Optoelectronic module and method for operating an optoelectronic module

Abstract

The invention specifies an optoelectronic module, comprising: - at least one light-emitting diode (2) which emits light with a light intensity (lv) during operation, - an integrated circuit (3) which adjusts an operating current (I) of the light-emitting diode (2) and measures a value of the forward voltage (Vf) of the light-emitting diode (2) during operation, wherein - the integrated circuit (3) determines a degradation of the light-emitting diode (2) by measuring the value of the forward voltage (Vf) and increases or decreases the electrical operating current (I) depending on the measured value of the forward voltage (Vf) in such a way that a change in the light intensity (lv) on account of the degradation is at least partially compensated for. The invention also specifies a method for operating an optoelectronic module.

Description

[0001] Description

[0002] OPTOELECTRONIC MODULE AND METHOD FOR OPERATING AN OPTOELECTRONIC MODULE

[0003] An optoelectronic module and a method for operating an optoelectronic module are specified.

[0004] The aim is to provide an optoelectronic module with improved stability against age-related changes in light intensity. This object is achieved by a subject matter having the features of independent patent claim 1.

[0005] Furthermore, a method for operating an optoelectronic module with improved stability against age-related changes in light intensity is to be specified. This object is achieved by a method having the features of independent patent claim 6.

[0006] Advantageous embodiments and further developments of the optoelectronic module and of the method for operating an optoelectronic module are specified in the dependent claims.

[0007] According to one embodiment, the optoelectronic module has at least one light-emitting diode which, during operation, emits light with a luminous intensity. For example, the light-emitting diode emits electromagnetic radiation during operation. In particular, the light-emitting diode emits light in a spectral range between infrared light and ultraviolet light. Preferably, the light-emitting diode emits light in a visible spectral range during operation. In particular, the

[0008] Light-emitting diode converts an electrical operating current into light.

[0009] The luminous intensity here and in the following refers to the luminous flux produced by the light-emitting diode per solid angle and is specified in particular in the unit "candela". The luminous flux corresponds to the radiant power of the light-emitting diode, which is weighted with a wavelength-dependent sensitivity of the human eye. The radiant power refers to the energy per time that is transported by the emitted light.

[0010] The light-emitting diode comprises, in particular, an epitaxial semiconductor layer stack having an active layer for converting the electrical operating current into electromagnetic radiation. The active layer has, for example, a pn junction, which can be formed as a quantum well structure or as a multiple quantum well structure.

[0011] According to a further embodiment, the optoelectronic module comprises an integrated circuit that, during operation, sets an operating current of the light-emitting diode and measures a value of the forward voltage of the light-emitting diode. The integrated circuit is, for example, an application-specific integrated circuit (AS IC for short).

[0012] The integrated circuit has, in particular, an electrical circuit for adjusting the electrical operating current of the light-emitting diode. For example, the electrical circuit comprises an adjustable electrical current source. Furthermore, the integrated circuit has an electrical circuit for measuring the forward voltage of the light-emitting diode. Here and below, the forward voltage refers, in particular, to an electrical voltage that drops across the semiconductor layer stack of the light-emitting diode while a constant electrical operating current flows in the forward direction through the light-emitting diode. In other words, the forward voltage corresponds to an electrical voltage drop between an anode and a cathode of the light-emitting diode operated in the forward direction.

[0013] According to a further embodiment of the optoelectronic module, the integrated circuit determines degradation of the light-emitting diode by measuring the value of the forward voltage. Here and below, degradation refers to an age-related change in the luminous intensity of the light-emitting diode at a given electrical operating current.

[0014] For example, defects form in the active layer during operation of the light-emitting diode. Furthermore, defects already present in the semiconductor layer stack can migrate into or out of the active layer during operation of the light-emitting diode. These defects are, for example, defects or dislocations in a crystalline order of the semiconductor layer stack. An increase in defect density in the active layer due to aging of the light-emitting diode can, for example, lead to a reduction in the internal quantum efficiency of the light-emitting diode. Thus, with increasing age of the light-emitting diode, in particular the luminous intensity of the light emitted by the light-emitting diode decreases at a given electrical operating current. The defect density in the active layer can also decrease with increasing age of the light-emitting diode, which for example increases the luminous intensity of the light-emitting diode.

[0015] The forward voltage of the light-emitting diode at given operating parameters, in particular at a given operating current and at a given temperature, can change, for example, as a function of the defect density in the active layer. In particular, the degradation of the light-emitting diode correlates with an age-related change in the forward voltage at given operating parameters. Thus, a change in the forward voltage of the light-emitting diode at given operating parameters can be used as a measure of the degradation of the light-emitting diode. For example, the forward voltage decreases when the luminous intensity decreases due to the degradation of the light-emitting diode, or vice versa.

[0016] According to a further embodiment of the optoelectronic module, the integrated circuit increases or decreases the electrical operating current of the light-emitting diode as a function of the measured value of the forward voltage such that a change in the luminous intensity due to degradation is at least partially compensated. For example, the integrated circuit increases or decreases a temporally constant operating current. The integrated circuit can also increase or decrease a temporal average value of the operating current, for example, if the luminous intensity of the light-emitting diode is adjusted by pulse-width modulation of the operating current.

