Method for controlling a pixelated light source

Abstract

The present invention relates to a method for controlling pixelated light sources for automobiles, which method makes it possible to prevent thermal runaway and premature degradation of the elementary pixels of the source independently of the projected light level. The control method provides protection for the semiconductor junctions of the pixels of the pixelated light source by dynamically adapting the current intensity in the elementary light source in order to extend the lifetime of the semiconductor junctions of the pixels of the pixelated light source and to avoid visible defects in the beam projected on the road due to thermal runaway or premature degradation of the semiconductor junctions.

Description

[Technical Field]

[0001] The present invention relates to the field of automotive lighting systems, and in particular to systems using pixelated light sources. [Background technology]

[0002] A light-emitting diode (LED) is an electronic semiconductor component capable of emitting light of a predetermined wavelength when a voltage at least equal to a threshold value is applied across its terminals. Above this threshold, called the forward voltage, the intensity of the luminous flux emitted by an LED generally increases with the average amplitude of the supply voltage. Heating the semiconductor junction tends to increase the amplitude of the current at a constant applied voltage. The small size and low power consumption of LED components make them advantageous in the field of automotive light-emitting modules. LED-based light sources may be used to generate distinctive optical signatures, for example, by arranging the components along a predetermined outline. The use of LED components also facilitates the generation of light capable of performing multiple lighting functions.

[0003] It is also known to use pixelated light sources in various types of technologies to project these light beams according to image data. For example, this involves monolithic technology, in which a large number of elementary LED sources are etched into a common semiconductor substrate, each representing a pixel. The substrate may further include on-board electronic components such as switching circuits. Integrated electrical connections allow the pixels to be activated independently of each other. In particular, it has been proposed to use voltages to drive such pixelated light sources: if a constant voltage is applied to the pixelated light source, the individual pixels may be controlled using one switch per pixel, each controlled by a binary signal. The control signal delivered to the pixel may be, for example, a PWM signal (PWM stands for Pulse Width Modulation), the duty cycle of which has a direct effect on the average amplitude of the current passing through the pixel and, therefore, on the luminous intensity of the pixel.

[0004] Alternatively, electric current may also be used to drive pixelated light sources. Each elementary light source forming a pixel is associated with a dedicated current source. In this way, the amplitude of the current passing through a given pixel, and therefore the intensity of the light emitted from this pixel, may be directly adjusted. By acting on the PWM signal, the average amplitude of the current may be reduced for a given DC current amplitude.

[0005] Pixelated light sources may be used to perform complex functions, such as the HB function (HB stands for High Beam) or, especially, the ADB function (ADB stands for Adaptive Driving Beam). Voltage-driven light sources are typically provided with a constant supply voltage. However, at a constant voltage, the amplitude of the current passing through a semiconductor junction, such as that of an electroluminescent pixel, increases linearly with temperature. As current passes through the junction, the junction temperature increases. Therefore, if a pixel is required to function for a long time, there is a risk of thermal runaway: the more the semiconductor junction is heated by the current passing through it, the greater the amplitude of the current increases until the junction fails or is irreversibly destroyed. This risk is more evident in pixels in the central region of a pixelated light source, which contribute to multiple vehicle lighting functions and are therefore required to function more regularly. A failure in this area can lead to a visible failure of the light beam projected onto the road. Currently, actual temperature measurements per pixel are not feasible, so it is difficult to predict which spots are potentially overheated among a pixelated light source that is responsible for projecting a series of different images when in operation.

[0006] With current control, the risk of thermal runaway is reduced, but substantial overheating of each semiconductor junction can accelerate premature degradation and increase the risk of failure. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to overcome at least one of the problems presented by the prior art, more precisely to provide a method for controlling a pixelated light source that makes it possible to avoid the risks associated with overheating of the elementary pixels of the source. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided a method for controlling a pixelated light source for a motor vehicle, the pixelated light source comprising a plurality of elementary light sources based on electroluminescent semiconductor components. It is noteworthy that the method comprises at least the following steps:

[0009] i) controlling, with a control unit, the pixelated light sources to project a light beam corresponding to image data by driving each elementary light source with a control signal that determines a first average amplitude of a current passing through said elementary light source;

[0010] ii) acquiring temperature characteristics of the pixelated light source using a plurality of temperature sensors arranged at predetermined locations;

[0011] iii) estimating, using a control unit, a location of a hot spot of the pixelated light source based on the image data and the acquired temperature characteristics;

[0012] iv) estimating, using a control unit, a temperature value of the hot spot in response to the acquired temperature characteristics and the estimated position of the hot spot relative to the location of the temperature sensor;

[0013] v) modifying, by means of the control unit, the commands delivered to the pixelated light sources when the estimated temperature value is higher than a predetermined threshold temperature value, so that at least one group of elementary light sources, comprising elementary light sources located at the estimated position of the hotspot, is passed by a current of a second average amplitude lower than the first amplitude.

