Method for controlling a pixelated light source

Abstract

The invention relates to a method of controlling a pixelated light source for a motor vehicle. This method makes it possible to prevent thermal runaway and premature aging of the elementary pixels of the (light) source, independently of the luminance level projected. By dynamically adjusting the current intensity at the elementary light source, this control method provides protection of the semiconductor junction of the pixels of the pixelated light source, thus increasing its lifetime and avoiding visible defects in the light beam projected onto the road resulting from thermal runaway or premature aging of the semiconductor junction.

Description

Technical Field

[0001] This invention relates to the field of motor vehicle lighting systems, and more particularly, to such a system using pixelated (light) sources. Background Technology

[0002] A light-emitting diode (LED) is an electronic semiconductor device capable of emitting light of a predetermined wavelength when a voltage at least equal to a threshold is applied across its terminals. Above this threshold (known as the forward voltage), the intensity of the luminous flux emitted by the LED typically increases with the average amplitude of the supply current. The amplitude of the current tends to increase at a constant applied voltage as the semiconductor junction heats up. Their small size and low power consumption make LED devices advantageous in the field of lighting modules for motor vehicles. LED-based light sources can be used, for example, to produce unique optical characteristics by placing components along a predetermined contour. The use of LED devices also facilitates the production of lamps capable of performing multiple lighting functions.

[0003] Pixelated light sources using various types of techniques are also known to project beams of light according to image data. For example, this involves monolithic technology, where a large number of basic LED (light) sources are etched into a common semiconductor substrate, making the basic LED (light) sources equivalent to pixels. The substrate may also include onboard electronic components, such as switching circuits. Integrated electrical connections allow pixels to be activated independently of each other. In particular, it has been proposed to use voltage to drive such pixelated light sources: this is achieved by applying a constant voltage to the pixelated light source, allowing individual pixels to be controlled in a one-to-one manner, with each switch controlled by a binary signal. For example, the control signal passed to the pixel could be a PWM signal (PWM stands for Pulse Width Modulation), whose duty cycle directly affects the average amplitude of the current passing through the pixel and thus its luminance.

[0004] Alternatively, current can also be used to drive pixelated light sources. Each basic light source forming a pixel is associated with a dedicated power supply. Therefore, the amplitude of the current passing through a given pixel can be directly adjusted, and thus the light intensity emitted by that pixel can be adjusted. The average amplitude of the current can also be reduced for a given DC current amplitude by applying a PWM signal.

[0005] Pixelated light sources can be used to perform HB (High Beam) functions or complex functions such as ADB (Adaptive High Beam), and so on. For voltage-driven light sources, a constant power supply voltage is typically specified. However, at a constant voltage, the amplitude of the current through semiconductor junctions (such as the junctions of electroluminescent pixels) increases linearly with temperature. As current passes through the junctions, the junction temperature rises. Therefore, for pixels that need to operate for extended periods, there is a risk of thermal runaway: the more the semiconductor junctions are heated by the current passing through them, the greater the increase in current amplitude, until the junctions fail or are irreversibly damaged. This risk is more pronounced in pixels in the central region of the pixelated light source, which participate in multiple vehicle lighting functions and therefore need to operate more regularly. Failure in this region can lead to visible malfunctions in the beam projected onto the road. Because it is currently impossible to measure the exact temperature of each pixel, it is difficult to predict which points in a pixelated light source, which may project a series of different images during operation, might overheat.

[0006] Under current control, the risk of thermal runaway is reduced. However, significant overheating at each semiconductor junction can accelerate premature aging and increase the risk of failure.

[0007] The object of this invention is to overcome at least one problem inherent in the prior art. More specifically, the object of this invention is to provide a method for controlling pixelated light sources, which allows the avoidance of risks associated with overheating of the basic pixels of the (light) source. Summary of the Invention

[0008] According to a first aspect of the present invention, a method for controlling a pixelated light source for a motor vehicle is provided. The pixelated light source includes a plurality of basic light sources based on electroluminescent semiconductor components. Notably, the method includes at least the following steps:

[0009] i) The pixelated light source is controlled by a control unit, thereby driving each basic light source with a control signal to project a beam of light corresponding to the image data, the control signal determining a first average amplitude of the current passing through the basic light source;

[0010] ii) Obtain the temperature profile of the pixelated light source using multiple temperature sensors placed at predetermined locations;

[0011] iii) The control unit estimates the location of the hotspot of the pixelated light source based on the image data and the obtained temperature curve;

[0012] iv) The control unit estimates the temperature value of the hot spot based on the obtained temperature curve and the estimated position of the hot spot relative to the temperature sensor.

