Method for determining temperature of lighting device

Abstract

A method and apparatus for determining a temperature of a light emitting device is described. The method comprises: operating (102) the light emitting device (502) during an on-interval and an off-interval; measuring (104) at least one electrical energy across the light emitting device during at least one sensing interval, where the at least one sensing interval is included in a turn-off interval, and where a duration of each of the at least one sensing interval is equal to or less than a duration of the turn-off interval; and determining (106) at least one temperature value of the light emitting device (502) based on the measured at least one electrical energy.

Description

Technical Field

[0001] The present invention relates to a method for determining the temperature of a light emitting device, in particular to a method for sensing the temperature of a light emitting diode (LED). Background Art

[0002] Today, more and more lighting tasks are performed by LED technology. This is not only due to improved energy efficiency and lower heat generation, but also due to improved brightness, smaller required installation space and improved lifespan.

[0003] For example, in modern automobiles, LED technology has been frequently used to realize headlights and taillights. Similarly, LEDs are often used to realize interior lights within the car itself, for example as signal lights. However, not only the automotive industry uses LED technology, but also other technical and engineering fields that require lighting with a given brightness and a desired color. For example, modern architecture uses the potential of LED lighting to realize daylight-adapted lighting schemes, whose color and brightness are dynamically controlled in response to the daylight conditions outside the building. However, several other applications of LED technology are also envisioned.

[0004] In order to guide the brightness and color of the lighting device as desired, the lighting device may include a plurality of different light emitting devices of different colors, which emit light that is mixed to produce light with the desired brightness and color. For example, a typical lighting device may include red, green and blue LEDs, and the power supplied to the red, green and blue LEDs is adjusted so that the superposition of the light emitted by the LEDs has the desired brightness and color. However, the lighting device may also include only one light emitting device that can be driven in different ways to emit light of different colors and brightness, such as organic LEDs, OLEDs.

[0005] Unfortunately, there is a conflict between simultaneously directing the brightness and the color of the light emitted from a lighting device. Depending on the brightness selected, the lighting device heats up in different ways and thus changes the color of the emission. For example, if the lighting device is driven in high brightness mode, it heats up more than if it is driven in low brightness mode. However, when the temperature of the lighting device changes, the color of the lighting device also changes. This effect can already be observed for conventional light bulbs, the more their filament heats up, the whiter the light they emit. Similarly, the color of an LED depends on its temperature. Therefore, if the brightness of the lighting device changes, the color of the resulting light also changes.

[0006] The influence of different device temperatures on the color of the emitted light can be compensated by adjusting the amount of electrical energy supplied to one or more light emitting devices based on their respective temperatures, which together can constitute the lighting device. This method can be referred to as temperature compensation. However, for this purpose, a reliable temperature estimate as a function of time is required for each of the light emitting devices. This is particularly important when the light emitting devices are not located at the same location inside the lighting device, but are located at a certain distance from each other.

[0007] In the art, it is known that individual temperature sensors can be attached to each light emitting device. For example, a semiconductor temperature sensor can be attached to each of the red, green and blue LEDs installed in a common semiconductor package of the lighting device. However, the use of external temperature sensors is expensive and requires additional installation space. In addition, the external temperature sensor never measures the temperature at the location of the light emitting device accurately, but measures the temperature at a location that deviates from the light emitting device. This requires complex offset calculations.

[0008] Therefore, methods have been developed to infer the temperature of a light emitting device using measurements of internal operating parameters of the light emitting device (eg, voltage and / or current).

[0009] However, a disadvantage of the existing methods is that the temperature measurement is performed without taking into account the operating cycle of the lighting device. Therefore, it cannot be ensured that the temperature measurement itself does not interfere with the adjustment and maintenance of the desired brightness and color.

[0010] Therefore, there is a need to sense the temperature of the light emitting device, which overcomes the above-mentioned disadvantages. Summary of the invention

[0011] This need is met by the method according to the invention for determining the temperature of a light emitting device and a corresponding electronic device.

[0012] The method according to the invention for determining the temperature of a light emitting device comprises operating the light emitting device during a switch-on interval and during a switch-off interval.

[0013] A light emitting device is a device that emits light when provided with energy. The energy may be provided in the form of electrical energy. The electrical energy may be quantified in the form of a current and / or voltage applied to the light emitting device. Thus, a non-limiting example of a light emitting device is a light emitting diode LED.

[0014] The on-interval and the off-interval are durations. The duration of the on-interval may be different from the duration of the off-interval. Thus, the duration of the off-interval may be significantly shorter than the duration of the on-interval, for example, one tenth, ..., one hundredth of the duration of the on-interval. However, it is also possible that the on-interval and the off-interval have the same duration, or that the duration of the off-interval is longer than the duration of the on-interval.

[0015] During the on-interval and the off-interval, the corresponding operating current and / or operating voltage can be used to operate the light-emitting device. The operating current and / or operating voltage can also be referred to as the operating power supplied to the light-emitting device. It can also be said that during the on-interval and the off-interval, the corresponding operating power can be used to operate the light-emitting device. The operating power during the on-interval can be different from the operating power during the off-interval. The operating power during the on-interval can be time-constant or time-dependent. Similarly, the operating power during the off-interval can be time-constant or time-dependent. It can also be said that the operating power during the on-interval and / or the off-interval can be a DC or AC current and / or voltage. It is also possible that the operating power during the on-interval and / or the off-interval is a segmented DC current and / or voltage and a segmented AC current and / or voltage. Therefore, it is possible to provide AC and DC currents and / or voltages to the light-emitting device during the on-interval and / or the off-interval. The peak power provided during the on-interval can be greater than the peak power provided during the off-interval. The total operating power supplied to the light emitting device during the on-interval may be greater than the total operating power supplied to the light emitting device during the off-interval. It can also be said that the total operating power supplied to the light emitting device during the off-interval is reduced compared to the total operating power supplied to the light emitting device during the on-interval. Thus, the on-interval and the off-interval differ not only in their duration, but also in the power supplied to the light emitting device during the respective durations.

[0016] Alternatively or additionally, any on-interval can be characterized by means of the brightness of the emitted light relative to the off-interval. Operating the light-emitting device using the corresponding operating electrical energy causes the light-emitting device to emit light having the corresponding brightness and color. It can also be said that adjusting the operating electrical energy supplied to the light-emitting device defines the brightness and color of the light emitted by the light-emitting device. Brightness is a photometric quantity that characterizes the emission power of the light emitted by the light-emitting device. Brightness is usually referred to as luminous flux and is measured in lumens (lm). During the on-interval, the brightness of the emitted light can be significantly increased compared to the off-interval. Similarly, during the off-interval, the brightness of the emitted light can be significantly reduced compared to the on-interval.

[0017] Color is referred to herein as the photometric quantity of a light-emitting device, measured by its wavelength λ and / or frequency ν. Any light emitted by a light-emitting device can be characterized by its spectral radiance, that is, by the relative distribution of radiant power as a function of the wavelength λ of the light. As is known in the art, many RGB color spaces can be defined, which have in common that a given perceived color is fully described by three tristimulus values ​​X, Y, and Z. The three values ​​appear because the human eye contains three types of cones (S, L, M) that are responsible for light reception, which results in trichromatic color vision. Typical examples of RGB color spaces are CIERGB, CIE XYZ, NTSC, and PAL / SECAM. Newer examples of RGB color spaces are DCI-P3, UHDTV, and RIMM / ROMM. The three tristimulus values ​​X, Y, and Z describe the color of the emitted light and are obtained by integrating the spectral radiance of the emitted light over the wavelength by the corresponding curves in the three spectral sensitivity curves x(λ), y(λ), and z(λ) of the CIE standard observer. It can also be said that the tristimulus values ​​X, Y and Z of a given emitted light flux are obtained by projecting the spectral radiance of the emitted light onto each of the three spectral sensitivity curves x(λ), y(λ) and z(λ) of the CIE standard observer. In this way, each individual color state of the light emitted by the light emitting device is characterized by another three-dimensional vector of tristimulus values ​​X, Y and Z.

