Light emitting devices for motor vehicles

Abstract

The invention proposes a light-emitting device including a converter intended to supply power to a pixelated light source controlled by a current. The proposed device makes it possible to reduce the power losses and the risk of overheating the element light sources of the pixelated light source. By using a control loop and measuring means capable of measuring, directly or indirectly, a value representative of the voltage drop at the terminals of at least one current source of the pixelated light source, it is possible to dynamically adapt the voltage supplied by the converter circuit.

Description

[Technical field]

[0001] The present invention relates to the field of automotive lighting systems, and in particular to such systems that use pixelated light sources controlled by current. [Background technology]

[0002] A light-emitting diode (LED) is a semiconductor electronic component capable of emitting light of a given wavelength when a voltage at least equal to a threshold value is applied to its terminals. Above this threshold, called the forward voltage, the intensity of the luminous flux emitted by the LED generally increases proportionally to the average intensity of the supply current. LED components are advantageous in the field of light-emitting modules for motor vehicles due to their small size and low power consumption. For example, LED light sources can be used to produce specific optical features by arranging the components along a given outline. The use of LED components also makes it easier to manufacture lights with multiple light-emitting functions.

[0003] It is also known to use pixelated light sources by various kinds of technologies to project these light beams based on image data. This is the case, for example, in monolithic technology, where a number of light emitting diode (LED) device sources, corresponding to pixels, are etched into a common semiconductor substrate. The substrate may further include built-in electronic components, such as switching circuits or others. While controlled by current, the intensity of the current passing through a given device source is adjusted by a current source coupled to that device source. Thus, the light intensity emitted by each of the pixels can be adjusted to project image data.

[0004] Pixelated light sources can be used to perform complex functions such as the "High Beam" (HB) function, or ADB (Adaptive Driving Beam) or others. The corresponding images, or photometry, can vary greatly in the degree of brightness and uniformity of emission. If the entire array emits light, the current draw of the pixelated source will be very large, whereas for example in the case of the low beam (LB) function, about half the pixels remain dark and therefore the current draw is divided by two.

[0005] In known methods, the converter circuit responsible for supplying power to such pixelated light sources controlled by current is statically configured to supply a constant voltage, allowing the pixelated light sources to operate at the maximum current draw (i.e. all element sources combined). This voltage level must also be high enough so that the voltage supplied to the pixelated light sources is at an adequate level even after the voltage drop due to the impedance presented by the longest connection harness between the converter and the pixelated light sources. Thus, in all cases requiring a lower current draw, for example during the operation of the LB, or in all cases where the length of the connection harness is shorter and therefore has a smaller impedance involved in a lower voltage drop, the constant voltage supplied by the converter circuit will be too high, over-excessive for the actual needs of the system. This leads to power losses in the current sources, which dissipate the excess power in the form of heat. However, semiconductor element sources, which have very fine dimensions and are in close proximity to the current sources in question, are very sensitive to overheating and can be irreversibly damaged in the event of excessive heat.

[0006] The object of the present invention is to alleviate at least one of the problems presented by the prior art, more specifically, to propose a light-emitting device including a converter intended to supply power to a pixelated light source controlled by a current, making it possible to reduce the power losses and the risk of overheating the element light sources of the pixelated light source.

[0007] According to a first aspect of the invention, a light emitting device for a motor vehicle is proposed. The device comprises a pixelated light source intended to be controlled by a current, the pixelated light source comprising a number of light emitting semiconductor elements and a number of current sources, each current source being coupled to one of the light emitting semiconductor elements. The device also comprises a controlled converter circuit connected to the pixelated light source for supplying electricity to the pixelated light source. The device further comprises control means connecting the pixelated light source to a control input of the converter circuit, the control means being configured to provide a control signal indicative of a voltage drop at at least one terminal of the current sources.

[0008] Preferably, the converter circuit may be configured, based on said control signal, to supply a voltage of such a value that, after subtracting a voltage drop due to a connection between the converter circuit and the pixelated light source, and after subtracting a forward voltage of at least one light emitting semiconductor element coupled to at least one current source comprised in the control means, the voltage drop at their terminals is within a predetermined value range.

