Device and method for controlling the power supply of light sources for a motor vehicle

Abstract

The invention relates to luminous systems for motor vehicles. The invention provides a device and method that make it possible to increase the efficiency of a converter depending on variations in its load. This is made possible through use of a synchronous-converter circuit rather than an asynchronous converter as is commonly used for automotive lighting applications.

Description

Description Title: DEVICE AND METHOD FOR CONTROLLING THE ELECTRICAL POWER SUPPLY OF LIGHT SOURCES FOR A MOTOR VEHICLE

[0001] This invention relates to the field of automotive vehicle lighting, and in particular it relates to such systems using light sources with electroluminescent semiconductor elements powered by means of a converter circuit.

[0002] A light-emitting diode, LED, is a semiconductor electronic component capable of emitting light of a predetermined wavelength when an electrical voltage at least equal to a threshold value is applied to its terminals. Beyond this threshold value, called forward voltage, the intensity of the luminous flux emitted by an LED generally increases proportionally with the average intensity of the supply electric current. Their small size and low power consumption make LED components interesting in the field of light modules for motor vehicles. LED light sources can, for example, be used to create distinctive optical signatures by placing the components along predetermined contours.The limited space available for the use of such light sources, their potentially large number to achieve interesting effects, as well as the limited electrical energy available within a closed system such as a motor vehicle, further accentuates the power losses, which result in undesirable localized heating.

[0003] It is known to power light-emitting diodes that perform a plurality of lighting functions of a motor vehicle by means of voltage step-down and / or step-up converter circuits. Thus, an input voltage, generally supplied by an internal battery of the motor vehicle, is converted into a charging voltage suitable for powering the required light sources.

[0004] In particular, a voltage boost converter (for example of the BOOST type) is often associated with at least one step-down converter (for example of the BUCK type) for example as described in fig. 6. A first voltage Vout is generated there by a voltage boost circuit 610 to power modules light sources 6010 and 6020, each comprising a voltage step-down circuit (6011, 6021) and at least one light source (6012, 6022).

[0005] The average output voltage of the step-up converter circuit corresponds to the input voltage requirements of the step-down circuits, and generally varies little or not at all. Therefore, a change in power requirement almost always corresponds to a change in current. The "load", i.e. the power requirement, therefore corresponds to an average current intensity.

[0006] It has been proposed in patent document EP 3503684 B1 to increase the efficiency of a converter as a function of variations in the input voltage supplied to the converter. While it is desirable to limit losses in such a system, it turns out in practice that the input voltage supplied by a motor vehicle battery generally remains constant and exhibits only minimal fluctuations. The impact of this solution on the efficiency of the system therefore remains limited.

[0007] The invention aims to overcome at least one of the problems posed by the prior art. More specifically, the invention aims to propose a device and a method which make it possible to increase the efficiency of a converter as a function of variations in its load.

[0008] According to a first aspect of the invention, a device for controlling the power supply of a plurality of light sources is proposed. Subsets of light sources are configured to selectively perform different light functions of a motor vehicle. The control device comprises a converter circuit controlled by a control unit. The control device is remarkable in that the converter circuit is a synchronous switching converter circuit comprising two transistors, in that the control unit is configured to provide a switching signal to the converter circuit, and in that the frequency of said switching signal is dependent on an average intensity of electric charging current to be supplied to the light sources, an indication of which is provided by an input signal and which depends on the light functions to be performed.

[0009] It is understood that the fact that the frequency is dependent on the average current intensity to be supplied means that the control device is configured to, in an initial state, receive a first indication of average non-zero load electric current intensity, and supply a corresponding first non-zero load electric current intensity, by supplying a switching signal clocked at a first frequency; and, in a subsequent state, receive a second indication of average non-zero load electric current intensity by the input signal, which is different from the first, and supply a corresponding second non-zero load electric current intensity, by supplying a switching signal clocked at a second non-zero frequency different from the first non-zero frequency.

