Optoelectronic circuit comprising light-emitting diodes

Abstract

The invention relates to an optoelectronic circuit (20) comprising a first power supply terminal (A1) and a second reference terminal (A2), the first power supply terminal (A1) and the second reference terminal (A2) being intended to be connected to a voltage source that delivers, to the optoelectronic circuit (20), a variable voltage (VALIM) containing alternating increasing positive phases and decreasing positive phases. The optoelectronic circuit (20) comprises: sets of light-emitting diodes (Di), the sets being connected to one another in series; a plurality of conduction components (SWi), wherein each conduction component (SWi) is associated with only one of the sets of light emitting diodes (Di); a plurality of connecting circuits (Li); and a control circuit (28) comprising a differential amplifier and the same number of output stages as there are conduction components (SWi) in the optoelectronic circuit (20).

Description

[0001]Title of the invention: OPTOELECTRONIC CIRCUIT COMPRISING LIGHT-EMITTING DIODES Technical field of the invention The present invention relates to an optoelectronic circuit comprising several sets of light-emitting diodes for emitting light when the optoelectronic circuit is powered, the optoelectronic circuit comprising a first power supply terminal and a second reference terminal, the first power supply terminal and the second reference terminal being intended to be connected to a voltage source delivering to the optoelectronic circuit a variable voltage containing an alternation of increasing positive phases and decreasing positive phases,the optoelectronic circuit comprising said sets of light-emitting diodes mounted in series and connected to the first power supply terminal as well as a plurality of conduction components. State of the prior art It is known to be able to supply an optoelectronic circuit comprising sets of light-emitting diodes with a variable voltage, for example alternating, in particular a sinusoidal voltage,like the mains voltage. The voltage applied to each set of LEDs must be greater than the sum of the threshold voltages of the LEDs in that set for them to emit light. The number of LEDs emitting light gradually increases during an increasing phase of the supply voltage and gradually decreases during a decreasing phase of the supply voltage. A disadvantage is that it is possible to have alternating increasing phases of light emission,of decreasing phases of light emission and phases of absence of light emission by the optoelectronic circuit when the supply voltage is insufficient and therefore does not allow any of the light-emitting diodes to be powered. This creates potential flickering effects visible to the naked eye and visual discomfort as well as stroboscopic effects involving a change in perception of the movement of objects. Document EP3223590B1 describes an optoelectronic circuit which makes it possible to solve this problem by reducing the duration of absence of light emission, or even eliminating it. For this,it is intended to maintain the current flowing through the light-emitting diodes at a substantially continuous value. But this results in the power value in the light-emitting diodes increasing at the same time as the voltage applied by the voltage source. This variation in power represents a disadvantage with respect to certain increasingly strict administrative and normative regulations in this area, which attempt to limit stroboscopic effects. Purpose of the invention The purpose of the present invention is to propose an optoelectronic circuit of the aforementioned type which addresses all or part of the disadvantages mentioned above in connection with the state of the art. In particular, the purpose of the invention is to propose an optoelectronic circuit of the aforementioned type which meets at least one of the following objectives: - avoid phases of increasing and decreasing emission of light, - avoid moments of extinction of the sets of diodes,- provide visual comfort, - have limited electrical consumption, - have limited heating effects. This aim can be achieved by implementing an optoelectronic circuit comprising a first power supply terminal and a second reference terminal, the first power supply terminal and the second reference terminal being intended to be connected to a voltage source delivering to the optoelectronic circuit a variable voltage containing an alternation of increasing positive phases and decreasing positive phases, the optoelectronic circuit comprising: - sets of light-emitting diodes connected together in a series arrangement, which series arrangement is connected to the first power supply terminal, - a plurality of conduction components where each conduction component is associated with a single one of the sets of light-emitting diodes,each conduction component having a variable electrical conductance as a function of a control signal, each conduction component comprising a first terminal, a second terminal and a third terminal, - a plurality of connection circuits, the second reference terminal being connected to each set of light-emitting diodes by one of said connection circuits, each connection circuit on the one hand comprising one of said conduction components and at least one resistive component connected in series with said conduction component of said connection circuit, on the other hand being configured so that the first terminal of the conduction component is connected to the set of light-emitting diodes associated with it and that a first connection terminal of the resistive component is connected to the second terminal of the conduction component of said