[0018] Furthermore, the method for determining the temperature of a light emitting device according to the invention comprises measuring at least one electrical energy across the light emitting device during at least one sensing interval.

[0019] A sensing interval is a duration during which electrical energy is measured. Each sensing interval can be characterized by its duration and its position in time. It is possible to measure the electrical energy once or multiple times during the same sensing interval. For example, the electrical energy can be at least a voltage and / or a current across the light emitting device. Therefore, the voltage and / or current across the light emitting device can be measured. In addition, the measurement of electrical energy can also include measuring other physical quantities, based on which the voltage and / or current across the light emitting device can be derived. For example, the resistance, inductance and / or capacitance across the light emitting device can be measured. It is also possible to simultaneously and / or continuously measure a combination of voltage, current, inductance and capacitance across the light emitting device.

[0020] During the sensing interval, operating power, such as an operating current and / or voltage, may be applied to the light emitting device. The operating power applied during the sensing interval may also be referred to as test power, such as a test current and / or a test voltage. The test power may be applied during the entire sensing interval, or only during one or more parts of the sensing interval. The test power may be significantly reduced compared to the operating power applied during the on-interval. If the voltage is measured during the sensing interval, the voltage may be referred to as the forward voltage. The forward voltage may be measured differentially. Specifically, the forward voltage may be measured differentially relative to the voltage to which the light emitting device is connected. It can also be said that the forward voltage may be measured between the voltage source and the light emitting device itself. When the forward voltage of the light emitting device is measured, the current passing through the light emitting device may be regulated and limited by a current source equal to the test current. In addition, when the forward voltage of the light emitting device is measured differentially, the forward voltage may be given as the difference between the voltage on the voltage source and the voltage at the current source. Additionally or alternatively, multiple forward voltages of the light emitting device may be measured during at least one sensing interval. The plurality of forward voltages may be averaged to produce a mean forward voltage for each of the at least one sensing interval. However, all and / or a subset of the plurality of forward voltages measured may also be stored without further processing. Thus, each of the at least one sensing interval may be associated with one or more values ​​of the forward voltage of the light emitting device.

[0021] At least one sensing interval may be included in the off interval of operating the light emitting device. In other words, the off interval may include at least one sensing interval. If multiple sensing intervals are included in the off interval, the individual sensing intervals in the multiple sensing intervals may not overlap with each other and / or may be adjacent to each other. It can also be said that the off interval may be covered by one or more sensing intervals.

[0022] Furthermore, the duration of each of the at least one sensing interval may be equal to or less than the duration of the off interval. This means that the start and end of each of the at least one sensing interval is located within the off interval. The temporal position of the at least one sensing interval may be freely arranged within the duration of the off interval. The sensing interval may occur at the beginning, in the middle or at the end of the off interval.

[0023] Finally, the method for determining the temperature of a light emitting device according to the present invention comprises determining at least one temperature value of the light emitting device based on the measured electrical energy. The measured electrical energy may be related to the temperature of the light emitting device and represent the temperature of the light emitting device. Typically, the temperature of the light emitting device is a function of the electrical energy supplied to the light emitting device. If no electrical energy is supplied to the light emitting device, the temperature of the light emitting device is given by the ambient temperature. Typically, if a voltage U and a current I are applied to the light emitting device, the set power P is equal to P=U*I. The electrical energy E set in the light emitting device is equal to the integral of the power P(t) over time t. A certain small portion of the set electrical energy E is dissipated in the light emitting device, and is not emitted in the form of light energy. This causes the light emitting device to heat up to a temperature T, which depends on the voltage U and the current I and other material parameters. Therefore, it can be said that the temperature T of the light emitting device is a function T(U,I), where U and I are the voltage and current applied across the light emitting device, respectively. Therefore, if at least one voltage U and one current I measured across the light emitting device are given, the function T(U,I) can be used to determine at least one temperature value T. The temperature increase due to the electrical power can be referred to as an "overtemperature" above the ambient temperature. The function T(U,I) and its inverse will therefore give the ambient temperature or, in the case of a temperature increase due to the electrical power, the ambient temperature plus the overtemperature dependency, respectively.

[0024] Furthermore, any light emitting device may be characterized by a temperature-dependent resistance R(T). For example, the resistance of a filament of a light bulb increases with increasing temperature. In contrast, the resistance of a light emitting diode decreases with increasing temperature. Thus, if a temperature-dependent resistance R(T) is given, the voltage U and current I across the light emitting device are related by R(T)=U / I, and one of the voltage U or current I may be substituted into the function T(U,I) to obtain the temperature T. For example, if the current I is substituted, a function T(U) of the temperature T of the light emitting device is obtained, which function T(U) is a function of the voltage U supplied across the light emitting device. If the voltage U is substituted, this results in a temperature T(I), which is a function of the current I flowing through the light emitting device. Thus, using the function T(U), a temperature value T may be determined for each of at least one measured voltage U across the light emitting device. Similarly, the function T(I) may be used to determine a temperature value T for each of at least one measured current I across the light emitting device. It can also be said that the temperature T of the light emitting device can be determined by evaluating one of the functions T(U,I), T(U) and / or T(I). Estimating these functions can utilize numerical approximations of calibration measurements.

[0025] This allows for the first time the local temperature of a light emitting device to be estimated during continuous operation without disturbing the delivery of emitted light with the desired brightness and color.

[0026] In a preferred embodiment of the invention, at least one sensing interval may be located at the beginning of the off-interval or at the end of the off-interval. When the at least one sensing interval is located at the beginning of the off-interval, the beginning of the at least one sensing interval coincides with the beginning of the off-interval. Furthermore, when the at least one sensing interval is located at the end of the off-interval, the end of the at least one sensing interval coincides with the end of the off-interval. The at least one sensing interval located at the beginning of the off-interval provides the technical advantage that the determined temperature or temperatures are close to the temperature of the light emitting device at the end of the on-interval. In this case, the temperature measurement constitutes an estimate of the maximum thermal stress applied to the light emitting device, because when the temperature is determined at the end of the on-interval, energy has been set in the light emitting device during (the entire) the preceding on-interval. If no electrical energy is supplied to the light emitting device before the off-interval, the temperature measurement in the sensing interval located at the beginning of the off-interval can be used as an estimate of the ambient temperature. At the end of the on-interval, the light emitting device usually reaches its maximum temperature. Therefore, placing the sensing interval at the beginning of the off-interval helps to infer information about the maximum thermal load experienced by the light emitting device during operation. This can be used, for example, to adjust the length of the on-interval and / or the voltage and / or current applied to the light emitting device during the on-interval in order to actively control aging effects of the light emitting device. On the other hand, at least one sensing interval located at the end of the off-interval provides the technical advantage that when the current and voltage applied to the light emitting device in the next on-interval are determined, the determined temperature or temperatures are as close as possible to the temperature of the light emitting device. This has the benefit that the desired brightness and color of the next on-cycle can be adjusted with high accuracy, because the dependence of the brightness and color of the emitted light on the temperature of the light emitting device can be taken into account when the voltage and current to be applied to the light emitting device are determined.

