Optoelectronic module and method for operating an optoelectronic module - Patents.com

Abstract

The present invention discloses an optoelectronic module (1) comprising at least one light emitting diode (2) that emits light at a luminous intensity (Iv) during operation, and an integrated circuit (3) that sets an operating current (I) for the light emitting diode (2) during operation and measures a value of a forward voltage (Vf) of the light emitting diode (2), wherein the integrated circuit (3) determines 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) in response to the measured value of the forward voltage (Vf) so as to at least partially compensate for changes in the luminous intensity (Iv) due to degradation. A method of operating the optoelectronic module is also disclosed.

Description

[Technical Field]

[0001] An optoelectronic module and a method of operating the optoelectronic module are presented. Summary of the Invention [Problem to be solved by the invention]

[0002] The object of the present invention is to provide an optoelectronic module with improved stability against age-related changes in luminous intensity. This problem is solved by the subject matter with the features of independent claim 1.

[0003] Furthermore, a method for operating an optoelectronic module with improved stability against age-related changes in luminous intensity is presented. This problem is solved by a method having the features of independent claim 6.

[0004] Advantageous embodiments and further configurations of the optoelectronic module and the method for operating an optoelectronic module are set forth in the dependent claims. [Means for solving the problem]

[0005] According to an embodiment, the optoelectronic module comprises at least one light-emitting diode that emits light with a luminous intensity (Iv) when in operation. For example, the light-emitting diode emits electromagnetic radiation when in operation. In particular, the light-emitting diode emits light in the spectral region between infrared and ultraviolet light. Preferably, the light-emitting diode emits light in the visible spectral region when in operation. In particular, the light-emitting diode converts an electrical operating current into light.

[0006] Hereafter, luminous intensity refers to the luminous flux produced by a light-emitting diode per solid angle, specifically in units of "candela". Luminous flux corresponds to the radiant power of a light-emitting diode weighted by the wavelength-dependent sensitivity of the human eye. Radiant power refers to the energy per unit time delivered by the emitted light.

[0007] In particular, a light-emitting diode comprises an epitaxial semiconductor layer stack having an active layer for converting an electrical operating current into electromagnetic radiation, the active layer having a pn junction which may be formed, for example, as a quantum well structure or as a multiple quantum well structure.

[0008] According to a further embodiment, the optoelectronic module comprises an integrated circuit, for example an application specific integrated circuit (ASIC for short), which in operation sets the operating current of the light emitting diode and measures the value of the forward voltage of the light emitting diode.

[0009] In particular, the integrated circuit comprises an electrical circuit for setting the electrical operating current of the light emitting diode, for example the electrical circuit includes an adjustable electrical current source.

[0010] The integrated circuit further includes an electrical circuit for measuring the forward voltage of the light-emitting diode. Hereinafter, the forward voltage specifically refers to the voltage dropped across the semiconductor layer stack of the light-emitting diode while a certain forward operating current flows through the light-emitting diode. In other words, the forward voltage corresponds to the voltage drop between the anode and cathode of a forward-biased light-emitting diode.

[0011] According to a further embodiment of the optoelectronic module, the integrated circuit determines the degradation of the light-emitting diode by measuring the value of the forward voltage, whereby degradation refers hereinafter to age-related changes in the luminous intensity of the light-emitting diode at a given electrical operating current.

[0012] For example, defects are formed in the active layer during operation of a light-emitting diode. Furthermore, defects already present in the semiconductor 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 the crystalline order of the semiconductor 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. Therefore, particularly as the light-emitting diode ages, 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 as the light-emitting diode ages, thereby, for example, increasing the luminous intensity of the light-emitting diode.

[0013] The forward voltage of a light-emitting diode at given operating parameters, particularly at a given operating current and a given temperature, can vary as a function of, for example, the defect density in the active layer. In particular, degradation of a light-emitting diode is correlated with aging-related changes in the forward voltage at given operating parameters. Therefore, the change in the forward voltage of a light-emitting diode at given operating parameters can be used as a measure of degradation of the light-emitting diode. For example, the forward voltage decreases when the luminous intensity decreases due to degradation of the light-emitting diode, or increases when the luminous intensity increases.

[0014] According to a further embodiment of the optoelectronic module, the integrated circuit increases or decreases the electrical operating current of the light-emitting diode in response to the measured value of the forward voltage so that changes in luminosity due to aging are at least partially compensated for. For example, the integrated circuit increases or decreases the operating current, which remains constant over time. The integrated circuit can also increase or decrease the time-averaged value of the operating current, for example, when the luminosity of the light-emitting diode is adjusted by pulse-width modulation of the operating current.

[0015] In particular, compensation is provided such that changes in luminous intensity due to degradation are at least partially compensated by an increase or decrease in operating current and a corresponding change in luminous intensity, i.e., the operating current increases when the luminous intensity of the light-emitting diode decreases due to degradation and / or decreases when the luminous intensity increases.

[0016] For example, during calibration, the light-emitting diode has a certain luminous intensity at a predetermined first operating current and a certain forward voltage at a predetermined second operating current. The first and second operating currents may be the same or different. After a certain operating time of the light-emitting diode following calibration, the luminous intensity at the first operating current and the forward voltage at the second operating current change due to degradation of the light-emitting diode. In particular, the integrated circuit determines the value of the changed forward voltage at the second operating current as a measure of degradation of the light-emitting diode. The first operating current is then increased or decreased depending on the measured value of the forward voltage, for example, so 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 calibration or deviates as little as possible from the luminous intensity at the first operating current at calibration.