[0014] Preferably, the pixelated light source may comprise a pixelated light source that is intended to be voltage controlled.

[0015] Preferably, the pixelated light source may comprise a pixelated light source that is intended to be voltage controlled.

[0016] According to another aspect of the present invention, there is provided a method for controlling a pixelated light source for a motor vehicle, the pixelated light source being intended to be voltage-driven and comprising a plurality of elementary light sources based on a plurality of electroluminescent semiconductor components, the method notably comprising at least the following steps:

[0017] i') controlling, with a control unit, the pixelated light sources to project a light beam corresponding to the image data by delivering a first voltage level to the pixelated light sources and by driving said elementary light sources with a DC current-modulated pulse-width modulated signal that determines a first average amplitude of a current passing through each elementary light source;

[0018] ii') acquiring temperature characteristics of the pixelated light source using a plurality of temperature sensors arranged at predetermined locations;

[0019] iii') estimating, using a control unit, the location of the hotspot of the pixelated light source based on the image data and the acquired temperature characteristics;

[0020] iv') estimating, by means of a control unit, a temperature value of the hot spot depending on the acquired temperature characteristics and the estimated position of the hot spot relative to the location of the temperature sensor;

[0021] v') modifying, by means of the control unit, the commands delivered to the pixelated light sources so that each of the elementary light sources is passed by a current of a second average amplitude lower than the first amplitude, when the estimated temperature value is higher than a predetermined threshold temperature value.

[0022] The step of estimating the location of the hotspot may include retrieving the acquired temperature characteristic from among a plurality of pre-recorded temperature characteristics previously stored in a memory element, each characteristic preferably being associated with particular image data and the hotspot location associated with those data.

[0023] Preferably, the step of estimating the temperature value of the hotspot may include the step of increasing at least one of the temperature values ​​of the obtained temperature characteristics by a predetermined increment that depends on the estimated location of the hotspot.

[0024] Preferably, the step of estimating the temperature value may further include considering the projected image data, where pixels with high luminosity values ​​correspond to hotter fundamental light sources.

[0025] Preferably, the pixelated light sources may be intended to be voltage controlled, and the command determining a first average amplitude of the current passing through each elementary light source may comprise a first voltage level.

[0026] Preferably, the step of modifying the command may include delivering a second voltage level to the pixelated light source that is lower than the first voltage level if the estimated temperature value is higher than a predetermined threshold temperature value.

[0027] The step of modifying the command may include a preceding step of comparing said estimated temperature value with said predetermined threshold temperature value, the predetermined threshold temperature value preferably being dependent on the delivered first voltage level.

[0028] Preferably, the method may include a preliminary step of making available in a memory element reference data for the pixelated light source, said data relating, for a sequence of operating temperatures of the pixelated light source, drive voltage values ​​with corresponding supply current amplitudes, and the step of modifying the command comprises choosing a second voltage level depending on the estimated temperature value so as to observe a predetermined threshold current amplitude.

[0029] Preferably, the pixelated light sources are intended to be current-controlled, and the command determining a first average amplitude of the current passing through each light source may comprise a first current amplitude for each elementary light source. Preferably, the step v of modifying the command may comprise delivering a second current level lower than the first current level to elementary light sources of at least one group of pixelated light sources if the estimated temperature value is higher than a predetermined threshold temperature value.

[0030] The step of modifying the command may include driving each fundamental light source with a DC current modulated pulse width modulated signal that determines a second average amplitude of the current passing through said fundamental light source, the second average amplitude preferably being lower than the first average amplitude when the estimated temperature is higher than a predetermined threshold temperature value.

[0031] According to another aspect of the present invention, a light emitting assembly for an automobile is provided. The assembly may be, for example, a lighting module. The assembly comprises a pixelated light source including a plurality of elementary light sources based on electroluminescent semiconductor components, the pixelated light source, a plurality of temperature sensors configured to deliver temperature characteristics of the pixelated light source when the pixelated light source projects image data, and a control unit. It is noteworthy that the control unit is configured to control the pixelated light source in response to an estimated temperature value of the hot spot of the pixelated light source, the estimated temperature value being dependent on the estimated position of the hot spot of the pixelated light source and the image data. Preferably, the pixelated light source may be intended to be either voltage-controlled or current-controlled.

[0032] Preferably, the control unit may be configured to carry out the steps of a method according to one aspect of the present invention.

[0033] Preferably, the assembly may comprise a memory element operatively connected to the control unit and containing pre-recorded reference data for the pixelated light sources.