[0010] A switching signal is a signal intended to switch the transistors of the converter. Preferably, the switching signal is periodic. Preferably, the switching signal turns on one of the two transistors while the other of the two transistors is turned off. Preferably, the signal is configured so that, when a transistor switches from the on state to the off state and / or vice versa, the converter passes through a dead point during which neither of the two transistors is on. This ensures that the transistors are never on at the same time.

[0011] The frequency of the switching signal corresponds to the repetition of cycles comprising an on state and a off state, for example it can be defined as the number of passages from an on state to a off state for one of the two transistors, over a given time period, divided by the duration of said given time period.

[0012] Preferably, the indication of an average intensity of electric charging current to be supplied to the light sources may comprise an indication of a subset of light sources to be powered. The indication may in particular comprise an indication of a light function to be performed or supplied with electricity.

[0013] The control device may preferably comprise a memory element in which a predetermined switching frequency is recorded for each average intensity of electric load current to be supplied to the light sources. The control unit is configured to read the switching frequency that corresponds to the average load electric current intensity indicated by the input signal in the memory element, in order to produce a switching signal having a corresponding frequency.

[0014] The converter circuit can preferably be operated in forced continuous conduction mode.

[0015] Preferably, the converter circuit is a voltage booster or "boost" type circuit. Alternatively, the converter circuit is a voltage booster or "buck" type circuit.

[0016] The synchronous converter circuit may preferably comprise MOS type transistors.

[0017] Preferably, the synchronous converter circuit may comprise GaN type transistors.

[0018] The control unit may preferably be configured to adapt the switching frequency according to an indication of the temperature of at least one light source to be powered.

[0019] Preferably, the indication of the temperature of at least one light source to be powered may comprise an indication of the charging voltage of the at least one light source.

[0020] Preferably, the control device may comprise a memory element which comprises, for predetermined temperature indications, a predetermined switching frequency for each average load electric current intensity to be supplied to the light sources. The control unit may preferably be configured to read the switching frequency which corresponds to the indicated temperature and the average load electric current intensity indicated by the input signal in the memory element, in order to produce a switching signal having a corresponding frequency.

[0021] Alternatively, the control unit comprises a memory element and is configured to determine the switching frequency based on the indication of at least one light function to be performed, by selecting a switching frequency value from among several predetermined switching frequency values ​​stored in the memory element.

[0022] Preferably, the light sources may comprise electroluminescent light elements. Preferably, the light sources may comprise light-emitting diodes, LEDs.

[0023] In accordance with another aspect of the invention, a method for limiting losses in a device for controlling the electrical power supply of a plurality of light functions of a motor vehicle according to aspects of the invention is provided. The method is in that the method comprises the steps of: receiving, by the control unit, an input signal comprising an indication of an average intensity of electric charging current to be supplied to the light sources; generating, by the control unit, a switching signal having a frequency which depends on the average intensity of electric charging current indicated by the input signal; controlling, by the control unit, the synchronous converter circuit of said control device, by means of said switching signal.

[0024] By using the measures proposed by the present invention, it becomes possible to propose a device and a method which make it possible to increase the efficiency of a converter as a function of variations in its load. This is made possible by using a synchronous converter circuit to the detriment of an asynchronous converter as is commonly used for automotive lighting applications. According to preferred embodiments of the invention, the synchronous converter circuit is operated in a forced continuous conduction mode, for which it has been observed that an increase in the switching frequency of the signal which controls the state of the transistors of the converter circuit increases the efficiency of the circuit at relatively low load.The efficiency increase effect is more pronounced when using Gallium Nitride (GaN) transistors, rather than Metal Oxide Semiconductor (MOSFET) field effect transistors, to realize the converter circuit. These transistors have reduced switching and conduction losses and, in particular, are more suitable for use at frequencies. above 400 kilohertz, for example frequencies in the order of megahertz. Thus, the use of higher switching frequencies than with a MOSFET type transistor becomes possible, opening up the possibility of further increasing efficiency for low loads.

