Method for operating a radiation-emitting semiconductor chip and illumination device

Abstract

The invention relates to a method for operating a radiation-emitting semiconductor chip, 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 measurement interval, - switching on a second number of pixels (6) in a second illumination mode according to a second illumination pattern (12). The invention also relates to an illumination device.

Description

[0001] Description

[0002] METHOD FOR OPERATING A RADIATION-EMITTING SEMICONDUCTOR CHIP AND LIGHTING DEVICE

[0003] A method for operating a radiation-emitting semiconductor chip and a lighting device are specified.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] Advantageous embodiments and further developments of the method and the lighting device are specified in the respective dependent claims.

[0008] 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.

[0009] 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.

[0010] 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 the present case, the term “voltage” refers in particular to a forward voltage.

[0011] 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.

[0012] For example, a pixel of the radiation-emitting semiconductor chip has an edge length between 1 micrometer and 200 micrometers inclusive.

[0013] In particular, the pixels are comprised by 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 epitaxially, for example. 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 placed on a common carrier. In other words, the radiation-emitting semiconductor chip is preferably a pixelated semiconductor chip.

[0014] 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.

[0015] 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 the operation of the pixels in the first illumination mode.

[0016] 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.

[0017] 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.

[0018] 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 are switched on 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.

[0019] The first lighting mode and the second lighting mode may 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 may 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 is a low beam mode or a high beam mode.

[0020] According to one embodiment, the method for operating the radiation-emitting semiconductor chip with a plurality of pixels comprises the following steps:

[0021] - switching on the first number of pixels in the first lighting mode according to the first lighting pattern,

[0022] - switching on at least one pixel according to the measurement pattern during the measurement interval,

[0023] - Determining the temperature of the active zone of at least one of the switched-on pixels during the measurement interval,

[0024] - Activating the second number of pixels in the second illumination mode according to the second illumination pattern. The steps of the method are carried out in the order specified above.

[0025] In particular, the specified steps can be repeated multiple times. This allows switching between different lighting modes with different lighting patterns. The measurement patterns and / or measurement intervals can be identical or different from one another.

[0026] 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 measuring interval in which only a few pixels are switched on. The measuring 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 in the measuring interval according to the measuring pattern 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 makes it possible, in particular, to advantageously at least reduce interference factors during the measurement.A small number of pixels during the determination of the temperature of the active zone also makes it possible to reduce the series resistance of the pixels whose temperature is being determined, thus eliminating interference. The present method advantageously enables a voltage measurement for determining the temperature 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, so that interference can be minimized and the temperature can be determined relatively accurately.

[0027] According to a further embodiment of the method, the duration of the measuring interval corresponds at most to the inverse of the flicker fusion frequency of the human eye. In other words, the measuring 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 inclusive.

[0028] 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, a duration of the measurement interval lies between 0.01 seconds and 0.045 seconds inclusive.

[0029] 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.

[0030] In particular, the radiation-emitting semiconductor chip has about 25,000 pixels.

[0031] 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 so that a predetermined current flows through the active zone. The pixel to which the voltage is applied typically lights up due to the current flow during the measurement interval.

[0032] 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 are switched on during the measurement interval whose measured voltage deviates from the measured voltage of the neighboring pixels by more than a predetermined value. In other words, the voltage of the pixels switched on during the first illumination mode is determined, and the measurement pattern is then designed 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 voltage measured in the neighboring pixels .

[0033] According to a further embodiment of the method, the first illumination pattern and / or the second illumination pattern has at least two sub-patterns, according to which different pixels of the first illumination pattern are switched on in order to generate grayscale. The change between the two sub-patterns takes place in particular also at a frequency which 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 sub-patterns, in particular at a frequency which 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. A further possibility for generating grayscale of individual pixels consists in pulse width modulation of the voltage which is 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, in particular rectangularly. If a rectangular voltage signal is applied to the active zone for pulse width modulation, its amplitude and / or duration can be varied. 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 sub-pattern during the first illumination mode and / or the second illumination mode. In other words, the temperature of the active zone of those pixels which are also switched on and illuminated during the first illumination mode and / or the second illumination mode is determined during the measurement interval.In particular, it can be prevented that oncoming traffic is dazzled if the radiation-emitting semiconductor chip is used as a light source in a headlight.