[0017] According to a preferred embodiment, the optoelectronic module comprises: at least one light emitting diode that emits light at a luminous intensity (Iv) when in operation; an integrated circuit that sets an operating current of the light-emitting diode during operation and measures a value of a forward voltage of the light-emitting diode; Equipped with The integrated circuit determines degradation of the light emitting diode by measuring the value of the forward voltage and increases or decreases the electrical operating current in response to the measured value of the forward voltage so as to at least partially compensate for changes in luminous intensity due to degradation.

[0018] In particular, the optoelectronic module described herein is based on the idea of ​​purely electronically controlling and, if necessary, compensating for changes in the luminous intensity of a light-emitting diode due to age-related degradation, which degradation is advantageously determined by measuring the forward voltage of the light-emitting diode by means of an integrated circuit which can also control the operating current of the light-emitting diode.

[0019] The forward voltage, particularly at relatively low operating currents, correlates with, for example, the defect density in the active layer of the light-emitting diode and thus with the degradation of the light-emitting diode. Thus, the measured value of the forward voltage can be used to adjust the operating current of the light-emitting diode so that aging-related changes in luminosity are at least partially compensated for.

[0020] For example, the optoelectronic modules described herein advantageously eliminate the need for expensive burn-in of light-emitting diodes as part of the manufacture of the optoelectronic modules. During burn-in, the light-emitting diodes are operated at maximum operating current for an extended period prior to optical calibration, particularly of luminous intensity, to prevent rapid initial degradation during operation after calibration. In contrast to burn-in, the optoelectronic modules described herein advantageously allow for monitoring of degradation during operation.

[0021] Furthermore, the optoelectronic modules described herein do not require costly recording of operating time and / or temperature evolution during operation in order to at least partially compensate for age-related changes in luminous intensity. In particular, the measured value of the forward voltage in the optoelectronic modules described herein is advantageously directly related to the degradation of the light-emitting diodes. In contrast, operating time or temperature evolution are, for example, only indirect gauges of the degradation of the light-emitting diodes. In particular, operating time or temperature evolution do not contain information about the individual state of degradation of the light-emitting diodes in the optoelectronic module. In contrast, the optoelectronic modules described herein can compensate for degradation depending on the individual state of the light-emitting diodes. This advantageously allows for compensation with greater precision.

[0022] Furthermore, the optoelectronic modules described herein do not require an optical light intensity sensor to monitor degradation of the light emitting diodes, and therefore can be advantageously manufactured at low cost.

[0023] According to a further embodiment of the optoelectronic module, the integrated circuit includes 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 given time. For example, the analog-to-digital converter measures voltages up to a maximum voltage of 1 to 3 volts with an accuracy of 0.1 to 10 millivolts. For example, the analog-to-digital converter has a resolution of 7 to 15 bits.

[0024] According to a further embodiment of the optoelectronic module, the integrated circuit or a measurement and control unit for controlling the integrated circuit has a memory in which measured values ​​of the forward voltage are stored. The measurement and control unit is, for example, arranged external to the optoelectronic module and configured to control the integrated circuit for measuring values ​​of the forward voltage of the light-emitting diode. Furthermore, the integrated circuit or the measurement and control unit can calculate a change in operating current based on the stored value of the forward voltage in order to at least partially compensate for age-related changes in the luminosity of the light-emitting diode.

[0025] Furthermore, calibration data of the optoelectronic module can be stored in the memory. In particular, the calibration data includes 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 includes a value of the forward voltage of the light-emitting diode as a reference value for determining degradation. The calibration data may 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 is stored in the memory, for example, after calibration of the optoelectronic module.

[0026] According to a further embodiment of the optoelectronic module, the integrated circuit includes a pulse-width modulator that modulates the operating current of the light-emitting diode to control the luminous intensity. In particular, the pulse-width modulator periodically varies the operating current as a function of time. For example, within one period, the operating current can assume two different values ​​for two corresponding time intervals of different lengths. Preferably, one value of the operating current corresponds to the maximum operating current of the light-emitting diode, and 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, and at the other value of the operating current, no light is emitted. This period is, for example, less than 20 milliseconds to avoid noticeable, disturbing flickering of the optoelectronic module.

[0027] By setting the duty cycle between two values ​​of the operating current, the pulse width modulator can provide any time-averaged value of the operating current between 0 amperes and the maximum operating current. The duty cycle indicates the time ratio between two time intervals during which the operating current has two different values. The duty cycle is preferably expressed as a percentage. For example, at a duty cycle of 0%, the light-emitting diode emits no light on average over time, while at a duty cycle of 100%, the light is emitted at the maximum luminous intensity on average over time. Setting the time-averaged value of the operating current with the pulse width modulator can advantageously reduce or avoid color shifts in the light emitted by the light-emitting diode compared to setting a corresponding constant operating current. Furthermore, the luminous intensity of the light emitted by the light-emitting diode is directly proportional to the duty cycle.