[0025] Other features and advantages of the present invention will be better understood with the help of the description of the examples and the drawings among which: Fig. 1 shows schematically a device in accordance with a preferred embodiment of the invention; Fig. 2 shows a synchronous converter circuit of the "boost" type, as it occurs in a preferred embodiment of the invention; Fig. 3 shows schematically a device in accordance with a preferred embodiment of the invention; Fig. 4 shows schematically a device in accordance with a preferred embodiment of the invention; Fig. 5 shows the main steps of a method in accordance with a preferred embodiment of the invention, Fig. 6 shows a conventional Buck-Boost type electrical diagram described above, Fig. 7 shows a synchronous converter circuit of the "buck" type, according to an embodiment of the invention.

[0026] Unless specifically indicated otherwise, technical features described in detail for a given embodiment may be combined with the technical features described in the context of other embodiments described by way of example and in a non-limiting manner. Similar reference numerals will be used to describe similar concepts across different embodiments of the invention. For example, references 100, 200 and 300 designate three embodiments of a control device according to the invention.

[0027] The illustration of Figure 1 shows a device for controlling the power supply 100 according to a first embodiment of the invention. The device allows the power supply of a plurality of light sources to be controlled. The light sources are for example grouped in light modules 10, 20, 30 which each allow one or more light functions of a motor vehicle to be carried out, such as dipped headlights, daytime running lights, or others. The light sources preferably comprise semiconductor electroluminescent elements such as light-emitting diodes. Depending on the light functions to be switched on at a given time, the load on the control device can vary significantly. It is clear that, for example, switching on two or a larger plurality of light modules will require a higher average electrical current intensity than switching on a single function with reduced light intensity.The control device 100 comprises a synchronous switching converter circuit 110, which makes it possible to transform an input voltage Vin supplied by an internal battery of the motor vehicle, into a charging voltage. The synchronous converter circuit 110 is controlled by a control unit 120, which is implemented by way of non-limiting example by a microcontroller element programmed for this purpose. The control unit 120 generates and supplies a control signal in the form of a switching signal 122 to the converter circuit, the operation of which will be described in relation to FIG. 2. The frequency of said switching signal is dependent on an average intensity of the charging electric current to be supplied to the light sources, an indication of which is provided by an input signal 102 and which depends on the lighting functions to be performed.The indication of an average electric current intensity can for example be carried out by a control signal 102 coming from a central module of the vehicle, which indicates the light functions to be powered. Each function or each set of functions can be assimilated to a corresponding average electric current intensity value. For example, and in a non-limiting manner, in a conventional dual-function light module, either a dipped beam function or a dipped beam and a main beam function may be required. Even if the power required to carry out these light functions depends on the temperature, a power range required to power either one or the other is known. The control unit is configured to determine an appropriate switching frequency, for example by means of a predetermined calculation rule or by means of a table of predetermined and pre- values. calibrated, and to generate the control signal 122 having the required frequency. The same circuit can be used to power light modules performing more advanced functions, for example segmented lighting functions, known to those skilled in the art of automotive lighting. A corresponding light module may be capable of projecting a plurality of segments dividing the produced light beam horizontally and / or vertically, and whose luminous flux is individually controllable. More complex control logic may then be required, including for example an evaluation of the switching frequency taking into account the number of lit segments.

[0028] Figure 2 illustrates a synchronous boost converter circuit 110 as used in embodiments of the invention. While an asynchronous converter circuit employs a diode, the circuit 110 uses a second transistor T2 instead of the diode, resulting in increased efficiency. The use of the second transistor T2 avoids power losses at the diode, which would increase with increasing switching frequency of the circuit. The operation of the circuit of Figure 2 is known in the art. The state of transistors T1 and T2 is alternated by the switching signal 122 provided by the control unit 120. The two transistors are preferably of the more efficient GaN type, but can alternatively be of the MOSFET type. When transistor T1 is on, transistor T2 is off and vice versa.For illustration purposes, the control signal of transistor T2 122' is therefore the synchronous inverse of the control signal of transistor T 1 .