[0034] 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.

[0035] 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 switched-on pixels during the measurement interval. If the sub-areas are notionally placed one above the other, the pixels switched on according to the measurement pattern are preferably congruent. In this way, the temperature of the active zones of the pixels can be determined evenly distributed over the radiation exit surface of the radiation-emitting semiconductor chip.

[0036] According to a further embodiment of the method, several pixels per sub-area are switched on according to the measurement pattern, and 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.

[0037] 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 these 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 carried out. The determined temperatures can be combined, and for example, an average value of the determined temperatures can be calculated. In this way, the measurement intervals can be made very short, so that the operation of the radiation-emitting semiconductor chip is only interrupted for a very short time during the different illumination modes.

[0038] 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 other pixels. Only pixels from this range are switched on according to the measurement pattern. In other words, a range of pixels is determined from the first illumination pattern which should have high or the highest temperatures due to the current supply to the pixels specified by the first illumination pattern. In this way, a range of pixels is predetermined which are of particular interest for determining the temperatures of the active zones and the determination of the temperatures of the active zones is restricted to the pixels in this range.

[0039] According to a further embodiment of the method, pixels that are not switched on according to the first illumination pattern and / or according to 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 that shine 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.

[0040] In particular, the radiation-emitting semiconductor chip can be comprised 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 steps, features, and embodiments as the method for operating the radiation-emitting semiconductor chip. According to one embodiment, the lighting device comprises a radiation-emitting semiconductor chip with a multiplicity of pixels. For example, the radiation-emitting semiconductor chip has the features and embodiments as already described.

[0041] According to a further embodiment, the lighting device has a control unit which is designed to control the radiation-emitting semiconductor chip during operation. For example, the control unit specifies a first lighting pattern and / or a second lighting pattern to the radiation-emitting semiconductor chip, which has the pixels which are to be switched on according to the first lighting pattern and / or the second lighting pattern. In other words, the control unit switches on the first number of pixels of the radiation-emitting semiconductor chip during operation, which are to be switched on according to the first lighting pattern in a first lighting mode. Furthermore, the control unit switches on the second number of pixels of the radiation-emitting semiconductor chip during operation, which are to be switched on according to the second lighting pattern in the second lighting 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 by pulse width modulation. For example, regions of the radiation exit surface of the radiation-emitting semiconductor chip are automatically dimmed so as not to dazzle other road users.

[0042] According to a further embodiment, the lighting device has a measuring unit which is designed to determine a temperature of an active zone of the pixels.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] According to a further embodiment of the

[0048] Lighting device, the measuring unit has an analog

[0049] Digital converter which 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.

[0050] 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.

[0051] 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 nData 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.

[0052] In particular, the measuring unit and the control unit are comprised in intelligent electronics. The intelligent electronics can furthermore also comprise a logic circuit which controls the measuring unit and the control unit. During operation of the lighting device, the intelligent electronics briefly interrupts the normal brightness pattern provided for illumination, for example the first illumination pattern and / or the second illumination pattern, and specifies a specific pattern of pixels, the measuring pattern, which 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 higher than a predetermined value, the intelligent electronics usually changes the voltage applied to the pixels in lighting mode so that the temperature drops.

[0053] The radiation-emitting semiconductor chip and / or the lighting device are in particular intended and configured to be comprised by 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.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, by the headlight accordingly. This improves lighting conditions for the driver of the vehicle without dazzling other road users.

[0054] Further advantageous embodiments and developments of the method for operating a radiation-emitting semiconductor chip and the lighting device emerge from the embodiments described below in conjunction with the figures.

[0055] Figure 1 shows a schematic representation of a lighting device according to an embodiment.