[0034] Preferably, the pixelated light source may comprise at least one temperature sensor capable of delivering a temperature reading to the control unit. Preferably, the temperature characteristic may comprise a temperature measurement or temperature reading delivered by each of the temperature sensors. Preferably, each temperature value of the temperature characteristic may be associated with the position relative to the pixelated light source of the temperature sensor that performed the measurement.

[0035] By using the proposed means, it is possible to provide a method for driving a voltage- or current-driven pixelated light source for a vehicle, which allows the risks associated with overheating of the constituent elementary light sources to be avoided. In particular, the risks of thermal runaway and premature degradation of the elementary pixels of the source are dramatically reduced. The driving method protects the semiconductor junctions of the pixels of the pixelated light source from the viewpoint of extending their lifespan and avoiding visible defects of the beam projected onto the road by reducing the supply voltage or the average amplitude of the current in each pixel when a threshold temperature, preferably corresponding to the maximum threshold current amplitude, is exceeded. A light-emitting module implementing the proposed driving and temperature regulation methods therefore constitutes a more durable and economical solution compared to known prior art products.

[0036] Other features and advantages of the present invention will be better understood with the aid of the description of examples and drawings. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a flow chart showing the main steps of a method according to one preferred embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a light emitting assembly according to one preferred embodiment of the present invention. [Figure 3] 1 is a schematic diagram of image data and a light source that projects these image data and includes a temperature sensor, according to one preferred embodiment of the present invention; [Figure 4] 1 is a schematic diagram of image data and a light source that projects these image data and includes a temperature sensor, according to one preferred embodiment of the present invention; [Figure 5] FIG. 2 is a diagram of reference data for a pixelated light source as involved in a method according to one preferred embodiment of the present invention. [Figure 6] 1 is a schematic diagram of a light emitting assembly according to one preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] Unless otherwise specified, technical features described in detail with respect to a given embodiment may be combined with technical features described in the context of other embodiments, which are described in a non-limiting manner by way of example.

[0039] The description focuses on the elements of the control method and the automotive light emitting assembly that are necessary to understand the present invention. For example, other elements in a known manner that form part of such an assembly are not described or explained in detail. For example, the presence of a carrier or heat dissipation element is implied for the operation of such a module.

[0040] A lighting module or assembly for an automobile, such as one implementing the control method according to the first embodiment of the present invention, allows for the projection of lighting functions based on image data. The module includes a light source capable of projecting a pixelated light beam. The image typically includes a matrix array of pixel values, each value corresponding to the luminous intensity to be generated by a corresponding elementary light source of the lighting module. Typically, the pixelated light source is supplied with either a voltage or a current. When the pixelated light source is supplied with a voltage, the same voltage is applied across the terminals of each pixel, which corresponds to an elementary source formed by a miniaturized electroluminescent semiconductor component, at a given time. The luminous intensity to be emitted by each pixel is controlled by the duty cycle of a PWM control signal (PWM stands for Pulse Width Modulation), which selectively and periodically switches the pixel on and off. When the duty cycle is 100%, the amplitude of the average current passing through the pixel is equal to its maximum or peak amplitude, which generates maximum luminosity. When the intensity is low, a lower duty cycle results in a lower average value of the average amplitude of the current passing through the pixel. The maximum amplitude of the current depends on the voltage value applied to the pixelated light source.

[0041] When a pixelated light source is of the type that is to be supplied with current, it generally incorporates one independently driven current source for each pixel. The luminous intensity to be emitted by each pixel is controlled via the value of the amplitude of the current to be delivered by the current source associated with that pixel. Also, the duty cycle of a PWM control signal that selectively and periodically switches pixels on and off may affect the average value of the amplitude of the current passing through that pixel without changing the nominal amplitude being delivered to that pixel.

[0042] FIG. 1 illustrates the main steps of a driving method according to a first embodiment of the present invention. In a first step, a first voltage level is applied to a pixelated light source intended to be voltage-driven. The pixelated light source comprises a number of elementary LED light sources (LED stands for light-emitting diode). Each elementary light source is intended to generate a glowing pixel image projected by the pixelated light source. Image data represents the image to be projected (e.g., a beam of a specific shape) and determines the luminous intensity (usually between 0 and 255) to be generated by each elementary light source. Each elementary light source is supplied with a current of the same amplitude at the same voltage and temperature. This maximum amplitude is individually reduced for each elementary light source by applying a DC current modulation PWM signal to each elementary light source, which modulates the DC current delivered by a control unit, e.g., in the form of a microcontroller element. The duty cycle of this signal directly affects the average amplitude of the current supplied to the elementary light sources, which is proportional to the emitted luminous intensity. Thus, the pixelated light sources are assumed to be supplied with a voltage having a first level, and each elementary light source is assumed to be supplied with a current of a first amplitude that determines the luminance of the projected pixel corresponding to each elementary light source.