[0009] The control means may preferably include a measurement means.

[0010] The measuring means may preferably include a comparator element arranged to measure the voltage drop across at least one terminal of the current source.

[0011] Preferably, the measuring means may include a comparator element configured to measure the voltage supplied to the pixelated light source, and at least one temperature sensor coupled to the plurality of light emitting semiconductor elements, as well as a memory element containing data defining a relationship between the measured temperature and current on the one hand and the forward voltage on the other hand.

[0012] Preferably, the control means may include circuitry arranged to generate a control signal indicative of a voltage drop across at least one terminal of the current source based on a quantity measured by the measurement means.

[0013] The control means may preferably be connected to the converter circuit by a data bus of the motor vehicle, which may preferably be the case of a CAN (Car Area Network) data bus. The use of a communication bus makes it possible to provide the control signals over any distance without disturbing the values ​​received at the control inputs (electrostatic, electromagnetic interference).

[0014] Preferably, the control means may be arranged to successively provide control signals indicative of the voltage drops at the terminals of the various current sources. Particularly suitable for carrying out this transmission is the use of a communication bus.

[0015] The predetermined range of values ​​may preferably have a span of up to 0.5V and include a lower limit substantially equal to the headroom value of at least one current source.

[0016] Preferably, the pixelated light source may include a monolithic pixel array, with each pixel representing a light emitting semiconductor device.

[0017] The electrical connections connecting the converter circuit to the pixelated light source may preferably include a resistive element that introduces a non-negligible voltage drop between the converter circuit and the pixelated light source.

[0018] Preferably, the converter circuit may include a voltage step-down circuit, a voltage step-up circuit, or a combination of these two types of circuits.

[0019] By using the means proposed by the invention, it is possible to propose a light-emitting device including a converter intended to supply power to a pixelated light source controlled by a current, which allows to reduce the power losses and the risk of overheating the element light sources of the pixelated light source. By using a control loop and a measuring means capable of measuring, directly or indirectly, a value representative of the voltage drop at the terminals of at least one current source of the pixelated light source, it is possible to dynamically adapt the voltage provided by the converter circuit. This control results in a headroom voltage at the terminals of the current source being maintained without being too high, which would contribute to power losses and overheating of the light source. This control is independent of the connection impedance and length between the converter circuit and the pixelated light source, and adapts the current draw that varies according to the photometry projected by the light-emitting device.

[0020] Other features and advantages of the invention will become better understood from the description of the examples and drawings. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of a light-emitting device according to one preferred embodiment of the present invention.

[0022] [Diagram 2] 1 is a schematic diagram of a light-emitting device according to one preferred embodiment of the present invention.

[0023] [Diagram 3] 1 is a schematic diagram of a light-emitting device according to one preferred embodiment of the present invention.

[0024] Unless otherwise specified, technical features described in detail in relation to one given embodiment may be combined with technical features described in relation to other embodiments, which are described by way of example and not of limitation.

[0025] This specification focuses on the elements of the light emitting device for automotive vehicles that are necessary to understand the present invention. Other elements that form part of such devices in a known manner are not mentioned or described in detail. For example, the presence of a carrier or heat dissipation elements is implied in order to operate such devices.

[0026] FIG. 1 shows a lighting device 100 for a motor vehicle according to a first embodiment. The device comprises a converter circuit 120. Voltage step-down converter circuits, e.g. buck converter circuits, and voltage step-up converter circuits, e.g. boost converter circuits, are known per se in the art and their operation will not be described in detail in connection with the present invention. The invention is not limited to a particular converter architecture. The converter circuit 120 is in particular capable of converting a voltage supplied to its input (not shown) into an output voltage Vout having a value different from the input voltage. The output voltage may be higher or lower than the input voltage according to the chosen architecture. Such circuits are commonly used in connection with powering light sources including, for example, light emitting diodes (LEDs). In particular, such light sources need to be supplied with a voltage level at least equal to the value of their forward voltage, which may be different from the available voltage supplied, for example, from the battery of the motor vehicle. The converter comprises an additional input 122 intended in particular to receive a control voltage value so as to be able to regulate the voltage supplied across its supply output terminals. One of the output terminals usually corresponds to ground potential. The device also includes a pixelated light source 110, which may, for example, include a monolithic array element. The light source 110 is controlled by current and is connected to the converter circuit by electrical connections. These electrical connections present an impedance that depends, inter alia, on their length and cross-sectional area, so that the voltage Vled supplied to the light source 110 is lower than the output voltage Vout of the converter circuit.