[0013] v) If the estimated temperature value is higher than a predetermined threshold temperature value, the control unit changes the command transmitted to the pixelated light source so that at least one group of basic light sources, including the basic light source located at the estimated position of the hot spot, is supplied with a current of a second average amplitude, which is lower than the first amplitude.

[0014] The pixelated light source may preferably include a pixelated light source that is voltage-controlled.

[0015] The pixelated light source may preferably include a pixelated light source that is voltage-controlled.

[0016] According to another aspect of the present invention, a method for controlling a pixelated light source for a motor vehicle is provided. The pixelated light source is voltage-driven and includes a plurality of basic light sources based on electroluminescent semiconductor components. Notably, the method includes at least the following steps:

[0017] i') The pixelated light source is controlled by a control unit, thereby projecting a beam of light corresponding to the image data by supplying a first voltage level to it and driving each basic light source with a DC current modulated pulse width modulation signal, the DC current modulated pulse width modulation signal determining a first average amplitude of the current passing through the basic light source;

[0018] ii') Obtain the temperature profile of the pixelated light source using multiple temperature sensors placed at predetermined locations;

[0019] iii') The control unit estimates the location of the hotspot of the pixelated light source based on the image data and the obtained temperature curve;

[0020] iv') The control unit estimates the temperature value of the hot spot based on the obtained temperature curve and the estimated position of the hot spot relative to the temperature sensor.

[0021] v') If the estimated temperature value is higher than a predetermined threshold temperature value, the control unit changes the command transmitted to the pixelated light source so that each of the basic light sources has a current with a second average amplitude that is lower than the first amplitude.

[0022] Preferably, the step of estimating the location of the hotspot may include searching for a obtained temperature curve among a plurality of pre-recorded temperature curves pre-stored in a memory element, each curve being associated with specific image data and the location of the hotspot associated with that data.

[0023] Preferably, the step of estimating the temperature value of the hot spot may include the step of using a predetermined increment to increase at least one of the temperature values ​​of the obtained temperature curve, the predetermined increment depending on the estimated location of the hot spot.

[0024] Preferably, the step of estimating the temperature value may further include taking into account the projected image data and the specular value of the pixel corresponding to the basic thermal light source.

[0025] Preferably, the pixelated light source can be used to be voltage-controlled, and the command to determine a first average amplitude of the current through each basic light source can preferably include a first voltage level.

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

[0027] Preferably, the step of changing the command may include a prior step of comparing the estimated temperature value with a predetermined threshold temperature value, the predetermined threshold temperature value depending on the first voltage level delivered.

[0028] Preferably, the method may include a preparatory step of making available reference data related to the pixelated light source in the memory element, the data relating a drive voltage value to a corresponding supply current amplitude for a series of operating temperatures of the pixelated light source, and the step of changing the command includes selecting the second voltage level based on the estimated temperature value to comply with a predetermined threshold current amplitude.

[0029] Preferably, the pixelated light source can be used to be controlled by current, and the command to determine a first average amplitude of the current through each light source can include a first current amplitude for each basic light source. Preferably, step v of changing the command can include the step of supplying a second current level lower than the first current level to at least one group of basic light sources of the pixelated light source if the estimated temperature value is higher than a predetermined threshold temperature value.

[0030] Preferably, the step of changing the command may include driving each basic light source with a DC current modulated pulse width modulated signal if the estimated temperature is higher than a predetermined threshold temperature value, the DC current modulated pulse width modulated signal determining a second average amplitude of the current passing through the basic light source, the second average amplitude being lower than the first average amplitude.

[0031] According to another aspect of the invention, a light-emitting component for a motor vehicle is provided. This could be a problem with, for example, an illumination module. The component includes a pixelated light source having a plurality of basic light sources based on electroluminescent semiconductor components, a plurality of temperature sensors for transmitting a temperature profile of the pixelated light source when it projects image data, and a control unit. Notably, the control unit is configured to control the pixelated light source based on an estimated temperature value of a hot spot, the estimated temperature value depending on the estimated location of the hot spot and the image data. Preferably, the pixelated light source can be voltage-controlled or current-controlled.

[0032] Preferably, the control unit can be configured to perform steps of the method according to one aspect of the invention.