connection circuit and that a second connection terminal of the resistive component is connected to the second reference terminal,- a control circuit comprising a difference amplifier and as many output stages as there are conduction components included in the optoelectronic circuit, each of said output stages being connected to the third terminal of one of said conduction components, the control circuit being adapted to provide, for each connection circuit, the control signal from the comparison between, on the one hand, a first voltage taken between a first potential, between the first connection terminal of the resistive component and the second terminal of the conduction component of this connection circuit, and the second reference terminal, and on the other hand, at least one second voltage identical for all the conduction components, the control circuit being adapted to control the first voltage to the second voltage offset by a third voltage, different for each output stage of the control circuit. This optoelectronic circuit advantageously allows,at substantially constant power, to limit energy consumption and heating problems, while avoiding the risks of periods of variation in light emission, thus promoting visual comfort in use by avoiding any uncomfortable stroboscopic effect. Some preferred aspects of this optoelectronic circuit, but not limiting, are as follows. According to one embodiment, the sets of light-emitting diodes are connected together so as to constitute a light-emitting circuit in which the sets of light-emitting diodes are in series with each other, the light-emitting circuit having a first end electrically connected to the first power supply terminal and a second end connected to a node; the optoelectronic circuit comprises as many resistive components as there are sets of light-emitting diodes, and said resistive components are connected in series with each other,between the node and the second reference terminal. According to one embodiment, the sets of light-emitting diodes are classified in increasing ranks from a first set of light-emitting diodes at the first end of the light-emitting circuit to a last set of light-emitting diodes at the second end of the light-emitting circuit; for each connection circuit of the optoelectronic circuit excluding the last set of light-emitting diodes (i.e. the set of light-emitting diodes having the highest rank), the second terminal of the conduction component is connected to an electrical connection connecting two resistive components connected in series together. According to one embodiment, for each conduction component,the control circuit is adapted to control the first voltage to the second voltage reduced by the third voltage which decreases with the rank of the set of light-emitting diodes to which the conduction component is connected. According to one embodiment, the difference amplifier receives as input a differential voltage corresponding to the difference between the first voltage and the second voltage. According to one embodiment, the difference amplifier is adapted to provide a first current and a second current, the control circuit comprising a first current mirror with several outputs adapted to copy, for each conduction component, the first current or a third current multiplied by a first copying factor, and a second current mirror with several outputs adapted to copy, for each conduction component, the second current or the third current multiplied by a second copying factor,the ratio between the first copying factor and the second copying factor being different for each conduction component. According to one embodiment, the optoelectronic circuit comprises, for each conduction component, a capacitor connected to the conduction component or integrated into the conduction component, the first current mirror comprising a capacitor charging circuit and the second current mirror comprising a capacitor discharging circuit. According to one embodiment, the difference amplifier comprises a differential pair comprising a first transistor receiving the first voltage and a second transistor receiving the second voltage. According to one embodiment, the first transistor may be a MOS transistor whose gate receives the first voltage and the second transistor may be a MOS transistor whose gate receives the second voltage. According to one embodiment,each conduction component comprises a MOS transistor. According to one embodiment, the first current mirror comprises, for each conduction component, a first copying block connected to the gate of the MOS transistor of the conduction component and adapted to provide the first current multiplied by the first copying factor and the second current mirror comprises, for each conduction component, a second copying block connected to the gate of the MOS transistor of the conduction component and adapted to provide the second current multiplied by the second copying factor. According to one embodiment,the optoelectronic circuit comprises a capacitor mounted between the first supply terminal and the second reference terminal and allowing the variable voltage to remain at a value higher than a threshold voltage of the first set of light-emitting diodes mounted between the first supply terminal and the first conduction component. The capacitor mounted at the input makes it possible to avoid the risks of periods of absence of light emission and therefore to avoid any uncomfortable stroboscopic effect. According to one embodiment, the third voltage varies as a function of the temperature. Brief description of the drawings Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example,and made with reference to the appended drawings in which: [Fig.1] Figure 1 represents an electrical diagram of an embodiment of an optoelectronic circuit according to the invention. [Fig.2] Figure 2 represents an electrical diagram of an embodiment of the control circuit used in the optoelectronic circuit of Figure 1. [Fig.3] Figure 3 represents a particular case of the embodiment of Figure 1 where N is equal to 3. [Fig.4] Figure 4 represents timing diagrams of voltage, currents and power during operation of the embodiment of the optoelectronic circuit according to the invention of Figure 1. Detailed description In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore,the different embodiments and variants are not mutually exclusive and may be combined with each other. Unless otherwise specified, the expression "substantially" means within 10%, preferably within 5%. Furthermore, in the present description, the term "connected" is used to designate a direct electrical connection, without an intermediate electronic component, for example by means of a conductive track, and the term "connected" is used to designate either a direct electrical connection (then meaning "connected") or a connection via one or more intermediate components (resistor, capacitor, etc.). Figure 1 represents an electrical diagram of an embodiment of an optoelectronic circuit 20 comprising a first power supply terminal A1 and a second reference terminal A2,the first supply terminal A1 and the second reference terminal A2 being intended to be connected to a voltage source delivering to the optoelectronic circuit 20 a variable voltage VALIM containing an alternation of increasing positive phases and decreasing positive phases. According to one embodiment, the optoelectronic circuit 20 may comprise a rectifier circuit 12 receiving a supply voltage VIN between two terminals IN1 and IN2 and supplying the rectified variable voltage VALIM between the first supply terminal A1 and the second reference terminal A2. As a variant, the optoelectronic circuit 20 may directly receive a rectified voltage, the rectifier circuit 12 then not being present. The potential at the second reference terminal A2 may correspond to a low reference potential Voff, for example 0V, relative to which the voltages of the optoelectronic circuit 20 are referenced. Unless otherwise indicated,the potentials are referenced in the remainder of the description relative to the low reference potential Voff. A high reference potential, called Von, can be provided from the variable voltage VALIM at the first supply terminal A1. The optoelectronic circuit 20 comprises sets of light-emitting diodes Di connected together in a series arrangement, which series arrangement is connected to the first supply terminal A1. The number i of the sets of light-emitting diodes Di is an integer varying from 1 to N, where N is an integer between 2 and 200. Each of the sets of light-emitting diodes D1 to DN comprises at least one elementary light-emitting diode. Preferably, each set of light-emitting diodes Di is composed of the series and / or parallel connection of at least two elementary light-emitting diodes. The sets of light-emitting diodes Di, i varying from 1 to N,may comprise the same number of elementary light-emitting diodes or different numbers of elementary light-emitting diodes. The optoelectronic circuit 20 comprises a plurality of conduction components SW i where each conduction component SW i is associated with a single one of the sets of light-emitting diodes Di. Each conduction component SW i has a variable electrical conductance as a function of a control signal Si and comprises a first terminal B1i, a second terminal B2i and a third terminal B3i. Each conduction component SW i is adapted to ensure the control of a set of light-emitting diodes Di which is associated with it. In the present exemplary embodiment, each conduction component SW i is associated with a single one of the sets of light-emitting diodes Di and each set of light-emitting diodes Di is associated with a single one of the conduction components SW i. Consequently,the number of sets of light-emitting diodes Di is identical to the number of conduction components SWi. In Figure 1, for i varying from 1 to N, Ii is the current flowing in the conduction component SWi. The optoelectronic circuit 20 also comprises a plurality of connection circuits Li, the second reference terminal A2 being connected to each set of light-emitting diodes Di by one of said connection circuits Li, each connection circuit Li on the one hand comprising one of said conduction components SWi and at least one resistive component Ri connected in series with said conduction component SWi of said connection circuit Li,on the other hand being configured so that the first terminal B1i of the conduction component SW i is connected to the set of light-emitting diodes Di associated with it and that a first connection terminal Bc1i of the resistive component Ri is connected to the second terminal B2i of the conduction component SW i of said connection circuit Li and that a second connection terminal Bc2i of the resistive component Ri is connected to the second reference terminal A2. The optoelectronic circuit 20 comprises a control circuit 28 comprising a difference amplifier 30 and as many output stages as there are conduction components SW i that the optoelectronic circuit 20 comprises, each of said output stages being connected to the third terminal B3i of one of said conduction components SW i, the control circuit 28 being adapted to provide, for each connection circuit Li,the control signal Si from the comparison between on the one hand a first voltage VSOURCE taken between a first potential, between the first connection terminal Bc1i