METHOD FOR OPERATING A RADIATION-EMPLOYING SEMICONDUCTOR CHIP AND LIGHTING DEVICE

Abstract

A method for operating a radiation-emitting semiconductor chip is described, comprising the following steps: - Switching on an initial number of pixels (6) in an initial lighting mode according to an initial lighting pattern (11), - Switching on at least one pixel (6) according to a measurement pattern (13) during a measurement interval, - Determining a temperature (T) of an active zone (14) of at least one of the switched-on pixels (6) during the measurement interval, - Switching on a second number of pixels (6) in a second lighting mode according to a second lighting pattern (12). A lighting device is also specified.

Description

[0001] A method for operating a radiation-emitting semiconductor chip and a lighting device are specified.

[0002] The aim is to provide an improved method for operating a radiation-emitting semiconductor chip, in which, in particular, a temperature of an active zone of the radiation-emitting semiconductor chip is determined.

[0003] Furthermore, an improved lighting device is to be specified which comprises a radiation-emitting semiconductor chip with an active zone, wherein in particular a temperature of the active zone can be determined in an improved manner.

[0004] These objects are achieved by a method having the steps of patent claim 1 and by a lighting device having the features of patent claim 13.

[0005] Advantageous embodiments and further developments of the method and the lighting device are specified in the respective dependent claims.

[0006] According to one embodiment of the method for operating a radiation-emitting semiconductor chip comprising a plurality of pixels, a first number of pixels are switched on in a first illumination mode according to a first illumination pattern. In particular, the first illumination pattern specifies an arrangement of pixels that are switched on while the remaining pixels are switched off.

[0007] The radiation-emitting semiconductor chip comprises, in particular, an epitaxial semiconductor layer sequence that is at least partially separated into a plurality of semiconductor layer stacks, wherein each pixel comprises at least one epitaxial semiconductor layer stack. Each epitaxial semiconductor layer stack has, in particular, an n-doped semiconductor layer, a p-doped semiconductor layer, and an active zone arranged between the p-doped semiconductor layer and the n-doped semiconductor layer.

[0008] If a pixel is switched on, a voltage is applied to the active zone such that a current flows through the active zone and the active zone generates electromagnetic radiation. When switched on, the pixel emits the electromagnetic radiation generated in the active zone and lights up. If the pixel is switched off, no current flows through the active zone of the pixel and no electromagnetic radiation is generated in the active zone. The switched off pixel does not light up. In particular, during the first illumination mode, the first number of pixels specified by the illumination pattern are switched on and emit electromagnetic radiation, while the remaining pixels are switched off and do not emit any electromagnetic radiation. In this case, the term “voltage” refers in particular to a forward voltage.

[0009] The pixels of the radiation-emitting semiconductor chip are encompassed by a radiation exit surface of the radiation-emitting semiconductor chip or form the radiation exit surface of the radiation-emitting semiconductor chip. The radiation exit surface is, in particular, the surface of the radiation-emitting semiconductor chip from which electromagnetic radiation is emitted during operation of all pixels.

[0010] For example, a pixel of the radiation-emitting semiconductor chip has an edge length between 1 micrometer and 200 micrometers.

[0011] In particular, the pixels are comprised of a common semiconductor chip. The epitaxial semiconductor layer stacks are in particular formed from a contiguous epitaxial semiconductor layer sequence, for example by etching recesses into the epitaxial semiconductor layer sequence. The pixels are in particular arranged on a contiguous semiconductor layer and / or on a common substrate on which the epitaxial semiconductor layer stack and / or the epitaxial semiconductor layer sequence were grown, for example, epitaxially. In particular, the radiation-emitting semiconductor chip is not an assembled device in which separate semiconductor chips, which were initially manufactured separately from one another, are mounted on a common carrier. In other words, the radiation-emitting semiconductor chip is preferably a pixelated semiconductor chip.

[0012] However, it is also possible that the pixels of the radiation-emitting semiconductor chip were manufactured separately and then arranged together on a substrate. In other words, it is also possible that the radiation-emitting semiconductor chip is non-monolithic.

[0013] According to a further embodiment of the method, at least one pixel is switched on according to a measurement pattern during a measurement interval. The measurement pattern specifies, in particular, one or more pixels that are switched on and illuminated during the measurement interval, while the remaining pixels are switched off. In particular, the switching on of the pixels according to the measurement pattern occurs immediately following operation of the pixels in the first illumination mode.

[0014] According to a further embodiment of the method, a temperature of an active zone of at least one of the switched-on pixels is determined during the measurement interval. In other words, the temperature of the active zone of at least one pixel that is switched on and illuminated according to the measurement pattern is determined during the measurement interval.

[0015] According to a further embodiment of the method, a second number of pixels are switched on in a second illumination mode according to a second illumination pattern. During the second illumination mode, the second number of pixels illuminate according to the second illumination pattern, while the remaining pixels are switched off. In particular, the pixels are switched on in the second illumination mode according to the second illumination pattern immediately after the temperature of the active zone has been determined during the measurement interval.

[0016] In particular, the pixels in the first illumination mode are first switched on according to the first illumination pattern, and then directly thereafter the pixels according to at least the measurement pattern during the measurement interval. At the same time, while the pixels are switched on according to the measurement pattern, the temperature of the active zone of at least one of the switched-on pixels is determined. Immediately thereafter, the pixels are switched on again in the second illumination mode according to the second illumination pattern.