[0017] The compensation is made in particular in such a way that the

[0018] The change in luminous intensity due to degradation is at least partially compensated for by increasing or decreasing the operating current and a concomitant change in luminous intensity. In other words, the operating current is increased if the luminous intensity of the LED decreases due to degradation, and / or vice versa.

[0019] For example, at the time of calibration the light-emitting diode has a certain luminous intensity at a predetermined first operating current, as well as a certain forward voltage at a predetermined second operating current. The first and second operating currents can be the same or different. After a certain operating time of the light-emitting diode following calibration, for example the luminous intensity at the first operating current and the forward voltage at the second operating current change due to the degradation of the light-emitting diode. The integrated circuit then determines in particular 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 as a function of the measured value of the forward voltage in such a way that the luminous intensity of the degraded light-emitting diode at the first operating current corresponds to the luminous intensity at the first operating current at the time of calibration, or deviates therefrom as little as possible.

[0020] According to a preferred embodiment, the optoelectronic module comprises:

[0021] - at least the light emitting diode which emits light with the luminous intensity during operation,

[0022] - the integrated circuit which, during operation, sets the operating current of the light-emitting diode and measures the value of the forward voltage of the light-emitting diode, wherein - the integrated circuit determines the degradation of the light-emitting diode by measuring the value of the forward voltage and increases or decreases the electrical operating current as a function of the measured value of the forward voltage in such a way that the change in the luminous intensity due to the degradation is at least partially compensated.

[0023] The optoelectronic module described here is based on the idea of ​​controlling, and if necessary compensating for, a change in the luminous intensity of the LED due to age-related degradation purely electronically. The degradation is advantageously determined by measuring the forward voltage of the LED with an integrated circuit that can also control the operating current of the LED.

[0024] The forward voltage correlates, especially at relatively low operating currents, with the defect density in the active layer of the LED and thus with the degradation of the LED. The measured value of the forward voltage can thus be used to adjust the operating current of the LED in such a way that the age-related change in luminous intensity is at least partially compensated.

[0025] For example, with the optoelectronic module described here, expensive burn-in of the LED during production can be advantageously dispensed with. During burn-in, the LED is operated at a maximum operating current for an extended period, particularly before optical calibration of the luminous intensity, to prevent rapid initial degradation during operation after calibration. In contrast to burn-in, the optoelectronic module described here advantageously allows monitoring of degradation during operation.

[0026] Furthermore, with the optoelectronic module described here, no complex recording of an operating time and / or a temperature profile during operation is necessary in order to at least partially compensate for the age-related change in luminous intensity. In particular, the measured value of the forward voltage in the optoelectronic module described here is advantageously directly related to the degradation of the light-emitting diode. In contrast, the operating time or the temperature profile, for example, is only an indirect measure of the degradation of the light-emitting diode. In particular, the operating time or the temperature profile provide no information about the individual state of degradation of the light-emitting diode in the optoelectronic module. In contrast, with the optoelectronic module described here, the degradation can be compensated depending on the individual state of the light-emitting diode.Thus, the compensation can advantageously be carried out with greater accuracy.

[0027] Furthermore, the optoelectronic module described here eliminates the need for an optical light intensity sensor to monitor the degradation of the LED. Thus, the optoelectronic module described here can be manufactured advantageously at low cost.

[0028] According to a further embodiment of the optoelectronic

[0029] Module, the integrated circuit has an analog-to-digital converter which, during operation, measures the value of the forward voltage. In particular, the analog-to-digital converter measures and digitizes the forward voltage at predetermined times. For example, the analog-to-digital converter measures electrical voltages up to a maximum voltage between 1 volt and 3 volts inclusive with an accuracy between 0.1 millivolt and 10 millivolts inclusive. Accordingly, the analog-to-digital converter has, for example, a resolution between 7 bits and 15 bits inclusive.

[0030] According to a further embodiment of the optoelectronic module, the integrated circuit or a 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 configured to control the integrated circuit for measuring 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 on the basis of the stored value of the forward voltage in order to at least partially compensate for the age-related change in the luminous intensity of the light-emitting diode.

[0031] Furthermore, calibration data of the optoelectronic module can be stored in the memory. The calibration data include, in particular, a relationship between the luminous intensity of the light-emitting diode and the electrical operating current of the light-emitting diode. Furthermore, the calibration data preferably include 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 a relationship between the luminous intensity of the light-emitting diode and the operating temperature of the light-emitting diode. The calibration data are stored in the memory, for example, after a calibration of the optoelectronic module.

[0032] According to a further 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 luminous intensity. In particular, the pulse width modulator changes the operating current periodically as a function of time. The operating current can, for example, assume two different values ​​within a period during two corresponding, differently long time intervals. Preferably, one value of the operating current corresponds to a maximum operating current of the light-emitting diode, while the other value corresponds to a vanishing operating current. In other words, at one value of the operating current the light-emitting diode emits light with maximum luminous intensity, whereas at the other value of the operating current no light is emitted.The period is, for example, less than 20 milliseconds to avoid noticeable, disturbing flickering of the optoelectronic module.

[0033] By setting a duty cycle between the two values ​​of the operating current, the pulse width modulator can in particular provide any desired time-average value of the operating current between 0 amperes and the maximum operating current. The duty cycle specifies a temporal relationship between the two time intervals during which the operating current assumes the two respective different values. The duty cycle is preferably specified as a percentage. For example, with a duty cycle of 0%, the light-emitting diode emits no light on average over time, whereas with a duty cycle of 100%, light is emitted at maximum luminous intensity on average over time.By adjusting the temporal average of the operating current with the pulse-width modulator, a color shift in the light emitted by the LED can be advantageously reduced or avoided compared to adjusting a corresponding temporally constant operating current. Furthermore, the luminous intensity of the light emitted by the LED is directly proportional to the duty cycle.

