Voltage-controlled matrix light source with diagnostic circuit for a motor vehicle

Abstract

A matrix light source intended to be supplied with a voltage and having a plurality of electroluminescent semiconductor element-based elementary light sources and a common substrate in contact with an integrated circuit. The integrated circuit includes, for each elementary light source, a switching device for selectively connecting it to a voltage source on the basis of a first control signal. The substrate includes, for at least one of the elementary light sources, an open-circuit fault detection circuit for detecting an open-circuit fault with the elementary light source.

Claims

1. A matrix light source intended to be supplied with a voltage and comprising an integrated circuit and a matrix array of electroluminescent semiconductor element-based elementary light sources, wherein the integrated circuit is in contact with the matrix array and comprises, for each elementary light source, a switching device for selectively connecting a respective elementary light source to a voltage source on the basis of a first control signal, wherein the integrated circuit comprises, for at least one of the elementary light sources, an open-circuit fault detection circuit for detecting an open-circuit fault with the elementary light source, wherein said open-circuit fault detection circuit comprises a load connected in parallel with the switching device, such that an electric current of non-negligible intensity flows through the load if the matrix source is supplied with electricity, unless the elementary light source has an open-circuit fault.

2. The matrix light source as claimed in claim 1, wherein the open-circuit fault detection circuit is configured so as to generate binary information on the detection of an open-circuit fault with said elementary light source.

3. The matrix light source as claimed in claim 2, wherein the open-circuit fault detection circuit comprises a memory element, the open-circuit fault detection circuit being configured so as to store the detection information in said memory element.

4. The matrix light source as claimed in claim 1, wherein said open-circuit fault detection circuit comprises a comparison unit, configured so as to compare the voltage drop across the terminals of said load to a predetermined threshold value.

5. The matrix light source as claimed in claim 1, wherein said load comprises a resistor connected in parallel with the switching device.

6. The matrix light source as claimed in claim 1, wherein said load comprises a transistor controlled by a second control signal, the transistor representing a non-negligible resistance when it is in the closed state, and wherein the open-circuit fault detection circuit comprises a control unit for generating said second control signal.

7. The matrix light source as claimed in claim 6, wherein the second control signal depends on the first control signal.

8. The matrix light source as claimed in claim 1, wherein the integrated circuit comprises a respective open-circuit fault detection circuit for each of the elementary light sources.

9. The matrix light source as claimed in claim 1, wherein the elementary light sources are arranged in at least two branches of parallel sources.

10. A lighting module for a motor vehicle, comprising a matrix light source and a circuit for driving the supply of electric power to said matrix light source, wherein the matrix light source is as claimed in claim 1.

11. A method for detecting an open-circuit fault with a matrix light source, wherein the method comprises the following steps: supplying a voltage to the matrix light source, the matrix light source comprising an integrated circuit and a matrix array of electroluminescent semiconductor element-based elementary light sources, wherein the integrated circuit is in contact with the matrix array and comprises, for each elementary light source, a switching device for selectively connecting a respective elementary light source to a voltage source on the basis of a first control signal; by way of a control device for the matrix light source, generating at least a first signal for controlling the state of the switching device so as to selectively connect at least one elementary light source of the matrix light source to the voltage source; when said elementary light source is not connected to the voltage source by way of its switching device, comparing the voltage drop across the terminals of a load connected in parallel with the switching device to a predetermined threshold voltage; and detecting the presence of an open-circuit fault with said elementary light source on the basis of the result of this comparison, wherein an electric current of non-negligible intensity flows through the load if the matrix source is supplied with electricity, unless the elementary light source has an open-circuit fault.

12. The matrix light source as claimed in claim 2, wherein said open-circuit fault detection circuit comprises a comparison unit, configured so as to compare the voltage drop across the terminals of said load to a predetermined threshold value.

13. The matrix light source as claimed in claim 12, wherein said load comprises a resistor connected in parallel with the switching device.

14. The matrix light source as claimed in claim 13, wherein said load comprises a transistor controlled by a second control signal, the transistor representing a non-negligible resistance when it is in the closed state, and wherein the open-circuit fault detection circuit comprises a control unit for generating said second control signal.