[0017] The first lighting mode and the second lighting mode can be the same or different. If the first lighting mode and the second lighting mode are the same, the first lighting pattern and the second lighting pattern can be the same or different. If the first lighting mode and the second lighting mode are different, in particular the first lighting pattern and the second lighting pattern are different. For example, the first lighting mode and / or the second lighting mode are a low beam mode or a high beam mode.

[0018] According to one embodiment, the method for operating the radiation-emitting semiconductor chip with a plurality of pixels comprises the following steps: - switching on the first number of pixels in the first lighting mode according to the first lighting pattern, - switching on at least one pixel according to the measurement pattern during the measurement interval, - Determining the temperature of the active zone of at least one of the switched-on pixels during the measurement interval, - switching on the second number of pixels in the second illumination mode according to the second illumination pattern.

[0019] In particular, the steps of the procedure are carried out in the order specified above.

[0020] In particular, the specified steps can be repeated multiple times. This allows switching between different illumination modes with different illumination patterns. The measurement patterns and / or measurement intervals can be identical or different from one another.

[0021] The method for operating the radiation-emitting semiconductor chip is based, among other things, on the idea of ​​determining the temperature of the active zones during the measurement interval in which only a few pixels are switched on. The measurement interval briefly interrupts normal operation of the radiation-emitting semiconductor chip, in which the pixels are switched on in the first illumination mode and / or the second illumination mode. In other words, the pixels are briefly energized according to the measurement pattern in the measurement interval, in which, as a rule, significantly fewer pixels are switched on than during the first illumination mode and / or the second illumination mode, and the temperatures of the active zones of the switched-on pixels are determined. Reducing the number of switched-on pixels during the determination of the temperatures of the active zones advantageously allows, in particular, to at least reduce interference factors during the measurement.A small number of pixels during the determination of the temperature of the active zone also allows to reduce the series resistance of the pixels whose temperature is being determined and thus eliminate interference.

[0022] The present method advantageously enables voltage measurement for temperature determination during ongoing operation. Furthermore, the temperature of the active zone is determined directly at the point of light generation in the radiation-emitting semiconductor chip, thus minimizing interference and allowing the temperature to be determined relatively accurately.

[0023] According to a further embodiment of the method, the duration of the measurement interval corresponds at most to the inverse of the flicker fusion frequency of the human eye. In other words, the measurement interval lasts at most as long as the inverse of the flicker fusion frequency of the human eye. The flicker fusion frequency is the frequency at which a sequence of light stimuli is perceived by the human eye as a continuous light. In other words, the human eye cannot distinguish between light stimuli that change faster than the inverse of the flicker fusion frequency. The temporal resolution of the eye is thus determined by the flicker fusion frequency. The flicker fusion frequency is, for example, between 22 Hz and 90 Hz.

[0024] In other words, the duration of the measurement interval is preferably selected to be so short that the human eye does not perceive the change in the light emission of the pixels due to switching from the first illumination mode and / or the second illumination mode to the measurement pattern. For example, the measurement interval is no longer than 0.045 seconds or no longer than 0.01 seconds. For example, the duration of the measurement interval is between 0.01 seconds and 0.045 seconds inclusive.

[0025] According to a further embodiment of the method, fewer pixels are switched on according to the measurement pattern than according to the first illumination pattern and / or according to the second illumination pattern. For example, between 0.0004% and 1% of the total number of pixels of the radiation-emitting semiconductor chip are switched on according to the measurement pattern. For example, the radiation-emitting semiconductor chip has between 1000 and 100,000 pixels. In particular, the radiation-emitting semiconductor chip has approximately 25,000 pixels.

[0026] According to a further embodiment of the method, the temperature of the active zone is determined from a voltage required for a predetermined current to flow through the active zone. In other words, a voltage is applied to the active zone during the measurement interval, causing a predetermined current to flow through the active zone. The pixel to which the voltage is applied typically illuminates due to the current flow during the measurement interval.

[0027] According to a further embodiment of the method, during the first illumination mode, the voltages of all pixels of the first illumination pattern are measured, which is necessary for a predetermined current to flow through the active zones of the pixels according to the first illumination pattern. Then, according to the measurement pattern, no pixels whose measured voltage deviates from the measured voltage of the neighboring pixels by more than a predetermined value are switched on during the measurement interval. In other words, the voltage of the pixels switched on during the first illumination mode is determined, and the measurement pattern is then configured such that pixels whose determined voltage deviates from the voltage of the neighboring pixels by more than a predetermined value are not switched on.For example, no pixels are switched on during the measurement interval according to the measurement pattern if the voltage measured during the first illumination mode differs by more than 10 mV or more than 100 mV from the measured voltage of the neighboring pixels.

[0028] According to a further embodiment of the method, the first illumination pattern and / or the second illumination pattern has at least two subpatterns, according to which different pixels of the first illumination pattern are switched on to generate grayscale. The switching between the two subpatterns also occurs, in particular, at a frequency that corresponds at least to the flicker fusion frequency. In other words, during the first illumination mode and / or the second illumination mode, switching back and forth takes place between at least two subpatterns, in particular at a frequency that corresponds at least to the flicker fusion frequency. In this way, grayscale of the first illumination pattern and / or the second illumination pattern can be achieved. Another possibility for generating grayscale of individual pixels is pulse width modulation of the voltage applied to the pixels for operation.In pulse-width modulation, the voltage applied to the active zone of the pixels is periodically modulated between two values, particularly in a rectangular pattern. If a rectangular voltage signal is applied to the active zone for pulse-width modulation, its amplitude and / or duration can be varied.