[0027] In a further embodiment of the present invention, the off interval may also include two sensing intervals, during each sensing interval, at least one temperature value is determined as described above. One of the two sensing intervals may be located at the beginning of the off interval, and the other of the two sensing intervals may be located at the end of the off interval. In this case, at least one temperature of the light emitting device at the beginning of the off interval and at least one temperature of the light emitting device at the end of the off interval are determined. When controlling the current and / or voltage of the light emitting device to achieve the target brightness and color in the next on interval, these temperature values ​​of the light emitting device can be used to determine the fatigue experienced by the light emitting device during the on interval and to compensate for the temperature effect. The two sensing intervals may be separated by a gap. During the gap, the light emitting device may be turned off, i.e., no operating current and / or voltage is applied. This allows the light emitting device to recover from operation. The duration of the gap may be adapted to allow the light emitting device to cool to a desired baseline temperature. The desired baseline temperature may be adjusted in such a way that the temperature at the end of the next on interval does not exceed the desired maximum temperature.

[0028] In another preferred embodiment of the present invention, the on-interval may be one of a plurality of on-intervals, and / or the off-interval may be one of a plurality of off-intervals. The on-intervals in the plurality of on-intervals may have the same duration or different durations. It is also possible that the on-intervals in one or more subsets of the plurality of on-intervals have similar durations, wherein the corresponding similar durations are characteristic of the corresponding subsets in the one or more subsets. Similarly, the off-intervals in the plurality of off-intervals may have the same duration or different durations. It is also possible that the off-intervals in one or more subsets of the plurality of off-intervals have similar durations, wherein the corresponding similar durations are characteristic of the corresponding subsets in the one or more subsets. In addition, the on-intervals in the plurality of on-intervals may alternate with the off-intervals in the plurality of off-intervals. In addition, each on-interval in the plurality of on-intervals may be adjacent to two off-intervals in the plurality of off-intervals. In this case, the first of the two off-intervals may be before the on-interval, and the second of the two off-intervals may be after the on-interval. This has the advantage that the total period is longer than when there is only one on-interval. It can also be said that by the presence of a plurality of on-intervals and off-intervals, regular light emission is promoted while providing repeated candidate intervals for temperature measurement. It is also achieved that during the off-intervals of the plurality of off-intervals, the light emitting device is given a repeated recovery period, in which less energy is set in the light emitting device compared to the on-intervals. This increases the service life of the light emitting device while ensuring the proper delivery of light of the desired brightness and color.

[0029] In addition, multiple on-intervals may be periodic, and / or multiple off-intervals may be periodic. It can also be said that the on-intervals and / or the off-intervals are repeated. Repetition may be characterized by a corresponding repetition time and frequency. For example, the on-interval may be repeated after a first repetition time and / or the off-interval may be repeated after a second repetition time. The first repetition time and the second repetition time may be equal. In a special case, the first repetition time and the second repetition time may be equal to the duration of the on-interval plus the duration of the off-interval. It is also possible that the on-intervals in a subset of the multiple on-intervals are repeated after a repetition time different from the on-intervals in another subset of the multiple on-intervals. Similarly, it is possible that the off-intervals in a subset of the multiple off-intervals are repeated after a repetition time different from the off-intervals in another subset of the multiple off-intervals. This has the technical advantage that quasi-steady-state operation of the light-emitting device can be achieved, because the periodically repeated on-intervals result in light emission with desired brightness and color properties. At the same time, the periodically repeated off-intervals allow a recovery period associated with the periodically repeated on-intervals. Likewise, the on interval may be repeated at a first repetition frequency and / or the off interval may be repeated at a second repetition frequency. The first repetition frequency and the second repetition frequency may be selected from frequencies between 100 Hz and 2 kHz. However, these values ​​are only examples and do not limit the claimed invention.

[0030] In addition, each off interval in the plurality of off intervals or each off interval in a subset of the plurality of off intervals may include at least one sensing interval. There are different ways to include a sensing interval in the off intervals in the plurality of off intervals. In one embodiment, at least one sensing interval may be included in each of the off intervals in the plurality of off intervals. In this case, the cardinality of the plurality of off intervals is equal to or less than the total number of sensing intervals, because each off interval carries at least one sensing interval. In another embodiment, it is possible that only the off intervals included in a subset of the plurality of off intervals include at least one sensing interval. In this case, the cardinality of the plurality of off intervals may be higher than the total number of sensing intervals. It can also be said that the sensing intervals may be sparsely distributed over the plurality of off intervals. If the plurality of off intervals are periodic, the off intervals in the plurality of off intervals may be sorted in ascending order relative to their occurrence in time, and only every 2nd, 10th, or 100th off interval in the plurality of time-sorted off intervals may include at least one sensing interval. In this particular case, the subset of the plurality of off-intervals corresponds to every 2nd, 10th or 100th off-interval of the plurality of time-ordered off-intervals. Not including a sensing interval into each of the plurality of off-intervals has the technical benefit that a microcontroller for processing the measured electrical energy to obtain the associated temperature of the light emitting device is not loaded with unnecessary calculations. In this way, a cost advantage of the required computing power of the microcontroller is provided.

[0031] In a further preferred embodiment of the present invention, operating the light emitting device may include applying operating electric energy to the light emitting device during the on-interval and reducing the operating electric energy during the off-interval. The operating electric energy may include an operating current and / or an operating voltage. Reducing the operating electric energy during the off-interval means adjusting the electric energy so that the total electric energy supplied to the light emitting device during the off-interval is less than the total electric energy supplied during the on-interval. Therefore, the operating electric energy applied during the off-interval may be less than the operating electric energy applied during the on-interval. Specifically, the peak electric energy applied during the off-interval may be less than the peak electric energy applied during the on-interval. Therefore, the operating electric energy may be cut off or reduced after the on-interval. However, it is also possible that the peak electric energy applied during the on-interval is less than the peak electric energy applied during the off-interval, as long as it is ensured that the total electric energy supplied during the off-interval is less than the on-interval. The off-interval may be distinguished from the on-interval in terms of the brightness of the light emitted by the light emitting device. In order to achieve a different brightness of the light emitted during the on-interval compared to the light emitted during the off-interval, a reduced electrical energy may be applied to the light-emitting device during the off-interval compared to the on-interval. Therefore, the light-emitting device may still emit light during the off-interval or may remain completely dark. However, the peak brightness of the light emitted during the off-interval may be lower than the peak brightness of the light emitted during the on-interval. It can also be said that the time integral of the radiant power of the emitted light over the on-interval is greater than the time integral of the radiant power of the emitted light over the off-interval. This does not exclude that the total energy of the light emitted during the off-interval is greater than zero. In other words, it can be said that the light-emitting device may still emit faint light during the off-interval, although the faint light emission is perceived by the human eye as being much weaker than the light emitted during the on-interval, or even not perceived by the human eye at all.

[0032] Furthermore, during at least part of the switch-off interval, the operating electrical energy can be reduced to zero. In this case, during at least part of the switch-off interval, no electrical energy is supplied to the light-emitting device at all. These parts of the switch-off interval can therefore be associated with a disappearing brightness and / or radiant power of the emitted light. This has the technical benefit that the light-emitting device is completely turned off so that it can cool down again. In this way, premature aging effects of the light-emitting device and unnecessary thermal stresses applied to the light-emitting device are avoided. However, during other parts of the switch-off interval, there may be a residual brightness and / or radiant power of the emitted light, since the applied electrical energy does not disappear.