[0043] In a second step (ii), multiple temperature sensors located at predetermined locations near the matrix array of elementary light sources transmit their ambient temperature readings to the control unit. Next, based on the projected image data available to the control unit, the location of the hotspot of the pixelated light source is estimated using a temperature profile constructed from the acquired temperature measurements. Ideally, each sensor transmits a measurement that forms part of the acquired temperature profile. This corresponds to step (iii). In the following step (iv), the control unit evaluates a temperature value representing the temperature of the hotspot thus determined. Ideally, this hotspot corresponds to the hottest spot among the pixelated light sources at the time of measurement. This temperature value is therefore the temperature of the hottest junction of all elementary light sources. If this temperature is higher than a predetermined threshold, the control unit generates a command to reduce the average amplitude of the current flowing through the matrix array of all elementary light sources to ensure different relative brightnesses among the projected pixels while reducing the risk of thermal runaway (corresponding to linear overheating over time) for the critical elementary light source, i.e., the hottest elementary light source.

[0044] FIG. 2 illustrates a first embodiment of a light emitting assembly 100 for a vehicle. The illustrated system includes a control unit 130 for a pixelated light source 110, e.g., a monolithic pixelated light source. The pixelated light source includes a plurality of elementary light sources 112 arranged in the form of a matrix array. The control unit may include, e.g., a driver circuit for powering the pixelated light source 110 and control the driver circuit via an electrical connection. In a known manner, such a driver circuit may include, e.g., a step-down converter circuit of the "buck" type and, e.g., a step-up converter circuit of the "boost" type. These circuits are known per se in the art, and their operation will not be described in detail in the context of the present invention. The converter circuit in particular converts a voltage delivered to its input (not shown) into an output voltage Vout, which is determined by the control unit 130 and has a value different from the input voltage. Depending on the architecture chosen, the output voltage may be higher or lower than the input voltage. Such circuits are often used in the context of powering light sources based on electroluminescent semiconductor components, i.e., components such as light-emitting diodes (LEDs). In particular, such light sources must be supplied with a voltage at least equal to their forward voltage, which may differ from the available voltage delivered by, for example, a car battery.

[0045] The pixelated light source 110 is supplied with a voltage and may comprise hundreds or thousands of pixels 112. The light intensity emitted by the individual pixels is controlled via a periodic on / off signal PWM, as described above. The control unit has access to image data I1, also called a photometric image, corresponding to at least one digital image. This photometric image may be stored in a memory element to which the control unit has read access. Following a signal received from the vehicle's central control unit, the control unit then selects an appropriate photometric image from multiple available photometric images. The control unit 130 may also be configured to generate the photometric image according to instructions received over a data bus (not shown) internal to the vehicle. Alternatively, the control unit 130 may receive the image data I1 over such a data bus, for example of the CAN type (CAN is an abbreviation for Car Area Network). The control unit 130 preferably comprises calculation means configured to convert the image data I1 received for the image of each pixel into a supply voltage Vout and into a signal PWM intended for the pixelated light source 110 and the basic light source 112, respectively, so that a light beam according to the data I1 is projected.

[0046] Higher luminous intensity leads to more heating of the corresponding elementary light source, but how much heat an elementary light source 112 will receive generally cannot be accurately predicted based only on the data of the projected image I1. This is due, among other things, to parasitic heating caused by neighboring light sources, imperfections in the light source due to the respective manufacturing process, or previous projections that may result in residual heat remaining in some elementary light sources.

[0047] The pixelated light source 110 preferably includes multiple temperature sensors 121, 122, 123, and 124 physically adjacent to the semiconductor junctions. In the example of FIG. 2, there are four sensors, but the invention is not limited to this example. The temperature sensors may be, for example, thermistors or other temperature sensors known in the art, or advantageously, PTAT sensors (PTAT stands for Proportional to Absolute Temperature). By being in close proximity to the matrix array of elementary light sources, the sensors can deliver realistic readings of the operating temperature of the pixel regions of the pixelated light source 110 when the pixelated light source 110 is powered. According to one preferred embodiment, multiple temperature sensors may be integrated into the light source substrate, and multiple temperature readings corresponding to multiple zones or multiple pixels may be delivered to the control unit 130 using electrical signals T1, T2, T3, and T4, thereby forming a temperature characteristic PT1 corresponding to the projection of the image data I1.