[0028] According to a further embodiment, the optoelectronic module has three light-emitting diodes that, when activated, emit electromagnetic radiation in the red, green, and blue spectral regions, respectively. 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 adjusting the relative luminosity of the three light-emitting diodes accordingly.

[0029] According to a further embodiment of the optoelectronic module, the integrated circuit controls the electrical operating currents of the three light-emitting diodes independently of one another and measures the forward voltages of the three light-emitting diodes independently of one another to determine degradation, so that the degradation of each of the three light-emitting diodes is determined independently of one another.

[0030] According to a further embodiment of the optoelectronic module, the integrated circuit at least partially compensates for changes in the luminous intensity of each of the three light-emitting diodes due to aging. Therefore, the color stability of the optoelectronic module can be advantageously increased when the three light-emitting diodes age differently. By compensating for aging-related changes in the luminous intensity of each of the three light-emitting diodes, the integrated circuit at least partially compensates for aging-related changes in the color coordinates of the mixed light emitted by the optoelectronic module.

[0031] Further provided is a method of operating an optoelectronic module. In particular, the method can be used to operate an optoelectronic module as described herein. Accordingly, all features of the optoelectronic module are also disclosed in the method of operating the optoelectronic module, and vice versa.

[0032] According to an embodiment of the method for operating an optoelectronic module, first, the luminous intensity of at least one light-emitting diode is set by controlling an electrical operating current by an integrated circuit. Preferably, the operating current is pulse-width modulated. The luminous intensity is set, for example, by defining a duty cycle or a time average of the pulse-width modulated operating current.

[0033] According to a further embodiment of the method, the degradation of the light-emitting diode is determined by measuring the value of the forward voltage using an integrated circuit. Preferably, the forward voltage is measured at predetermined operating parameters of the light-emitting diode, such as a predetermined electrical operating current and / or a predetermined temperature. For example, in addition to its dependence on degradation, the forward voltage also depends on the temperature of the light-emitting diode. Measuring the forward voltage at the same operating parameters, in particular, allows the influence of degradation on the forward voltage to be separated from other effects. This improves the accuracy of compensation for changes in luminosity due to aging, for example.

[0034] According to a further embodiment of the method, when setting the light intensity, the change in light intensity due to degradation is compensated for by increasing or decreasing the electrical operating current in response to the measured value of the forward voltage. In particular, the operating current is changed by increasing or decreasing. For example, the electrical operating current of the light-emitting diode is changed in response to the measured value of the forward voltage so that the luminous intensity of light emitted by the degraded light-emitting diode at least approximately corresponds to the luminous intensity of a light-emitting diode with an operating current that does not change during calibration.

[0035] According to a preferred embodiment, a method of operating an optoelectronic module comprises the steps of: setting the luminous intensity of at least one light emitting diode by controlling an electrical operating current with the integrated circuit; determining degradation of the light emitting diode by measuring the value of the forward voltage by means of an integrated circuit; Including, When setting the light intensity, changes in light intensity due to aging are compensated for by increasing or decreasing the electrical operating current depending on the measured value of the forward voltage.

[0036] Preferably, the steps of the method are performed in the order listed above. The above steps of the method can be performed as frequently as desired.

[0037] According to a further embodiment of the method, the degradation of the light-emitting diode is determined when the light-emitting diode is switched on and / or at a predetermined time point, for example the value of the forward voltage is determined each time the optoelectronic module is switched on and / or after a defined service interval.

[0038] Furthermore, the value of the forward voltage can be measured continuously, for example, during operation of the optoelectronic module. For example, in the case of pulse width modulation, one of two values ​​of the operating current can be configured to measure the forward voltage. This is particularly possible when the predetermined value of the operating current for measuring the forward voltage is so small that the light-emitting diode does not emit light or does not emit perceptible light. In this case, the forward voltage of the light-emitting diode is measured during a partial period of pulse width modulation, during which the light-emitting diode does not emit perceptible light.

[0039] According to a further embodiment of the method, the forward voltage is measured at a predetermined value of the operating current. Preferably, the forward voltage is measured at several points in time, and the predetermined value of the operating current is the same for each measurement of the forward voltage. This improves the accuracy of compensation for age-related changes in luminosity, for example. In particular, the predetermined operating current for measuring the forward voltage is selected so that the change in forward voltage due to ageing is particularly sensitive to ageing of the light-emitting diode.

[0040] According to a further embodiment of the method, the predetermined value of the electrical operating current for measuring the forward voltage is selected to maximize the statistical correlation between the change in forward voltage and the change in luminous intensity due to degradation of the light-emitting diode after a predetermined operating time. For example, the forward voltage and luminous intensity are measured at both the beginning and end of the predetermined operating time for a plurality of identical optoelectronic modules for a plurality of different operating currents. For example, the change in forward voltage is determined as the ratio of the measured values ​​of forward voltage at the beginning and end of the predetermined operating time for a predetermined operating current. Similarly, the change in luminous intensity is determined, for example, as the ratio of the measured values ​​of luminous intensity at the beginning and end of the predetermined operating time for a predetermined operating current. From the measured change in forward voltage and the measured change in luminous intensity of each of the plurality of optoelectronic modules, a measure of their statistical correlation for different operating currents can be calculated. The predetermined operating time is, for example, between 1 hour and 48 hours.