[0029] According to a further embodiment of the method, pixels are switched on according to the measurement pattern, which are also switched on according to the first illumination pattern and / or according to the second illumination pattern and / or at least according to at least one subpattern during the first illumination mode and / or the second illumination mode. In other words, the temperature of the active zone of those pixels that are also switched on and illuminated during the first illumination mode and / or the second illumination mode is determined during the measurement interval. This can, in particular, prevent oncoming traffic from being dazzled when the radiation-emitting semiconductor chip is used as a light source in a headlight.

[0030] According to a further embodiment of the method, the pixels are divided into subregions, and at least one pixel per subregion is switched on according to the measurement pattern, and the temperature of its active zone is determined during the measurement interval. In particular, the subregions completely fill the radiation exit surfaces of the radiation-emitting semiconductor chip.

[0031] The sub-areas are, in particular, imaginary subdivisions of the pixels. For each sub-area, the temperature of the active zone of at least one pixel specified by the measurement pattern is determined. In particular, the measurement pattern provides for a regular distribution of the activated pixels during the measurement interval. If the sub-areas are conceptually placed on top of one another, the pixels activated according to the measurement pattern are preferably congruent. This allows the temperature of the active zones of the pixels to be determined evenly distributed across the radiation exit surface of the radiation-emitting semiconductor chip.

[0032] According to a further embodiment of the method, several pixels per sub-area are switched on according to the measurement pattern, the temperature of the active zones of the switched-on pixels is determined, and their average value is calculated. The several pixels per sub-area can be switched on simultaneously or sequentially, and the temperature of the active zones of the switched-on pixels is determined and their average value is calculated.

[0033] According to a further embodiment of the method, different pixels are switched on according to different measurement patterns, and the temperature of the active zone of the switched-on pixels is determined when they are switched on. In particular, the different measurement patterns can be switched on during different measurement intervals, between which different or identical illumination modes with different or identical illumination patterns are executed. The determined temperatures can be combined, and, for example, an average of the determined temperatures can be calculated. Thus, the measurement intervals can be very short, so that the operation of the radiation-emitting semiconductor chip is only very briefly interrupted during the different illumination modes.

[0034] According to a further embodiment of the method, a range of pixels is determined from the first illumination pattern whose active zones have a high temperature or the highest temperatures compared to the active zones of the remaining pixels. According to the measurement pattern, only pixels from this range are switched on. In other words, a range of pixels is determined from the first illumination pattern that should have high or the highest temperatures due to the current supply to the pixels specified by the first illumination pattern. This predetermines a range of pixels that are particularly interesting for determining the temperatures of the active zones, and the determination of the temperatures of the active zones is limited to the pixels in this range.

[0035] According to a further embodiment of the method, pixels that are not switched on according to the first illumination pattern and / or the second illumination pattern, or that are only operated with a current that does not exceed a predetermined value, are not included in the measurement pattern. In other words, only those pixels that are switched on immediately before the measurement interval and / or immediately after the measurement interval and illuminate with a certain brightness are switched on according to the measurement pattern. This avoids dazzling oncoming traffic when the radiation-emitting semiconductor chip is used as a light source in a headlight.

[0036] In particular, the radiation-emitting semiconductor chip can be included in a lighting device. All features and embodiments described in connection with the method for operating the radiation-emitting semiconductor chip can also be implemented in the lighting device, and vice versa. In particular, a method for operating the lighting device can comprise all the steps, features, and embodiments as the method for operating the radiation-emitting semiconductor chip.

[0037] According to one embodiment, the lighting device comprises a radiation-emitting semiconductor chip with a plurality of pixels. For example, the radiation-emitting semiconductor chip has the features and embodiments already described.

[0038] According to a further embodiment, the lighting device comprises a control unit configured to control the radiation-emitting semiconductor chip during operation. For example, the control unit specifies a first illumination pattern and / or a second illumination pattern to the radiation-emitting semiconductor chip, which has the pixels that are to be switched on according to the first illumination pattern and / or the second illumination pattern. In other words, during operation, the control unit switches on the first number of pixels of the radiation-emitting semiconductor chip that are to be switched on according to the first illumination pattern in a first illumination mode. Furthermore, during operation, the control unit switches on the second number of pixels of the radiation-emitting semiconductor chip that are to be switched on according to the second illumination pattern in the second illumination mode.Likewise, the control unit switches on the pixels of the radiation-emitting semiconductor chip that are to be switched on according to a measurement pattern during a measurement interval. In other words, the control unit switches the pixels on and off according to the first illumination pattern, the second illumination pattern, and / or the measurement pattern. It is also possible for the control unit to be configured to dim individual, several, or all pixels according to predetermined patterns, for example, through pulse width modulation. For example, areas of the radiation exit surface of the radiation-emitting semiconductor chip are automatically dimmed to avoid dazzling other road users.