[0048] The transmitted temperature characteristic PT1 does not allow the actual temperature values ​​of all the basic light sources to be accessed. Thus, in step iii of the proposed method, the location of the hot spot is estimated by the control unit. In the given example, the central zone of the image data I1 is turned on. Thus, the basic light source corresponding to the center of the pixelated light source 110 is most at risk of heating up during the projection of the image I1. This zone is far from all the temperature sensors 121, 122, 123, 124, whose positions are known. Therefore, in this example, it is almost certain that the display temperatures T1, T2, T3, and T4 are similar or similar. Conversely, such a uniform temperature characteristic may allow it to be estimated that the hot spot is located in the central zone of the matrix array.

[0049] However, none of these values ​​corresponds to the actual temperature of the central zone. To estimate the temperature of the central zone, the control unit 130 may, for example, make a request to a database comprising predetermined temperature characteristics associated with predetermined photometric images I1, I2, ..., IN and the corresponding maximum temperatures. These data may, for example, be obtained by prior simulation or by measurements using a thermal camera of the primary light source while the primary light source projects the corresponding photometric image. The control unit may then determine the temperature or temperature increment that must be added to the obtained value of the temperature characteristic PT1 by comparing the temperature characteristic PT1 with the characteristics of the database, specifically for the projected image I1, to obtain a realistic indication of the temperature in the central, switched-on zone. In the provided example, for the zones furthest from the sensors 121, 122, 123, 124 at the corners of the pixel matrix array 110, the increment ΔT1 may be a value between 15 and 30°C, for example 25°C. The estimated temperature T is calculated, for example, by T2 + ΔT1°C.

[0050] The incremental value or temperature value stored in the database, which depends on the determined hotspot location, may optionally be adapted depending on the operating time of the temperature sensor to take into account measurement errors due to variations in sensor sensitivity, which generally worsen with operating time.

[0051] The increment depends at least on the estimated location of the hot spot, the known location of the temperature sensor, and the projected image. Figure 3 provides another example. The projected photometric image I2 comprises a first switched-on zone Z1 and a smaller, brighter central zone Z2. The four central elementary light sources 112 run the risk of obvious overheating. However, due to the large distance of the sensors 121, 122, 123, and 124 from this central zone and their lack of sensitivity, the temperature values ​​T1, T2, T3, and T4 are very similar to those of the previous example. Therefore, it is advantageous to compare the image data of zone Z2 with the image data of zone Z1 to determine the temperature of the central zone. Knowing that image I2, not I1, is being projected, the image data allows control unit 130 to remove ambiguity induced by acquired temperature characteristics considered in isolation and determine that an increment ΔT2 greater than ΔT1 should be added to the temperature acquired by the sensor in order to deliver a realistic estimate of the hottest temperature of pixelated light source 110. Using temperature values ​​alone, the hot spot in this example would not be distinguishable from the hot spot in the example of FIG. 3, even though the four central pixels may experience significantly greater heating and therefore risk more pronounced thermal runaway. A more accurate estimation would allow control unit 130 to react differently in a more nuanced manner in the two examples of projections I1 and I2 shown.

[0052] Another example is shown in FIG. 4. The projected photometric image I3 has an activated zone in the upper left. In this example, the temperature value T1 is clearly higher than the temperatures T2, T3, and T4. Thus, the temperature characteristics delivered by the sensor, taken in isolation, allow the location of the hot spot in the zone directly adjacent to the sensor 121 to be estimated: this zone is in the upper left quadrant of the pixel matrix array 110. Taking the image data I3 into account optionally allows this location estimation to be refined. In the case shown, the temperature value T1 should be increased by a small value or by an increment of 0 to achieve a correct hot spot estimate. In particular, a primary light source susceptible to overheating is close to one of the available temperature sensors.

[0053] In this way, the control unit is configured to, after estimating the position of the hotspot of the pixelated light source 110, determine an estimate of a temperature value T of the hotspot depending on the estimated position and preferably depending on the projected image data I1, I2, I3. The control unit 130 is further configured to determine, based on the delivered first supply voltage level and on the corresponding estimated temperature T of the hotspot of the pixelated light source, if there is a need to reduce the amplitude of the current in the pixelated light source to prevent thermal runaway from occurring.

[0054] For example, if the estimated temperature value T of the hot spot exceeds a predetermined threshold, then the first voltage level is reduced to a lower second voltage level, which reduces the maximum or peak current amplitude passing through the pixel 121 of the pixelated light source 110, thus avoiding overheating of the corresponding semiconductor junction.

[0055] According to one preferred embodiment of the present invention, the control unit 130 comprises or has read access to a memory element 132 (shown in FIG. 2) in which reference data for the pixelated light source 110 is stored. These data may be provided, for example, during production or assembly of the light emitting module.