[0041] Specifically, to calculate statistical correlation, the change in forward voltage and the change in luminous intensity are considered as two statistical random variables. For example, Pearson's correlation coefficient between the measured change in luminous intensity and the measured change in forward voltage can be calculated as a measure of their statistical correlation. Specifically, Pearson's correlation coefficient corresponds to the covariance between two random variables divided by the standard deviations of the 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.

[0042] The statistical correlation between the change in forward voltage and the change in luminous intensity is particularly a function of the electrical operating current of the light emitting diode. Preferably, the electrical operating current at which the statistical correlation between the change in forward voltage and the change in luminous intensity is greatest is selected when measuring the value of the forward voltage to determine degradation.

[0043] According to a further embodiment of the method, the predetermined electrical operating current for measuring the forward voltage is greater than or equal to 50 microamps and less than or equal to 5 milliamps.

[0044] According to a further embodiment of the method, when setting the luminous intensity of the light-emitting diode, the electrical operating current is corrected with a compensation factor that is linearly dependent on the measured value of the forward voltage. For example, to compensate for degradation, a value of the operating current that remains constant over time is changed by the compensation factor. To compensate for degradation, the duty cycle of the pulse width modulation of the operating current may also be changed by the compensation factor. For example, the duty cycle may be increased or decreased inversely proportional to the compensation factor. Alternatively, the duty cycle may be increased or decreased proportionally to the compensation factor.

[0045] In particular, the compensation factor is a linear function of the measured value of the forward voltage. The compensation factor may also be any function of the value of the forward voltage. For example, the compensation factor is a polynomial, i.e., a sum of multiples of powers of the measured value of the forward voltage.

[0046] According to a further embodiment of the method, the compensation coefficient depends on a predetermined compensation parameter, for example, the coefficient of a polynomial formed by raising the measured value of the forward voltage to a power, or, if there is a linear relationship between the measured value of the forward voltage and the compensation coefficient, the compensation coefficient includes, for example, two compensation parameters.

[0047] According to a further embodiment of the method, the compensation parameters are determined by measuring the change in luminous intensity due to degradation for a plurality of identical light-emitting diodes and subsequent statistical evaluation. For example, both the change in luminous intensity and the change in forward voltage value are measured for a plurality of identical light-emitting diodes after a predetermined operating time. A relationship between the change in luminous intensity and the change in forward voltage is then determined using regression analysis. In particular, a polynomial, e.g., linear, relationship between the change in luminous intensity and the change in forward voltage is assumed, and the coefficients of the polynomial, i.e., the compensation parameters, are determined by regression analysis. For example, the compensation parameters are determined by minimizing the mean square deviation of the measured change in luminous intensity and the measured change in forward voltage from the assumed polynomial relationship.

[0048] According to a further embodiment of the method, the temperature of the light-emitting diode is determined immediately before or immediately after measuring the value of the forward voltage in order to determine the degradation, for example by using a temperature sensor.

[0049] 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 for determining degradation. The forward voltage of the light-emitting diode at a predetermined electrical operating current depends, inter alia, on the temperature of the active layer. Therefore, the temperature of the light-emitting diode can be determined from the measurement of the forward voltage at a predetermined operating current. For example, the temperature of the light-emitting diode is measured at an operating current value recommended for continuous operation of the light-emitting diode. The higher the predetermined operating current, the greater the change in forward voltage due to, for example, a change in temperature. This advantageously increases the accuracy of the temperature measurement.

[0050] According to a further embodiment of the method, when determining degradation of a light-emitting diode, if the temperature deviates from a predetermined temperature, the measured value of the forward voltage is corrected. In particular, the measured value of the forward voltage for determining degradation is corrected so that the corrected value corresponds at least approximately to the value of the forward voltage at the predetermined temperature. Thus, temperature differences between different measurements of the forward voltage for determining degradation can be at least partially compensated for. This advantageously improves the accuracy of the degradation compensation.

[0051] According to a further embodiment of the method, the measured value of the forward voltage is corrected using a known relationship between the forward voltage at a given operating current and the temperature of the light-emitting diode. For example, the forward voltage decreases or increases by a known amount when the temperature of the light-emitting diode increases by one degree Celsius. The temperature deviation, i.e., the difference between the measured temperature of the light-emitting diode and the given temperature, can be multiplied by the known amount of increase or decrease in forward voltage per degree Celsius to determine a corrected value, specifically the forward voltage.

[0052] According to a further 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 after a specific operation time of the optoelectronic module or at several points in time after different operation times. During the calibration, for example, the luminous intensity and / or color coordinates of the emitted light of the optoelectronic module are measured at predetermined operating parameters, for example, operating current and temperature. In particular, the measured values ​​are stored in the memory of the integrated circuit.

[0053] According to a further embodiment of the method, the relationship between the electrical operating current of the light-emitting diode and the luminous intensity is determined during calibration. In particular, the luminous intensity of the emitted light is measured for a number of predetermined values ​​of the operating current. Furthermore, the relationship between temperature and luminous intensity can be measured at a given operating current.

[0054] According to a further embodiment of the method, the value of the forward voltage of the light-emitting diode is measured in a calibration under the same conditions as when determining the degradation at a later point in time. The measured value of the forward voltage is then stored. In particular, the value of the forward voltage measured in the calibration is stored in a memory of the integrated circuit or in a memory of an external measurement and control unit.