[0033] Preferably, the component may include a memory element functionally connected to the control unit and including pre-recorded reference data related to the pixelated light source.

[0034] Preferably, the pixelated light source may include at least one temperature sensor capable of transmitting a temperature indication to the control unit. Preferably, the temperature profile may include temperature measurement results or indications transmitted by each temperature sensor. Preferably, each temperature value of the temperature profile may be associated with the position of the temperature sensor performing the measurement relative to the pixelated light source.

[0035] By employing the measures proposed in this invention, a method for driving a pixelated light source for motor vehicles, whether voltage-driven or current-driven, is provided, allowing avoidance of risks associated with overheating of the constituent basic light source. Specifically, the risk of thermal runaway and premature aging of the basic pixels of the (light) source is dynamically reduced. When a threshold temperature, preferably corresponding to the maximum threshold current amplitude, is exceeded, the driving method protects the semiconductor junctions of the pixels of the pixelated light source by reducing the power supply voltage or by reducing the average amplitude of the current in each pixel, thereby extending its lifespan and preventing visible failures in the beam projected onto the road. Therefore, the light-emitting module implementing the proposed driving and temperature regulation method constitutes a more durable and economical solution compared to known prior art products. Attached Figure Description

[0036] Other features and advantages of the invention will be better understood with the aid of the description of the embodiments and accompanying drawings, wherein:

[0037] -[ Figure 1 [ ] is a diagram illustrating the main steps of a method according to a preferred embodiment of the present invention;

[0038] -[ Figure 2 [Illustration] is a schematic diagram of a light-emitting component according to a preferred embodiment of the present invention;

[0039] -[ Figure 3 [Illustration of image data and a light source that projects the image data and includes a temperature sensor, according to a preferred embodiment of the present invention;]

[0040] -[ Figure 4 [Illustration of image data and a light source that projects the image data and includes a temperature sensor, according to a preferred embodiment of the present invention;]

[0041] -[ Figure 5 [Illustration of reference data for a pixelated light source involved in a method according to a preferred embodiment of the present invention;]

[0042] -[ Figure 6 [Illustration] is a schematic diagram of a light-emitting component according to a preferred embodiment of the present invention.

[0043] 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 described in an exemplary and non-limiting manner. Detailed Implementation

[0044] This specification focuses on the elements essential for understanding the present invention: the light-emitting components and control methods for motor vehicles. Other elements that are known in a manner, such as forming part of such components, will not be mentioned or described in detail. For example, the presence of a carrier or heat dissipation element is implicit for the operation of such a module.

[0045] Light-emitting modules or components for motor vehicles (such as those relating to the implementation of the control method according to a first embodiment of the invention) enable projection illumination functions based on image data. The module includes a light source capable of projecting pixelated beams of light. An image typically comprises a matrix array of pixel values, each corresponding to the luminance to be produced by a corresponding primary light source of the illumination module. Typically, the pixelated light source is supplied with voltage or current. When the pixelated light source is supplied with voltage, the same voltage is applied across the terminals of each pixel at a given time, which corresponds to a primary (light) source formed by miniature electroluminescent semiconductor components. The luminance 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 turns the pixel on and off. For a 100% duty cycle, the amplitude of the average current through the pixel is equal to its maximum or peak amplitude, resulting in maximum luminance. For lower intensities, a lower duty cycle results in a lower average amplitude of the average current through the pixel. The maximum amplitude of the current depends on the voltage value applied to the pixelated light source.

[0046] When the pixelated light source is of the type that is supplied with current, each pixel is typically associated with an independently driven power supply. The luminance to be emitted by each pixel is controlled by the value of the current amplitude delivered via the power supply associated with the pixel. The duty cycle of the PWM control signal that selectively and periodically turns the pixel on and off can also affect the average value of the current amplitude passing through the pixel without changing the nominal value of the current delivered to the pixel.

[0047] Figure 1 The main steps of a driving method according to a first embodiment of the present invention are illustrated. In a first step i, a first voltage level is supplied to a pixelated light source to be driven by the voltage. The pixelated light source comprises a plurality of basic LED light sources (LED stands for Light Emitting Diode). Each basic light source will produce a light-emitting pixel of an image projected by the pixelated light source. Image data represents the image to be projected (e.g., a beam of light of a specific shape) and determines the luminance to be produced by each basic light source (typically between 0 and 255). Each basic light source is supplied with a current of the same amplitude under equal voltage and equal temperature. By applying a DC-current-modulated PWM signal to each basic light source, the PWM signal modulates the DC current supplied by a control unit, which is, for example, in the form of a microcontroller element, such that the maximum amplitude is reduced individually for each basic light source. The duty cycle of this signal directly affects the average amplitude of the current supplied to the basic light source, which is proportional to the emitted luminance. Therefore, assuming that the pixelated light source is supplied with a voltage of the first level and that each basic light source is supplied with a current of the first amplitude, this determines the luminance of the corresponding projected pixel.