[0056] Figure 2 shows a schematic representation of a radiation-emitting semiconductor chip which is, for example, part of the lighting device according to Figure 1 and can be operated using the method described here.

[0057] 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 Figure 2 as a function of the location x .

[0058] Figure 4 shows, by way of example, the variation of the voltage AV relative to the voltage at T=25°C with temperature T. Figures 5 to 7 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to an embodiment.

[0059] Figure 8 shows a schematic representation of a stage of a method for operating a radiation-emitting semiconductor chip according to a further embodiment.

[0060] Figure 9 schematically shows the dependence of the temperature T of the active zone of the pixels of the radiation-emitting semiconductor chip according to Figure 8 on the location x .

[0061] Figure 10 schematically shows a sub-region of the radiation-emitting semiconductor chip according to Figure 8.

[0062] Figures 11 to 20 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to a further embodiment.

[0063] Figures 21 to 23 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to a further embodiment.

[0064] Figures 24 to 26 schematically show stages of a method for operating a radiation-emitting semiconductor chip according to a further embodiment.

[0065] Identical, similar, or functionally identical elements are provided with the same reference symbols in the figures. The figures and the relative sizes of the elements shown in the figures are not to scale. Rather, individual elements, particularly layer thicknesses, may be exaggerated for clarity and / or clarity.

[0066] The lighting device according to the embodiment of Figure 1 has a radiation-emitting semiconductor chip 1 which comprises a plurality of pixels 6. Figure 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. A radiation-emitting semiconductor chip 1, as can be comprised by the lighting device according to Figure 1, is described in more detail in conjunction with Figure 2.

[0067] Furthermore, the lighting device according to the embodiment of Figure 1 comprises intelligent electronics 3, which has a control unit 2, a logic circuit 5 and a measuring unit 4.

[0068] The control unit 2, the logic circuit 5 and the measuring unit 4 are shown here as separate units for reasons of 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 AS IC (short for "Application Specific Integrated Circuit"), a

[0069] Microcontroller or a companion IC.

[0070] The control unit 2 is designed to control the radiation-emitting semiconductor chip 1 during operation of the lighting device. For example, the control unit 2 specifies during operation which first number of pixels 6 of the radiation-emitting semiconductor chip 1 are switched on according to a first lighting pattern 11 in a first lighting mode and which pixels 6 are switched off according to the first lighting pattern 11. Further lighting patterns such as a second lighting pattern 12, a third lighting pattern or a fourth lighting pattern can also be specified for the pixels 6 by the control unit 2. In this way, the radiation-emitting semiconductor chip 1 can be operated in different lighting modes, such as a low beam mode or a high beam mode.

[0071] 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.

[0072] 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, which is 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.

[0073] In this case, the measuring unit 4 comprises a multiplexer circuit 9, whose n inputs are connected to the active zones 14 of n pixels 6 and which transmits precisely 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.

[0074] 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. This is based, for example, on a relationship between a voltage change AV and temperature T, as shown by way of example in Figure 4.

[0075] In contrast to the embodiment of Figure 1, it is also possible for each pixel 6 to be assigned its own analog-digital converter 7 and its own sample and hold circuit 8.

[0076] Furthermore, the intelligent electronics 3 has a logic circuit 5 which 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 and at what point in time. In addition, 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 gives the control unit 2 feedback to reduce the current supply to the pixels 6 accordingly.

[0077] The radiation-emitting semiconductor chip 1 according to Figure 2 has a plurality of pixels 6, each pixel 6 comprising an epitaxial semiconductor layer stack 15.

[0078] 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 has 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.

[0079] The pixels 6 of the radiation-emitting semiconductor chip 1 according to Figure 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 contained as a light source in a headlight, the road is illuminated and oncoming traffic is not dazzled.

[0080] In Figure 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.

[0081] 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 in an incorrect manner. In the present case, it is proposed to switch on only a small number of pixels 6 for temperature determination, so that only very few voltage values ​​add up when the voltage V is tapped via the substrate 16. In this way, the temperature T of the active zone 14 of the switched-on pixels 6 can be determined simply and reliably.