15. The matrix light source as claimed in claim 14, wherein the second control signal depends on the first control signal.

16. The matrix light source as claimed in claim 2, wherein the integrated circuit comprises a respective open-circuit fault detection circuit for each of the elementary light sources.

17. The matrix light source as claimed in claim 2, wherein the elementary light sources are arranged in at least two branches of parallel sources.

18. A matrix lighting module for a motor vehicle, comprising a matrix light source and a circuit for driving the supply of electric power to said matrix light source, wherein the matrix light source is as claimed in claim 2.

Description

(1) Other features and advantages of the present invention will be better understood with the aid of the description of the examples and of the drawings, in which:

(2) FIG. 1 schematically shows a matrix light source according to one preferred embodiment of the invention;

(3) FIG. 2 schematically shows a matrix light source according to one preferred embodiment of the invention;

(4) FIG. 3 schematically shows a matrix light source according to one preferred embodiment of the invention;

(5) FIG. 4 schematically shows a matrix light source according to one preferred embodiment of the invention;

(6) FIG. 5 schematically shows a matrix light source according to one preferred embodiment of the invention.

(7) Unless specified otherwise, technical features that are described in detail for one given embodiment may be combined with the technical features that are described in the context of other embodiments described by way of example and without limitation. Similar reference numerals will be used to describe similar concepts across various embodiments of the invention. For example, the references 100, 200, 300, 400 and 500 denote five embodiments of a matrix light source according to the invention.

(8) The illustration in FIG. 1 shows a pixelated light source or matrix light source 100 according to one preferred embodiment of the invention. The matrix light source 100 is intended to be voltage-driven and comprises a plurality of electroluminescent semiconductor element-based elementary light sources 110 and a common substrate, not illustrated, in mechanical and electrical contact with and functionally connected to an integrated circuit 120. The elementary light sources are typically light-emitting diodes (LEDs).

(9) The matrix light source 100 preferably comprises a monolithic matrix array component, in which the semiconductor layers of the elementary light sources 110 are for example arranged on the common substrate. The matrix array of elementary light sources 110 preferably comprises a parallel assembly of a plurality of branches, each branch comprising electroluminescent semiconductor light sources 110.

(10) By way of example and without limitation, the matrix array of elementary light sources comprises, along the thickness of the substrate and starting at the end opposite the location of the elementary sources 110, a first electrically conductive layer deposited on an electrically insulating substrate. This is followed by an n-doped semiconductor layer whose thickness is between 0.1 and 2 μm. This thickness is much smaller than that of known light-emitting diodes, for which the corresponding layer has a thickness of the order of 1 to 2 μm. The following layer is the active quantum well layer having a thickness of around 30 nm, followed by an electron-blocking layer, and finally a p-doped semiconductor layer, the latter having a thickness of around 300 nm. Preferably, the first layer is an (Al)GaN:Si layer, the second layer is an n-GaN:Si layer, and the active layer comprises quantum wells made of InGaN alternating with barriers made of GaN. The blocking layer is preferably made of AlGaN:Mg and the p-doped layer is preferably made of p-GaN:Mg. n-doped gallium nitride has a resistivity of 0.0005 ohm/cm, whereas p-doped gallium nitride has a resistivity of 1 ohm/cm. The thicknesses of the proposed layers make it possible in particular to increase the internal series resistance of the elementary source, while at the same time significantly reducing its manufacturing time, as the n-doped layer is not as thick in comparison with known LEDs and requires a shorter deposition time. By way of example, a time of 5 hours is typically required for MOCVD depositions for a standard-configuration LED with 2μ of n layer, and this time may be reduced by 50% if the thickness of the n layer is reduced to 0.2μ.