[0027] The pixelated light source 110 typically includes a number of light-emitting semiconductor elements, such as light-emitting diodes 112. Each of these elements 112 is coupled to a dedicated current source 114. A photometric setting (not shown) provided to the pixelated light source 110 causes the pixelated light source 110 to apply a current of appropriate intensity to each pixel generated by the elements 112 and the current source 114. Each pixel thus emits a brightness that matches the photometric setting. For a given extraction current, the forward voltage Vf at the terminals of the light-emitting diode corresponds to a given value, which is an intrinsic property of the diode. The forward voltage generally depends on the temperature of the semiconductor junction. To operate correctly, the current source 114 requires a constant headroom voltage Vh across its terminals of a given value, typically around 0.5V. If Vled is much higher than Vf, the residual potential difference Vh will be high, which will cause heat losses.

[0028] In the example of Fig. 1, measuring means are connected to the converter circuit, capable of measuring a value representative of this potential difference Vh, for example by a control loop generated by a data connection. The control means 130 thus allows the converter circuit to lower Vout if the control value represents a value of Vh higher than the headroom voltage required for the current source 114. If Vh approaches a lower limit, Vout can be increased. This allows to avoid power losses while at the same time controlling each element light source 112 with a current. The maximum value of several voltage drops measured at the terminals of several current sources 114 coupled to several semiconductor elements 112 can also serve as the control value, without departing from the scope of the invention. Indirectly, this architecture also allows to take into account the voltage drop between the converter circuit 120 and the light source 110.

[0029] Fig. 2 shows a diagram of a pixelated light source 210 and control means 230 according to a second preferred embodiment. Part of the converter circuit remains unchanged with respect to the above-mentioned embodiment and is not shown. A number of sets formed by connecting in series the luminescent light sources 212 and the current sources 214 coupled thereto are connected in parallel. The measuring means 232 comprises an analog-to-digital converter circuit referenced to ground potential, so that the value 234 of the voltage drop at at least one terminal of the current sources 214 can be directly fed to the control input of the converter circuit.

[0030] Fig. 3 shows a diagram of a pixelated light source 310 and control means 330 according to a third preferred embodiment. Part of the converter circuit remains unchanged with respect to the above-mentioned embodiment and is not shown. A number of sets formed by connecting the light-emitting light sources 312 and the current sources 314 coupled thereto in series are connected in parallel. Groups 316 of such sets are thermally coupled due to their physical proximity. The measuring means comprises at least for each group 316 at least one temperature sensor 332 capable of providing an indication of the junction temperature of the light sources 312 of the group in question. This sensor can be made for example by a thermistor, without restricting the invention to this example. Knowing the temperature and the drawn current of a given light-emitting diode 312 makes it possible to deduce therefrom the forward voltage Vf at the terminals of the light-emitting diode. To this end, data for calibrating the light-emitting diodes are pre-provided in a memory element 336, for example in tabular form. Thus, for example by measuring the voltage Vled provided by the analog-to-digital converter circuit 332', a processing circuit, not shown, has access to estimates of the voltages Vled and Vf, allowing indirectly to deduce the voltage drop Vh at the terminals of the current source 314. This estimate of Vh is relayed as a control signal to a control input of the converter circuit. Alternatively, the control signal may include an estimate of the temperature, an estimate of the voltage Vled and / or an estimate of Vf. Processing of these quantities in the converter circuit by corresponding processor circuits allows to recover an estimate of the voltage drop Vh. Once an estimate of Vh has been obtained, the control described in the previous embodiment can be carried out.