of the resistive component Ri and the second terminal B2i of the conduction component SW i of this connection circuit Li, and the second reference terminal A2, and on the other hand at least a second voltage VREF identical for all the conduction components SWi, the control circuit 28 being adapted to control the first voltage VSOURCE to the second voltage VREF offset by a third voltage VOFFSETi, different for each output stage of the control circuit 28. In order to explain the operation of the optoelectronic circuit 20, an optoelectronic circuit having a simplified structure is considered. Figure 3 represents a particular case of the embodiment of Figure 1 where N is equal to 3. The control circuit 28 comprises three output stages connected to the three conduction components SW1,SW2 and SW3 at the third terminals B31, B32 and B33 respectively. A capacitor C1 mounted at the input of the optoelectronic circuit 20 between the first supply terminal A1 and the second reference terminal A2 makes it possible to maintain the variable voltage VALIM at a value higher than the threshold voltage of the first set of light-emitting diodes D1. This arrangement makes it possible to ensure that the first set of light-emitting diodes D1 is always on and that the optoelectronic circuit emits light continuously, independently of the variation of the variable voltage VALIM. In the following, the emphasis is placed on the operation of the simplified optoelectronic circuit 20 of FIG. 3. When the value of the variable voltage VALIM is lower than the sum of the threshold voltages of the sets of diodes D1 and D2,only the diode assembly D1 is conducting. The control circuit 28 provides the connection circuit L1 (comprising R1 and SW1) with the control signal S1 from the comparison between the first voltage VSOURCE (taken between a first potential between the first connection terminal Bc11 and the second terminal B21 and the second reference terminal A2) and the second voltage VREF. The control circuit 28 makes it possible to control the first voltage VSOURCE to the second voltage VREF offset by the third voltage VOFFSET1. In this case, the three conduction components are conducting. When the value of the variable voltage VALIM becomes greater than the sum of the threshold voltages of the diode assemblies D1 and D2 but remains less than the sum of the threshold voltages of the diode assemblies D1, D2 and D3, only the diode assemblies D1 and D2 are conducting. The control circuit 28 provides the connection circuit L2 (comprising R1,R2 and SW2) the control signal S2 from the comparison between the first voltage VSOURCE (taken between a first potential between the first connection terminal Bc12 and the second terminal B22 and the second reference terminal A2) and the second voltage VREF. The control circuit 28 makes it possible to control the first voltage VSOURCE to the second voltage VREF offset by the third voltage VOFFSET2. In this case, the conduction components SW2 and SW3 are conducting and SW1 is blocked. When the value of the variable voltage VALIM is greater than the sum of the threshold voltages of the diode assemblies D1, D2 and D3, all the diode assemblies D1, D2 and D3 are conducting. The control circuit 28 supplies the connection circuit L3 (comprising R1, R2,R3 and SW3) the control signal S3 from the comparison between the first voltage VSOURCE (taken between a first potential between the first connection terminal Bc13 and the second terminal B23 and the second reference terminal A2) and the second voltage VREF. The control circuit 28 makes it possible to control the first voltage VSOURCE to the second voltage VREF offset by the third voltage VOFFSET3. In this case, the conduction components SW1 and SW2 are blocked and SW3 is conducting. Let us now consider again the optoelectronic circuit 20 of FIG. 1. Each conduction component SW i is a circuit whose equivalent electrical resistance varies between a maximum value and a minimum value depending on the control signal Si that it receives from the control circuit 28. When the equivalent electrical resistance of the conduction component SW i is at its maximum value,the conduction component SW i is substantially equivalent to an open switch. According to this embodiment, for i varying from 1 to N, when a conduction component SW i is conducting, the conduction components SW i to SW i-1 are blocked and the conduction components SW i+1 to SWN are conducting. According to one embodiment, the control signal Si of each conduction component SW i is a signal that can vary continuously between a first value and a second value. According to the embodiments, the equivalent electrical resistance of the conduction component SW i can decrease or increase when the control signal Si varies from the first value to the second value. The first and second values ​​of the control signals Si, i varying from 1 to N, may not be the same for all the conduction components SW i. According to one embodiment,the sets of light-emitting diodes Di are connected together so as to constitute a light-emitting circuit in which the sets of light-emitting diodes Di are in series with each other, the light-emitting circuit having a first end electrically connected to the first power supply terminal A1 and a second end connected to a node A3; the optoelectronic circuit 20 comprises as many resistive components Ri as sets of light-emitting diodes Di, and said resistive components Ri are connected in series with each other, between the node A3 and the second reference terminal A2. According to one embodiment,the light-emitting diodes Di are classified in ascending ranks from a first set of light-emitting diodes Di at the first end of the light-emitting