[0055] In particular, the value of the forward voltage measured during calibration represents a reference value with respect to which the degradation of the light-emitting diode is determined. For example, to determine the degradation of the light-emitting diode, the value of the forward voltage is measured after a determined operating time and compared with the reference value. The change in the forward voltage is, for example, proportional to the degradation of the light-emitting diode.

[0056] Further advantageous embodiments and further configurations of the optoelectronic module and of the method for operating an optoelectronic module will become apparent from the exemplary embodiments described below in conjunction with the figures. [Brief explanation of the drawings]

[0057] [Figure 1] 1 illustrates a schematic diagram of an optoelectronic module in accordance with an exemplary embodiment; [Figure 2] 1A-1D show schematic block diagrams of optoelectronic modules according to different exemplary embodiments; [Figure 3] 1A-1D show schematic block diagrams of optoelectronic modules according to different exemplary embodiments; [Figure 4] 10 shows a schematic circuit diagram of an optoelectronic module according to a further exemplary embodiment; [Figure 5] 10 shows a schematic circuit diagram of an optoelectronic module according to a further exemplary embodiment; [Figure 6] 1 illustrates a simplified flowchart of a method of operating an optoelectronic module in accordance with an exemplary embodiment. [Figure 7] 1 shows an example of a schematic diagram of the internal quantum efficiency of a light-emitting diode as a function of the operating current. [Figure 8] 1 shows an example of a diagram of the statistical correlation between degradation-related change in forward voltage and degradation-related change in luminous intensity as a function of operating current of a light-emitting diode. [Figure 9] 1 shows an example of a diagram of degradation-related changes in luminous intensity as a function of degradation-related changes in forward voltage of a light-emitting diode; [Figure 10] 1 shows an example of compensated degradation relative to uncompensated degradation for multiple optoelectronic modules. [Figure 11] 4 illustrates compensated degradation of an optoelectronic module according to various exemplary embodiments as a function of the optoelectronic module's operating time. [Figure 12] 4 illustrates compensated degradation of an optoelectronic module according to various exemplary embodiments as a function of the optoelectronic module's operating time. [Figure 13]4 illustrates compensated degradation of an optoelectronic module according to various exemplary embodiments as a function of the optoelectronic module's operating time.

[0058] In the figures, identical, similar or similarly acting elements are provided with the same reference symbols. The figures and the proportions of the elements shown therein should not be taken to scale. Rather, individual elements may be shown exaggeratedly large for better visualization and / or for better understanding. DETAILED DESCRIPTION OF THE INVENTION

[0059] The optoelectronic module 1 according to the exemplary embodiment of Fig. 1 comprises 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 on the side opposite the main surface for external electrical contacting of the optoelectronic module 1. The carrier 8 may comprise, for example, plastic, ceramic and / or metal or may consist of one of these materials. In particular, the optoelectronic module 1 is surface-mountable.

[0060] 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. The luminous intensity Iv of the light emitted by the light-emitting diode 2 can be adjusted via the electrical operating current I.

[0061] The integrated circuit 3 includes an electrical circuit for setting the electrical operating current I of the light-emitting diode 2 and an electrical circuit for measuring the forward voltage Vf of the light-emitting diode 2. The integrated circuit 3 is configured to determine age-related degradation of the light-emitting diode 2 by measuring the 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, the forward voltage Vf of which is particularly sensitive to degradation of the light-emitting diode 2. In other words, at a predetermined operating current I, there is a high statistical correlation between the age-related changes in luminous intensity Iv and the age-related changes in forward voltage Vf of the light-emitting diode 2.

[0062] Furthermore, the integrated circuit 3 is configured to at least partially compensate for age-related changes in the luminous intensity Iv of the light emitted by the light-emitting diode 2 based on the measured value of the forward voltage Vf. For this purpose, 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 so that the luminous intensity Iv of the light emitted by the light-emitting diode 2 corresponds at least approximately to the optically calibrated luminous intensity Iv of the light-emitting diode 2 at an unchanged operating current I.

[0063] Figure 2 shows a schematic block diagram of an optoelectronic module 1 according to the exemplary embodiment described in relation to Figure 1. The anode of the light-emitting diode 2 is connected to an electrical supply voltage VLED, and the cathode of the light-emitting diode 2 is connected to a reference potential GND via a current source 10 within the integrated circuit 3. In particular, the current source 10 is configured to provide an electrical operating current I for the light-emitting diode 2.

[0064] The integrated circuit 3 further includes an electric circuit for measuring the forward voltage Vf of the light-emitting diode 2, in particular an analog-to-digital converter 4, 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 this value in the memory 6.

[0065] 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 determines the duty cycle of the pulse width modulated operating current I for adjusting the luminous intensity Iv of the light emitting diode 2.

[0066] Furthermore, the control unit 9 calculates a compensation factor F from the measured value of the forward voltage Vf and predetermined compensation parameters A, B. In particular, to at least partially compensate for age-related changes in the luminous intensity Iv of the light-emitting diode 2, the duty cycle of the pulse-width-modulated operating current I is varied inversely proportional to the compensation factor F. The compensation parameters A, B are stored in the memory 6, for example, during the manufacture of the optoelectronic module 1.