[0029] When the converter circuit 110 is operated in normal continuous conduction mode (CCM), the current flowing through the inductor L is positive and increases when the transistor T1 is on. In neutral, when T1 and T2 are off, a positive electric current flows through the intrinsic diode of the transistor T2. Then, when T2 turns on, the current flowing through the inductor L is positive and decreases. When the switching signal cycle restarts, the transistors T1 and T2 are off and a positive current flows through the intrinsic diode of the transistor T2, which is therefore biased in this direction. This implies that when T1 is on again, the diode of T2 does not immediately turn off and thus generates a loss.

[0030] When the converter circuit 110 is operated in forced continuous conduction mode (FCCM), the current through inductance L is positive and increases when transistor T1 is on. In the neutral position, when T1 and T2 are off, a positive electric current flows through the diode of transistor T2. Then, when T2 turns on, the current through inductance L is positive and decreases. Transistor T2 continues to be left on to allow the electric current through inductance L to decrease further and become negative. From this point on, the intrinsic diode of transistor T2 is reverse-biased. At the dead time when the switching signal cycle restarts, transistors T1 and T2 are off and there is no current through the intrinsic diode of transistor T2. However, a current does flow through the intrinsic diode of transistor T1.When transistor T1 turns on again, the electric current flowing through the inductor begins to increase again without there being any losses at the intrinsic diode of transistor T2.

[0031] It is therefore preferable in all embodiments of the invention to operate the synchronous converter circuit 110 in FCCM mode. It has been observed that for low loads, an increase in switching frequency in FCCM mode makes it possible to increase the efficiency of the converter circuit.

[0032] The illustration of Figure 3 shows a power supply control device 200 according to a second embodiment of the invention. The device makes it possible to control the power supply of a plurality of light sources. The light sources are for example grouped in light modules 10, 20, 30 which each make it possible to carry out one or more lighting functions of a motor vehicle. The control device 200 comprises a synchronous switching converter circuit 210, as just described, which makes it possible to transform an input voltage Vin supplied by an internal battery of the motor vehicle, into a charging voltage. The synchronous converter circuit 210 is preferably operated in FCCM mode and is controlled by a control unit 220. The control unit 220 generates and supplies a control signal in the form of a switching signal 222 to the converter circuit.The frequency of said chopping signal is dependent on an average intensity. of charging electric current to be supplied to the light sources, an indication of which is provided by an input signal 202 and which depends on the light functions to be performed. The indication of an average intensity of electric current can for example be provided by a control signal 202 coming from a central module of the vehicle, which indicates the light functions to be supplied. The control unit is configured to read an appropriate switching frequency in a memory element 230. For each value of average intensity of the electric current to be supplied, a corresponding frequency is pre-recorded 232 in the memory element. The determination of the optimal frequencies can be done by laboratory tests or by simulations, during which for each average intensity of electric current to be supplied, the switching frequency which produces the best efficiency at the converter circuit 220 is retained.After reading the frequency, the control unit generates the control signal 222 having the required frequency. If the converter circuit is operated in FCCM mode, for low average electric currents, the optimal switching frequencies will be higher, while they will be lower for higher average electric currents.

[0033] The illustration of Figure 4 shows a power supply control device 300 according to a third embodiment of the invention. The device makes it possible to control the power supply of a plurality of light sources. The light sources are for example grouped in light modules 10, 20, 30 which each make it possible to carry out one or more lighting functions of a motor vehicle. The control device 300 comprises a synchronous switching converter circuit 310, as just described, which makes it possible to transform an input voltage Vin supplied by an internal battery of the motor vehicle, into a charging voltage. The synchronous converter circuit 310 is preferably operated in FCCM mode and is controlled by a control unit 320. The control unit 320 generates and supplies a control signal in the form of a switching signal 322 to the converter circuit.The frequency of said switching signal is dependent on an average intensity of electric charging current to be supplied to the light sources, an indication of which is provided by a first input signal 302 and which depends on the light functions to be performed. The indication of an average current intensity. electrical can for example be carried out by a control signal 302 coming from a central module of the vehicle, which indicates the light functions to be powered. It is understood that the indication of an average intensity of electric current can therefore take the form of a signal, for example logic, indicating the combination of light functions to be powered. In another example of the invention, this indication is transmitted to the control unit in the form of an average current intensity value.