[0039] According to a further embodiment, the lighting device comprises a measuring unit which is configured to determine a temperature of an active zone of the pixels.

[0040] According to a further embodiment of the lighting device, the control unit switches on a first number of pixels during operation in a first lighting mode according to a first lighting pattern. The remaining pixels are in particular switched off.

[0041] According to a further embodiment, the control unit switches on at least one pixel according to at least one measurement pattern during a measurement interval. The remaining pixels are, in particular, switched off.

[0042] According to a further embodiment, the measuring unit determines the temperature of the active zone of at least one of the switched-on pixels during the measuring interval.

[0043] According to a further embodiment, the control unit switches on a second number of pixels in a second illumination mode according to a second illumination pattern. The remaining pixels are, in particular, switched off.

[0044] According to a further embodiment of the lighting device, the measuring unit comprises an analog-to-digital converter that converts an analog voltage signal into a digital voltage signal, such as a numerical value. In particular, when determining the temperature of the active zone of at least one switched-on pixel, an analog voltage signal is first measured and forwarded to the analog-to-digital converter, which converts the measured analog voltage signal into a digital voltage signal. In particular, the measured analog voltage signal corresponds to a temperature of the active zone.

[0045] According to a further embodiment of the lighting device, the measuring unit comprises a sample-and-hold circuit that samples the analog voltage signal of at least one pixel and holds it for a predetermined period of time. The sample-and-hold circuit is connected upstream of the analog-to-digital converter. The sample-and-hold circuit samples the analog voltage signal to be digitized later by sampling a voltage value and holding the sampled voltage value for a specific period of time.

[0046] According to a further embodiment of the lighting device, at least two pixels are connected to the analog-to-digital converter via a multiplexer circuit. The multiplexer circuit has, in particular, 2 nIt has n data inputs, n control inputs, and exactly one output. The multiplexer circuit forwards an analog voltage value from exactly one active input to exactly one output. The multiplexer circuit is also part of the measuring unit, for example.

[0047] In particular, the measuring unit and the control unit are comprised of intelligent electronics. The intelligent electronics can further comprise a logic circuit that controls the measuring unit and the control unit. During operation of the lighting device, the intelligent electronics briefly interrupts the normal brightness pattern intended for illumination, such as the first illumination pattern and / or the second illumination pattern, and specifies a specific pattern of pixels, the measuring pattern, that are switched on. In a very short period of time, the measuring interval, which is not perceived by the human eye, the voltage required to operate the pixels switched on according to the measuring pattern is measured. This voltage is then converted by the intelligent electronics into temperatures of the active zones of the switched-on pixels.If the temperature of the active zone is detected to be above a specified value, the intelligent electronics usually changes the voltage applied to the pixels in lighting mode so that the temperature drops.

[0048] The radiation-emitting semiconductor chip and / or the lighting device are, in particular, intended and configured to be included in a headlight for a motor vehicle. In particular, the radiation-emitting semiconductor chip and / or the lighting device are intended and configured to be used as a light source in the headlight. All features and embodiments described in connection with the lighting device and / or the radiation-emitting semiconductor chip can therefore also be implemented in the headlight, and vice versa. In particular, the headlight can be operated using a method described here for operating a radiation-emitting semiconductor chip.

[0049] The headlight is, in particular, an intelligent, high-resolution headlight that continuously analyzes driving conditions, weather conditions, and / or traffic situations and adjusts the illumination of the surroundings, particularly the roadway, accordingly. This improves lighting conditions for the driver without dazzling other road users.

[0050] Further advantageous embodiments and developments of the method for operating a radiation-emitting semiconductor chip and the lighting device emerge from the exemplary embodiments described below in conjunction with the figures. The Fig. 1 shows a schematic representation of a lighting device according to an embodiment. The Fig. 2 shows a schematic representation of a radiation-emitting semiconductor chip, which is, for example, part of the lighting device according to Fig. 1 and can be operated using the method described here. The Fig. Figure 3 shows schematically the course of a voltage V of the active zone of the pixels of the radiation-emitting semiconductor chip according to Fig. 2 depending on the location x. The Fig. Figure 4 shows an example of the deviation of the voltage ΔV from the voltage at T=25°C with the temperature T. The Fig. 5 to 7 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to an embodiment. The Fig. 8 shows a schematic representation of a stage of a method for operating a radiation-emitting semiconductor chip according to a further embodiment. The Fig. Figure 9 shows schematically the dependence of the temperature T of the active zone of the pixels of the radiation-emitting semiconductor chip according to the Fig. 8 from place x. The Fig. 10 schematically shows a sub-region of the radiation-emitting semiconductor chip according to the Fig. 8. The Fig. 11 to 20 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to a further embodiment. The Fig. 21 to 23 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to a further embodiment. The Fig. 24 to 26 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to a further embodiment.

[0051] Identical, similar, or functionally identical elements are provided with the same reference numerals in the figures. The figures and the relative sizes of the elements depicted in the figures are not to be considered to scale. Rather, individual elements, particularly layer thicknesses, may be exaggerated for clarity and / or clarity.