[0034] According to a further embodiment, the optoelectronic module has three light-emitting diodes that, during operation, emit electromagnetic radiation in a red, green, or blue spectral range. In particular, a first light-emitting diode emits red light, a second light-emitting diode emits blue light, and a third light-emitting diode emits green light. For example, the optoelectronic module can emit light of any desired mixed color by adjusting the relative luminous intensities of the three light-emitting diodes accordingly.

[0035] According to a further embodiment of the optoelectronic module, the integrated circuit controls electrical operating currents of the three light-emitting diodes separately and measures the forward voltage values ​​of the three light-emitting diodes independently of one another to determine the degradation. Thus, in particular, the degradation of each of the three light-emitting diodes is determined independently of one another. According to a further embodiment of the optoelectronic module, the integrated circuit at least partially compensates for the change in the luminous intensity of each of the three light-emitting diodes due to the degradation. Thus, the color stability of the optoelectronic module can advantageously be increased if the three light-emitting diodes degrade differently.By compensating for the age-related changes in the respective luminous intensities of the three light-emitting diodes, the integrated circuit at least partially compensates for an age-related change in the color coordinates of the mixed light emitted by the optoelectronic module.

[0036] Furthermore, a method for operating an optoelectronic module is specified. In particular, the method can be used to operate an optoelectronic module described here. All features of the optoelectronic module are also disclosed for the method for operating an optoelectronic module, and vice versa.

[0037] According to one embodiment of the method for operating an optoelectronic module, the luminous intensity of at least one light-emitting diode is first adjusted by controlling an electrical operating current with an integrated circuit. The operating current is preferably pulse-width modulated. The luminous intensity is adjusted, for example, by specifying the duty cycle or the time-average value of the pulse-width modulated operating current.

[0038] According to a further embodiment of the method, a degradation of the light-emitting diode is determined by measuring a value of a forward voltage with the integrated circuit. The forward voltage is preferably measured at predetermined operating parameters of the light-emitting diode, for example at a predetermined electrical operating current and / or at a predetermined temperature. For example, the forward voltage is dependent not only on the degradation but also on the temperature of the light-emitting diode. By measuring the forward voltage under the same operating parameters, the influence of the degradation on the forward voltage can in particular be separated from other effects. This improves, for example, the accuracy of the compensation for age-related changes in luminous intensity.

[0039] According to a further embodiment of the method, when adjusting the luminous intensity, a change in the luminous intensity due to the degradation is compensated by increasing or decreasing the electrical operating current as a function of the measured value of the forward voltage. In particular, the operating current is changed by increasing or decreasing it. For example, the electrical operating current of the light-emitting diode is changed as a function of the measured value of the forward voltage such that the luminous intensity of the light emitted by the degraded light-emitting diode at least approximately corresponds to the luminous intensity of the light-emitting diode at the unchanged operating current at the time of calibration.

[0040] According to a preferred embodiment, the method for operating the optoelectronic module comprises the steps of: - adjusting the luminous intensity of at least one light-emitting diode by controlling the electrical operating current with the integrated circuit, - determining the degradation of the light-emitting diode by measuring the value of the forward voltage with the integrated circuit, wherein

[0041] - when adjusting the luminous intensity, the change in luminous intensity due to degradation is compensated by increasing or decreasing the electrical operating current as a function of the measured value of the forward voltage.

[0042] Preferably, the steps of the method are carried out in the order stated above. The above steps of the method can be carried out as often as desired.

[0043] According to a further embodiment of the method, the degradation of the LED is determined when the LED is switched on and / or at predetermined times. For example, the value of the forward voltage is determined each time the optoelectronic module is put into operation and / or after specified service intervals.

[0044] Furthermore, it is also possible to measure the value of the forward voltage, for example continuously during operation of the optoelectronic module. For example, in pulse width modulation, one of the two values ​​of the operating current can be set up to measure the forward voltage. This is particularly possible if the predetermined value of the operating current for measuring the forward voltage is so small that the light-emitting diode emits no light or no perceptible light. In this case, the forward voltage of the light-emitting diode is measured during a partial period of the pulse width modulation in which the light-emitting diode emits no perceptible light. According to a further embodiment of the method, the

[0045] Forward voltage is measured at a predetermined value of the operating current. The forward voltage is preferably measured at several points in time, with the predetermined value of the operating current having the same value for each measurement of the forward voltage. This improves, for example, the accuracy of the compensation for the age-related change in luminous intensity. The predetermined operating current for measuring the forward voltage is selected in particular such that the change in the forward voltage due to the degradation is particularly sensitive to the degradation of the light-emitting diode.