[0067] FIG. 3 shows a schematic block diagram of an optoelectronic module 1 according to a further exemplary embodiment. In contrast to the exemplary embodiment described in connection with FIG. 2, the optoelectronic module 1 further comprises an external measurement and control unit 5. For example, the external measurement and control unit 5 is not arranged on a common carrier 8 but is spatially separated from the integrated circuits 3 and the light-emitting diodes 2. Furthermore, the external measurement and control unit 5 can, for example, control several integrated circuits 3 together with associated light-emitting diodes 2. In particular, the memory 6 is not part of the integrated circuits 3 but is part of the measurement and control unit 5. The measurement and 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 this value in the memory 6. In particular, in this exemplary embodiment, in order to vary the duty cycle of the pulse-width modulator 7, the control unit 9 of the measurement and control unit 5 calculates a compensation factor F from the compensation parameters A and B and the measured value of the forward voltage Vf and sends the compensation factor F to the control unit 9 of the integrated circuit. Furthermore, the measurement and control unit 5 controls the time point at which the value of the forward voltage Vf is measured by the integrated circuit 3.

[0068] 4 comprises an integrated circuit 3 and three light-emitting diodes 21, 22, 23 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, and the cathodes of the three light-emitting diodes 21, 22, 23 are electrically connected to corresponding connection sites of the integrated circuit 3. In operation, the first light-emitting diode 21 emits light in the red spectral region, the second light-emitting diode 22 emits light in the green spectral region, and the third light-emitting diode 23 emits light in the blue spectral region.

[0069] The integrated circuit 3 controls the operating current I of the three light-emitting diodes 21, 22, 23 independently of one another, so that the relative luminous 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 desired color during operation.

[0070] 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 their respective forward voltages Vf. Using the measured forward voltages Vf, the integrated circuit compensates for age-related changes in the luminous intensity Iv of the three light-emitting diodes 21, 22, 23. This advantageously at least partially compensates for color shifts due to aging, particularly of the optoelectronic module 1.

[0071] The optoelectronic module 1 comprises connection contacts 11 for connecting the integrated circuit 3 to a serial bus via which the integrated circuit 3 exchanges data, for example, with an external measurement and control unit 5 (not shown here, see for example FIG. 3).

[0072] In contrast to the exemplary embodiment of Fig. 4, the optoelectronic module 1 according to the exemplary embodiment of Fig. 5 comprises 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 the three light-emitting diodes 21, 22, 23. This allows, for example, the light-emitting diodes 21, 22, 23 of several optoelectronic modules 1 to be arranged next to each other in a particularly compact manner, and the associated integrated circuits 3 to be arranged at a distance from the light-emitting diodes 21, 22, 23.

[0073] FIG. 6 illustrates different steps 101, 102, 103, 104 of a method for operating an optoelectronic module 1 according to the exemplary embodiment of FIG. 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 for the luminous intensity Iv0. Furthermore, the forward voltage Vf of the light-emitting diode is measured and stored at a predetermined electrical operating current I and at a constant temperature. The predetermined operating current I is selected so that changes in the forward voltage Vf are particularly sensitive to degradation of the light-emitting diode 2. The selection of the predetermined operating current I is described, for example, in connection with FIG. 8. The measured value of the forward voltage Vf is stored in the memory 6 of the integrated circuit 3 as a reference value Vf0.

[0074] 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, where the luminous intensity Iv is set by pulse-width modulation of the operating current I by the integrated circuit 3. In particular, the luminous intensity Iv is proportional to the duty cycle of the pulse-width modulated operating current I.

[0075] 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 calibration. In particular, Vf is measured at the same predetermined operating current I and temperature of the optoelectronic module 1 as during calibration. By measuring this value of the forward voltage Vf, the degradation of the light-emitting diode 2 is determined. For example, degradation-related changes in the luminous intensity Iv / Iv0 of the light emitted by the light-emitting diode 2 are at least approximately proportional to changes in the value of the forward voltage Vf / Vf0, the changes relative to the reference values ​​Iv0,Vf0 being determined from the calibration.

[0076] In a fourth step 104, changes in the luminous intensity Iv due to degradation of the light-emitting diode 2 during further operation of the optoelectronic module 1 are at least partially compensated for 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, the reference value measured in step 101 and the compensation parameters A, B. In particular, the compensation factor F is:

number

[0077] The duty cycle PWM of the pulse-width modulated operating current I is corrected by a compensation factor F during further operation of the optoelectronic module 1 .

number

[0078] In the formula, PWM c indicates the corrected duty cycle, and PWM indicates the original duty cycle. Corrected Duty Cycle PWM c By pulse width modulation of the operating current I of the light-emitting diode 2 with a duty cycle PWM cThe luminous intensity Iv of the light generated at the duty cycle PWM during calibration corresponds at least approximately to the luminous intensity Iv of the light generated at the duty cycle PWM during calibration. 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 advantageously decreases with the above-mentioned duty cycle PWM c can be at least partially compensated for in a simple manner by correcting

[0079] Steps 101 to 104 are preferably performed in this order. Steps 103 and 104 may be repeated several times during operation of the optoelectronic module 1. As a result, the degradation of the light-emitting diodes 2 during operation of the optoelectronic module 1 can advantageously be determined more accurately and can then be compensated for with greater precision.