[0033] In a further preferred embodiment of the present invention, determining at least one temperature value may include estimating the at least one temperature value based on a correlation between the temperature of the light-emitting device and the electrical energy occurring across the light-emitting device. The correlation between two values ​​is the dependence of one of the two values ​​on the other of the two values. It can also be said that if a correlation is given, knowledge of one value implies knowledge of the other value. The temperature of the light-emitting device is related to the electrical energy occurring across the light-emitting device. For example, the temperature is not independent of the operating electrical energy. The dependence of the temperature on the operating electrical energy is a correlation in the above sense. Therefore, if the operating electrical energy is known, knowledge of the temperature value is implied. The operating electrical energy may include an operating current and / or an operating voltage. As outlined above, for at least one voltage U and one current I measured across the light-emitting device, a function T(U,I) may be used to infer at least one temperature value T. The function T(U,I) may be known in analytical form as a formula. Therefore, in order to infer the temperature from the measured voltage U and current I, the function T(U,I) may be evaluated at the point (U,I). Specifically, if the current I=I0 is fixed, the function T(U,I) is simplified to the function T(U)=T(U,I=I0), which relates the temperature T of the light-emitting device to the voltage U measured across the light-emitting device. As outlined above, there may be a relationship R(T) that defines the resistance R of the light-emitting device as a function of its temperature T. Therefore, the simplified function T(U) may also be given as T(U)=T(U,U / R(T)). Similarly, the simplified function T(I) that describes the temperature T of the light-emitting device as a function of the current I may be given as T(I)=T(R(T)*I,I). In addition, the functions T(U) and / or T(I) may be given in closed form as analytical formulas. Therefore, if the temperature T of the light-emitting device is to be inferred from the voltage U measured across the light-emitting device or the measured current I, the functions T(U) and T(I) may also be evaluated. In one embodiment of the present invention, the measured voltage may be a forward voltage. The functions T(U,I), T(U) and / or T(I) do not need to exist in analytical form, but can also be saved in a numerical format. For example, for a given number of data points i=1...N, the functions T(U,I), T(U) and / or T(I) can exist as an index list of temperature values ​​T[i] and voltage values ​​U[i] and / or current values ​​I[i]. In addition, the functions T(U,I), T(U) and / or T(I) can be saved as a lookup table for a given number of data points. This has the technical advantage that the relationship between temperature and electrical energy (e.g., voltage and / or current) can be adapted to the type of light-emitting device or light-emitting device. For example, calibration measurements can be performed on the light-emitting device to generate an index list and / or a lookup table. The index list and / or the lookup table can be saved to a memory or a hard disk. When estimating the temperature of the light-emitting device from a given measured voltage and / or current, the index list and / or the lookup table can be interpolated.In this way, sufficient accuracy of temperature estimation can be achieved while optimizing the memory space usage of the index list and / or lookup table. Interpolation can utilize piecewise linear interpolation or linear regression. However, higher-order and / or high-dimensional interpolation schemes that associate more than two pairs of data points through nonlinear functions (e.g., spline interpolation) can also be used. In another example, a neural network can be trained based on temperature values ​​T[i] and voltage values ​​U[i] and / or current values ​​I[i] for a given number of data points i=1…N.

[0034] If more than one electrical energy (i.e., multiple electrical energy values) is measured during at least one sensing interval, more than one temperature value may be estimated for at least one sensing interval. The highest temperature among the more than one temperature values ​​may be referred to as a peak temperature in at least one sensing interval. If the peak temperature is sensed to be greater than a threshold temperature, the peak temperature may trigger a reduction in operating electrical energy (e.g., current and / or voltage) supplied to the light emitting device and / or trigger the delivery of emergency feedback. This has the technical advantage of avoiding damage to the light emitting device.

[0035] In addition, the method may include averaging at least a portion of the electrical energy before estimating at least one temperature value based on the correlation and / or averaging at least a portion of the at least one temperature value after estimating at least one temperature value based on the correlation. If more than one temperature value is estimated for at least one sensing interval, these more than one temperature values ​​can be averaged to produce an average temperature. It is also possible to form a median of more than one temperature value. Such average / median temperature values ​​can be used to detect faulty temperature measurements. For example, the average / median temperature value can be compared with each of the estimated more than one temperature value. It can also be said that if a specific temperature value in more than one temperature value is detected as an abnormal value in more than one temperature value, the specific temperature value can be marked as an error. Such errors may, for example, be caused by a failure of the electromagnetic compatibility EMC of the light emitting device. If the average / median temperature value is of interest, it is also possible to average at least a portion of the measured electrical energy before determining the associated average / median temperature value from the average electrical energy using the correlation. Therefore, a single average / median electrical energy value can be determined from multiple electrical energy values. The single average / median electrical energy value may be transformed using an index list, a lookup table and / or a neural network to produce an associated single average / median temperature value. This has the technical advantage that the index list, the lookup table and / or the neural network must only be evaluated once, which reduces the computational burden compared to averaging and / or forming the median after the temperature value is estimated.

[0036] In addition, the correlation can be based on a temperature gradient and a dedicated voltage and / or current across the light-emitting device, wherein the dedicated voltage and / or current corresponds to the voltage and / or current at a dedicated reference temperature of the light-emitting device. It can be said that in this case, at least one of the measured electrical energies can be a voltage and / or current across the light-emitting device, and the correlation can be a correlation between the temperature of the light-emitting device and the voltage and / or current across the light-emitting device. The gradient describes the linear slope of the function in one direction of the function parameter space. Therefore, the temperature gradient describes the linear slope of the temperature in one direction of the temperature parameter. In one example, the functions T(U,I), T(U) and / or T(I) that describe the dependence of the temperature on the current and / or voltage can be approximated in a linear manner. It can also be said that in this case, the function can be globally linear. In this case, each of the functions T(U,I), T(U) and / or T(I) can be characterized by its slope and intercept. Therefore, the slope can be the temperature gradient grad(T), and the intercept can be the dedicated reference temperature T d , T d Via the function T(U,I), T(U) and / or T(I) and the dedicated reference voltage U d and / or reference current I d Corresponding. These two values ​​- slope and intercept - completely define the local linear approximation of each of the functions T(U,I), T(U) and / or T(I). In another example, it is possible to store multiple local temperature gradients and corresponding multiple local dedicated reference temperatures. It can also be said that in this case, the function can be piecewise linear. Therefore, the global behavior of the functions T(U,I), T(U) and / or T(I) can be represented by piecewise linear interpolation using multiple local gradients and corresponding multiple local dedicated reference temperatures. In another example, the global behavior of the functions T(U,I), T(U) and / or T(I) can be approximated using nonlinear basis functions. For example, the function can be approximated by polynomials of different orders, especially using spline interpolation, or by Fourier decomposition. It can also be said that, in general, the functions T(U,I), T(U) and / or T(I) can be decomposed into series on any complete set of basis functions. In this case, the coefficients of the series (i.e., the projections of the functions T(U,I), T(U) and / or T(I) onto each basis function in the set of basis functions) can be stored and used when it is necessary to evaluate parameters U and / or I that are not consistent with the support sampled by the functions T(U,I), T(U) and / or T(I), thereby requiring interpolation.