[0046] According to a further embodiment of the method, the predetermined value of the electrical operating current for measuring the forward voltage is selected such that a statistical correlation between a change in the forward voltage and a change in the luminous intensity due to the degradation of the light-emitting diode is greatest after a predetermined operating time. For example, the forward voltage and the luminous intensity are measured both at the beginning and at the end of the predetermined operating time for a large number of identical optoelectronic modules for a large number of different operating currents. The change in the forward voltage is determined, for example, as the ratio of the measured values ​​of the forward voltage at the beginning and at the end of the predetermined operating time at a predetermined operating current.Likewise, the change in luminous intensity is determined, for example, as the ratio of the measured luminous intensity values ​​at the beginning and end of the specified operating time at the specified operating current. From the measured change in forward voltage and the measured change in luminous intensity of each of the numerous optoelectronic modules, a measure of their statistical correlation for different operating currents can be calculated. The specified operating time is, for example, between one hour and 48 hours.

[0047] To calculate the statistical correlation, the change in forward voltage and the change in luminous intensity are considered as two statistical random variables. For example, a Pearson correlation coefficient can be calculated between the measured changes in luminous intensity and the measured changes in forward voltage as a measure of their statistical correlation. The Pearson correlation coefficient corresponds in particular to a covariance between the two random variables divided by the standard deviations of the two random variables. The covariance corresponds to an 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 luminous intensity is, in particular, a function of the electrical operating current of the light-emitting diode. Preferably, the electrical operating current selected for measuring the forward voltage value for determining degradation is that at which the statistical correlation between the change in forward voltage and the change in luminous intensity is greatest. According to a further embodiment of the method, the predetermined electrical operating current for measuring the forward voltage is between 50 microamperes and 5 milliamperes.

[0049] According to a further embodiment of the method, when adjusting the luminous intensity of the light-emitting diode, the electrical operating current is corrected using a compensation factor that is linearly dependent on the measured value of the forward voltage. For example, to compensate for the degradation, a value of a temporally constant operating current is changed by the compensation factor. To compensate for the 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 proportionally to the compensation factor.

[0050] The compensation factor is, in particular, a linear function of the measured forward voltage value. The compensation factor can also be any function of the forward voltage value. For example, the compensation factor is a polynomial, i.e., a sum of multiples of powers of the measured forward voltage value.

[0051] According to a further embodiment of the method, the compensation factor depends on predetermined compensation parameters. The compensation parameters are, for example, coefficients in the polynomial formed from powers of the measured value of the forward voltage. In the case of a linear relationship between the measured value of the

[0052] Forward voltage and the compensation factor, the

[0053] Compensation factor for example two compensation parameters.

[0054] According to a further embodiment of the method, the compensation parameters are determined by measuring the change in luminous intensity due to degradation in a large number of identical light-emitting diodes and a subsequent statistical evaluation. For example, for the large number of identical light-emitting diodes, both the change in luminous intensity and the change in the value of the forward voltage are measured after a predetermined operating time. A relationship between the change in luminous intensity and the change in the forward voltage is then determined by means of a regression analysis. In particular, a polynomial, for example linear, relationship between the change in luminous intensity and the change in the forward voltage is assumed and the coefficients of the polynomial, i.e. the compensation parameters, are determined by the regression analysis.For example, the compensation parameters are determined by minimizing a mean square deviation of the measured changes in luminous intensity and forward voltage from the assumed polynomial relationship.

[0055] According to a further embodiment of the method, a temperature of the light-emitting diode is determined immediately before or after the measurement of the value of the forward voltage to determine the degradation. For example, the temperature of the light-emitting diode is measured using a temperature sensor. According to a further embodiment of the method, the temperature of the light-emitting diode is determined by measuring the value of the forward voltage at a predetermined electrical operating current that is greater than the electrical operating current to determine the degradation. The forward voltage of the light-emitting diode at a predetermined electrical operating current depends in particular on the temperature of the active layer. Thus, the temperature of the light-emitting diode can be determined in particular from a measurement of the forward voltage at a predetermined operating current.For example, the temperature of the LED is measured at a value of the operating current recommended for continuous operation of the LED. The higher the specified operating current, the greater the change in the forward voltage due to a change in temperature. This can advantageously increase the accuracy of the temperature measurement.

[0056] According to a further embodiment of the method, the measured value of the forward voltage is corrected if the temperature deviates from a predetermined temperature when determining the degradation of the light-emitting diode. In particular, the measured value of the forward voltage for determining the degradation is corrected such that the corrected value corresponds at least approximately to the value of the forward voltage at the predetermined temperature. Thus, temperature differences in different measurements of the forward voltage for determining the degradation can be at least partially compensated. This advantageously improves the accuracy of the degradation compensation.

[0057] According to a further embodiment of the method, the measured value of the forward voltage is corrected based on a known relationship between the forward voltage and the temperature of the light-emitting diode at a predetermined operating current. For example, if the temperature of the light-emitting diode increases by one degree Celsius, the forward voltage decreases or increases 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 the increase or decrease in the forward voltage per degree Celsius, the corrected value of the forward voltage can be determined.

[0058] According to a further embodiment of the method, the optoelectronic module is calibrated before a first operation. In particular, the optoelectronic module is optically calibrated before the first operation. The calibration can also be carried out after a specific operating period of the optoelectronic module or at several points in time after different operating periods. During calibration, for example, the luminous intensity of the emitted light and / or color coordinates of the optoelectronic module are measured at predetermined operating parameters, for example operating current and temperature. The measured values ​​are stored in particular in the memory of the integrated circuit.

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

[0060] According to a further embodiment of the method, during calibration, the forward voltage value of the LED is measured under the same conditions as when determining the degradation at later times. The measured forward voltage value is then stored.