[0034] The control unit uses a second input signal 304 from a means 50 for obtaining a value indicative of the temperature of at least one of the light sources. This may, for example, be a voltage value across a thermistor whose resistance varies as a function of its temperature. Alternatively, the means 50 for obtaining may be an input voltage value of a light source or a light module which is lower than a predetermined threshold value, which indicates that a semiconductor element light source or the light module in question is in an overheating situation.

[0035] The control unit is configured to read an appropriate switching frequency as a function of the temperature indication 304 in a memory element 330. For each average intensity value of the electric current to be supplied, a corresponding frequency is pre-recorded 332 in the memory element, and this for each temperature indication or by indicated temperature ranges T1, T2. The determination of the optimal frequencies per temperature can be done by laboratory tests or by simulations, during which for each average intensity of electric current to be supplied at a given junction temperature, the switching frequency which produces the best efficiency at the converter circuit 320 is retained. This principle makes it possible to take into account a "de-rating" of the light sources with semiconductor elements. The control unit 320 then generates the control signal 322 having the required frequency.

[0036] Finally, Figure 5 illustrates the main steps of a method according to a preferred embodiment of the invention: a) receiving, by the control unit 120, 230, 320, an input signal 102, 202, 302 comprising an indication of an average intensity of electric charging current to be supplied to the light sources 10, 20, 30; b) generating, by the control unit 120, 220, 320, a switching signal 122, 222, 322 having a frequency which depends on the average intensity of electric charging current indicated by the input signal 102, 202, 302; c) controlling, by the control unit 120, 220, 320, the synchronous converter circuit 110, 210, 310 of said control device, by means of said switching signal 122, 222, 322.

[0037] Figure 7 illustrates a synchronous converter circuit of the "BUCK" type 410 as used in other embodiments of the invention. While an asynchronous converter circuit employs a diode, the circuit 410 uses a second transistor T1 instead of the diode, which results in increased efficiency. The use of the second transistor T1 avoids power losses at the diode, which would increase with the increase in the switching frequency of the circuit. The operation of the circuit of Figure 7 is per se known in the art. The state of the transistors T1 and T2 is alternated by the switching signal 422 provided by the control unit 420. The two transistors are preferably of the more efficient GaN type, but can alternatively be of the MOSFET type. When the transistor T1 is on, the transistor T2 is off and vice versa.For illustration purposes, the control signal of transistor T2 422' is therefore the synchronous inverse of the control signal of transistor T 1 .

[0038] When the converter circuit 410 is operated in normal continuous conduction mode (CCM), the current flowing through the inductor L is positive and increases when the transistor T2 is on. In neutral, when T1 and T2 are off, a positive electric current flows through the intrinsic diode of the transistor T1. Then, when T1 turns on, the current flowing through the inductor L is positive and decreases. When the switching signal cycle restarts, the transistors T1 and T2 are off and a positive current flows through the intrinsic diode of the transistor T1, which is therefore biased in this direction. This implies that when T2 is on again, the diode of T1 does not immediately turn off and thus generates a loss.

[0039] When the converter circuit 410 is operated in forced continuous conduction mode (FCCM), the current through inductor L is positive and increases when transistor T2 is on. In the neutral position, when T1 and T2 are off, a positive electric current flows through the diode of transistor T2. Then, when T1 turns on, the current through inductor L is positive and decreases. Transistor T1 continues to be left on to allow the electric current through inductor L to decrease further and become negative. From this point on, the intrinsic diode of transistor T1 is reverse-biased. At the dead time when the switching signal cycle restarts, transistors T1 and T2 are off. A current flows through the intrinsic diode of transistor T2 because the current is positive in inductor L.When transistor T2 turns on again, the electric current flowing through the inductor begins to increase again without there being any losses at the intrinsic diode of transistor T1.