circuit to a last set of light-emitting diodes Di at the second end of the light-emitting circuit; for each connecting circuit Li of the optoelectronic circuit 20 excluding the last set of light-emitting diodes DN, the second terminal B2i of the conduction component SW i is connected to an electrical connection connecting two resistive components Ri connected in series with each other. According to the present embodiment, the plurality of connecting circuits Li may be presented as follows: - the circuit L1, connecting A2 to D1, comprises R1 and SW1, - the circuit L2, connecting A2 to D2, comprises R1 and R2 associated with each other in a series connection and SW2, - the circuit L3, connecting A2 to D3, comprises R1, R2 and R3 associated with each other in a series connection and SW3, - ……. - the LN circuit,connecting A2 to DN, comprises R1, R2…. RN associated with each other in a series circuit and SWN. Said resistive components Ri are intended to be traversed by a current ISOURCE, corresponding to the current supplying the sets of light-emitting diodes Di passing. In an ascending phase of the variable voltage VALIM, the number of sets of light-emitting diodes Di passing increases progressively when the value of the variable voltage VALIM becomes greater than the value of the threshold voltage of the set of light-emitting diodes Di considered. Similarly, in a descending phase of the variable voltage VALIM, the number of sets of light-emitting diodes Di passing decreases progressively when the value of the variable voltage VALIM becomes lower than the value of the threshold voltage of the set of light-emitting diodes Di considered. Thus,the number of resistive components Ri and of light-emitting diode assemblies Di passing varies proportionally with the variable voltage VALIM. Increasing the number of resistive components Ri then advantageously makes it possible to limit the value of the current ISOURCE when there is an increase in the value of the variable voltage VALIM. Consequently, the present arrangement of the resistive components Ri makes it possible to maintain the power of the light-emitting diode assemblies Di at a substantially constant value independently of the variation of the variable voltage VALIM. Figure 4 represents timing diagrams, obtained by simulation, of the variable voltage VALIM, of the current ISOURCE, of the currents I1, I2, I3 and I4 flowing in the conduction components SW i in a particular case where N is equal to 4 and of the power PLED of the light-emitting diode assemblies Di. It can be seen that on a falling phase of the variable voltage VALIM, the value of the current ISOURCE,circulating in the sets of light-emitting diodes Di passing and in the resistive components Ri forming part of the connection circuit Li considered, increases progressively. This increase is linked to the decrease in the number of resistive components Ri which varies proportionally with the variable voltage VALIM. Similarly, on an ascending phase of the variable voltage VALIM, the value of the current ISOURCE, circulating in the sets of light-emitting diodes Di passing and in the resistive components Ri, decreases progressively. This decrease is linked to the increase in the number of resistive components Ri which varies proportionally with the variable voltage VALIM. This makes it possible to have a power in the sets of light-emitting diodes Di which is substantially constant independently of the variable voltage value VALIM, as can be seen on the timing diagram of the PLED power. According to one embodiment, for each conduction component SW i,the control circuit 28 is adapted to control the first voltage VSOURCE to the second voltage VREF reduced by the third voltage VOFFSETi which decreases with the rank of the set of light-emitting diodes Di to which the conduction component SWi is connected. The second voltage VREF can be supplied to the optoelectronic circuit 20 by a circuit 26, depending on the embodiment, either internal or external to the optoelectronic circuit 20. The second voltage VREF can also be obtained from a modulation signal supplied to the optoelectronic circuit 20 by an external circuit. The second voltage VREF or the modulation signal can be supplied by a dimmer, in particular a dimmer that can be actuated by a user or a brightness sensor. According to one embodiment,the difference amplifier 30 receives as input a differential voltage corresponding to the difference between the first voltage VSOURCE and the second voltage VREF. Figure 2 represents an electrical diagram of an embodiment of the control circuit 28 used in the optoelectronic circuit 20. The difference amplifier 30 is adapted to provide a first current Id1 and a second current Id2, the control circuit 28, comprising a first current mirror 32, 34 with several outputs adapted to copy, for each conduction component SW i, the first current Id1 or a third current multiplied by a first copying factor, and a second current mirror 36 with several outputs adapted to copy, for each conduction component SWi, the second current Id2 or the third current multiplied by a second copying factor,the ratio between the first copying factor and the second copying factor being different for each conduction component SW i. According to one embodiment, for each conduction component SW i, a capacitor is connected to the conduction component SW i or integrated into the conduction component SW i, the first current mirror 34 comprising a circuit Tsup-i for charging the capacitor and the second current mirror 36 comprising a circuit for discharging Tinf-i the capacitor. According to one embodiment, the difference amplifier 30 comprises a differential pair comprising a first transistor