[0061] In particular, the value of the forward voltage measured during calibration is stored in the memory of the integrated circuit or in the memory of the external measurement control unit.

[0062] The forward voltage value measured during calibration represents a reference value against which the degradation of the LED is determined. For example, to determine the degradation of the LED, the forward voltage value is measured after a certain operating time and compared with the reference value. The change in the forward voltage is, for example, proportional to the degradation of the LED.

[0063] Further advantageous embodiments and developments of the optoelectronic module and of the method for operating an optoelectronic module emerge from the embodiments described below in conjunction with the figures.

[0064] Figure 1 shows a schematic representation of an optoelectronic module according to one embodiment. Figures 2 and 3 show schematic block diagrams of optoelectronic modules according to various embodiments.

[0065] Figures 4 and 5 show schematic circuit diagrams of optoelectronic modules according to further embodiments.

[0066] Figure 6 shows a schematic flow diagram of a method for operating an optoelectronic module according to an embodiment.

[0067] Figure 7 shows an example of a schematic diagram of an internal quantum efficiency of a light-emitting diode as a function of an operating current.

[0068] Figure 8 shows an example diagram of a statistical correlation between a degradation-related change in the forward voltage and a degradation-related change in the luminous intensity as a function of an operating current of a light-emitting diode.

[0069] Figure 9 shows an example diagram of a degradation-related change in luminous intensity as a function of a degradation-related change in the forward voltage of a light-emitting diode.

[0070] Figure 10 shows an example diagram of a compensated degradation as a function of an uncompensated degradation for a large number of optoelectronic modules.

[0071] Figures 11, 12 and 13 show compensated degradations of optoelectronic modules according to various embodiments as a function of the operating time of the optoelectronic module.

[0072] Identical, similar, or functionally identical elements are provided with the same reference symbols in the figures. The figures and the relative sizes of the elements depicted in the figures are not to scale. Rather, individual elements may be exaggerated for clarity and / or clarity.

[0073] The optoelectronic module 1 according to the embodiment in Figure 1 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 electrical contact surfaces via which the light-emitting diode 2 and the integrated circuit 3 are electrically contacted. Furthermore, the carrier 8 has electrical connection contacts for external electrical contacting of the optoelectronic module 1 on a surface opposite the main surface. The carrier 8 has, for example, a plastic, a ceramic, and / or a 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 with an active layer for converting an electrical operating current I into electromagnetic radiation. In particular, the light-emitting diode 2 emits light in the visible spectral range during operation. A luminous intensity Iv of the light emitted by the light-emitting diode 2 can be adjusted via the electrical operating current I. The integrated circuit 3 comprises an electrical circuit for adjusting the electrical operating current I of the light-emitting diode 2, and an electrical circuit for measuring a forward voltage Vf of the light-emitting diode 2. The integrated circuit 3 is designed to determine an age-related degradation of the light-emitting diode 2 by measuring a value of the forward voltage Vf.In particular, to measure the forward voltage Vf, a predetermined constant operating current I is applied to the light-emitting diode 2, at which 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 a degradation-related change in the luminous intensity Iv and a degradation-related change in the forward voltage Vf of the light-emitting diode 2.

[0075] Furthermore, the integrated circuit 3 is designed to at least partially compensate for the degradation-related change in the luminous intensity Iv of the light emitted by the light-emitting diode 2 using 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 depending on the measured value of the forward voltage Vf. In particular, the operating current I is changed such that the luminous intensity Iv of the light emitted by the light-emitting diode 2 at least approximately corresponds to the luminous intensity Iv at the time of an optical calibration of the light-emitting diode 2 with the unchanged operating current I.

[0076] Figure 2 shows a schematic block diagram of an optoelectronic module 1 according to the exemplary embodiment described in connection with Figure 1. The anode of the light-emitting diode 2 is connected to an electrical supply voltage VLED, while the cathode of the light-emitting diode 2 is connected to a reference potential GND via a current source 10 in the integrated circuit 3. The current source 10 is configured, in particular, to provide the electrical operating current I of the light-emitting diode 2.

[0077] The integrated circuit 3 further comprises an electrical circuit, in particular an analog-to-digital converter 4, for measuring the forward voltage Vf of the light-emitting diode 2, as well as 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 the 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.

[0078] 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 specifies a duty cycle of the pulse-width modulated operating current I for adjusting the luminous intensity Iv of the light-emitting diode 2.

[0079] Furthermore, the control unit 9 calculates a compensation factor F from the measured value of the forward voltage Vf and from predetermined compensation parameters A, B. In particular, the duty cycle of the pulse-width-modulated operating current I is changed inversely proportional to the compensation factor F in order to at least partially compensate for the degradation-related change in the luminous intensity Iv of the light-emitting diode 2. The compensation parameters A, B are stored in the memory 6, for example, during the manufacture of the optoelectronic module 1.

[0080] Figure 3 shows a schematic block diagram of an optoelectronic module 1 according to a further embodiment. In contrast to the embodiment described in connection with Figure 2, 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, for example, control a plurality of integrated circuits 3 with associated light-emitting diodes 2. In particular, the memory 6 is part of the measurement control unit 5 instead of the integrated circuit 3. The measurement control unit has a control unit 9 which 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 particular, in this embodiment, the control unit 9 of the measurement control unit 5 calculates the compensation factor F from 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 for changing the duty cycle of the pulse width modulator 7. Furthermore, the measurement control unit 5 controls the times at which the value of the forward voltage Vf is measured by the integrated circuit 3.