[0056] 5 shows one non-limiting example of reference data that may be used by the control unit to perform step v of the control method according to one preferred embodiment of the present invention. The subject data characterizes the electro-thermal behavior of the pixels of the pixelated light source.

[0057] In the illustrated example, exceeding the threshold current amplitude, set at 35 mA, would put the pixels of the pixelated light source at risk of permanent failure. Therefore, the control unit ensures that this threshold is not exceeded for extended periods. The reference data provides a curve relating the drive voltage (in volts) to the resulting current amplitude (in amperes) over an operating temperature range, for example, spanning -40°C to 150°C. It should be apparent that the threshold temperature to which the temperature reading T is compared by the control unit may depend on the value of the first voltage initially delivered to the pixelated light source, which is the origin of the estimated temperature T of the hot spot of the matrix array. For example, at a voltage of 3.2 V, the maximum current amplitude is reached at the temperature Te indicated by the intersection of the curve Te with the upper threshold current limit I. If the hot spot temperature estimate T obtained by this method is higher than Te while the delivered first drive voltage level is higher than 3.2 V, the control unit commands the driver to deliver a second drive voltage level lower than 3.2 V. In contrast, with an initially delivered voltage of 3 V, the hot spot's operating temperature Te may rise up to 150°C before a drop in the drive voltage is commanded by the control unit. Continuous application of this method allows the temperature to be dynamically adjusted without risking thermal runaway. Thus, the threshold against which the reading of the hot spot's estimated temperature T is compared depends on the delivered first voltage. The second voltage level is chosen so that the maximum current passing through the pixel of the pixelated light source does not exceed a predetermined maximum threshold amplitude, e.g., 35 mA.

[0058] In an alternative embodiment, the voltage level Vout may be kept at a first level, and in order to reduce the average amplitude of the currents flowing through the fundamental light sources, the PWM signals controlling these average current amplitudes may be adapted by reducing the duty cycle of the PWM signals by a predetermined factor, which is preferably the same for all fundamental light sources. A combination of voltage control adaptation and PWM signal adaptation may also be envisaged without departing from the scope of the invention.

[0059] Figure 6 shows an embodiment of a light emitting assembly 200 for an automobile according to the second embodiment, which makes it possible to carry out the adaptation described by way of example in the context of Figures 3 to 5 when the pixelated light source is current-controlled.

[0060] The depicted system comprises a control unit 230 for a pixelated light source 210. The pixelated light source comprises a plurality of elementary light sources 212 arranged in the form of a matrix array. The control unit may for example comprise a driving circuit for the power supply of the pixelated light source 210 or may control said driving circuit via an electrical connection.

[0061] The pixelated light source 210 is supplied with current and may comprise hundreds or thousands of pixels 212. The light intensity emitted by individual pixels depends on the amplitude of the respective current passing through them. Each pixel 212 is associated with a dedicated current source. These current sources are integrated into the pixelated light source 210. Following receipt of a current command Iout(212) for that pixel 212, the current source associated with that pixel 212 can deliver a current of a corresponding amplitude to that pixel. The pixels may also be controlled via a periodic on / off signal PWM, as described above. At a constant nominal current, modulation of the signal PWM allows for affecting the average amplitude of the current passing through the pixel. The control unit 230 has access to image data I1, also referred to as a photometric image, corresponding to at least one digital image. This photometric image may also be stored in a memory element to which the control unit has read access. Following a signal received from the vehicle's central control unit, the control unit then selects an appropriate photometric image from multiple available photometric images. The control unit 230 can also be configured to generate photometric images according to commands received on a data bus (not shown) inside the motor vehicle. Alternatively, the control unit 230 may receive image data I1 on such a data bus, for example of the CAN type (CAN being the abbreviation for Car Area Network). The control unit 230 preferably comprises calculation means configured to convert the image data I1 received for each pixel's image into current values ​​Iout(212) for each pixel 212 grouped together in a control signal Iout and into signals PWM intended for the pixelated light source 210 and the elementary light source 212, so that a light beam according to the data I1 is projected.

[0062] Higher luminous intensity leads to more heating of the corresponding elementary light source, but how much heat an elementary light source 212 will receive generally cannot be accurately predicted based solely on the data of the projected image I1. This is due, among other things, to parasitic heating caused by neighboring light sources, imperfections in the light source due to the respective manufacturing process, or previous projections that may result in residual heat remaining in some elementary light sources.