[0037] In addition, the temperature gradient may also be the same for a group of light-emitting devices of the same type as the light-emitting device. In one example, some coefficients used to expand the functions T(U, I), T(U) and / or T(I) as described above into a series on a complete set of basis functions may depend solely on the light-emitting device. For example, the intercept used for linear interpolation may be a separate parameter for each individual light-emitting device. If the light-emitting device is a red, green or blue LED, the intercept at temperature T=0°C is typically equivalent to a value of a forward voltage in the range of 1V…4V. However, in another example, some coefficients used to expand the functions T(U, I), T(U) and / or T(I) as described above into a series on a complete set of basis functions may be independent of each light-emitting device. These coefficients may also be referred to as "common coefficients" because they are shared by, for example, multiple light-emitting devices of the same type. In contrast, coefficients that are different for each light-emitting device may be referred to as "individual coefficients". For example, the temperature gradient used for linear interpolation may depend only on the type of the light-emitting device, not on the individual light-emitting devices themselves. If the light-emitting device is a red, green or blue LED, the temperature gradient relative to the forward voltage typically totals a value in the range of -1mV / K…-5mV / K. It can also be said that in this case, if multiple light emitting devices are manufactured, each of the multiple light emitting devices manufactured can have the same temperature gradient. Therefore, the intercept of the linear interpolation can be a separate coefficient, and the temperature gradient of the linear interpolation can be a common coefficient. This provides a technical benefit in that the common coefficient only needs to be initialized once for each group of light emitting devices of the same type. This provides a cost advantage if more than one light emitting device of a particular type is used.

[0038] In a further preferred embodiment of the present invention, the method may further include applying test power to the light emitting device during at least one sensing interval. The test power may include a test voltage and / or a test current. The test power is power that has a purpose different from the operating power. During the provision of the test power, the operation of the light emitting device may still occur, but it can be ignored. For example, if one of the test voltage or the test current is applied, the other of the voltage or current can be measured. The resistance R(T) of any light emitting device (which is related to the current and voltage applied to the light emitting device) is a function of the temperature T of the light emitting device. Therefore, if a test voltage U is applied to the light emitting device 测试 , and the current I is measured, then according to Ohm's law R(T) = U 测试 / I, which determines the temperature T of the light emitting device. Similarly, if a test current I is applied to the light emitting device 测试 , and measure the voltage U, then again according to Ohm's law R(T) = U / I 测试, which determines the temperature T of the light emitting device. Specifically, the measured voltage U may be the forward voltage across the light emitting device. If the light emitting device is a red, green or blue LED, the test current is typically equivalent to I for the LED temperature range T = -50°C ... 120°C. 测试 is approximately equal to 500 μA, while the measured forward voltage U is usually equivalent to U = 1 ... 4 V. However, these values ​​should not be limiting, but are given only as examples to illustrate the typical magnitudes of the parameters involved. From a technical point of view, it can also be said that when the other of the current I or the voltage U is adjusted, the test current I 测试 Or test voltage U 测试 It can only be maintained under temperature changes. If the temperature T changes, then the resistance R(T) will also change. However, in order to ensure that Ohm's law R(T) = U / I is followed, one of the current I or voltage U is fixed to be equal to the test current I 测试 Or test voltage U 测试 The other of the current I or the voltage U needs to be adjusted. The adjusted current I or voltage U can be measured. The test current I can be applied during the entire at least one sensing interval. 测试 Or test voltage U 测试 However, it is also possible to apply the test current or test voltage only during a portion of at least one sensing interval. Applying a relatively low test current or test voltage to the light emitting device provides a technical benefit in that the light emitting device only dissipates low power during sensing, so that during the sensing period the light emitting device maintains its temperature and does not heat up further.

[0039] Furthermore, the test electrical energy may be adapted to cause the lighting device to emit light only at a very low intensity and / or remain dark during at least one sensing interval. 测试 and / or test voltage U 测试 Zero, absent or negligible light emission can be caused during at least one sensing interval. This provides the benefit of not interfering with the emission of light having a target brightness and color, because operation only in the on-interval identifiably contributes to the perceived light flow. In other words, operation during the sensing interval does not interfere with normal operation during the on-interval. In particular, control of the brightness and / or color of the emitted light is not interfered with. It can also be said that the disappearance or very low intensity of light emitted during one or more sensing intervals is not recognizable by the human eye. Even if very low intensity light is emitted during at least one sensing interval, the sensing interval can be relatively short compared to the on-interval, so that the low intensity during the sensing interval contributes little to the overall light flow, which is primarily determined by the light flow emitted during operation in the on-interval. For example, if even if a test current I is applied 测试 Or test voltage U 测试, there is no light emission during at least one sensing interval, then the test current I can be applied during at least one sensing interval. 测试 Or test voltage U 测试 The test current I is applied more frequently than the case where low intensity light is emitted during 测试 Or test voltage U 测试 .

[0040] Furthermore, the test electrical energy may be adapted to ensure a linear behavior of the voltage and / or current across the light emitting device in relation to the temperature of the light emitting device. A linear behavior of two parameters means that the two parameters are proportional to each other. Thus, the relationship between the two parameters can be parameterized in a simple manner, namely by using a slope and an intercept. For example, a linear behavior of the voltage and / or current across the light emitting device with respect to its temperature provides the benefit that, when the current and / or voltage are measured, the temperature can be determined in a relatively simple manner. However, if the power dissipated in the light emitting device when the electrical energy is applied becomes too large, the current and / or voltage across the light emitting device is no longer associated in a linear manner with the temperature of the light emitting device. Thus, it can be said that in order to ensure a linear behavior, the test electrical energy must be limited in order to achieve a reliable temperature estimate.

[0041] The electronic device for determining the temperature of a light emitting device according to the present invention also meets the above needs. The electronic device for determining the temperature of a light emitting device comprises at least one light emitting device. In addition, the electronic device according to the present invention comprises a driving unit for operating at least one light emitting device during an on-interval and during an off-interval. The driving unit is adapted to apply operating electrical energy to at least one light emitting device during the on-interval. The electrical energy may be a current and / or a voltage. If more than one light emitting device is included in the electronic device, the driving unit may provide separate operating electrical energy to each light emitting device. In addition, the electronic device may comprise a test electrical energy generation unit for applying test electrical energy (e.g., a test current and / or a test voltage) to the light emitting device. If more than one light emitting device is included in the electronic device, the test electrical energy generation unit may apply electrical energy to each light emitting device individually. The test electrical energy generation unit may be part of the driving unit. Alternatively, the test electrical energy generation unit may be located outside the driving unit. In addition, the electronic device for determining the temperature of a light emitting device according to the present invention comprises a measuring unit for measuring at least one electrical energy across at least one light emitting device during at least one sensing interval, wherein at least one sensing interval is included in an off-interval, and wherein the duration of each of the at least one sensing interval is equal to or less than the duration of the off-interval. The measuring unit may record the measured electrical energy across one or more light-emitting devices. Thus, in response to the test electrical energy generating unit driving the light-emitting device in each sensing interval, information flows from the light-emitting device to the measuring unit. Finally, the electronic device for determining the temperature of the light-emitting device according to the present invention comprises a determination unit for determining at least one temperature value of at least one light-emitting device based on at least one electrical energy measured. The determination unit is responsible for estimating the temperature value of one or more light-emitting devices according to the value of the electrical energy measured by the measuring unit. Thus, it is possible that the determination unit comprises a microcontroller, which converts electrodynamic quantities (e.g., voltage and / or current) into thermodynamic quantities (e.g., temperature) based on the above-mentioned method, for example, using an analytical formula, an interpolation of an index list or a lookup table, or a trained neural network. The electronic device may additionally include an averaging and diagnostic unit. The averaging and diagnostic unit may be part of the determination unit, or may be independent of the determination unit. The averaging and diagnostic unit may include a microcontroller. The microcontroller may average one or more measured electrical energy sets and / or one or more estimated temperature value sets to form one or more mean values ​​and / or one or more median values ​​of the measured electrical energy and temperature, respectively. In addition, the microcontroller can diagnose faulty values ​​in one or more sets of measured electrical energy and / or one or more sets of estimated temperature values. The diagnosis can utilize comparison of at least one value in one or more sets of measured electrical energy with one or more mean values ​​and / or one or more median values ​​of the measured electrical energy.Likewise, the diagnosis can utilize at least one value in one or more estimated temperature sets to compare with one or more mean values ​​and / or one or more median values ​​of the temperature. Thus, it can also be said that outliers in these multiple values ​​are identified by statistically analyzing multiple measured electrical energies and / or estimated temperatures. These outliers can then be discarded or processed separately to obtain mean and / or median values ​​with higher accuracy.