[0048] In step ii, multiple temperature sensors placed at predetermined locations near the matrix array of primary light sources transmit their ambient temperature indications to the control unit. Next, based on image data available to the control unit and using a temperature profile composed of the obtained temperature measurements, the location of a hot spot in the pixelated light source is estimated. Ideally, each sensor transmits a measurement that forms a portion of the obtained temperature profile. This corresponds to step iii. In the next step, step iv, the control unit evaluates a temperature value representing the temperature of the thus determined hot spot. Ideally, this hot spot corresponds to the hottest point of the pixelated light source at the time of measurement: therefore, this is the issue of the highest junction temperature among all primary light sources. If this temperature exceeds a predetermined threshold, the control unit generates a command to reduce the average amplitude of the current flowing through all primary light sources in the matrix array to ensure the relative brightness difference between projected pixels while reducing the risk of thermal runaway (corresponding to linear overheating) of the primary light source at risk (i.e., the hottest primary light source).

[0049] Figure 2A light-emitting assembly 100 for a motor vehicle according to a first embodiment is shown. The system shown includes a control unit 130 for pixelated light sources 110 (e.g., monolithic pixelated light sources). The pixelated light sources include a plurality of basic light sources 112 arranged in a matrix array. For example, the control unit may include, or via electrical connection, a drive circuit that controls the power supply of the pixelated light sources 110. In a known manner, such a drive circuit may include a buck converter circuit (e.g., a “buck” type) and a boost converter circuit (e.g., a “boost” type). These circuits are known in the art and their operation will not be described in detail in the context of this invention. In particular, the converter circuit enables the conversion of a voltage supplied 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 chosen architecture, the output voltage may be higher or lower than the input voltage. For example, such circuits are typically used to power light sources based on electroluminescent semiconductor components (i.e., components such as light-emitting diodes (LEDs)). Specifically, such a light source must be supplied with a voltage having a value at least equal to its positive voltage, which may be different from the available voltage supplied, for example, by the battery of a motor vehicle.

[0050] The pixelated light source 110 is supplied with voltage and may comprise hundreds or thousands of pixels 112. As described above, the luminous intensity emitted by each pixel is controlled via a periodic on / off signal PWM. The control unit has access to image data I1 corresponding to at least one digital image (also referred to as a photometric image). The photometric image may be stored in a memory element that the control unit has read access to. After receiving a signal from the central control unit of the vehicle, the control unit then selects a suitable photometric image from among a plurality of available photometric images. The control unit 130 may also be configured to generate a photometric image according to instructions received on a data bus (not shown) within the vehicle. Alternatively, the control unit 130 may receive the image data I1 on such a data bus (e.g., a CAN-type data bus (CAN stands for Automotive Area Network)). The control unit 130 preferably includes a computing device configured to convert the image data I1 received for each pixel of the image into a power supply voltage Vout and a signal PWM required for the pixelated light source 110 and the basic light source 112, respectively, such that a beam of light conforming to the data I1 is projected.

[0051] Although high luminance leads to more heating of the corresponding primary light source, the exact amount of heat the primary light source 112 will generate cannot usually be accurately predicted based solely on data from the projected image I1. This is due to parasitic heating caused by adjacent light sources, light source defects resulting from the manufacturing processes of the respective light sources, previous projections that may leave residual heat in multiple primary light sources, and so on.

[0052] Preferably, the pixelated light source 110 includes a plurality of temperature sensors 121, 122, 123, and 124 physically located near the semiconductor junction. Figure 2 In the example, there are four sensors, but the invention is not limited to this example. For example, this could be a problem with thermistors or other temperature sensors known in the art, or advantageously, a PTAT sensor (PTAT stands for proportional to absolute temperature). The matrix array close to the basic light source allows the sensors to provide a true indication of the operating temperature of the pixel region of the pixelated light source 110 when the pixelated light source 110 is powered. According to a preferred embodiment, multiple temperature sensors can be integrated into the substrate of the light source, and multiple temperature indications corresponding to multiple regions or multiple pixels can be transmitted to the control unit 130 in the form of electrical signals T1, T2, T3, T4, thereby forming a temperature profile PT1 corresponding to the projection of the image data I1.