[0052] The lighting device according to the embodiment of the Fig. 1 comprises a radiation-emitting semiconductor chip 1, which comprises a plurality of pixels 6. In the Fig. 1 schematically shows a plan view of a radiation exit surface 10 of the radiation-emitting semiconductor chip 1. The radiation exit surface 10 of the radiation-emitting semiconductor chip 1 comprises the plurality of pixels 6. The plurality of pixels 6 is arranged in rows and columns in the present case. However, it is also possible for the pixels 6 to have a different arrangement. In conjunction with the Fig. 2, a radiation-emitting semiconductor chip 1, as used by the lighting device according to Fig. 1 may be included, is described in more detail.

[0053] Furthermore, the lighting device according to the embodiment of the Fig. 1 an intelligent electronics 3, which has a control unit 2, a logic circuit 5 and a measuring unit 4.

[0054] The control unit 2, the logic circuit 5, and the measuring unit 4 are shown here as separate units for clarity. In practice, however, it is not necessary for the functional units of the intelligent electronics 3, such as the control unit 2, the logic circuit 5, and the measuring unit 4, to be spatially separated from one another. In particular, the intelligent electronics 3 can be comprised of a single electronic semiconductor chip. For example, the intelligent electronics 3 is an ASIC (short for "Application Specific Integrated Circuit"), a microcontroller, or a companion IC.

[0055] The control unit 2 is configured to control the radiation-emitting semiconductor chip 1 during operation of the lighting device. For example, during operation, the control unit 2 specifies which first number of pixels 6 of the radiation-emitting semiconductor chip 1 are switched on according to a first illumination pattern 11 in a first illumination mode and which pixels 6 are switched off according to the first illumination pattern 11. Further illumination patterns, such as a second illumination pattern 12, a third illumination pattern, or a fourth illumination pattern, can also be specified for the pixels 6 by the control unit 2. Thus, the radiation-emitting semiconductor chip 1 can be operated in various illumination modes, such as a low beam mode or a high beam mode.

[0056] In particular, the control unit 2 specifies a measurement pattern 13 during a measurement interval, according to which at least one pixel 6 of the radiation-emitting semiconductor chip 1 is switched on, while all other pixels 6 are switched off.

[0057] Furthermore, the intelligent electronics 3 of the lighting device comprises a measuring unit 4, which determines the temperature T of an active zone 14 of the at least one switched-on pixel 6 during the measuring interval. Preferably, the measuring unit 4 determines the temperatures T of the active zones 14 of all pixels 6 switched on according to the measuring pattern 13. In particular, the measuring unit 4 determines the temperature T of the active zone 14 from a voltage V applied to the active zone 14 of the pixel 6 during the measuring interval in order to drive a predetermined current through the active zone 14 of the pixel 6.

[0058] The measuring unit 4 here comprises a multiplexer circuit 9, whose n inputs are connected to the active zones 14 of n pixels 6 and which transmits exactly one analog voltage signal from one of the active zones 14 to a sample-and-hold circuit 8. The sample-and-hold circuit 8 holds the analog voltage signal from the active zone 14 of the pixel 6 for a predetermined period of time before the analog voltage signal is transmitted to an analog-to-digital converter 7. It is also possible for the measuring unit not to have a sample-and-hold circuit 8.

[0059] The analog-to-digital converter 7 converts the analog voltage signal into a digital voltage signal, from which the temperature T of the active zone 14 is then determined. For example, a relationship between a voltage change ΔV and temperature T is used as a basis, as shown in Fig. 4 is shown as an example.

[0060] In contrast to the embodiment of the Fig. 1, it is also possible for each pixel 6 to be assigned its own analog-to-digital converter 7 and its own sample and hold circuit 8.

[0061] Furthermore, the intelligent electronics 3 has a logic circuit 5 that tells the measuring unit 4 at which pixels 6 the voltage V of the active zone 14 should be measured and the temperature T of the active zone 14 should be determined at what time. Furthermore, the logic circuit 5 tells the control unit 2 which pixels 6 should be switched on according to the first illumination pattern 11, the second illumination pattern 12, or the measuring pattern 13, and which pixels 6 should be switched off. If the logic circuit 5 receives a message from the measuring unit 4 that the determined temperatures T of some or all of the active zones 14 of the pixels 6 exceed a predetermined temperature value, the logic circuit 5 tells the control unit 2 to reduce the current supply to the pixels 6 accordingly.

[0062] The radiation-emitting semiconductor chip 1 according to the Fig. 2 has a plurality of pixels 6, each pixel 6 comprising an epitaxial semiconductor layer stack 15.

[0063] The epitaxial semiconductor layer stacks 15 are applied to a substrate 16 and are electrically insulated from one another. The epitaxial semiconductor layer stacks 15 can be controlled individually. Each epitaxial semiconductor layer stack 15 comprises an n-doped semiconductor layer 18 and a p-doped semiconductor layer 19, between which the active light-generating zone 14 is arranged. The substrate 16 is, for example, a growth substrate for the epitaxial semiconductor layer stacks 15.

[0064] The pixels 6 of the radiation-emitting semiconductor chip 1 according to the Fig. 2 are encompassed by a radiation exit surface 10 of the radiation-emitting semiconductor chip or form a radiation exit surface 10 of the radiation-emitting semiconductor chip 1. The pixels 6 can be switched on according to various illumination patterns, for example, a first illumination pattern 11 and / or a second illumination pattern 12. The illumination pattern 11, 12 shown here symbolizes an illumination pattern of a low-beam mode, in which pixels 6 of a lower region 23 of the radiation exit surface 10 are illuminated, while pixels 6 of an upper region 24 of the radiation exit surface 10 are switched off. If the radiation-emitting semiconductor chip 1 is incorporated as a light source in a headlight, the road is illuminated and oncoming traffic is not dazzled.