[0042] The driving unit may include at least one voltage source and / or current source for providing the desired operating power to the light emitting device. Similarly, the test power generation unit may include at least one voltage source and / or current source for providing the desired test power to the light emitting device. It can also be said that the driving unit may include a current source for providing an operating current and / or a voltage source for providing an operating voltage. Similarly, it can also be said that the test power generation unit may include a current source for providing a test current and / or a voltage source for providing a test voltage. Both the driving unit and the test power generation unit may have corresponding input interfaces, and information indicating that the driving unit and the test power generation unit provide the desired operating power and test power, respectively, is received through the corresponding input interfaces. In addition, the driving unit and the test power generation unit may include at least one output interface for handing over the operating power and the test power to the light emitting device, respectively. The measuring unit may include a differential amplifier for measuring at least one power occurring across the light emitting device. The differential amplifier may compare at least one power occurring across the light emitting device with one or more reference physical quantities. In addition, the measuring unit may include a processor. The processor may process data generated by the differential amplifier in response to the at least one power measured. In addition, the measuring unit may include at least one input interface for sensing at least one electrical energy and at least one output interface for transmitting the measurement of at least one electrical energy. The output interface may deliver data from a processor or a differential amplifier or both. The data may represent the electrical energy across the light-emitting device. The determining unit may include an input interface for receiving data from the measuring unit. For example, the input interface of the determining unit may receive data output at the output interface of the measuring unit. The determining unit may include a processor for processing the data received at the input interface. In addition, the determining unit may include a memory. For example, the processor may use the correlation between the value of the electrical energy occurring across the light-emitting device and the value of the temperature of the light-emitting device to infer one or more temperature values ​​from the data received at the input interface. In addition, the determining unit may include an output interface for outputting one or more temperature values. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In the following, other advantages and details of the present invention will become apparent from the detailed description of the accompanying drawings. It should be understood that none of the elements shown should be considered limiting and any software / hardware element or module that performs the corresponding described function should be covered.

[0044] Figure 1 A flow chart of the method according to the present invention is shown;

[0045] Figure 2a A schematic diagram showing a single on-interval and a single off-interval and a single sensing interval placed in the middle of the off-interval according to the present invention;

[0046] Figure 2b A schematic diagram showing another embodiment of a single on-interval and a single off-interval and a single sensing interval according to the present invention, wherein the sensing interval is placed at the beginning of the off-interval;

[0047] Figure 2c A schematic diagram showing another embodiment of a single on-interval and a single off-interval and a single sensing interval according to the present invention, wherein the sensing interval is placed at the end of the off-interval; and

[0048] Figure 2d A schematic diagram showing another embodiment of a single on-interval and a single off-interval and a plurality of sensing intervals according to the present invention;

[0049] Figure 3a A schematic diagram showing a repetition scheme according to the present invention, wherein each off interval includes a sensing interval; and

[0050] Figure 3b shows a schematic diagram of another embodiment of a repetition scheme according to the present invention, wherein only a periodic subset of the switch-off intervals comprises a sensing interval;

[0051] Figure 4 a schematic diagram showing an exemplary dependence of the voltage across a light emitting device as a function of the temperature of the light emitting device according to the invention; and

[0052] Figure 5 An exemplary block diagram of an electronic device according to the present invention is shown. DETAILED DESCRIPTION

[0053] Figure 1A method 100 for determining a temperature of a light emitting device according to the present invention is shown. The method 100 comprises: operating 102 a light emitting device during an on-interval and during an off-interval; measuring 104 at least one electrical energy across the light emitting device during at least one sensing interval, wherein the at least one sensing interval is included in the off-interval, and wherein the duration of each of the at least one sensing interval is equal to or less than the duration of the off-interval; and determining 106 at least one temperature value of the light emitting device based on the measured at least one electrical energy.

[0054] The method 100 for determining a light emitting temperature can be performed by an electronic device according to the present invention. For example, the light emitting device can be operated 102 by a driving unit of the electronic device. Therefore, the driving unit can supply operating power to the light emitting device. In addition, a test power generation unit of the electronic device can supply test power to the light emitting device. The measuring unit of the electronic device can measure 104 at least one power across the light emitting device during at least one sensing interval. Based on the at least one power measured 104, the determination unit of the electronic device can determine 106 at least one temperature value of the light emitting device.

[0055] Figure 2a A timing diagram 200 is depicted that includes an on-interval 202, an off-interval 204, and a sensing interval 206. The on-interval 202 is characterized by a first length, the off-interval 204 is characterized by a second length, and the sensing interval 206 is characterized by a third length. Typically, the sensing interval 206 is included in the off-interval 206. Thus, the third length is equal to or less than the second length. In an exemplary manner, Figure 2a , the sensing interval 206 is shown as being located inside the off interval 204. Figure 2a In the example of , the third length is less than the second length. Therefore, a first gap is formed between the end of the on-interval 202 and the beginning of the sensing interval 206, and a second gap is formed between the end of the sensing interval 206 and the end of the off-interval 204.

[0056] During the on-interval 202, an operating current and / or voltage may be supplied to the light emitting device. Figure 2a, a constant operating current I0 is shown. However, it is known to those skilled in the art that any light emitting device may also be driven by a time-dependent operating current I0(t). This results in the emission of light having a desired brightness and color during the on-interval 202. In other words, a power supply having an operating current I0(t) during the on-interval 202 may have the effect of emitting light having a desired time-dependent radiant power P(t). At the beginning of the off-interval 204, the operating current and / or voltage is significantly reduced, possibly even to zero. As a result, the time-dependent radiant power P(t) drops to a lower value, possibly also to zero. The radiant power P(t) may lag behind the operating current I0(t). Therefore, the first gap may be used to allow the radiant power to be adjusted and relaxed to the operating mode during the sensing interval. During the sensing interval 206, a relatively low test current I 测试 (t) is applied to the light emitting device, which results in a new radiated power P(t). Figure 2a The example shows a constant test current I 测试 (t) = constant. However, this should not be considered limiting of the present disclosure as any time-dependent test current I applied during the sensing interval (206) should also be included. 测试 (t). The energy of the light emitted during the sensing interval 206 may be absent or relatively low, such that the emitted light cannot be perceived by the human eye or is only perceived by the human eye as a faint light. In a more quantitative manner, the difference between the on-interval 202 and the off-interval 204 is that the energy of the light emitted during the on-interval 202 is significantly greater than the energy of the light emitted during the off-interval 204. Using the radiant power P(t), it can be said that the following inequality holds true with respect to the energy of the emitted light over the on-interval 202 and the off-interval 204:

[0057] ∫ 接通-间隔 P(t)dt>>∫ 关断-间隔 P(t)dt

[0058] When the test current I is applied during the sensing interval 206 测试 At (t), one or more voltage values ​​U are measured across the light emitting device. The one or more voltage values ​​U may include a forward voltage U measured on the light emitting device. F . One or more temperature T values ​​of the temperature of the light emitting device are determined from one or more voltage values ​​U using the above method. For example, the temperature can be inferred from a given measured forward voltage using a correlation between the forward voltage and the temperature. The correlation can be evaluated using an interpolation of a lookup table of temperature and forward voltage. The interpolation can be a global linear interpolation, a piecewise local linear interpolation, a Fourier approximation, or a polynomial interpolation, such as a spline interpolation as described above. In Figure 2aIn the example, the second gap after the sensing interval 206 can be used to calculate the operating current I0(t) by using the determined temperature value to Figure 2a The desired radiation power P(t) is obtained in the next on-interval after the off-interval 204 depicted in FIG.