[0053] The transmitted temperature profile PT1 does not allow access to the exact temperature values ​​of all the primary light sources. Therefore, 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 region of image data I1 is switched on. Therefore, the primary light source corresponding to the center of the pixelated light source 110 has the greatest risk of heating during the projection of image I1. This region is far from all temperature sensors 121, 122, 123, 124, the locations of which are known. Therefore, in this example, there may be similar or identical indications T1, T2, T3, T4. In contrast, this uniform temperature profile allows the estimation that the hot spot is located in the central region of the matrix array.

[0054] However, none of these values ​​correspond to the exact temperature of the central region. To estimate the temperature of the central region, the control unit 130 may, for example, resort to a database containing predetermined temperature curves associated with predetermined photometric images I1, I2, ... IN and their corresponding highest temperatures. These data may be obtained in advance through simulation or by measurement using a thermal imager of the basic light source when the corresponding photometric image is projected by the basic light source. Specifically, with respect to the projected image I1, the control unit can thus determine the temperature, or the temperature increment that must be added to the value of the obtained temperature curve PT1, by comparing the temperature curve PT1 with the curve in the database to obtain a true indication of the temperature in the activated central region. In the provided example, for the region furthest from sensors 121, 122, 123, 124 (sensors 121, 122, 123, 124 are at the corners of pixel matrix array 110), the value of the increment ΔT1 may include between 15°C and 30°C, for example, 25°C. For example, the estimated temperature T is given by T2 + ΔT1°.

[0055] The incremental or temperature values ​​stored in the database (which depend on the location of the identified hot spot) can optionally be adjusted based on the operating time of the temperature sensor to account for measurement errors due to variations in sensor sensitivity, which typically degrades over operating time.

[0056] The increment depends at least on the estimated location of the hotspot, the known location of the temperature sensor, and the projected image. Figure 3 Another example is given. The projected luminous image I2 includes a first on-state region Z1 and a smaller, brighter central region Z2. The four primary light sources 112 in the center have a significant risk of overheating. However, due to the large distance of sensors 121, 122, 123, and 124 from this central region, the temperature values ​​T1, T2, T3, and T4 are very similar to those in the previous example due to a lack of sensitivity. To determine the temperature of the central region, it is therefore advantageous to compare the image data of region Z2 with the image data of region Z1. Since it is known that image I2, not image I1, is projected, the image data allows control unit 130 to remove the ambiguity caused by individually considering the obtained temperature profiles and to determine to add an increment ΔT2 greater than ΔT1 to the temperature obtained by the sensors, thereby conveying a true estimate of the hottest temperature of the pixelated light source 110. Using only the temperature values, even though the four central pixels may experience significantly greater heating and therefore have a more significant risk of thermal runaway, it is impossible to compare the hot spot of this example with... Figure 3 The hotspots in the examples are distinguished. More accurate estimation allows the control unit 130 to react differently in a more subtle way in the two examples shown in projections I1 and I2.

[0057] Figure 4 Another example is shown. The projected photometric image I3 includes a closed area located in the upper left quadrant. In this example, the temperature value T1 will be significantly higher than temperatures T2, T3, and T4. Therefore, considered alone, the temperature profile transmitted by the sensor will allow for the assessment of the hotspot location in the area directly adjacent to sensor 121: this area is the upper left quadrant of the pixel matrix array 110. Alternatively, considering the image data I3 allows for finer estimation of this location. In the case shown, the temperature value T1 increases in small increments or even zero increments to achieve accurate hotspot estimation. Specifically, a basic light source prone to overheating is located near one of the available temperature sensors.

[0058] Therefore, after estimating the location of the hot spot in the pixelated light source 110, the control unit is configured to determine an estimate of the temperature value T of the hot spot based on the estimated location and preferably based on the projected image data I1, I2, I3. Furthermore, the control unit 130 is configured to determine, based on the delivered first power supply voltage level and the corresponding estimated temperature T of the hot spot in the pixelated light source, whether it is necessary to reduce the current amplitude in the pixelated light source to prevent thermal runaway.

[0059] For example, if the estimated temperature T of the hot spot exceeds a predetermined threshold, the first voltage level is reduced to a lower second voltage level. This reduces the amplitude of the maximum or peak current through the pixel 121 of the pixelated light source 110, thereby preventing overheating of the corresponding semiconductor junction.

