OPTOELECTRONIC CIRCUIT INCLUDING LIGHT-EMITTING DIODES

Abstract

The optoelectronic circuit (20) comprises a first power supply terminal (A1) and a second reference terminal (A2). The first power supply terminal (A1) and the second reference terminal (A2) are intended to be connected to a voltage source supplying the optoelectronic circuit (20) with a variable voltage (VALIM) containing alternating increasing and decreasing positive phases. The optoelectronic circuit (20) comprises: sets of light-emitting diodes (Di) connected together in a series arrangement; a plurality of conduction components (SWi), where each conduction component (SWi) is associated with a single set of light-emitting diodes (Di); a plurality of coupling circuits (Li); and a control circuit (28) comprising a difference amplifier and as many output stages as there are conduction components (SWi) in the optoelectronic circuit (20). Figure to be published with the abbreviation: Fig. 1.

Description

Title of the invention: OPTOELECTRONIC CIRCUIT COMPRISING LIGHT-EMITTING DIODES Technical field of the invention

[0001] 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. Prior art

[0002] It is known that an optoelectronic circuit comprising arrays of light-emitting diodes (LEDs) must be able to be powered by a variable voltage, for example, alternating current, particularly a sinusoidal voltage, such as the mains voltage. The voltage applied to each array of LEDs must be greater than the sum of the threshold voltages of the LEDs in that array for them to emit light. The number of LEDs emitting light increases progressively during an increasing phase of the supply voltage and decreases progressively during a decreasing phase of the supply voltage.

[0003] One drawback is that the optoelectronic circuit may experience alternating phases of increasing light emission, decreasing light emission, and periods of no light emission when the supply voltage is insufficient to power any of the light-emitting diodes. This creates potential scintillating effects visible to the naked eye, causing visual discomfort and stroboscopic effects that alter the perception of object movement.

[0004] Document EP3223590B1 describes an optoelectronic circuit that solves this problem by reducing the period of light-emitting silence, or even eliminating it. To achieve this, the current flowing through the light-emitting diodes is maintained at a substantially continuous value. However, this results in the power value in the light-emitting diodes increasing along with the voltage applied by the voltage source. This variation in power represents a disadvantage with regard to certain increasingly strict administrative and regulatory standards in this area, which attempt to limit stroboscopic effects. Object of the invention

[0005] The present invention aims to provide an optoelectronic circuit of the aforementioned type which addresses all or part of the disadvantages mentioned above in relation to the prior art.

[0006] In particular, the aim of the invention is to provide an optoelectronic circuit of the aforementioned type which meets at least one of the following objectives: - avoid the phases of increasing and decreasing light emission, - avoid periods of diode array shutdown, - to provide visual comfort, - exhibit limited electricity consumption - exhibit limited heating effects.

[0007] This goal can be achieved through the implementation of 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 being connected to the first power supply terminal, - a plurality of conduction components where each conduction component is associated with a unique set of light-emitting diodes, each conduction component having a variable electrical conductance depending on a control signal, each conduction component having a first terminal, a second terminal and a third terminal, - a plurality of connecting circuits, the second reference terminal being connected to each set of LEDs by one of said connecting circuits, each connecting circuit comprising, on the one hand, one of said conduction components and at least one resistive component connected in series with said conduction component of said connecting circuit, on the other hand, being configured such that the first terminal of the conduction component is connected to the associated set of LEDs and that a first connection terminal of the resistive component is connected to the second terminal of the conduction component of said connecting circuit and that a The 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 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 link 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 link circuit, and the second reference terminal, and on the other hand at least a second identical voltage for all 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.

[0008] This optoelectronic circuit advantageously allows, at substantially constant power, the limitation of 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.

[0009] Some preferred, but not limiting, aspects of this optoelectronic circuit are as follows.

[0010] According to one embodiment, the light-emitting diode assemblies are connected together so as to constitute a light-emitting circuit in which the light-emitting diode assemblies are in series with each other, the light-emitting circuit having a first end electrically connected to the first supply terminal and a second end connected to a node; the optoelectronic circuit comprises as many resistive components as light-emitting diode assemblies, and said resistive components are mounted in series with each other, between the node and the second reference terminal.

[0011] According to one embodiment, the light-emitting diode assemblies are ranked in ascending order from a first set of LEDs at the first end of the light-emitting circuit to a last set of LEDs at the second end of the light-emitting circuit; for each linking circuit of the optoelectronic circuit excluding the last set of LEDs (i.e. the set of LEDs with the highest order), the second terminal of the conduction component is connected to an electrical link connecting two resistive components mounted in series together.

[0012] According to one embodiment, for each conduction component, the circuit of The control is adapted to control the first voltage to the second voltage reduced by the third voltage which is decreasing with the rank of the set of light-emitting diodes to which the conduction component is connected.

[0013] According to one embodiment, the difference amplifier receives at input a differential voltage corresponding to the difference between the first voltage and the second voltage.