[0065] In the Fig. 2, the substrate 16 with the pixels 6 is shown schematically in a sectional view, while the illumination pattern 11, 12 is shown schematically in a plan view of the radiation exit surface 10.

[0066] If the voltages V of the active zones 14 of the pixels 6 are tapped directly via the substrate 16, the resistances R of the return channels, which are connected in series, add up. Depending on the illumination pattern, the temperature T of an individual active zone 14 cannot be determined from this cumulative voltage value, or can only be determined inaccurately. In the present case, it is proposed to connect only a small number of pixels 6 for temperature determination, so that only very few voltage values ​​accumulate when the voltage V is tapped via the substrate 16. This allows the temperature T of the active zone 14 of the connected pixels 6 to be determined simply and reliably.

[0067] Fig. Figure 3 shows the voltage V as a function of the location x of the radiation-emitting semiconductor chip 1 according to the Fig. 2. The voltage V is presently highest in a central region 20 of the radiation-emitting semiconductor chip 1, since the currents from all other pixels 6 overlap on the way to the lateral connection

[0068] Fig. Figure 4 shows the dependence of the change in the voltage ΔV that must be applied to the active zone 14 of the radiation-emitting semiconductor chip 1 in order to drive a certain current through the active zone 14. How Fig. As shown in Figure 4, with increasing temperature T of the active zone 14, less voltage V must be applied to the active zone 14 to drive a given current through the active zone 14. Based on this relationship between voltage V and temperature T, the temperature T of the active zone 14 of the respective pixel 6 can be determined from the voltage V.

[0069] Based on the Fig. 5 to 7, an embodiment of a method for operating a radiation-emitting semiconductor chip 1 is described in more detail, which, for example, is used by the lighting device according to Fig. 1 is included. The Fig. 5 and Fig. 7 show schematic plan views of a radiation exit surface 10 of the radiation-emitting semiconductor chip 1 during a first illumination mode of the radiation-emitting semiconductor chip 1 and the Fig. 6 shows a plan view of the radiation exit surface 10 of the radiation-emitting semiconductor chip 1 during a measuring interval during which the pixels 6 are switched on according to a measuring pattern 13.

[0070] As in Fig. 5, the pixels 6 of the radiation-emitting semiconductor chip 1 are initially switched on in the first illumination mode according to a first illumination pattern 11. The first illumination pattern 11 in this case is a lighting pattern for a low beam mode as the first illumination mode. In a lower region 23 of the radiation exit surface 10, a first number of pixels 6 are switched on and illuminated, while in an upper region 24, the remaining pixels 6 of the radiation-emitting semiconductor chip 1 are switched off and do not illuminate in order not to dazzle oncoming traffic.

[0071] In a further step, the pixels 6 of the radiation-emitting semiconductor chip 1 are switched on according to the measurement pattern 13 during a measurement interval ( Fig. 6). Here, pixels 6 in a periodic grid-shaped measurement pattern 13 are switched on, while the remaining pixels 6 are switched off. The measurement pattern 13 does not change during the measurement interval. The duration of the measurement interval is at most as long as the inverse of a flicker fusion frequency of the human eye. During the measurement interval, a temperature T of the active zone 14 of at least one of the switched-on pixels 6 is determined. This is done, for example, as already described with reference to the Fig. 1 to 4 described.

[0072] In a next step, the pixels 6 are switched on in a second illumination mode according to a second illumination pattern 12. In this case, the first illumination pattern 11 corresponds to the second illumination pattern 12. In other words, after determining the temperature T of the switched-on pixels 6 of the measurement pattern 13, the radiation-emitting semiconductor chip 1 is again operated in a low-beam mode. The measurement interval is so short that the human eye does not perceive the change in illumination due to the determination of the temperature T.

[0073] In the method for operating a radiation-emitting semiconductor chip 1 according to the embodiment of the Fig. 9 to 11, the pixels 6 are divided into sub-areas 21. Fig. Figure 10 shows a plan view of the radiation exit surface 10 of the radiation-emitting semiconductor chip 1 with the subregions 21. The subregions 21 are of similar design, arranged in rows and columns, and each have a rectangular area. The subregions 21 completely fill the radiation exit surface 10.

[0074] The method for operating a radiation-emitting semiconductor chip according to the embodiment of the Fig. 8 to 10 is based in particular on the idea that the temperatures T of the active zones 14 of the pixels 6 of the radiation-emitting semiconductor chip 1 vary only slightly with the location x. Fig. 9 shows the temperature T of the active zone 14 as a function of location x. In a region of the curve T(x) corresponding to a sub-region 21 of the radiation exit surface 10, the change in the temperature T of the active zone 14 is very small. For example, the variation in the temperature T of the active zone 14 within a sub-region 21 is not greater than 10 K or 1 K. During the measurement interval, a few representative pixels 6 of each sub-region 21 are switched on according to the measurement pattern 13, and the temperature T of their active zone 14 is determined.