[0081] The optoelectronic module 1 according to the embodiment in Figure 4 has an integrated circuit 3 and three light-emitting diodes 21, 22, 23 which are arranged on a common carrier 8. The anodes of the three light-emitting diodes 21, 22, 23 are connected to a common electrical supply voltage VLED, while 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, while 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.

[0082] The integrated circuit 3 controls the operating currents I of the three light-emitting diodes 21, 22, 23 independently of one another, so that the relative luminous intensities 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.

[0083] Furthermore, the integrated circuit 3 determines the degradation of each of the three light-emitting diodes 21, 22, 23 independently of one another by measuring the respective forward voltage Vf. Based on the measured forward voltages Vf, the integrated circuit compensates for age-related changes in the luminous intensities Iv of the three light-emitting diodes 21, 22, 23. In particular, this advantageously at least partially compensates for an age-related color shift of the optoelectronic module 1.

[0084] The optoelectronic module 1 has connection contacts 11 for connecting the integrated circuit 3 to a serial bus. The integrated circuit 3 exchanges data with the external measurement control unit 5 via the serial bus (not shown here, see, for example, Figure 3).

[0085] In contrast to the embodiment in Figure 4, the optoelectronic module 1 according to the embodiment in Figure 5 has an integrated circuit 3 that is not arranged together with the three light-emitting diodes 21, 22, 23 on the carrier 8, but is spatially separated from them. For example, this allows the light-emitting diodes 21, 22, 23 of several optoelectronic modules 1 to be arranged particularly compactly next to one another, while the associated integrated circuits 3 are arranged away from the light-emitting diodes 21, 22, 23.

[0086] Figure 6 shows different steps 101, 102, 103, 104 of a method for operating the optoelectronic module 1 according to the embodiment in Figure 2. In a first step 101, the optoelectronic module 1 is calibrated. In particular, the luminous intensity Iv of the light emitted by the light-emitting diode 2 is measured as a function of the electrical operating current I at a constant temperature and stored as a reference value of the luminous intensity Ivo. Furthermore, the forward voltage Vf of the light-emitting diode is measured at a predetermined electrical operating current I and at a constant temperature and stored. 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. The selection of the predetermined operating current I is described, for example, in connection with Figure 8.The measured value of the forward voltage Vf is stored as a reference value Vfo in the memory 6 of the integrated circuit 3. In a second step 102, the optoelectronic module 1 is in operation, and the light-emitting diode 2 emits light with an adjustable luminous intensity Iv. The luminous intensity Iv is adjusted by pulse-width modulation of the operating current I with the integrated circuit 3. In particular, the luminous intensity Iv is proportional to the duty cycle of the pulse-width modulated operating current I.

[0087] In a 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 the calibration. In particular, Vf is measured at the same predetermined operating current I and at the same temperature of the optoelectronic module 1 as during the calibration. By measuring this value of the forward voltage Vf, the degradation of the light-emitting diode 2 is determined. For example, the degradation-related change in the luminous intensity Iv / Ivo of the light emitted by the light-emitting diode 2 is at least approximately proportional to the change in the value of the forward voltage Vf / Vfo, the changes being determined relative to the reference values ​​Ivo, Vfo from the calibration.

[0088] In a fourth step 104, the change in the luminous intensity Iv due to the degradation of the light-emitting diode 2 during the further operation of the optoelectronic module 1 is at least partially compensated by the integrated circuit 3. For this purpose, the integrated circuit 3 calculates a compensation factor F, which depends on the value of the forward voltage Vf measured in step 103, on the reference value measured in step 101 and on compensation parameters A, B. In particular, the compensation factor F has the

[0089] form where A and B are the compensation parameters, Vf denotes the measured value of the forward voltage from step 103 and Vfo denotes the reference value of the forward voltage from step 101. The compensation factor F describes in particular a change in the luminous intensity Iv of the light emitted by the degraded light-emitting diode 2 relative to the luminous intensity Iv at the time of calibration of the optoelectronic module 1. The determination of the compensation parameters A, B takes place, for example, as described in connection with Figure 9. In particular, the compensation parameters A, B are stored in the memory 6 of the integrated circuit 3 during manufacture of the optoelectronic module 1.

[0090] The duty cycle PWM of the pulse width modulated

[0091] Operating current I is corrected during further operation of the optoelectronic module 1 with the compensation factor F:

[0092] PWM

[0093] PWMC = ( G2 )

[0094] A v Ifö~ +B

[0095] PWM C the corrected duty cycle and PWM the original duty cycle. By pulse width modulation of the operating current I of the LED 2 with the corrected duty cycle PWM C the degradation-related change in the luminous intensity Iv of the light-emitting diode 2 is at least partially compensated. In particular, the luminous intensity Iv of the light-emitting diode 2 with the corrected duty cycle PWM C generated light is at least approximately equal to the luminous intensity Iv of the light generated at the time of calibration with the duty cycle PWM . Since the time-averaged luminous intensity Iv of the light emitted by the light-emitting diode 2 is directly proportional to the duty cycle PWM of the pulse-width modulated operating current I , the degradation can be advantageously prevented by the above-described correction of the duty cycle PWM Cbe compensated at least partially in a simple way.