(11) In order to achieve elementary light sources 110 having semiconductor layers having homogeneous thicknesses, the monolithic component 100 is preferably manufactured by depositing the layers homogeneously and uniformly over at least part of the surface of the substrate so as to cover it. The layers are deposited for example using a metal oxide chemical vapor deposition (MOCVD) method. Such methods and reactors for implementing them are known for depositing semiconductor layers on a substrate, for example from patent documents WO 2010/072380 A1 or WO 01/46498 A1. Details on their implementation will therefore not be described in the context of the present invention. The layers thus formed are then pixelated. By way of example and without limitation, the layers are removed using known lithographic methods and by etching at the sites that subsequently correspond to the spaces separating the elementary light sources 110 from one another on the substrate. A plurality of several tens or hundreds or thousands of pixels 110 having a surface area smaller than one square millimeter for each individual pixel, and having a total surface area greater than 2 square millimeters, having semiconductor layers with homogeneous thicknesses, and therefore having homogeneous and high internal series resistances, are thus able to be produced on the substrate of a matrix light source 100. Generally speaking, the more the size of each LED pixel decreases, the more its series resistance increases, and the more this pixel is able to be driven by a voltage source. As an alternative, the substrate comprising the epitaxial layers covering at least part of the surface of the substrate is sawn or divided into elementary light sources, each of the elementary light sources having similar characteristics in terms of their internal series resistance.

(12) The invention also relates to types of semiconductor element-based elementary light sources involving other configurations of semiconductor layers. In particular the substrates, the semiconductor materials of the layers, the layout of the layers, their thicknesses and any vias between the layers may be different from the example that has just been described, as long as the structure of the semiconductor layers is such that the internal series resistance of the elementary light source resulting therefrom is at least 1 ohm, and preferably at least 5 or 10 ohms, or else between 1 and 100 ohms.

(13) The integrated circuit 120 is preferably soldered to the substrate of the monolithic source and furthermore comprises, for at least one but preferably for all of the elementary light sources 110, an open-circuit fault detection circuit 130. The matrix light source 100 is intended to be voltage-driven by an electric power supply drive circuit 10. Such circuits are known per se in the art, and their operation will not be described in detail in the context of the present invention. They involve at least one converter circuit capable of converting an input voltage, supplied for example by a voltage source internal to a motor vehicle, such as a battery, into an output voltage, having an intensity suitable for supplying power to the matrix light source. When the matrix light source is voltage-driven, the driving of each elementary source, or equivalently, of each pixel, merely entails controlling a switching device 132 as shown schematically in FIG. 1. By controlling the state of the device 132, the elementary light source 110 may be selectively connected to the voltage source 10. The switching device is for example formed by a MOSFET field-effect transistor, preferably characterized by a low voltage drop between its drain and source terminals, and controlled by a control signal from a control unit external to the matrix light source.

(14) Preferably, not only the switch elements 132 but also a power supply circuit may be integrated into the substrate 120 when the monolithic component 100 is manufactured.

(15) The illustration in FIG. 2 shows a pixelated light source or matrix light source 200 according to another preferred embodiment of the invention. The matrix light source 200 is intended to be voltage-driven and comprises a plurality of electroluminescent semiconductor element-based elementary light sources 210 and a common substrate, not illustrated, in contact with an integrated circuit 220 to which the substrate is functionally connected. The elementary light sources are typically light-emitting diodes (LEDs).

(16) The integrated circuit 220 furthermore comprises, for at least one elementary light source 210, an open-circuit fault detection circuit 230. When the matrix light source is voltage-driven, the driving of each elementary source, or equivalently, of each pixel, merely entails controlling a switching device 232. By controlling the state of the device 232, the elementary light source 210 may be selectively connected to the voltage source 10. The switching device 232 is for example formed by a MOSFET field-effect transistor, preferably characterized by a low voltage drop between its drain and source terminals, and controlled by a control signal 12 from a control unit external to the matrix light source. FIG. 2 shows a control signal 12 intended for a plurality of elementary light sources 210. However, it goes without saying that the invention extends to the case where each elementary light source 210 is controlled by a control signal 12 that is specific thereto.