[0063] The pixelated light source 210 preferably includes multiple temperature sensors 221, 222, 223, and 224 physically adjacent to the semiconductor junctions. In the example of FIG. 6, there are four sensors, but the invention is not limited to this example. The temperature sensors may be, for example, thermistors or other temperature sensors known in the art, or advantageously, PTAT sensors (PTAT stands for Proportional to Absolute Temperature). By being in close proximity to the matrix array of elementary light sources, the sensors can deliver realistic readings of the operating temperature of the pixel regions of the pixelated light source 210 when the pixelated light source 210 is powered. According to one preferred embodiment, multiple temperature sensors may be integrated into the light source substrate, and multiple temperature readings corresponding to multiple zones or multiple pixels may be delivered to the control unit 230 using electrical signals T1, T2, T3, and T4, thereby forming a temperature characteristic PT1 corresponding to the projection of the image data I1.

[0064] The transmitted temperature characteristic PT1 does not allow the actual temperature values ​​of all the basic light sources to be accessed. Thus, in step iii of the proposed method, the location of the hot spot is estimated by the control unit. In the given example, the central zone of the image data I1 is turned on. Thus, the basic light source corresponding to the center of the pixelated light source 210 is most at risk of heating up during the projection of the image I1. This zone is far from all the temperature sensors 121, 122, 123, 124, whose positions are known. Therefore, in this example, it is almost certain that the display temperatures T1, T2, T3, and T4 are similar or similar. Conversely, such a uniform temperature characteristic may allow it to be estimated that the hot spot is located in the central zone of the matrix array.

[0065] However, none of these values ​​corresponds to the actual temperature of the central zone. To estimate the temperature of the central zone, the control unit 230 may, for example, make a request to a database comprising predetermined temperature characteristics associated with predetermined photometric images I1, I2, ..., IN and the corresponding maximum temperatures. These data may, for example, be obtained by prior simulation or by measurements using a thermal camera of the primary light source while the primary light source projects the corresponding photometric image. The control unit may then determine the temperature or temperature increment that must be added to the obtained value of the temperature characteristic PT1 by comparing the temperature characteristic PT1 with the characteristics of the database, specifically for the projected image I1, to obtain a realistic indication of the temperature in the central, switched-on zone. In the provided example, for the zones furthest from the sensors 221, 222, 223, 224 at the corners of the pixel matrix array 210, the increment ΔT1 may be a value between 15 and 30°C, for example 25°C. The estimated temperature T is calculated, for example, by T2 + ΔT1°.

[0066] The incremental value or temperature value stored in the database, which depends on the determined hotspot location, may optionally be adapted depending on the operating time of the temperature sensor to take into account measurement errors due to variations in sensor sensitivity, which generally worsen with operating time.

[0067] After estimating the location of the hotspot of the pixelated light source 210, the control unit 230 is configured to determine an estimate of a temperature value T of the hotspot in response to the estimated location and preferably in response to the projected image data I1. The control unit 230 is further configured to determine, if there is a need to reduce the amplitude of the current in the pixelated light source to prevent overheating, based on the delivered first current amplitude delivered to the area of ​​the light source 210 that includes the location of the hotspot and based on the corresponding estimated temperature T of the hotspot of the pixelated light source.

[0068] For example, if the estimated temperature value T of the hot spot exceeds a predetermined threshold, then the first current level is reduced to a lower second current level, thereby reducing the maximum or peak current amplitude passing through the pixel corresponding to the hot spot 221 of the pixelated light source 210, thus avoiding overheating of the corresponding semiconductor junction.

[0069] The reduced current amplitude is applied via a command Iout, which includes a current amplitude setpoint Iout(212) either for a particular elementary light source 212, for a group of elementary light sources preferably including the location of the identified hotspot, or for all elementary light sources 212 of the pixelated light source.

[0070] In an alternative embodiment, the voltage level Iout may be kept at a first level, and in order to reduce the average amplitude of the currents flowing through the fundamental light sources, the PWM signals controlling these average current amplitudes may be adapted by reducing their duty cycle by a predetermined factor. A combination of peak current control adaptation and PWM signal adaptation may also be envisaged without departing from the scope of the invention.

[0071] Needless to say, the described embodiments do not limit the scope of protection of the present invention, other embodiments can be contemplated using the description provided above without further departing from the scope of the present invention.

[0072] The scope of protection is defined by the claims.