[0096] Steps 101 to 104 are preferably performed in this order. Steps 103 and 104 can be repeated multiple times during operation of the optoelectronic module 1. This advantageously allows the degradation of the light-emitting diode 2 during operation of the optoelectronic module 1 to be determined more precisely and subsequently compensated with greater accuracy.

[0097] Figure 7 shows, by way of example, a schematic internal quantum efficiency IQE of a 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 number of charge carriers injected into the active layer. The internal quantum efficiency IQE is limited, for example, by non-radiative recombination processes of charge carriers in the active layer. At small operating currents I, for example, non-radiative Shockley-Read-Hall (SRH) recombination dominates, whereas at large operating currents, non-radiative Auger (AUG) recombination dominates. During Shockley-Read-Hall recombination, the charge carriers recombine, for example, at a defect in the crystal lattice of the active layer. The degradation, for example, changes the internal quantum efficiency IQE of the light-emitting diode 2.The internal quantum efficiency IQE decreases particularly sharply at low operating currents I (see arrow and dashed line in Figure 7), where Shockley-Read-Hall recombination dominates. The forward voltage Vf of the light-emitting diode 2 is advantageously particularly sensitive to the defect density in the active layer and thus to the degradation of the light-emitting diode 2 at these low operating currents I. The operating current I for measuring the forward voltage Vf is advantageously not chosen to be too small, so that the measured value of the forward voltage Vf is not influenced by noise, or is influenced as little as possible. Furthermore, the operating current I for measuring the forward voltage Vf is advantageously not too large, so that the degradation has the greatest possible effect on the measured value of the forward voltage Vf.A preferred range 12 of operating currents I , at which the degradation of the light-emitting diode 2 can be determined from the measured value of the forward voltage Vf, is marked in Figure 7 .

[0098] Figure 8 shows the Pearson correlation coefficient PC between the relative change in the forward voltage Vf / Vfo and the relative change in the luminous intensity IV / IVQ . The Pearson correlation coefficient PC is calculated from the measured changes in the forward voltage Vf / Vfo and the luminous intensity IV / IVQ for a large number of identical light-emitting diodes 2 after an operating time of 24 hours as a function of the operating current I . The Pearson correlation coefficient PC is calculated, for example, from measured values ​​of the change in the forward voltage Vf / Vfo and the change in the luminous intensity IV / IVQ of at least one hundred identical light-emitting diodes 2 . In particular, Figure 8 shows Pearson correlation coefficients PC for three different types of light-emitting diodes 21, 22, 23. The first light-emitting diode 21 emits red light, while the second light-emitting diode 22 emits green light and the third light-emitting diode 23 emits blue light.

[0099] For the first light-emitting diode 21 and the second light-emitting diode 22, the Pearson correlation coefficient PC is greatest at an operating current I of approximately 100 microamperes, while the Pearson correlation coefficient PC for the third light-emitting diode 23 is greatest at an operating current I of approximately 3 milliamperes. Advantageously, the predetermined operating current I for determining the degradation of the light-emitting diodes 21, 22, 23 is selected on the basis of the measurement of the value of the forward voltage Vf such that the Pearson correlation coefficient PC is greatest at this predetermined operating current I. As a result, the degradation-induced change in the luminous intensity Iv of the light-emitting diodes 21, 22, 23 can be compensated for with high accuracy by measuring the forward voltage Vf.

[0100] Figure 9 shows measured values ​​of a relative change in the luminous intensity Iv / Ivo as a function of the relative change in the value of the forward voltage Vf / Vfo at a predetermined operating current I after an operating time of the light-emitting diode 2 of 24 hours. In particular, measured values ​​are shown for a plurality of first, second and third light-emitting diodes 21, 22, 23, which are part of an optoelectronic module 1 in which no compensation for degradation takes place. The predetermined operating current I for measuring the value of the forward voltage Vf is selected as described in connection with Figure 8. In particular, Figure 9 shows linear relationships between the relative change in the forward voltage Vf / Vfo and the relative change in the luminous intensity Iv / Ivo, which were obtained by linear regression of the corresponding measured values ​​for the first, second and third light-emitting diodes 21, 22, 23, respectively. The linear relationship is given by the equation parameterized , where A and B are the compensation parameters and the right side of equation ( G3 ) corresponds to the compensation factor from equation ( Gl ) described in connection with Figure 6. The linear regression is used in particular to determine the compensation parameters A and B which are used in the method for operating the optoelectronic module to compensate for the degradation.

[0101] The linear relationships shown in Figure 9 are shifted, in particular, away from the point (Iv / Ivo, Vf / Vfo) = (1, 1). In other words, a change in the measured luminous intensity Iv may occur on average even though the forward voltage Vf of the light-emitting diode 2 has not changed. This deviation may arise, for example, from an age-related change in an absorption coefficient of the carrier 8 or other parts of the optoelectronic module 1, which influences the measured luminous intensity Iv.

[0102] Figure 10 shows measured values ​​of the relative change in luminous intensity Iv c / Ivo of a plurality of optoelectronic modules 1 according to an embodiment, wherein the degradation was compensated according to the method described here, as a function of the relative change in the luminous intensity Iv / Ivo without compensation of the degradation. In particular, the measured values ​​along the vertical axis are around Iv c / Ivo = 1. This shows that the degradation can be at least partially compensated by the method described here.