[0060] According to a preferred embodiment of the present invention, the control unit 130 includes a memory element 132 (such as...). Figure 2 (As shown) or has write access to memory element 132, in which reference data about the pixelated light source 110 is stored. This data may be provided, for example, during the production or assembly of the light-emitting module.

[0061] Figure 5 A non-limiting example of reference data is shown, which can be used by a control unit to perform step v of a control method according to a preferred embodiment of the invention. This relates to data characterizing the electrothermal behavior of pixels in a pixelated light source.

[0062] In the example shown, exceeding the threshold current amplitude set at 35mA risks permanent failure of the pixels in the pixelated light source. Therefore, the control unit ensures that this threshold is not exceeded over extended periods. For an operating temperature range, such as from -40°C to 150°C, reference data provides curves relating the drive voltage (in volts) to the amplitude of the generated current (in amperes). It should be clear that the threshold temperature compared by the control unit with the temperature indication T can depend on the value of the first voltage initially supplied to the pixelated light source, which is the original value of the estimated temperature T of the hotspots in the matrix array. For example, at a voltage of 3.2V, the maximum current amplitude is reached at temperature Te, as shown by the intersection of curve Te and the upper limit of the threshold current I. If the estimated hotspot temperature T obtained by this method is higher than Te, and the supplied first drive voltage level is higher than 3.2V, the control unit commands a second drive voltage level lower than 3.2V to be supplied to the drive unit. Conversely, at an initial supply voltage of 3V, the operating temperature Te of the hotspots may rise to 150°C before the control unit commands a reduction in the drive voltage. Continuous application of this method allows for dynamic temperature control without the risk of thermal runaway. Therefore, the threshold compared to the estimated temperature T of the hotspot depends on the first voltage level supplied. The second voltage level is selected such that the maximum current through the pixels of the pixelated light source does not exceed a predetermined maximum threshold amplitude (e.g., 35 mA).

[0063] In an alternative embodiment, the voltage level Vout can be maintained at a first level, and to reduce the average amplitude of the current flowing through the primary light source, the PWM signal controlling these average current amplitudes can be adjusted by reducing the duty cycle of the PWM signal by a predetermined factor, which is preferably the same for all primary light sources. Adaptive combinations of voltage control and the PWM signal are also conceivable without departing from the scope of the invention.

[0064] Figure 6 An embodiment of a light-emitting component 200 for a motor vehicle according to a second embodiment is shown. This embodiment enables performance when the pixelated light source is controlled by current. Figure 3-5 The adjustments are explained in the context of examples.

[0065] The system shown includes a control unit 230 for a pixelated light source 210. The pixelated light source includes a plurality of basic light sources 212 arranged in a matrix array. The control unit may include, for example, a drive circuit that controls the power supply to the pixelated light source 210 via an electrical connection.

[0066] The pixelated light source 210 is supplied with current and may comprise hundreds or thousands of pixels 212. The light intensity emitted by each pixel depends on the amplitude of the current passing through them. Each pixel 212 is associated with a power supply dedicated to it. These power supplies are integrated into the pixelated light source 210. Upon receiving a current command Iout(212) for a pixel 212, the power supply associated with that pixel 212 is able to deliver a current of the corresponding amplitude to that pixel. Pixels can also be controlled via a periodic on / off signal PWM, as described above: at a constant nominal current, the modulation of the signal PWM allows the average amplitude of the current passing through the pixel to be applied. The control unit 230 has access to image data I1 corresponding to at least one digital image (also referred to as a photometric image). The photometric image can be stored in a memory element that the control unit has read access to. After receiving a signal from the central control unit of the vehicle, the control unit then selects a suitable photometric image from among a plurality of available photometric images. The control unit 230 can also be configured to generate a photometric image according to instructions received on a data bus (not shown) inside the vehicle. Alternatively, the control unit 230 may receive image data I1 on a data bus such as a CAN-type data bus (CAN stands for Automotive Local Area Network). The control unit 230 preferably includes a computing device configured to convert the received image data I1 for each pixel of the image into a current value Iout(212) grouped together in a control signal Iout for each pixel 212 and a PWM signal required for the pixelated light source 210 and the primary light source 112, such that a beam of light conforming to the data I1 is projected.