[0075] In Fig. Figure 10 shows an exemplary top view of a measurement pattern 13 of a sub-region 21 during the measurement interval. The measurement pattern 13 is identical in each sub-region 21 and, in this case, has four switched-on, centrally arranged pixels 6.

[0076] In the method for operating a radiation-emitting semiconductor chip according to the embodiment of the Fig. 11 to 20, the pixels 6 are switched on according to different measurement patterns 13, and the temperature T of the active zones 14 of the switched-on pixels 6 is determined. The determined temperatures T are then combined into a common data set.

[0077] As the top view of the radiation exit surface 10 of the radiation-emitting semiconductor chip 1 of the Fig. 11 schematically shows, the pixels 6 are initially operated in a first illumination mode in which they are switched on according to a first illumination pattern 11. The first illumination pattern 11 is an illumination pattern for a low beam mode as already shown in FIG. Fig. 5 described.

[0078] In a next step, the schematically in Fig. 12, the pixels 6 are switched on according to a measurement pattern 13 during a measurement interval and the temperature T of their active zones 14 is determined. In this case, only a few pixels 6 are switched on in a periodic measurement pattern 13 according to the measurement pattern 13. The Fig. 12 switched on pixel 6 are also from the measurement pattern 13 of the Fig. 6. Then the pixels 6 are operated in a second lighting mode, which corresponds to the first lighting mode ( Fig. 13).

[0079] In a further step, the pixels are switched on in another measuring pattern 13 and the temperatures T of their active zones 14 are determined during a measuring interval ( Fig. 14). The measurement pattern 13 of the Fig. 14 differs from the measurement pattern 13 of the Fig. 12. The values ​​measured according to the measurement pattern 13 of the Fig. However, 14 switched on pixels 6 are also from the measurement pattern 13 of the Fig. 6. Then the pixels 6 are operated in a third lighting mode, which corresponds to the first lighting mode ( Fig. 15).

[0080] In a further step, the pixels 6 are switched on in another measurement pattern 13 and the temperatures T of their active zones 14 are determined during a measurement interval ( Fig. 16). The measurement pattern 13 of the Fig. 16 differs from the measurement patterns 13 of the Fig. 12 and Fig. 14. The values ​​measured according to the measurement pattern 13 of the Fig. However, 16 switched on pixels 6 are also from the measurement pattern 13 of the Fig. 6. Then the pixels 6 are operated in a fourth lighting mode, which corresponds to the first lighting mode ( Fig. 17).

[0081] In a further step, the pixels 6 are switched on in another measurement pattern 13 and the temperatures T of their active zones 14 are determined during a measurement interval ( Fig. 18). The measurement pattern 13 of the Fig. 18 differs from the measurement patterns 13 of the Fig. 12, Fig. 14 and Fig. 16. The values ​​measured according to the measurement pattern 13 of the Fig. However, 18 switched on pixels 6 are also from the measurement pattern 13 of the Fig. 6. Then the pixels 6 are operated in a fifth lighting mode, which corresponds to the first lighting mode ( Fig. 19).

[0082] The values ​​measured during the measurement intervals according to the measurement patterns 13 of the Fig. 12, Fig. 14, Fig. 16 and Fig. 18 measured temperatures T are combined in a further step. This creates a data set of temperatures T as it occurs in a measurement interval with a measurement pattern 13 of the Fig. 6 is achieved ( Fig. 20). Fewer or more individual measurements can also be performed and combined into a data set.

[0083] In a method according to this exemplary embodiment, the measurement patterns 13 are designed to differ from one another. Furthermore, the individual measurement intervals can be particularly short, since only a few pixels 6 are measured during the individual measurement intervals and the temperatures T of their active zones 14 are determined.

[0084] In the method for operating a radiation-emitting semiconductor chip 1 according to the embodiments of the Fig. 21 to 23, the pixels 6 are again initially switched on in a first lighting mode with a first lighting pattern 11 ( Fig. 21). The first illumination mode corresponds to a low-beam mode. Here, the pixels 6 in a central region 20 of the radiation exit surface 10 are operated with a higher current than in the remaining region of the radiation exit surface 10.

[0085] Then, the pixels 6 are switched on during a measuring interval according to a measuring pattern 13 and the temperatures T of their active zones 14 are determined ( Fig. 22). The measurement pattern 13 comprises only pixel 6 from the central area 20. After the temperatures T of the active zones 14 of the pixel 6 in the central area 20 have been determined, the 6 pixels are again operated in a low beam mode ( Fig. 23).

[0086] In the method for operating a radiation-emitting semiconductor chip 1 according to the embodiment of the Fig. 24 to 26, the radiation-emitting semiconductor chip 1 is again initially operated in a first illumination mode, for example a low beam mode according to a first illumination pattern 11. From the first illumination pattern 11, a region 22 is determined in which the highest temperatures T of the active zones 14 of the pixels 6 are expected ( Fig. 24). This can be achieved, for example, by the logic circuit of the lighting device of the Fig. 1 should be carried out.

[0087] In a next step, the pixels 6 of the radiation-emitting semiconductor chip 1 are switched on according to a measurement pattern 13 during a measurement interval ( Fig. 25). Here, only pixels 6 are included in the measurement pattern 13, which lie in the predicted region 22 with the highest temperatures T. In a next step, the radiation-emitting semiconductor chip 1 is again operated in a second illumination mode, for example, again the low beam mode ( Fig. 26).