[0103] Figures 11, 12 and 13 show a relative change in the luminous intensity Iv c / Ivo of the light-emitting diode 2 in an optoelectronic module 1 according to an embodiment, wherein the degradation is at least partially compensated, as a function of the operating time. Figure 11 shows the change in the luminous intensity Iv for a first light-emitting diode 21, Figure 12 for a second light-emitting diode 22 and Figure 13 for a third light-emitting diode 23 according to the embodiment in Figure 4. The compensation is carried out as described in connection with the embodiment in Figure 6. The dotted line shows, for comparison, the relative change in the luminous intensity Iv / Ivo without compensation for the degradation of the light-emitting diode 2. In particular, Figures 11, 12 and 13 show mean values ​​of the relative change in the luminous intensity Iv c / Ivo, where the luminous intensity Iv was averaged over 280 identical light-emitting diodes 2. Furthermore, a three-fold standard deviation (±3o) of the relative change in the luminous intensity Iv for a large number of identical light-emitting diodes 2 is shown. In particular, Figures 11, 12, and 13 show that the compensation of degradation according to the method described here is particularly effective over long operating periods.

[0104] This patent application claims priority from German patent application DE 102022129162 . 6 , the disclosure of which is hereby incorporated by reference. The invention is not limited to the exemplary embodiments by the description. Rather, the invention encompasses any novel feature and any combination of features, including, in particular, any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

[0105] Reference symbol list

[0106] 1 optoelectronic module

[0107] 2 LEDs

[0108] 21 first LED

[0109] 22 second LED

[0110] 23 third LED

[0111] 3 integrated circuit

[0112] 4 analog-to-digital converters

[0113] 5 Measurement control unit

[0114] 6 storage

[0115] 7 Pulse width modulator

[0116] 8 carriers

[0117] 9 Control unit

[0118] 10 Power source

[0119] 11 Connection contact

[0120] 12 Area

[0121] 101 first step

[0122] 102 second step

[0123] 103 third step

[0124] 104 fourth step

[0125] A, B compensation parameters

[0126] AUG Auger recombination

[0127] I Operating current

[0128] IQE internal quantum efficiency

[0129] Iv luminous intensity

[0130] Ivo reference value of luminous intensity

[0131] IV c compensated luminous intensity

[0132] PC Pearson correlation coefficient

[0133] SRH Shockley-Read-Hall recombination t time

[0134] Vf forward voltage

[0135] Vfo reference value of the forward voltage VLED supply voltage

[0136] GND reference potential

Claims

Patent claims 1. Optoelectronic module (1) comprising: - at least one light-emitting diode (2) which emits light with a luminous intensity (Iv) during operation, - an integrated circuit (3) which, during operation, sets an operating current (I) of the light-emitting diode (2) and measures a value of the forward voltage (Vf) of the light-emitting diode (2), wherein - the integrated circuit (3) determines a degradation of the light-emitting diode (2) by measuring the value of the forward voltage (Vf) and increases or decreases the electrical operating current (I) depending on the measured value of the forward voltage (Vf) such that a change in the luminous intensity (Iv) due to the 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 are stored, wherein the calibration data comprise a value of the forward voltage (Vf) as a reference value for determining the degradation.

2. Optoelectronic module (1) according to the preceding claim, wherein the integrated circuit (3) comprises an analog-to-digital converter (4) which measures the value of the forward voltage (Vf) during operation.

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

4. Optoelectronic module (1) according to one of the preceding claims, wherein - the integrated circuit (3) comprises a pulse width modulator (7), and - the pulse width modulator (7) modulates the operating current (I) of the light-emitting diode (2) to control the luminous intensity (Iv).

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

6. Method for operating an optoelectronic module (1) comprising the steps: - Adjusting a luminous intensity (Iv) of at least one light-emitting diode (2) by controlling an electrical operating current (I) with an integrated circuit (3), - Determining a degradation of the light-emitting diode (2) by measuring a value of a forward voltage (Vf) with the integrated circuit (3), wherein - when adjusting the luminous intensity (Iv), a change in the luminous intensity (Iv) due to degradation by increasing or decreasing the electrical operating current (I) as a function of the measured value of the forward voltage (Vf), and - the optoelectronic module (1) is calibrated before a first operation and the calibration comprises a step in which a value of the forward voltage (Vf) of the light-emitting diode (2) measured and stored under the same conditions as for the determination of degradation at later times.

7. Method according to the preceding claim, wherein the determination of the degradation of the light-emitting diode (2) takes place when the light-emitting diode (2) is switched on and / or at predetermined times.

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

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

10. Method according to one of claims 6 to 9, wherein the predetermined electrical operating current (I) for measuring the forward voltage (Vf) is between 50 microamperes and 5 milliamperes inclusive.

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

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

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

14. 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 electrical operating current (I) which is greater than the electrical operating current (I) for determining the degradation.

15. The method according to any one of claims 13 or 14, wherein - the measured value of the forward voltage (Vf) is corrected if the temperature deviates from a predetermined temperature when determining the degradation of the light-emitting diode (2), and - the correction of the measured value of the forward voltage (Vf) based on a known relationship between the forward voltage (Vf) and the temperature of the light-emitting diode (2) at a given operating current (I).

16. The method according to any one of claims 6 to 15, wherein the calibration comprises a further step in which a relationship between the electrical operating current (I) and the luminous intensity (Iv) of the light-emitting diode (2) is determined.

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