[0059] Figure 2b Depicted are an on-interval 202, an off-interval 204 and a sensing interval 208 according to a second embodiment 205 of the present invention. Figure 2b In FIG. 2 , the sensing interval 208 is located at the beginning of the off interval 204. Therefore, in Figure 2b The temperature determined during the sensing interval 208 can constitute an estimate of the temperature of the light emitting device immediately at the end of the aforementioned on-interval 202. In other words, positioning the sensing interval 208 at the beginning of the off-interval 204 produces one or more temperature measurements that best characterize the temperature of the light emitting device at the time of maximum heating during operation (i.e., at the end of the on-interval 202 when the maximum energy has been set in the light emitting device). Such temperature measurements can be used to supervise the operation of the light emitting device, to issue a warning when the maximum allowed temperature is exceeded, and to take proactive action by, for example, re-adjusting the operating electrical energy. In addition, aging effects of the light emitting device due to operation in the on-interval 202 can be quantified based on the determined temperature.

[0060] Figure 2c Depicted are an on-interval 202, an off-interval 215, and a sensing interval 210 according to a third embodiment 215 of the present invention. Figure 2c In FIG. 2 , the sensing interval 210 is located at the end of the off interval 204. During the gap formed between the end of the on interval 202 and the beginning of the sensing interval 210, the light emitting device can reduce its temperature and cool down, because no further energy is set in the light emitting device during the gap due to the disappearance of the operating current. Figure 2c The one or more temperatures determined during the sensing interval 210 constitute a Figure 2c An estimate of the temperature of the light emitting device after thermal relaxation at the start of the next on-interval after the off-interval 204 depicted in FIG. These temperatures can be used to compensate for temperature effects when adjusting the operating power of the light emitting device for the next on-interval.

[0061] Figure 2dAn on-interval 202, an off-interval 220 and a plurality of sensing intervals 212-a, 212-b, 212-c according to a fourth embodiment 220 of the present invention are depicted. The plurality of sensing intervals 212-a, 212-b, 212-c are distributed over the off-interval 204. In this way, a plurality of temperature measurements characterizing the temperature of the light-emitting device at different points in time during the off-interval 204 are obtained. Specifically, the temperature determined during a first sensing interval 212-a located at the beginning of the off-interval 204 can be used as an estimate of the temperature of the light-emitting device at the end of the on-interval 202, while the temperature determined during a third sensing interval 212-c located at the end of the off-interval 204 can be used as an estimate of the temperature of the light-emitting device directly at the beginning of the next on-interval. The temperature determined during a second sensing interval 212-b located in the middle of the off-interval 204 can be used to estimate the speed of temperature relaxation of the light-emitting device. Instead of a second sensing interval 212-b located in the middle of the shut-off interval 204, multiple sensing intervals (not shown) located between the first sensing interval 212-a and the third sensing interval 212-c can be used. During the multiple sensing intervals, multiple associated temperatures can be determined. Determining a large number of temperature values ​​has the technical advantage of sampling the temperature relaxation speed with high time resolution. In addition, the temperature values ​​can be averaged to produce one or more mean temperature estimates with higher statistical stability. In addition, it is possible to detect erroneous temperature measurements in multiple temperature measurements, for example via outlier detection, so that only those temperature measurements that have passed the quality test are used to establish the speed of temperature relaxation. Based on the speed of temperature relaxation of the light-emitting device, the length of the shut-off interval 204 can be adjusted. For example, the length of the shut-off interval 204 can be adjusted in such a way that the light-emitting device has cooled to the desired temperature at the end of the shut-off interval 204. The length of the gap between the respective sensing intervals 212-a, 212-b, 212-c can be adjusted to avoid heating of the light-emitting device due to energy dissipated by supplying the test current. In other words, the gaps can be selected in such a way that the heat loss during each gap is greater than or equal to the heat gain during the previous sensing interval in the plurality of sensing intervals 212-a, 212-b, 212-c. In this way, each of the gaps compensates for the heating of the light emitting device during the corresponding sensing interval.

[0062] Figure 3a and Figure 3b A fifth embodiment 300 and a sixth embodiment 305 of the present invention are depicted, wherein on-intervals 302 and off-intervals 304 alternate. Figure 3a and Figure 3b Each on interval 302 and each off interval 304 may be similar to the above Figure 2a-2d The on-interval 202 and off-interval 204 of FIG. 204 are constructed in a similar manner. Figure 2c The off interval 204 is depicted in a similar manner to Figure 3a , that is, each off interval 304 includes only one sensing interval 306 at the end of the corresponding off interval 304. Although not shown, Figure 3a and Figure 3b The flow of on-intervals 302 and off-intervals 304 depicted in FIG. 304 may continue in a repetitive manner beyond the third off-interval 304. Thus, the on-intervals 302 and off-intervals 304 may occur periodically. In this manner, continuous operation of the delivery of light having a desired brightness and color is ensured while generating a light source that can be used in a repetitive manner in conjunction with the above Figure 2a-2d For example, the temperature measurement in each of the sensing intervals 306 can be repeatedly used to adjust the operating current in the corresponding on-interval 302 after the corresponding sensing interval 306. Figure 3b As depicted in , the sensing intervals 306 may occur only in a subset of the plurality of off-intervals 304, e.g., every other off-interval 304. However, the sensing intervals 306 may also occur in a subset of the plurality of off-intervals 304 with other periodicities, e.g., every 10 or every 100 off-intervals 304, or even aperiodically, i.e., without any periodicity at all (not shown). In other words, the plurality of off-intervals 306 may be more sparse than the plurality of off-intervals 304. In this way, those off-intervals 304 that do not contain any sensing intervals 306 or fewer sensing intervals 306 than other off-intervals 304 do not trigger the calculation of a temperature estimate at the microcontroller, which reduces the computational burden by reducing the number of operations at the microcontroller.

[0063] Figure 4 An embodiment of a correlation 400 between a temperature T of a light emitting device and a voltage U across the light emitting device according to the present invention is depicted. As described above, the voltage U across the light emitting device may be a forward voltage measured on the light emitting device. The correlation 400 defines a relationship between the voltage U(T) and the temperature T. Figure 4 In the case of , this relationship is linear. However, nonlinear functions (not shown) that describe the relationship between voltage U(T) and temperature T may also occur. Correlation 400 is determined by a dedicated temperature T d , for special temperature T d Measured dedicated voltage U d and a temperature gradient ΔU / ΔT, which describes the slope of the correlation 400. These values ​​clearly determine Figure 4 The linear correlation 400 shown in FIG. can be determined by applying linear regression to calibration measurements of temperature and voltage for a given light emitting device. Figure 4 Dedicated temperature T dand temperature gradient ΔU / ΔT. When the measurement voltage U is given, the gradient ΔU / ΔT, the dedicated temperature T d And dedicated voltage U d Can be used to find the temperature T(U) according to the following equation:

[0064] T(U)=T d +ΔT / ΔU*(UU d )[*].