[0088] The invention is not limited to the embodiments by the description. Rather, the invention encompasses any novel feature and any combination of features, including, in particular, any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or embodiments. List of reference symbols 1 radiation-emitting semiconductor chip 2 control unit 3 intelligent electronics 4 measuring unit 5 logical circuit 6 pixels 7 analog-to-digital converters 8 Sample and hold circuit 9 Multiplexer circuit 10 Radiation exit surface 11 first lighting pattern 12 second lighting pattern 13 measurement patterns 14 active zones 15 epitaxial semiconductor layer stack 16 Substrat 18 n-doped semiconductor layer 19 p-doped semiconductor layer 20 central area 21 Subsection 22 Area 23 lower area 24 upper area T Temperature V voltage R resistance ΔV Change in voltage x Location

Claims

[1] Method for operating a radiation-emitting semiconductor chip (1) comprising a plurality of pixels (6), comprising the following steps: - switching on a first number of pixels (6) in a first illumination mode according to a first illumination pattern (11), - switching on at least one pixel (6) according to a measurement pattern (13) during a measurement interval, - Determining a temperature (T) of an active zone (14) of at least one of the switched-on pixels (6) during the measuring interval, - switching on a second number of pixels (6) in a second illumination mode according to a second illumination pattern (12). [2] Method according to the preceding claim, wherein a duration of the measuring interval corresponds at most to the inverse fraction of the flicker fusion frequency of the human eye. [3] Method according to one of the preceding claims, wherein fewer pixels (6) are switched on according to the measurement pattern (13) than according to the first illumination pattern (11) and / or according to the second illumination pattern (12). [4] Method according to one of the preceding claims, wherein the temperature (T) of the active zone (14) is determined from a voltage (V) which is necessary for a predetermined current to flow through the active zone (14). [5] Method according to one of the preceding claims, wherein - during the first illumination mode, the voltages (V) of all pixels (6) of the first illumination pattern (11) are measured, which are necessary for a predetermined current to flow through the active zone (14) of the pixels (6) according to the first illumination pattern (11), and - according to the measuring pattern (13), no pixels (6) are switched on during the measuring interval whose measured voltage (V) deviates from the measured voltage (V) of the adjacent pixels (6) more than a predetermined value. [6] Method according to one of the preceding claims, wherein the first illumination pattern (11) and / or the second illumination pattern (12) has at least two sub-patterns, according to which different pixels (6) of the first illumination pattern (11) are switched on to generate gray levels. [7] Method according to one of the preceding claims, wherein pixels (6) are switched on according to the measurement pattern (13) which are also switched on according to the first illumination pattern (11) and / or according to the second illumination pattern (12) and / or at least according to at least one sub-pattern. [8] Method according to one of the preceding claims, wherein - the pixels (6) are divided into sub-areas (21), and - at least one pixel (6) is switched on per sub-area (21) according to the measuring pattern (13) and the temperature (T) of its active zone (14) is determined in the measuring interval. [9] Method according to the preceding claim, wherein - several pixels (6) are switched on per sub-area (21) according to the measuring pattern (13), and - the temperature (T) of the active zone (14) of the switched-on pixels (6) is determined and its mean value is calculated. [10] Method according to one of the preceding claims, wherein different pixels (6) are switched on according to different measurement patterns (13) and the temperature (T) of the active zone (14) of the switched on pixels (6) is determined in each case when these are switched on. [11] Method according to one of the preceding claims, wherein - from the first illumination pattern (11) a region (22) of pixels (6) is determined whose active zones (14) have a high temperature (T) compared to the active zones (14) of the remaining pixels (6), and - only pixels (6) from this area (22) are switched on according to the measuring pattern (13). [12] Method according to one of the preceding claims, wherein pixels (6) which are not switched on according to the first illumination pattern (11) and / or according to the second illumination pattern (12) or are only operated with a current which does not exceed a predetermined value are not included in the measurement pattern (13). [13] Lighting device comprising: - a radiation-emitting semiconductor chip (1) with a plurality of pixels (6), - a control unit (2) which is designed to control the radiation-emitting semiconductor chip (1) during operation, - a measuring unit (4) which is arranged to determine a temperature (T) of an active zone (14) of the pixels (6), where - the control unit (2) switches on a first number of pixels (6) during operation in a first illumination mode according to a first illumination pattern (11), - the control unit (2) switches on at least one pixel (6) according to at least one measurement pattern (13) during a measurement interval, - the measuring unit (4) determines the temperature (T) of the active zone (14) of at least one of the switched-on pixels (6) during the measuring interval, and - the control unit (2) switches on a second number of pixels (6) in a second illumination mode according to a second illumination pattern (12). [14] Lighting device according to the preceding claim, wherein - the measuring unit (4) has an analog-digital converter (7) which converts an analog voltage signal into a digital voltage signal, and - the measuring unit (13) has a sample and hold circuit (8) which samples the analog voltage signal of at least one pixel (6) and holds it for a predetermined period of time. [15] Lighting device according to one of claims 13 to 14, wherein at least two pixels (6) are connected to an analog-digital converter (7) via a multiplexer circuit (9). [16] Headlight for a motor vehicle with a lighting device according to one of claims 13 to 14.

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