(17) The open-circuit fault detection circuit 230 furthermore comprises a load 234, connected in parallel with the switching device 232. When the matrix light source is powered and the elementary light source 210 is not connected to the voltage source (switch 232 open) and an electric leakage current is flowing through the load, it may be concluded that the light source 210 does not have an open-circuit fault. If on the other hand the electric current flowing through the load 234 is of zero or negligible intensity, it should be concluded that the light source 210 has an open-circuit fault. In the latter case, a fault detection indication is recorded in a memory element 236 provided for this purpose. This makes the information, which is preferably binary information, accessible to an external entity that is designed to read the contents of the memory element 236.

(18) The illustration in FIG. 3 shows a pixelated light source or matrix light source 300 according to another preferred embodiment of the invention. The matrix light source 300 is intended to be voltage-driven and comprises a plurality of electroluminescent semiconductor element-based elementary light sources 310 and a common substrate, not illustrated, in contact with an integrated circuit 320.

(19) The integrated circuit 320 furthermore comprises, for at least one elementary light source 310, an open-circuit fault detection circuit 330. When the matrix light source is voltage-driven, the driving of each elementary source, or equivalently, of each pixel, merely entails controlling a MOSFET field-effect transistor device 332. By controlling the state of the transistor 332, the elementary light source 310 may be selectively connected to the voltage source 10. The transistor is preferably characterized by a low voltage drop between its drain and source terminals. It is and controlled by a control signal 12 from a control unit external to the matrix light source. If the transistor 232 is in the on state, the elementary light source 310 is powered and it lights up if it is not defective. If on the other hand the transistor is in its off state, the elementary light source 310 is not connected to the voltage source.

(20) The open-circuit fault detection circuit 330 furthermore comprises a load 334 comprising a resistor, for example of 700 ohms, connected in parallel with the switching device 332. When the matrix light source is powered and the elementary light source 310 is not connected to the voltage source (transistor 332 in the off state) and an electric leakage current of non-negligible intensity is flowing through the load, it may be concluded that the light source 310 does not have an open-circuit fault. If on the other hand the electric current flowing through the load 334 is of zero or negligible intensity, it should be concluded that the light source 310 has an open-circuit fault. A comparison circuit 338 compares the voltage drop across the terminals of the resistor 334 to a predetermined threshold value. The threshold value may for example be 0.7 V. If the voltage drop across the terminals of the resistor 334 is less than 0.7 V, a fault detection indication is recorded in a memory element 336 provided for this purpose. This makes the detection information, which is preferably binary information, accessible to an external entity that is designed to read the contents of the memory element 336. This embodiment solves the problem of diagnosing an open-circuit fault. However, it generates a constant current leakage.

(21) The illustration in FIG. 4 shows a pixelated light source or matrix light source 400 according to another preferred embodiment of the invention. The matrix light source 400 is intended to be voltage-driven and comprises a plurality of electroluminescent semiconductor element-based elementary light sources 410 and a common substrate 420.

(22) The substrate 420 furthermore comprises, for at least one elementary light source 410, an open-circuit fault detection circuit 430. When the matrix light source is voltage-driven, the driving of each elementary source, or equivalently, of each pixel, merely entails controlling a MOSFET field-effect transistor device 432. By controlling the state of the transistor 432, the elementary light source 410 may be selectively connected to the voltage source 10. The transistor 432 is preferably characterized by a low voltage drop between its drain and source terminals. It is controlled by a control signal 12 from a control unit external to the matrix light source.

(23) The open-circuit fault detection circuit 440 furthermore comprises a load 434 comprising a second transistor preferably characterized by a large voltage drop between its drain and source terminals, for example of the order of 0.7 V, connected in parallel with the first transistor 432. The state of the transistor 434 is controlled by a control signal 14 from, in the case illustrated by FIG. 4, a control unit external to the matrix light source. This arrangement makes it possible to put the transistor 434 only into the on state when an open-circuit fault diagnosis takes place.