[0080] Figure 7 shows an example of 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. For example, at small operating currents I, non-radiative Shockley-Read-Hall (SRH) recombination dominates, while at large operating currents I, non-radiative Auger (AUG) recombination dominates. In Shockley-Read-Hall recombination, for example, charge carriers recombine at defects in the crystal lattice of the active layer.

[0081] This degradation, for example, changes the internal quantum efficiency IQE of the light-emitting diode 2. The internal quantum efficiency IQE decreases particularly strongly at low operating currents I (see the arrow and dashed line in FIG. 7 ), where Shockley-Read-Hall recombination is dominant. Advantageously, the forward voltage Vf of the light-emitting diode 2 is particularly sensitive to the defect density in the active layer and, therefore, to degradation of the light-emitting diode 2 at these low operating currents I. The operating current I for measuring the forward voltage Vf is preferably not selected to be too small so that the measured value of the forward voltage Vf is not, or as little as possible, affected by noise. Furthermore, the operating current I for measuring the forward voltage Vf is preferably not too large so that degradation has the greatest possible influence on the measured value of the forward voltage Vf. FIG. 7 shows a preferred region 12 of the operating current I, at which degradation of the light-emitting diode 2 can be determined from the measured value of the forward voltage Vf.

[0082] FIG. 8 shows the Pearson correlation coefficient PC between the relative change in forward voltage Vf / Vf0 and the relative change in luminous intensity Iv / Iv0. The Pearson correlation coefficient PC is calculated from measured changes in forward voltage Vf / Vf0 and luminous intensity Iv / Iv0 for a number of identical light-emitting diodes 2 after 24 hours of operation as a function of the operating current I. The Pearson correlation coefficient PC is calculated, for example, from measured values ​​of changes in forward voltage Vf / Vf0 and changes in luminous intensity Iv / Iv0 for at least 100 identical light-emitting diodes 2. In particular, the Pearson correlation coefficient PC for three different types of light-emitting diodes 21, 22, and 23 is shown in FIG. 8. 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.

[0083] For the first light-emitting diode 21 and the second light-emitting diode 22, the Pearson's correlation coefficient Pc is greatest at an operating current I of about 100 microamperes, while for the third light-emitting diode 23, the Pearson's correlation coefficient Pc is greatest at an operating current I of about 3 milliamperes. Advantageously, the predetermined operating current I for determining degradation of the light-emitting diodes 21, 22, 23 is selected based on measuring the value of the forward voltage Vf such that the Pearson's correlation coefficient Pc is greatest at this predetermined operating current I. As a result, degradation-related changes in the luminous intensity Iv of the light-emitting diodes 21, 22, 23 can be compensated for with high precision by measuring the forward voltage Vf.

[0084] 9 shows measured values ​​of the relative change in luminous intensity Iv / Iv0 as a function of the relative change in the value of the forward voltage Vf / Vf0 at a given operating current I after 24 hours of operation of the light-emitting diodes 2. Measured values ​​are shown for a number of first, second and third light-emitting diodes 21, 22, 23 that are part of an optoelectronic module 1 without degradation compensation. The given operating current I for measuring the value of the forward voltage Vf is selected as described in connection with FIG. 8.

[0085] In particular, Figure 9 shows the linear relationship between the relative change in forward voltage Vf / Vf0 and the relative change in luminous intensity Iv / Iv0 obtained by linear regression of the corresponding measured values ​​of the first, second, and third light-emitting diodes 21, 22, and 23, respectively. This linear relationship is expressed by the equation:

number

[0086] 9 is shifted away 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 a change in the measured luminous intensity Iv on the statistical average. This deviation may be caused, for example, by age-related changes in the absorption coefficient of the carrier 8 or other parts of the optoelectronic module 1, which affect the measured luminous intensity Iv.

[0087] FIG. 10 illustrates the luminous intensity Iv of a plurality of optoelectronic modules 1 according to an exemplary embodiment. c 1 shows the measured values ​​of the relative change in luminous intensity Iv / Iv0 in the absence of compensation for degradation, and the degradation has been corrected according to the method described herein. In particular, the measured values ​​along the vertical axis are Iv c / Iv0=centered at 1. This shows that the degradation can be at least partially compensated for by the methods described herein.

[0088] 11, 12, and 13 show the luminous intensity Iv of the light-emitting diode 2 in the optoelectronic module 1 according to the exemplary embodiment. c 11 shows the relative change in luminous intensity Iv / Iv0 as a function of operating time, with degradation at least partially compensated for. Here, FIG. 11 shows the change in luminous intensity Iv for the first light-emitting diode 21 according to the exemplary embodiment of FIG. 4, FIG. 12 shows the change in luminous intensity Iv for the second light-emitting diode 22 according to the exemplary embodiment of FIG. 4, and FIG. 13 shows the change in luminous intensity Iv for the third light-emitting diode 23 according to the exemplary embodiment of FIG. 4. Compensation is performed as described in connection with the exemplary embodiment of FIG. 6. By way of comparison, the dotted lines show the relative change in luminous intensity Iv / Iv0 when degradation of the light-emitting diodes 2 is not compensated for. In particular, FIGS. 11, 12, and 13 show the relative change in luminous intensity Iv c11, 12, and 13 show the average value of the relative change in luminous intensity Iv / Iv0, where the luminous intensity Iv is averaged over 280 identical light-emitting diodes 2. Also shown are three times the standard deviation (±3σ) of the relative change in luminous intensity Iv for multiple identical light-emitting diodes 2. In particular, FIGS. 11, 12, and 13 show that compensation for degradation according to the methods described herein is particularly effective for long operating times.