[0065] As described above, non-linear dependencies (not shown) may be approximated using piecewise linear interpolation, polynomial, or spline approximations.

[0066] Figure 5 An embodiment of an electronic device or apparatus 500 for determining the temperature of a light emitting device according to the present invention is depicted. The electronic device 500 may perform Figure 1 , and as described above. In the embodiment example shown here, the electronic device 500 encompasses a light emitting device 502. However, it is also conceivable that the electronic device 500 is implemented separately from the light emitting device 502. Therefore, the electronic device 500 may be connected to one light emitting device 502 or several light emitting devices (not shown here). Therefore, the electronic device 500 may be positioned close to at least one light emitting device 502 or even spaced apart from at least one light emitting device 502, for example as part of a controller. In the embodiment example shown here, the electronic device 500 further includes a drive unit 504, a test power generation unit 506, a measuring unit 508 and a determination unit 510. The light emitting device 502 may include a light emitting diode LED. It is also possible that the light emitting device 502 includes a plurality of light emitting devices, for example a plurality of light emitting diodes LED (not shown). The light emitting device 502 emits light of desired brightness and color when supplied with corresponding operating power. The drive unit 504 is adapted to control the light emitting device 502 to emit light of desired brightness and color according to the control unit 510. Figure 2a-2d and / or Figure 3a and Figure 3b The driving unit 504 supplies operating power to the light emitting device 502 during the on-time interval in one or more of the time schemes depicted in FIG. Therefore, the driving unit 504 is responsible for controlling the light emitting device 502 during normal operation according to the driving algorithm. If more than one light emitting device 502 is included in the electronic device 500, the driving unit 504 can apply a plurality of different control algorithms, wherein a corresponding control algorithm of the different control algorithms is applied to each individual light emitting device (not shown). To this end, the driving unit 504 interfaces with the light emitting device 502. The interface enables the operating power to be applied to the light emitting device 502. The test power generation unit 506 is responsible for controlling the light emitting device 502 according to the driving algorithm during normal operation. Figure 2a-2d , Figure 3a or Figure 3bThe test power generation unit 506 applies the test power to the light emitting device 502 in one or more of the sensing intervals. The interface between the test power generation unit 506 and the light emitting device enables the application of the test power. The test power generation unit 506 may include a variable current source and / or a variable voltage source that supplies a test current and / or a test voltage. The test power generation unit 506 may be separate from the drive unit 504 or included in the drive unit 504. The measuring unit 508 measures one or more power occurring across the light emitting device 502 during one or more sensing intervals. In order to sense the power, the measuring unit 508 interfaces with the light emitting device 502. The measuring unit 508 may include a differential amplifier that amplifies one or more power measured on the light emitting device 502. In addition, the measuring unit 508 may include an analog-to-digital AD converter system, into which one or more amplified power is fed, and the analog-to-digital AD converter system converts one or more amplified power into a digital format. Finally, the measuring unit 508 may include a processor that converts one or more amplified power in a digital format into a corresponding forward voltage value. The measuring unit 508 is docked with the determining unit 510 so that the corresponding forward voltage value is known at the determining unit 510. As described above, the determining unit 510 may include a processor that converts the forward voltage value into a temperature value. The determined temperature value may then be fed back (dashed arrow) to the driving unit 504 so as to adapt the operating power to the temperature of the light device 502. For example, the driving unit 504 may be adapted to compensate the operating power for the temperature effect of the temperature on the brightness and color of the light emitted by the light emitting device 504, and adjust the operating power accordingly. Similarly, when the temperature of the light emitting device 502 becomes intolerably high, the driving unit 504 may be adapted to take action. In this case, the driving unit 504 may reduce the operating power or shorten the duration of the current on interval or one or more future on intervals. The driving unit 504 may also issue a warning message when the temperature exceeds a temperature limit.

[0067] Although specific hardware elements are described herein, this should not be construed as limiting and the invention should also encompass other hardware elements that can provide the same functionality as described herein.

Claims

1. A method for determining a temperature of a light emitting device (502), the method comprising: operating (102) the light emitting device (502) during an on-interval and during an off-interval; measuring (104) at least one electrical energy across the light emitting device (502) during at least one sensing interval, wherein the at least one sensing interval is included in the off-interval, and wherein the duration of each of the at least one sensing interval is equal to or less than the duration of the off-interval; as well as At least one temperature value of the light emitting device (502) is determined (106) based on the at least one measured electrical energy.

2. The method according to claim 1, characterized in that The at least one sensing interval is located at the beginning of the off interval or at the end of the off interval.

3. The method according to any one of the preceding claims, characterized in that The on-interval is one on-interval of a plurality of on-intervals, and / or wherein the off-interval is one off-interval of a plurality of off-intervals.

4. The method according to claim 3, characterized in that The plurality of on-intervals are periodic, and / or wherein the plurality of off-intervals are periodic.

5. The method according to claim 3 or 4, characterized in that Each of the plurality of off-intervals or each of a subset of the plurality of off-intervals includes at least one sensing interval.

6. A method according to any one of the preceding claims, characterised in that Operating the light emitting device (502) comprises: applying operating power to the light emitting device (502) during the on-interval; and The operating power is reduced during the off interval.

7. The method according to claim 6, characterized in that During at least part of the off interval, the operating power is reduced to zero.

8. A method according to any one of the preceding claims, characterised in that Determining the at least one temperature value comprises: The at least one temperature value is estimated based on a correlation between a temperature of the light emitting device (502) and electrical energy occurring across the light emitting device (502).

9. The method of claim 8, further comprising: averaging at least a portion of the electrical energy before estimating the at least one temperature value based on the correlation; and / or After estimating the at least one temperature value based on the correlation, at least a portion of the at least one temperature value is averaged.

10. The method according to any one of claims 8 and 9, characterized in that The correlation is based on: A temperature gradient and a dedicated voltage and / or current across the light emitting device (502), wherein the dedicated voltage and / or current corresponds to a voltage and / or current at a dedicated reference temperature of the light emitting device (502).

11. The method according to claim 10, characterized in that The temperature gradient is the same for a group of light emitting devices (502) of the same type as the light emitting device (502).

12. The method of any one of the preceding claims, further comprising: During the at least one sensing interval, test power is applied to the light emitting device (502).

13. The method according to claim 12, characterized in that The test power is adapted to cause the lighting device (502) to emit light only at a very low intensity and / or remain dark during the at least one sensing interval.

14. The method according to claim 12 or 13, characterized in that The test power is adapted to ensure a linear behavior of the voltage and / or current across the light emitting device (502) in relation to the temperature of the light emitting device (502).

15. An apparatus (500) for determining a temperature of a light emitting device (502), the apparatus (500) comprising: a driving unit (504) for operating the at least one light emitting device (502) during an on-interval and during an off-interval; a measuring unit (508) for measuring at least one electrical energy across the at least one light emitting device (502) during at least one sensing interval, wherein the at least one sensing interval is included in the off-interval, and wherein a duration of each of the at least one sensing interval is equal to or less than a duration of the off-interval; as well as A determination unit (510) is used to determine at least one temperature value of the at least one light emitting device (502) based on the at least one measured electrical energy.

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