit (3) determines the degradation of the light-emitting diode (2) by measuring the value of the forward voltage (Vf), and increases or decreases the operating current (I) based on the measured value of the forward voltage (Vf) such that the change in the light intensity (Iv) due to degradation is at least partially compensated; and - the integrated circuit (3) or a measurement control unit (5) for controlling the integrated circuit (3) has a memory (6) in which calibration data is stored, and the calibration data includes the value of the forward voltage (Vf) as a reference value for determining degradation.

2. The optoelectronic module (1) according to the preceding claim, Among them, wherein the integrated circuit (3) has an analog-to-digital converter (4) that measures the value of the forward voltage (Vf) during operation.

3. The optoelectronic module (1) according to any one of the preceding claims, wherein the measured value of the forward voltage (Vf) is stored in the memory (6).

4. The optoelectronic module (1) according to any one of the preceding claims, wherein - the integrated circuit (3) has a pulse width modulator (7); - the pulse width modulator (7) modulates the operating current (I) of the light-emitting diode (2) to control the light intensity (Iv).

5. The optoelectronic module (1) according to any one of the preceding claims, wherein - the optoelectronic module (1) has three light-emitting diodes (21, 21, 22) that emit light in the red, green, or blue spectral range during operation; - the integrated circuit (3) controls the operating currents (I) of the three light-emitting diodes (21, 22, 23) separately from each other and measures the values of the forward voltages (Vf) of the three light-emitting diodes (21, 22, 23) independently of each other to determine degradation; and - the integrated circuit (3) at least partially compensates for the change in the light intensity (Iv) due to degradation for each of the three light-emitting diodes (21, 22, 23).

6. A method for operating an optoelectronic module (1), comprising the following steps: - adjusting the light intensity (Iv) of at least one light-emitting diode (2) by controlling the operating current (I) using an integrated circuit (3); - determining the degradation of the light-emitting diode (2) by measuring the value of the forward voltage (Vf) using the integrated circuit (3), wherein - when adjusting the light intensity (Iv), compensating for the change in the light intensity (Iv) due to degradation by increasing or decreasing the operating current (I) based on the measured value of the forward voltage (Vf); and - calibrating the optoelectronic module (1) before the first operation, the calibration including the step of measuring and storing the value of the forward voltage (Vf) of the light-emitting diode (2) under the same conditions as when determining degradation at a subsequent time point.

7. The method according to the preceding claim, wherein the degradation of the light-emitting diode (2) is determined when the light-emitting diode (2) is turned on and / or at a predetermined point in time.

8. The method according to any one of claims 6 or 7, wherein the forward voltage (Vf) is measured at a predetermined value of the operating current (I).

9. The method according to the preceding claim, wherein the predetermined value of the operating current (I) for measuring the forward voltage (Vf) is selected such that the statistical correlation between the change in the forward voltage (Vf) due to the degradation of the light-emitting diode (2) and the change in the light intensity (Iv) is maximized after a predetermined operating time.

10. The method according to any one of claims 6 to 9, wherein the predetermined operating current (I) for measuring the forward voltage (Vf) is from 50 μA to 5 mA, including the boundary values.

11. The method according to any one of claims 6 to 10, wherein when adjusting the light intensity (Iv) of the light-emitting diode (2), the operating current (I) is corrected using a compensation factor that is linearly related to the measured value of the forward voltage (Vf).

12. The method according to the preceding claim, wherein: - the compensation factor depends on predetermined compensation parameters (A, B); - the compensation parameters (A, B) are determined by measuring the change in the light intensity (Iv) due to degradation in a plurality of identical light-emitting diodes (2) and performing a subsequent statistical evaluation.

13. The method according to any one of claims 6 to 12, wherein the temperature of the light-emitting diode (2) is determined immediately before or after measuring the value of the forward voltage (Vf) for determining the degradation.

14. The method according to the preceding claim, wherein the temperature of the light-emitting diode (2) is determined by measuring the value of the forward voltage (Vf) at a predetermined operating current greater than the operating current (I) for determining the degradation.

15. The method according to any one of claims 13 or 14, wherein: - if the temperature at which the degradation of the light-emitting diode (2) is determined is different from a predetermined temperature, the measured value of the forward voltage (Vf) is corrected; and - the measured value of the forward voltage (Vf) is corrected according to the known relationship between the forward voltage (Vf) and the temperature of the light-emitting diode (2) at a predetermined operating current (I).

16. The method according to any one of claims 6 to 15, wherein the calibration includes an additional step of determining the relationship between the operating current (I) and the light intensity (Iv) of the light-emitting diode (2).

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