[0040] Such a control device is capable of powering a high-definition pixelated light source, comprising hundreds, preferably thousands or tens of thousands of pixels comprising at least one elementary light source, each generating a portion of a high-definition light beam, the luminous flux generated by each pixel being individually controllable. An adjustment of the switching frequency can then be carried out according to, for example, an average luminous flux over all the pixels.

[0041] The scope of protection is determined by the claims.

Claims

Claims

1. Device for controlling the electrical power supply (100, 200, 300) of a plurality of light sources, sub-assemblies of which are configured to selectively perform different lighting functions of a motor vehicle, the control device comprising a converter circuit (110, 210, 310) controlled by a control unit (120, 220, 320), characterized in that the converter circuit (110, 210, 310) is a synchronous switching converter circuit comprising two transistors, in that the control unit (120, 220, 320) is configured to supply a switching signal (122, 222, 322) to the converter circuit, and in that the frequency of said switching signal is dependent on an average intensity of electrical charging current to be supplied to the light sources, an indication of which is provided by an input signal (102, 202, 302) and which depends on the light functions to be performed.

2. Control device (100, 200, 300) according to the preceding claim, characterized in that the indication of an average intensity of electric charging current to be supplied to the light sources comprises an indication of a subset of light sources to be supplied.

3. Control device (200) according to one of the preceding claims, characterized in that it comprises a memory element (230) in which a predetermined switching frequency is recorded (232) for each average intensity of electric load current to be supplied to the light sources, and in that the control unit (220) is configured to read the switching frequency which corresponds to the average intensity of electric load current indicated by the input signal (202) in the memory element (230), in order to produce a switching signal (222) having a corresponding frequency.

4. Control device (100, 200, 300) according to one of the preceding claims, characterized in that the converter circuit (110, 210, 310) is operated in forced continuous conduction mode. [Claim s] Control device (100, 200, 300) according to one of the preceding claims, characterized in that the converter circuit synchronous (110, 210, 310) comprises metal-oxide-semiconductor, MOS, type transistors. [Claim s] Control device (100, 200, 300) according to one of claims 1 to 4, characterized in that the synchronous converter circuit (110, 210, 310) comprises transistors of the Gallium nitride, GaN, type.

7. Control device (300) according to one of the preceding claims, characterized in that the control unit (320) comprises a memory element and is configured to determine the switching frequency as a function of the indication (302) of at least one light function to be performed, by selecting a switching frequency value from among several predetermined switching frequency values ​​stored in the memory element.

8. Control device (300) according to one of claims 1 to 6, characterized in that the control unit (320) is configured to adapt the switching frequency as a function of an indication of the temperature (304) of at least one light source to be supplied.

9. Control device (300) according to claim 8, characterized in that it comprises a memory element (330) in which are recorded (332), for predetermined temperature indications (T1, T2), a predetermined switching frequency for each average intensity of electric charging current to be supplied to the light sources, and in that the control unit (320) is configured to read the switching frequency which corresponds to the indicated temperature (304) and to the at least one light function to be carried out indicated by the input signal (302) in the memory element (330), in order to produce a switching signal (322) having a corresponding frequency.

10. Control device (100, 200, 300) according to one of the preceding claims, characterized in that the synchronous converter circuit (110, 210, 310) is a “boost” voltage booster circuit.

11. Method for limiting losses in a device (100, 200, 300) for controlling the electrical power supply of a plurality of light functions of a motor vehicle according to one of claims 1 to 9, characterized in that the method comprises the steps: a) receiving, by the control unit (120, 230, 320), an input signal (102, 202, 302) comprising an indication of an average intensity of electric load current to be supplied to the light sources (10, 20, 30); b) generating, by the control unit (120, 220, 320), a switching signal (122, 222, 322) having a frequency which depends on the average intensity of electric load current indicated by the input signal (102, 202, 302); c) controlling, by the control unit (120, 220, 320), the synchronous converter circuit (110, 210, 310) of said control device, by means of said switching signal (122, 222, 322).

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