[0082] Figure 3 shows the voltage V as a function of the location x of the radiation-emitting semiconductor chip 1 according to Figure 2. In the present case, the voltage V is highest in a central region 20 of the radiation-emitting semiconductor chip 1 because the currents from all other pixels 6 up to that point overlap on the way to the lateral connection. Figure 4 shows the dependence of the change in the voltage AV that has to be applied to the active zone 14 of the radiation-emitting semiconductor chip 1 in order to drive a specific current through the active zone 14. As Figure 4 shows, with increasing temperature T of the active zone 14, less voltage V has to be applied to the active zone 14 in order to drive a predetermined current through the active zone 14. On the basis of 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.

[0083] An exemplary embodiment of a method for operating a radiation-emitting semiconductor chip 1, which is comprised, for example, by the lighting device according to Figure 1, is described in more detail with reference to Figures 5 to 7. Figures 5 and 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 Figure 6 shows a plan view of the radiation exit surface 10 of the radiation-emitting semiconductor chip 1 during a measurement interval during which the pixels 6 are switched on according to a measurement pattern 13.

[0084] As shown schematically in Figure 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 the present case is an illumination pattern for a low beam mode as the first illumination mode. In this case, in a lower region 23 of the radiation exit surface 10, a first number of pixels 6 are switched on and illuminate, 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.

[0085] In a further step, the pixels 6 of the radiation-emitting semiconductor chip 1 are switched on according to the measuring pattern 13 during a measuring interval (Figure 6). In this case, pixels 6 are switched on in a periodic grid-shaped measuring pattern 13, while the remaining pixels 6 are switched off. The measuring pattern 13 does not change during the measuring interval. The duration of the measuring interval is at most as long as the reciprocal of a flicker fusion frequency of the human eye. During the measuring interval, a temperature T of the active zone 14 of at least one of the switched-on pixels 6 is determined. This takes place, for example, as already described with reference to Figures 1 to 4.

[0086] 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 the temperature T of the switched-on pixels 6 of the measurement pattern 13 has been determined, 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.

[0087] In the method for operating a radiation-emitting semiconductor chip 1 according to the exemplary embodiment of Figures 9 to 11, the pixels 6 are divided into subregions 21. 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 identical design, arranged in rows and columns, and each have a rectangular area. The subregions 21 completely fill the radiation exit surface 10.

[0088] The method for operating a radiation-emitting semiconductor chip according to the embodiment of Figures 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. Figure 9 shows the profile of the temperature T of the active zone 14 as a function of the location x. In a region of the curve T(x) which corresponds to a sub-region 21 of the radiation exit surface 10, the change in the temperature T of the active zone 14 is only 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 measuring interval, a few representative pixels 6 of each sub-region 21 are switched on according to the measuring pattern 13 and the temperature T of their active zone 14 is determined.

[0089] 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.

[0090] In the method for operating a radiation-emitting

[0091] In semiconductor chips according to the exemplary embodiment of Figures 11 to 20, the pixels 6 are switched on according to various 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.

[0092] As the plan view of the radiation exit surface 10 of the radiation-emitting semiconductor chip 1 in Figure 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 described with reference to Figure 5.

[0093] In a next step, which is schematically shown in Figure 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 pixels 6 switched on according to the measurement pattern 13 of Figure 12 are also included in the measurement pattern 13 of Figure 6. The pixels 6 are then operated in a second illumination mode which corresponds to the first illumination mode (Figure 13).

[0094] In a further step, the pixels are switched on in another measurement pattern 13, and the temperatures T of their active zones 14 are determined during a measurement interval (Figure 14). The measurement pattern 13 of Figure 14 differs from the measurement pattern 13 of Figure 12. However, the pixels 6 switched on according to the measurement pattern 13 of Figure 14 are also included in the measurement pattern 13 of Figure 6. The pixels 6 are then operated in a third illumination mode, which corresponds to the first illumination mode (Figure 15).