[0067] Although high luminance leads to more heating of the corresponding primary light source, the exact amount of heat the primary light source 112 will generate cannot usually be accurately predicted based solely on data from the projected image I1. This is due to parasitic heating caused by adjacent light sources, light source defects resulting from the manufacturing processes of the respective light sources, previous projections that may leave residual heat in multiple primary light sources, and so on.

[0068] Preferably, the pixelated light source 210 includes a plurality of temperature sensors 221, 222, 223, and 224 physically located near the semiconductor junction. Figure 6In the example, there are four sensors, but the invention is not limited to this example. For example, this could be a problem with thermistors or other temperature sensors known in the art, or advantageously, PTAT sensors (PTAT stands for proportional to absolute temperature). The matrix array close to the basic light source allows the sensors to provide a true indication of the operating temperature of the pixel region of the pixelated light source 210 when the pixelated light source 210 is powered. According to a preferred embodiment, multiple temperature sensors can be integrated into the substrate of the light source, and multiple temperature indications corresponding to multiple regions or multiple pixels can be transmitted to the control unit 230 in the form of electrical signals T1, T2, T3, T4, thereby forming a temperature profile PT1 corresponding to the projection of image data I1.

[0069] The transmitted temperature profile PT1 does not allow access to the exact temperature values ​​of all the primary light sources. Therefore, in step iii of the proposed method, the location of the hotspot is estimated by the control unit. In the given example, the central region of image data I1 is switched on. Therefore, the primary light source corresponding to the center of the pixelated light source 210 has the greatest risk of heating up during the projection of image I1. This region is far from all the temperature sensors 121, 122, 123, 124, the locations of which are known. Therefore, in this example, the indicators T1, T2, T3, T4 may be similar or analogous. In contrast, this uniform temperature profile allows the estimation that the hotspot is located in the central region of the matrix array.

[0070] However, none of these values ​​correspond to the exact temperature of the central region. To estimate the temperature of the central region, the control unit 230 may, for example, resort to a database containing predetermined temperature curves associated with predetermined photometric images I1, I2, ... IN and their corresponding highest temperatures. These data may be obtained in advance through simulation or by measurement using a thermal imager of the basic light source when the corresponding photometric image is projected by the basic light source. Specifically, with respect to the projected image I1, the control unit can thus determine the temperature, or the temperature increment that must be added to the value of the obtained temperature curve PT1, by comparing the temperature curve PT1 with the curve in the database to obtain a true indication of the temperature in the activated central region. In the provided example, for the region furthest from sensors 221, 222, 223, 224 (sensors 221, 222, 223, 224 are at the corners of pixel matrix array 110), the value of the increment ΔT1 may include between 15°C and 30°C, for example, 25°C. For example, the estimated temperature T is given by T2 + ΔT1°.

[0071] The incremental or temperature values ​​stored in the database (which depend on the location of the identified hot spot) can optionally be adjusted based on the operating time of the temperature sensor to account for measurement errors due to variations in sensor sensitivity, which typically degrades over operating time.

[0072] After estimating the location of the hot spot in the pixelated light source 210, the control unit 230 is configured to determine an estimate of the temperature value T of the hot spot based on the estimated location, and preferably based on the projected image data I1. Furthermore, the control unit 230 is configured to determine whether it is necessary to reduce the current amplitude in the pixelated light source to prevent overheating, based on the first current amplitude delivered to the region including the hot spot location of the light source 210, and based on the corresponding estimated temperature T of the hot spot in the pixelated light source.

[0073] For example, if the estimated temperature T of the hot spot exceeds a predetermined threshold, the first current level is therefore reduced to a lower second current level. This reduces the amplitude of the maximum or peak current through the pixel corresponding to the hot spot 221 of the pixelated light source 210, thereby preventing overheating of the corresponding semiconductor junction.

[0074] A reduced-amplitude current is applied via command Iout, which includes a current amplitude setpoint Iout(212) for a specific basic light source 212, or a group of basic light sources (preferably including the location of the identified hot spot), or all basic light sources 212 of a pixelated light source.

[0075] In an alternative embodiment, the voltage level Iout can be maintained at a first level, and to reduce the average amplitude of the current flowing through the primary light source, the PWM signal controlling these average current amplitudes can be adjusted by reducing the duty cycle of the PWM signal by a predetermined factor. Adaptive combinations of peak current control and the PWM signal are also conceivable without departing from the scope of the invention.

[0076] Needless to say, the described embodiments do not limit the scope of protection of the present invention. Other embodiments can be considered using the above description without departing from the scope of the present invention.