T1 receiving the first voltage VSOURCE and a second transistor T2 receiving the second voltage VREF. The first transistor T1 may be a MOS transistor whose gate receives the first voltage VSOURCE and the source is connected to the terminal of a current source Idiff, as can be seen in FIG. 2,and the other terminal of the current source Idiff can be connected to the source of the high reference potential Von. The second transistor T2 can be a MOS transistor whose gate receives the second voltage VREF and the source is connected to the current source Idiff. The current at the drain of the transistor T1 corresponds to the first current Id1 and the current at the drain of the transistor T2 corresponds to the second current Id2. According to one embodiment, the transistors T1 and T2 have the same characteristics, in particular the same form factor W / L. The form factor of the channel of a transistor is the ratio between the width and the length of the channel. The first current mirror 32 can comprise two transistors T3 and T4, for example N-channel MOS transistors. The drain of the transistor T3 is connected to the drain of the transistor T1 and the source of the transistor T3 is connected to the source of the low reference potential Voff,and its gate is connected to the drain. The source of transistor T4 is connected to the source of the low reference potential Voff and its gate is connected to the gate of transistor T3. According to one embodiment, the two transistors T3 and T4 have the same characteristics, in particular the same form factor, and the current flowing in transistor T4 is therefore equal to the current Id1 flowing in T3. The first current mirror 34 may comprise a transistor T5, for example a P-channel MOS transistor, the drain of which is connected to the drain of transistor T4, the source of which is connected to the source of the high reference potential Von, and the gate of which is connected to the drain. The first current mirror 34 may further comprise, for each conduction component SW i, i varying from 1 to N, one of said circuit Tsup-i. The circuit Tsup-i may, for example, be a P-channel MOS transistor, the source of which is connected to the source of the high reference potential Von,whose gate is connected to the gate of transistor T5, and whose drain is connected to the third terminal B3i of the conduction component SW i. According to one embodiment, the transistors Tsup-i may not have the same characteristics with respect to each other and with respect to the transistor T5. Rsup-i is the ratio between the channel form factor of the transistor Tsup-i and the channel form factor of the transistor T5. In particular, Rsup-i may be different from Rsup-j, with i different from j. IGi is the current at the drain of the transistor Tsup-i. The second current mirror 36 may comprise a transistor T6, for example an N-channel MOS transistor, whose drain is connected to the drain of the transistor T2, whose source is connected to the source of the low reference potential Voff, and whose gate is connected to the drain. The second current mirror 36 may further comprise for each conduction component SW i, i varying from 1 to N,one of said Tinf-i circuit. The Tinf-i circuit may for example be an N-channel MOS transistor, the source of which is connected to the source of the low reference potential Voff, the gate of which is connected to the gate of the transistor T6, and the drain of which is connected to the third terminal B3i of the conduction component SWi. According to one embodiment, the Tinf-i transistors may not have the same characteristics with respect to each other and with respect to the transistor T6. Rinf-i is called the ratio between the channel form factor of the transistor Tinf-i and the channel form factor of the transistor T6. In particular, Rinf-i may be different from Rinf-j, with i different from j. IG'i is called the current at the drain of the transistor Tsup-i. According to one embodiment,each conduction component SW i comprises a MOS transistor. The control signal Si is the potential at the gate of the MOS transistor of the conduction component SW i at its third terminal B3i. The drain of the MOS transistor corresponds to the first terminal B1i and the source of the MOS transistor corresponds to the second terminal B2i. According to another embodiment, the conduction component SW i may comprise two MOS transistors, which advantageously makes it possible to increase the switching speed of the conduction component SW i. As a variant, the conduction component SW i may correspond to a transistor other than a MOS transistor, to a relay, to a microelectromechanical system and generally to any element whose electrical conductivity can be controlled by voltage or current. According to one embodiment, the first current mirror 34 comprises, for each conduction component SW i,a first copying block Tsup-i connected to the gate of the MOS transistor of the conduction component SW i and adapted to provide the first current Id1 multiplied by the first copying factor and the second current mirror 36 comprises, for each conduction component SW i, a second copying block Tinf-i connected to the gate of the MOS transistor of the conduction component SW i and adapted to provide the second current Id2 multiplied by the second copying factor. According to one embodiment and in an ascending phase of the variable voltage VALIM, while the sets of light-emitting diodes D1 to Di-1 are conducting, the sets of light-emitting diodes Di to DN are blocked, the control signals S1 to Si-2 are at Voff, the signals Si to SN are at Von and the signal Si-1 is at a voltage value allowing the single conduction component SW i-1 to impose the current