[0089] This patent application claims priority from German Patent Application No. 102022129162.6, the disclosure of which is incorporated herein by reference.

[0090] The present invention is not limited to the exemplary embodiments described herein, but rather includes each and every novel feature and each and every combination of features, and specifically encompasses each and every combination of features in the claims, even if those features or combinations themselves are not explicitly recited in the claims or exemplary embodiments. [Explanation of symbols]

[0091] 1 Optoelectronics Module 2. Light-emitting diodes 21 First light-emitting diode 22 Second light-emitting diode 23 Third Light-Emitting Diode 3. Integrated Circuits 4 Analog-to-Digital Converter 5. Measurement and Control Unit 6. Memory 7 Pulse Width Modulator 8. Career 9. Control Unit 10 Current source 11 Connecting Contact 12 areas 101 First step 102 Second step 103 Third step 104 Fourth step A, B compensation parameters AUG Auger recombination I Operating current IQE Internal Quantum Efficiency IV Luminosity Iv0 luminosity reference value IV c Compensated luminous intensity PC Pearson correlation coefficient SRH Shockley-Read-Hall Recombination t time Vf forward voltage Vf0 forward voltage reference value VLED supply voltage GND reference potential

Claims

1. at least one light emitting diode (2) that emits light at a luminous intensity (Iv) when in operation; an integrated circuit (3) for setting an operating current (I) of the light-emitting diode (2) during operation and measuring a value of a forward voltage (Vf) of the light-emitting diode (2); An optoelectronic module (1) comprising: the integrated circuit (3) determines 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) so as to at least partially compensate for changes in the luminous intensity (Iv) due to the degradation; 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, the calibration data including the value of the forward voltage (Vf) as a reference value for determining the degradation; Optoelectronic module (1).

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

3. The measured value of the forward voltage (Vf) is stored in the memory (6). An optoelectronic module (1) according to claim 1 or 2.

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

5. The optoelectronic module (1) comprises three light-emitting diodes (21, 22, 23) which, in operation, emit light in the red, green and blue spectral regions, respectively; the integrated circuit (3) controls the electrical operating currents (I) of the three light emitting diodes (21, 22, 23) independently of one another 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; the integrated circuit (3) at least partially compensates for the change in luminous intensity (Iv) of each of the three light-emitting diodes (21, 22, 23) due to the degradation; An optoelectronic module (1) according to any one of claims 1 to 4.

6. setting the luminous intensity (Iv) of at least one light-emitting diode (2) by controlling the electrical operating current (I) by means of an integrated circuit (3); determining the degradation of said light emitting diode (2) by measuring the value of the forward voltage (Vf) by said integrated circuit (3); A method of operating an optoelectronic module (1) comprising: When setting the luminous intensity (Iv), a change in the luminous intensity (Iv) due to degradation is compensated for by increasing or decreasing the electrical operating current (I) depending on the measured value of the forward voltage (Vf); the optoelectronic module (1) is calibrated before first operation, said calibration comprising measuring and storing the value of the forward voltage (Vf) of the light-emitting diode (2) under the same conditions as when the degradation is to be determined at a later time, A method for operating an optoelectronic module (1).

7. the degradation of the light-emitting diode (2) is determined when the light-emitting diode (2) is switched on and / or at a predetermined time point; The method of claim 6.

8. The forward voltage (Vf) is measured at a predetermined value of the operating current (I).

8. The method according to claim 6 or 7.

9. the predetermined value of the electrical operating current (I) for measuring the forward voltage (Vf) is selected so as to maximize the statistical correlation between the change in the forward voltage (Vf) and the change in the luminous intensity (Iv) due to the degradation of the light-emitting diode (2) after a predetermined operating time. The method of claim 8.

10. The predetermined electrical operating current (I) for measuring the forward voltage (Vf) is 50 microamperes or more and 5 milliamperes or less; The method according to any one of claims 6 to 9.

11. When setting the luminous intensity (Iv) of the light-emitting diode (2), the electrical operating current (I) is corrected by a compensation coefficient that is linearly dependent on the measured value of the forward voltage (Vf). The method according to any one of claims 6 to 10.

12. The compensation coefficient depends on predetermined compensation parameters (A, B), the compensation parameters (A, B) are determined by measuring the change in luminous intensity (Iv) due to aging for a number of identical light-emitting diodes (2) and by subsequent statistical evaluation; The method of claim 11.

13. determining the temperature of the light emitting diode (2) immediately before or immediately after measuring the value of the forward voltage (Vf) in order to determine the degradation; The method according to any one of claims 6 to 12.

14. 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) greater than the electrical operating current (I) for determining the degradation. The method of claim 13.

15. correcting the measured value of the forward voltage (Vf) if the temperature deviates from a predetermined temperature when determining the degradation of the light-emitting diode (2); The measured value of the forward voltage (Vf) is corrected using a known relationship between the forward voltage (Vf) at a given operating current (I) and the temperature of the light emitting diode (2).

15. The method of claim 13 or 14.

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

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