[0077] 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 basic light sources (112, 212) based on electroluminescent semiconductor components, said method comprising at least the following steps: i. The pixelated light source is controlled by a control unit (130, 230) to project a beam of light corresponding to image data (I1, I2, I3) by driving each basic light source with a control signal, the control signal determining a first average amplitude of the current passing through the basic light source; ii. Obtain the temperature profile (PT1) of the pixelated light source using multiple temperature sensors (121, 122, 123, 124; 221, 222, 223, 224) placed at predetermined locations; iii. The control unit estimates the location of the hotspot of the pixelated light source based on the image data (I1) and the obtained temperature curve (PT1); iv. The control unit estimates the temperature value of the hot spot based on the obtained temperature curve and the estimated position of the hot spot relative to the temperature sensor; v. If the estimated temperature value is higher than a predetermined threshold temperature value, the control unit (130, 230) changes the command transmitted to the pixelated light source (110, 210) so that at least one group of basic light sources (112, 212) including the basic light source located at the estimated position of the hot spot passes through a current with a second average amplitude, which is lower than the first average amplitude. Step iii, which involves estimating the location of hotspots, includes searching for a obtained temperature curve (PT1) among multiple pre-recorded temperature curves stored in a memory element. Each curve is associated with specific image data (I1, I2, I3) and the location of a hotspot associated with these data.

2. The control method according to claim 1, characterized by, Step iv, which estimates the temperature value of the hot spot, includes the step of increasing at least one of the temperature values ​​(T1, T2, T3, T4) of the obtained temperature curve (PT1) using a predetermined increment, the predetermined increment depending on the estimated location of the hot spot.

3. The control method according to claim 2, characterized by, Step iv, which estimates the temperature value, also includes taking into account the specular value of the pixel corresponding to the basic thermal light source (112), which depends on the image data (I1, I2, I3).

4. The control method according to any one of claims 1 to 3, characterized by, The pixelated light source (110) is used to be voltage controlled, wherein the command for determining a first average amplitude of the current through each basic light source includes a first voltage level (Vout), and wherein the step v of changing the command includes the step of supplying a second voltage level lower than the first voltage level (Vout) to the pixelated light source (110) if the estimated temperature value is higher than a predetermined threshold temperature value.

5. The control method according to claim 4, characterized by Step v of changing the command includes a previous step of comparing the estimated temperature value with a predetermined threshold temperature value, which depends on the first voltage level delivered.

6. The control method according to claim 4, characterized in that, The method includes a preparatory step of making reference data related to the pixelated light source (110) available in a memory element (132), the data relating a drive voltage value to a corresponding supply current amplitude for a series of operating temperatures of the pixelated light source, and wherein the step of changing the command includes selecting a second voltage level based on an estimated temperature value in order to comply with a predetermined threshold current amplitude.

7. The control method according to any one of claims 1 to 3, characterized in that, The pixelated light source (210) is used to be controlled by current, wherein the command to determine a first average amplitude of the current through each basic light source includes a first current amplitude of each basic light source, and wherein the step v of changing the command includes the step of supplying a second average amplitude lower than the first average amplitude to at least one group of basic light sources of the pixelated light source (210) if the estimated temperature value is higher than a predetermined threshold temperature value.

8. The control method according to any one of claims 1 to 3, characterized in that, The step of changing the command includes driving each basic light source (112, 212) with a DC current modulated pulse width modulation (PWM) signal if the estimated temperature value is higher than a predetermined threshold temperature value, the DC current modulated pulse width modulation signal determining a second average amplitude of the current passing through the basic light source, the second average amplitude being lower than the first average amplitude.

9. A light-emitting component (100, 200) for a motor vehicle, the light-emitting component comprising a pixelated light source (110, 210) having a plurality of basic light sources (112, 212) based on electroluminescent semiconductor components, a plurality of temperature sensors (121, 122, 123, 124; 221, 222, 223, 224) for transmitting a temperature curve (PT1) of the pixelated light source when the pixelated light source projects image data (I1, I2, I3), and a control unit (130, 230), characterized in that, The control unit is configured to control the pixelated light source based on an estimated temperature value of a hotspot of the pixelated light source, the estimated temperature value depending on the estimated location of the hotspot and the image data. The control unit (130, 230) is configured to perform the steps according to any one of claims 1 to 8.

10. The light-emitting component according to claim 9, characterized in that, The component includes a memory element functionally connected to the control unit and includes pre-recorded reference data related to the pixelated light source.

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