ISOURCE in the sets of light-emitting diodes,when the voltage across the set of light-emitting diodes Di becomes greater than the threshold voltage of the set of light-emitting diodes Di, the latter becomes conductive and a current begins to flow through the set of light-emitting diodes Di, the conduction component SW i and the resistive components Ri. This results in a temporary decrease in the equivalent total impedance between the first supply terminal A1 and the node A3, and therefore a temporary increase in the voltage VSOURCE. This increase in the voltage VSOURCE results in a decrease in the current Id1 flowing through the transistor T1 of the differential pair 30. As a result, the current reproduced by each transistor Tsup-i decreases for i varying from 1 to N. Given that there is an equivalent capacitance at each third terminal B3i, i varying from 1 to N, which may correspond to a separate capacitor or to a parasitic capacitance of another electronic component,the voltage at the third terminal B3i-1 decreases until it substantially reaches the potential Voff while the voltage at the third terminal B3i also decreases to its equilibrium point, allowing the conduction component SW i to impose the voltage VSOURCE on its own at VREF-VOFFSETi. The conduction component SW i-1 therefore opens and simultaneously the conduction component SW i becomes increasingly conductive. All the current then flows in the conduction component SW i. The control circuit 28 then controls the voltage VSOURCE to the voltage VREF reduced by VOFFSETi by the conduction component SW i, the offset voltage VOFFSETi between the voltage VSOURCE and the voltage VREF being lower than the offset voltage VOFFSETi-1. In the case where each conduction component SW i comprises a MOS transistor whose gate receives the signal Si,this means that the voltage at the gate of transistor SW i-1 decreases and transistor SW i-1 becomes less and less conductive until it reaches its non-conductive state. At equilibrium, the potential at the third terminal B3i is equal to the sum of the voltage VSOURCE and the gate-source voltage of transistor SW i. According to one embodiment and in a falling phase of the variable voltage VALIM, while the sets of light-emitting diodes D1 to Di are conductive, the light-emitting diodes Di+1 to DN are blocked, the signals S1 to Si-1 are at Voff, the signals Si+1 to SN are at Von and the signal Si is at a voltage value allowing the single conduction component SW i to impose the current ISOURCE in the sets of light-emitting diodes, when the voltage across the terminals of the set of light-emitting diodes Di decreases and becomes lower than the threshold voltage of the set of light-emitting diodes Di,this one begins to block. This results in a temporary increase in the equivalent total impedance between the first supply terminal A1 and the node A3, and therefore a temporary decrease in the voltage VSOURCE. This decrease in the voltage VSOURCE causes an increase in the current Id1 flowing through the transistor T1 of the differential pair 30. As a result, the current reproduced by each transistor Tsup-i increases. Since there is an equivalent capacitance at each third terminal B3i,the voltage at the third terminal B3i increases until it substantially reaches the potential Von while the voltage at the third terminal B3i-1 also increases until its equilibrium point allowing the conduction component SW i-1 to impose the voltage VSOURCE on its own at VREF-VOFFSETi-1. The conduction component SW i therefore closes completely and the conduction component SW i-1 becomes increasingly conductive. All the current then flows in the conduction component SW i-1. The control circuit 28 then controls the voltage VSOURCE to the voltage VREF reduced by VOFFSETi-1 by the conduction component SW i-1, the offset voltage VOFFSETi-1 being higher than the offset voltage VOFFSETi. In the case where each conduction component SW i comprises a MOS transistor whose gate receives the signal Si,this means that the voltage at the gate of transistor SW i-1 increases and that transistor SW i-1 becomes more and more conductive and transistor SWi reaches its fully conductive state. Furthermore, in the embodiments described above, each transistor Tsup-i is adapted to copy the current Id1 multiplied by the copying factor Rsup-i and each transistor Tinf-i is adapted to copy the current Id2 multiplied by the copying factor Rinf-i. As a variant, each of the transistors Tinf-i and Tsup-i may be adapted to copy a reference current, for example a constant current. According to one embodiment,the optoelectronic circuit 20 comprises a capacitor C1 mounted between the first power supply terminal A1 and the second reference terminal A2 and allowing the variable voltage VALIM to remain at a value higher than a threshold voltage of the set of light-emitting diodes D1 connected to the first power supply terminal A1. The capacitor C1 at the input of the optoelectronic circuit 20 advantageously makes it possible to avoid the risks of periods of absence of light emission and therefore to avoid any uncomfortable stroboscopic effect. According to one embodiment, the third voltage VOFFSETi varies as a function of the temperature. The offset voltage VOFFSETi can either increase when the temperature increases or decrease when the temperature increases. In the case where the offset voltage VOFFSETi decreases when the temperature increases,an increase in temperature results in a reduction in the current flowing through the resistive components Ri and therefore a reduction in the thermal power supplied by the optoelectronic circuit 20. This provides protection for the optoelectronic circuit 20 against thermal runaway.