[0031] In an alternative embodiment not shown, the pixelated light source includes a diagnostic circuit capable of diagnosing, periodically or continuously, the forward voltage value Vf for each element light source individually. If Vf is close to 0V, the corresponding pixel is diagnosed as being in a short-circuited state. If Vf is close to Vled, the pixel is open. If the measured forward voltage Vf is within the range of acceptable and functional values, this measurement may be used to infer therefrom the voltage drop at the terminals of the current source coupled to the diagnosed pixel, as in the previous embodiment, by using the relationship Vh=Vled-Vf. This arrangement allows Vh to be continuously evaluated for all element light sources.

[0032] Needless to say, the described embodiments do not limit the scope of protection of the present invention. In particular, more complex and more accurate measurement methods, including, for example, more temperature and / or voltage sensors, can be implemented to produce the measurement means just described, without departing from the scope of the present invention. By taking advantage of the description just provided, other embodiments can be envisaged, without departing from the scope of the present invention.

[0033] The scope of protection is determined by the claims.

Claims

1. a pixelated light source (110, 210, 310) intended to be controlled by a current, the pixelated light source (110, 210, 310) comprising a plurality of light emitting semiconductor elements (112, 212, 312) and a plurality of current sources (114, 214, 314), each current source being coupled to one of the light emitting semiconductor elements; a controlled converter circuit (120) connected to said pixelated light source for supplying electricity to said pixelated light source; and a control means (130, 230, 330) for connecting the pixelated light source to a control input (122) of the converter circuit, the control means (130, 230, 330) being configured to provide a control signal (134, 234) indicative of a voltage drop across at least one terminal of the current source (114, 214, 314).

2. 2. The light-emitting device according to claim 1, characterized in that the converter circuit (120) is configured, based on the control signal (134, 234), to supply a voltage Vout of such a value that, after subtracting a voltage drop due to a connection between the converter circuit and the pixelated light source and after subtracting a forward voltage Vf of the at least one light-emitting semiconductor element (112, 212, 312) coupled to the at least one current source (114, 214, 314) comprised in the control means (130, 230, 330), the voltage drop at the terminals thereof is within a predetermined value range.

3. A light-emitting device according to any one of the preceding claims, characterized in that the control means (130, 230, 330) comprise measuring means (132, 232, 332).

4. 4. A light emitting device according to claim 3, characterized in that the measuring means (232) comprise an analog-to-digital converter element configured to measure a voltage drop across at least one terminal of the current source (214).

5. 4. The light emitting device according to claim 3, characterized in that the measuring means comprises an analog-to-digital converter element (332') configured to measure a voltage Vled supplied to the pixelated light source (310), and at least one temperature sensor (332) coupled to a plurality of light emitting semiconductor elements (312), as well as a memory element containing data (336) defining a relationship between the measured temperature and current, on the one hand, and a forward voltage Vf, on the other hand.

6. A light-emitting device according to any one of claims 3 to 5, characterized in that the control means (130, 230, 330) includes a circuit configured to generate the control signal indicative of a voltage drop at at least one terminal of the current source based on a quantity measured by the measurement means (132, 232, 332, 332').

7. A light emitting device according to any one of the preceding claims, characterized in that the control means (130, 230, 330) are connected to the converter circuit (120) by a data bus of the motor vehicle.

8. A light-emitting device according to any one of the preceding claims, characterized in that the control means are arranged to successively provide control signals indicative of the voltage drops at the terminals of the various current sources.

9. A light emitting device according to claim 2 or, if dependent on claim 2, any one of claims 3 to 8, characterized in that the predetermined range of values ​​has a span of up to 0.5 V and includes a lower limit value substantially equal to a headroom value Vh of the at least one current source (114, 214, 314).

10. A light emitting device according to any one of the preceding claims, characterized in that the pixelated light source (110, 210, 310) comprises a monolithic pixel array, each pixel representing a light emitting semiconductor element (112, 212, 312).

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