[0095] 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 (Figure 16). The measurement pattern 13 of Figure 16 differs from the measurement patterns 13 of Figures 12 and 14. However, the pixels 6 switched on according to the measurement pattern 13 of Figure 16 are also included in the measurement pattern 13 of Figure 6. The pixels 6 are then operated in a fourth illumination mode, which corresponds to the first illumination mode (Figure 17).

[0096] 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 (Figure 18). The measurement pattern 13 of Figure 18 differs from the measurement patterns 13 of Figures 12, 14, and 16. However, the pixels 6 switched on according to the measurement pattern 13 of Figure 18 are also included in the measurement pattern 13 of Figure 6. The pixels 6 are then operated in a fifth illumination mode, which corresponds to the first illumination mode (Figure 19).

[0097] The temperatures T determined during the measuring intervals according to the measuring patterns 13 of Figures 12, 14, 16 and 18 are combined in a further step. In this way, a data set of temperatures T is obtained, as achieved in a measuring interval with a measuring pattern 13 of Figure 6 (Figure 20). Fewer or more individual measurements can also be carried out and combined to form a data set. In a method according to this exemplary embodiment, the measuring patterns 13 are designed to be different from one another. Furthermore, the individual measuring intervals can be particularly short, since only a few pixels 6 are measured during the individual measuring intervals and the temperatures T of their active zones 14 are determined.

[0098] In the method for operating a radiation-emitting semiconductor chip 1 according to the exemplary embodiments of Figures 21 to 23, the pixels 6 are again initially switched on in a first illumination mode with a first illumination pattern 11 (Figure 21). The first illumination mode corresponds to a low-beam mode. In this case, the pixels 6 are operated with a higher current in a central region 20 of the radiation exit surface 10 than in the remaining region of the radiation exit surface 10.

[0099] Then, the pixels 6 are switched on during a measurement interval according to a measurement pattern 13, and the temperatures T of their active zones 14 are determined (Figure 22). The measurement pattern 13 comprises only pixels 6 from the central region 20. After the temperatures T of the active zones 14 of the pixels 6 in the central region 20 have been determined, the 6 pixels are again operated in a low-beam mode (Figure 23).

[0100] In the method for operating a radiation-emitting semiconductor chip 1 according to the exemplary embodiment of Figures 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 (Figure 24). This can be carried out, for example, by the logic circuit of the illumination device of Figure 1.

[0101] 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 (Figure 25). In this case, the measurement pattern 13 only includes pixels 6 that 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 (Figure 26).

[0102] This application claims priority from German application DE 102023120140 . 9 , the disclosure of which is hereby incorporated by reference .

[0103] The invention is not limited to the embodiments described herein. 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

[0104] 1 radiation-emitting semiconductor chip

[0105] 2 control unit

[0106] 3 intelligent electronics

[0107] 4 measuring unit

[0108] 5 logical circuit

[0109] 6 pixels

[0110] 7 analog-to-digital converters

[0111] 8 Sample and hold circuit

[0112] 9 Multiplexer circuit

[0113] 10 Radiation exit area

[0114] 11 first lighting pattern

[0115] 12 second lighting pattern

[0116] 13 measurement patterns

[0117] 14 active zones

[0118] 15 epitaxial semiconductor layer stack

[0119] 16 Substrat

[0120] 18 n-doped semiconductor layer

[0121] 19 p-doped semiconductor layer

[0122] 20 central area

[0123] 21 Subsection

[0124] 22 Area

[0125] 23 lower area

[0126] 24 upper area

[0127] T Temperature

[0128] V voltage

[0129] R resistance

[0130] AV Change in voltage x location

Claims

Patent claims 1. A 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 neighboring 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 in order 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 - per sub-area (21) several pixels (6) according to the Measuring pattern (13) is switched on, 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) 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-to-digital converter (7) via a multiplexer circuit (9).

16. Front headlight for a motor vehicle with a lighting device according to one of claims 13 to 14.

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