(24) An open-circuit fault with the elementary light source 410 is able to be detected when the first transistor (switch) 432 is in the off state, while the second transistor (load) 434 is in the on state. In fact, the second transistor 434 may for example be put into the on state briefly before the first transistor changes to the on state. As an alternative, the second transistor 434 may be put into the on state briefly before the first transistor 432 is switched from its on state to the off state, the second transistor 434 thereafter remaining in the on state for a predetermined period of time. Other combinations may be contemplated without otherwise departing from the scope of the present invention and without creating optically perceptible effects in the luminous flux emitted by the matrix light source.

(25) When diagnosing an open-circuit fault, the comparison circuit 438 compares the voltage drop across the terminals of the load 434 to a predetermined threshold value. The threshold value may for example be 0.7 V. If the voltage drop across the terminals of the resistor 434 is less than 0.7 V, a fault detection indication is recorded in a memory element 436 provided for this purpose. This makes the detection information, which is preferably binary information, accessible to an external entity that is designed to read the contents of the memory element 436. This embodiment solves the problem of diagnosing an open-circuit fault. However, it generates a constant current leakage.

(26) FIG. 5 schematically shows another preferred embodiment of the invention, which is a variant of the embodiment that has just been described with reference to the illustration of FIG. 4.

(27) The matrix light source 500 is intended to be voltage-driven and comprises a plurality of electroluminescent semiconductor element-based elementary light sources 510 and a common substrate, not illustrated, functionally connected to an integrated circuit 520.

(28) The integrated circuit 520 furthermore comprises, for at least one elementary light source 510, an open-circuit fault detection circuit 530. When the matrix light source is voltage-driven, the driving of each elementary source, or equivalently, of each pixel, merely entails controlling a MOSFET field-effect transistor device 532. By controlling the state of the transistor 532, the elementary light source 510 may be selectively connected to the voltage source 10. The transistor 532 is preferably characterized by a low voltage drop between its drain and source terminals. It is controlled by a control signal 12 from a control unit external to the matrix light source.

(29) The open-circuit fault detection circuit 540 furthermore comprises a load 534 connected in parallel with the switching transistor 532. The load 534 comprises a second transistor and a resistor connected in series with the second transistor. The intensity of the leakage current that is able to flow in this branch is defined primarily by the value of the resistor. In fact, the second transistor, forming part of the load branch 534, may have a low voltage drop between its drain and source terminals. The state of the transistor 534 is controlled by a control signal 14 from, in the case illustrated by FIG. 5, a control unit that generates it from the control signal 12 that is intended to control the state of the switching transistor 532. The control signal 12 is generated in this example by a control unit external to the matrix light source. This arrangement makes it possible to put the second, and therefore to connect the entire load 534, only into the on state when an open-circuit fault diagnosis takes place.

(30) An open-circuit fault with the elementary light source 510 is able to be detected when the first transistor (switch) 532 is in the off state, while the second transistor (load) 534 is in the on state. In fact, the control unit having, as input, the control signal 12 that is relayed to the first switching transistor 532, and generating the control signal 14 for the second transistor of the load 534, is preferably configured so as to generate the control signal 14 such that the second transistor changes to the on state when the first transistor 532 switches to its off state. The falling edge of the binary signal 12 thus coincides with the rising edge of the binary signal 14. Electronic circuits for implementing the functionality described for the control unit are within the ability of those skilled in the art, without otherwise departing from the scope of the present invention. This control circuit is preferably integrated into the integrated circuit 520 of the matrix light source.

(31) When diagnosing an open-circuit fault, the comparison circuit 538 compares the voltage drop across the terminals of the load 534 to a predetermined threshold value. The threshold value may for example be 0.7 V. If the voltage drop across the terminals of the load 534 is less than 0.7 V, a fault detection indication is recorded in a memory element 536 provided for this purpose. This makes the detection information, which is preferably binary information, accessible to an external entity that is designed to read the contents of the memory element 536. This embodiment generates a leakage current through the load 532 only when an open-circuit fault diagnosis takes place. If this is not the case, no electrical energy is dissipated by the load.

(32) It goes without saying that the integrated circuit may comprise other electronic circuits and/or memory elements used for other functions in connection with the matrix light source and/or with the elementary light sources.

(33) The scope of protection is defined by the claims.