Claims

1. A method for controlling a pixelated light source (110, 210) for a motor vehicle, said pixelated light source comprising a plurality of elementary light sources (112, 212) based on electroluminescent semiconductor components, said method comprising at least i. controlling said pixelated light sources using a control unit (130, 230) to project a light beam corresponding to image data (I1, I2, I3) by driving each elementary light source with a control signal (Vout, Iout, PWM) that determines a first average amplitude of a current passing through said elementary light source; ii. acquiring the temperature characteristic (PT1) of said pixelated light source using a plurality of temperature sensors (121, 122, 123, 124; 212, 222, 223, 224) arranged at predetermined locations; iii. estimating, using the control unit, a hot spot position of the pixelated light source based on the image data (I1) and the acquired temperature characteristic (PT1); iv. estimating, using the control unit, a temperature value of the hot spot in response to the acquired temperature profile and the estimated location of the hot spot relative to the location of the temperature sensor; v modifying, by means of said control unit (130, 230), if said estimated temperature value is higher than a predetermined threshold temperature value, the commands (Vout, Iout, PWM) delivered to said pixelated light sources (110, 210) so that at least one group of said elementary light sources (112, 212) comprising said elementary light sources located at said estimated position of said hotspot is passed by a current of a second average amplitude lower than said first average amplitude; a preliminary step of making available in a memory element (132) reference data for said pixelated light source (110), said reference data relating drive voltage values ​​to corresponding supply current amplitudes for a series of operating temperatures of said pixelated light source; the pixelated light sources (110) are intended to be voltage-controlled, and the command determining a first average amplitude of the current passing through each elementary light source comprises a first voltage level (Vout); 1. A method for controlling a pixelated light source (110, 210) for an automobile, wherein the step v of modifying the command comprises delivering a second voltage level (Vout) to the pixelated light source (110) that is lower than the first voltage level (Vout) if the estimated temperature value is higher than a predetermined threshold temperature value, wherein the second voltage level is chosen depending on the estimated temperature value to maintain a predetermined threshold current amplitude.

2. 2. The method of claim 1, wherein the step iii of estimating the location of the hotspot comprises retrieving the acquired temperature characteristic (PT1) from among a plurality of pre-recorded temperature characteristics previously stored in a memory element, each characteristic being associated with specific image data (I1, I2, I3) and a hotspot location associated with these data.

3. 3. A control method according to claim 1 or 2, characterized in that step iv of estimating the temperature value of the hotspot comprises the step of increasing at least one of the temperature values ​​(T1, T2, T3, T3) of the obtained temperature characteristic (PT1) by a predetermined increment that depends on the estimated location of the hotspot.

4. 4. The control method according to claim 3, characterized in that the step iv of estimating the temperature value further comprises a step of taking into account the projected image data (I1, I2, I3), wherein pixels with high luminosity values ​​correspond to hotter elementary light sources (112).

5. 2. The method of claim 1, wherein step v of modifying the command includes a preceding step of comparing the estimated temperature value with the predetermined threshold temperature value, the predetermined threshold temperature value being dependent on the delivered first voltage level.

6. 6. The control method of claim 1, wherein the step of modifying the command comprises driving each basic light source (112, 212) with a DC current-modulated pulse-width modulated signal (PWM) that determines a second average amplitude of the current passing through the basic light source, the second average amplitude being lower than the first average amplitude when the estimated temperature is higher than a predetermined threshold temperature value.

7. a plurality of pixelated light sources (110, 210) including a plurality of elementary light sources (112, 212) based on electroluminescent semiconductor components; a plurality of temperature sensors (121, 122, 123, 124) arranged at predetermined locations and intended to deliver temperature characteristics (PT1, T1, T2, T3, T4) of said pixelated light source when said pixelated light source is projecting image data (I1, I2, I3); a control unit (130, 230); a memory element operatively connected to said control unit and containing pre-recorded reference data for said pixelated light source; The pixelated light source is intended to be voltage controlled, the reference data relating drive voltage values ​​to corresponding supply current amplitudes for a sequence of operating temperatures of the pixelated light source; The control unit controlling the pixelated light sources to project a light beam corresponding to the image data by driving each elementary light source with a control signal that determines a first average amplitude of a current passing through the elementary light source; acquiring the temperature characteristics from the plurality of temperature sensors; estimating a location of a hot spot of the pixelated light source based on the image data and the temperature characteristics; estimating a temperature value of the hotspot in response to the temperature characteristic and the estimated location of the hotspot relative to the location of the temperature sensor; modifying commands delivered to the pixelated light sources, when the estimated temperature value is higher than a predetermined threshold temperature value, so that at least one group of elementary light sources, comprising the elementary light source located at the estimated position of the hotspot, is passed by a current of a second average amplitude lower than the first average amplitude, wherein the commands determining the first average amplitude of the current passing through each elementary light source include a first voltage level, and when the estimated temperature value is higher than a predetermined threshold temperature value, delivering a second voltage level lower than the first voltage level to the pixelated light sources, and choosing the second voltage level depending on the estimated temperature value in order to observe the predetermined threshold current amplitude; A light emitting assembly (100, 200) for an automobile.

8. 8. A light emitting assembly according to claim 7, characterized in that the control unit (130, 230) is configured to carry out the steps according to any one of claims 1 to 6.

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