Claims

CLAIMS 1. Optoelectronic circuit (20) comprising a first power supply terminal (A1) and a second reference terminal (A2), the first power supply terminal (A1) and the second reference terminal (A2) being intended to be connected to a voltage source delivering to the optoelectronic circuit (20) a variable voltage (VALIM) containing an alternation of increasing positive phases and decreasing positive phases, the optoelectronic circuit (20) comprising: - sets of light-emitting diodes (Di) connected together in a series arrangement, which series arrangement is connected to the first power supply terminal (A1), - a plurality of conduction components (SW i) where each conduction component (SW i) is associated with a single one of the sets of light-emitting diodes (Di), each conduction component (SW i) having a variable electrical conductance as a function of a control signal (Si),each conduction component (SW i) comprising a first terminal (B1i), a second terminal (B2i) and a third terminal (B3i), - a plurality of connection circuits (Li), the second reference terminal (A2) being connected to each set of light-emitting diodes (Di) by one of said connection circuits (Li), each connection circuit (Li) on the one hand comprising one of said conduction components (SW i) and at least one resistive component (Ri) mounted in series with said conduction component (SW i) of said connection circuit (Li),on the other hand being configured so that the first terminal (B1i) of the conduction component (SW i) is connected to the set of light-emitting diodes (Di) associated therewith and that a first connection terminal (Bc1i) of the resistive component (Ri) is connected to the second terminal (B2i) of the conduction component (SW i) of said connection circuit (Li) and that a second connection terminal (Bc2i) of the resistive component (Ri) is connected to the second reference terminal (A2), - a control circuit (28) comprising a difference amplifier (30) and as many output stages as there are conduction components (SW i) that the optoelectronic circuit (20) comprises, each of said output stages being connected to the third terminal (B3i) of one of said conduction components (SW i), the control circuit (28) being adapted to provide, for each connection circuit (Li),the control signal (Si) from the comparison between on the one hand a first voltage (VSOURCE) taken between a first potential, between the first connection terminal (Bc1i) of the resistive component (Ri) and the second terminal (B2i) of the component of, conduction (SW i) of this connection circuit (Li), and the second reference terminal A2, and on the other hand at least a second voltage (VREF) identical for all the conduction components (SW i), the control circuit (28) being adapted to control the first voltage (VSOURCE) to the second voltage (VREF) offset by a third voltage (VOFFSETi), different for each output stage of the control circuit (28). 2.Optoelectronic circuit (20) according to claim 1, wherein: - the sets of light-emitting diodes (Di) are connected together so as to constitute a light-emitting circuit in which the sets of light-emitting diodes (Di) are in series with each other, the light-emitting circuit having a first end electrically connected to the first power supply terminal (A1) and a second end connected to a node (A3); - the optoelectronic circuit (20) comprises as many resistive components (Ri) as sets of light-emitting diodes (Di); - said resistive components (Ri) being connected in series with each other, between the node (A3) and the second reference terminal (A2). 3.Optoelectronic circuit (20) according to claim 2, wherein: - the sets of light-emitting diodes (Di) are classified in increasing ranks from a first set of light-emitting diodes (Di) at the first end of the light-emitting circuit to a last set of light-emitting diodes (Di) at the second end of the light-emitting circuit; - for each connection circuit (Li) of the optoelectronic circuit (20) excluding the last set of light-emitting diodes (DN), the second terminal (B2i) of the conduction component (SW i) is connected to an electrical connection connecting two resistive components (Ri) connected in series with each other. 4.Optoelectronic circuit (20) according to claim 3, in which, for each conduction component (SW i), the control circuit (28) is adapted to control the first voltage (VSOURCE) to the second voltage (VREF) reduced by the third voltage (VOFFSETi) which decreases with the rank of the set of light-emitting diodes (Di) to which the conduction component (SW i) is connected.

5. Optoelectronic circuit (20) according to any one of claims 1 to 4, in which the difference amplifier (30) receives as input a differential voltage corresponding to the difference between the first voltage (VSOURCE) and the second voltage (VREF). 6.

7. Optoelectronic circuit (20) according to any one of claims 1 to 5, in which the difference amplifier (30) is adapted to provide a first current (Id1) and a second current (Id2), the control circuit (28) comprising a first current mirror (32, 34) with several outputs adapted to copy, for each conduction component (SW i), the first current (Id1) or a third current multiplied by a first copying factor, and a second current mirror (36) with several outputs adapted to copy, for each conduction component (SW i), the second current (Id2) or the third current multiplied by a second copying factor, the ratio between the first copying factor and the second copying factor being different for each conduction component (SW i).Optoelectronic circuit (20) according to claim 6, comprising, for each conduction component (SW i), a capacitor connected to the conduction component (SW i) or integrated with the conduction component (SW i), the first current mirror (34) comprising a circuit (Tsup-i) for charging the capacitor and the second current mirror (36) comprising a circuit for discharging (Tinf-i) the capacitor.

8. Optoelectronic circuit (20) according to any one of claims 1 to 7, wherein the difference amplifier (30) comprises a differential pair comprising a first transistor (T1) receiving the first voltage (VSOURCE) and a second transistor (T2) receiving the second voltage (VREF).

9. Optoelectronic circuit (20) according to claim 8, wherein the first transistor (T1) is a MOS transistor whose gate receives the first voltage (VSOURCE) and wherein the second transistor (T2) is a MOS transistor whose gate receives the second voltage (VREF).

10. Optoelectronic circuit (20) according to any one of claims 1 to 9, in which each conduction component (SW i) comprises a MOS transistor.

11. Optoelectronic circuit (20) according to claim 10 and one of claims 6 or 7, in which the first current mirror (34) comprises, for each conduction component (SW i), a first copying block (Tsup-i) connected to the gate of the MOS transistor of the conduction component (SW i) and adapted to supply the first current (Id1) multiplied by the. first copying factor and in which the second current mirror (36) comprises, for each conduction component (SW i), a second copying block (Tinf-i) connected to the gate of the MOS transistor of the conduction component (SWi) and adapted to supply the second current (Id2) multiplied by the second copying factor.

12. Optoelectronic circuit (20) according to any one of claims 1 to 11, comprising a capacitor (C1) mounted between the first supply terminal (A1) and the second reference terminal (A2) and allowing the variable voltage (VALIM) to remain at a value greater than a threshold voltage of the set of light-emitting diodes (D1) connected to the first supply terminal (A1).

13. Optoelectronic circuit (20) according to any one of claims 1 to 12, in which the third voltage (VOFFSETi) varies as a function of the temperature.

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