[0014] According to one embodiment, the difference amplifier is adapted to provide a first current and a second current, the control circuit comprising a first multi-output current mirror adapted to copy, for each conduction component, the first current or a third current multiplied by a first copy factor, and a second multi-output current mirror adapted to copy, for each conduction component, the second current or the third current multiplied by a second copy factor, the ratio between the first copy factor and the second copy factor being different for each conduction component.

[0015] 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.

[0016] According to one embodiment, the differential amplifier comprises a differential pair including a first transistor receiving the first voltage and a second transistor receiving the second voltage.

[0017] According to one embodiment, the first transistor can be a MOS transistor whose gate receives the first voltage and the second transistor can be a MOS transistor whose gate receives the second voltage.

[0018] According to one embodiment, each conduction component comprises a MOS transistor.

[0019] According to one embodiment, the first current mirror comprises, for each conduction component, a first copy block connected to the gate of the MOS transistor of the conduction component and adapted to provide the first current multiplied by the first copy factor and the second current mirror comprises, for each conduction component, a second copy block connected to the gate of the MOS transistor of the conduction component and adapted to provide the second current multiplied by the second copy factor.

[0020] According to one embodiment, the optoelectronic circuit includes a capacitor mounted between the first supply terminal and the second reference terminal, allowing the variable voltage to remain above a threshold voltage. The first set of LEDs is mounted between the first power supply terminal and the first conduction component. The input capacitor prevents periods of no light emission and thus avoids any uncomfortable stroboscopic effect.

[0021] According to one embodiment, the third voltage varies according to the temperature. Brief description of the drawings

[0022] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0023] [Fig-1] Fig. 1 represents an electrical diagram of one embodiment of a optoelectronic circuit according to the invention.

[0024] [Fig.2] Fig.2 represents an electrical diagram of one embodiment of the control circuit used in the optoelectronic circuit of [Fig.1].

[0025] [Fig.3] [Fig.3] represents a particular embodiment of [Fig.1] where N is equal to 3.

[0026] [Fig.4] Fig.4 represents timing diagrams of voltage, current and power during operation of the embodiment of the optoelectronic circuit according to the invention of [Fig.1]. Detailed description

[0027] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined.

[0028] Unless otherwise specified, the expression "approximately" means within 10%, preferably within 5%. Furthermore, in this description, the term "connected" is used to designate a direct electrical connection, without an intermediate electronic component, for example by means of a conductive trace, and the term "linked" is used to designate either a direct electrical connection (meaning "connected") or a connection via one or more intermediate components (resistor, capacitor, etc.).

[0029] Figure 1 shows an electrical diagram of an embodiment of an optoelectronic circuit 20 comprising a first power supply terminal Ai and a second reference terminal A2, the first power supply terminal Ai and the second reference terminal A2 being intended to be connected to a voltage source supplying the optoelectronic circuit 20 with a variable voltage Valim containing an alternation of increasing positive phases and decreasing positive phases.

[0030] According to one embodiment, the optoelectronic circuit 20 may include a rectifier circuit 12 receiving a supply voltage V1N between two terminals INi and IN2 and providing the rectified variable voltage Valim between the first supply terminal Ai and the second reference terminal A2. As an alternative, the optoelectronic circuit 20 may directly receive a rectified voltage, the rectifier circuit 12 then not being present.

[0031] The potential at the second reference terminal A2 can correspond to a low reference potential Voff, for example 0V, relative to which the voltages of the optoelectronic circuit 20 are referenced. Unless otherwise specified, 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 supplied from the variable voltage Valim at the first supply terminal Ab.

[0032] 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 power supply terminal Ab. The number i of sets of light-emitting diodes Di is an integer ranging from 1 to N, where N is an integer between 2 and 200. Each set of light-emitting diodes Di to DN comprises at least one elementary light-emitting diode. Preferably, each set of light-emitting diodes D; is composed of at least two elementary light-emitting diodes connected in series and / or in parallel. The sets of light-emitting diodes D;, i ranging from 1 to N, may comprise the same number of elementary light-emitting diodes or different numbers of elementary light-emitting diodes.

[0033] The optoelectronic circuit 20 comprises a plurality of conduction components SW; where each conduction component SW; is associated with one unique set of light-emitting diodes D;. Each conduction component SW; has a variable electrical conductance depending on a control signal Si and has a first terminal B1;, a second terminal B2; and a third terminal B3;. Each conduction component SW; is adapted to drive a set of light-emitting diodes D; associated with it. In the present embodiment, each conduction component SW; is associated with one unique set of light-emitting diodes D; and each set of light-emitting diodes D; is associated with one unique conduction component SW;. Therefore, the number of sets of light-emitting diodes D; is identical to the number of conduction components SW;. In [Fig.[l], for i varying from 1 to N, we call h the current flowing in the conduction component SW;. .

[0034] The optoelectronic circuit 20 also comprises a plurality of circuits of link L;, the second reference terminal A2 being connected to each set of light-emitting diodes D; by one of said linking circuits L;, each linking circuit Li on the one hand comprising one of said conduction components SW; and at least one resistive component R; mounted in series with said conduction component SW; of said linking circuit L;, on the other hand being configured such that the first terminal Bl; of the conduction component SW; is connected to the set of light-emitting diodes D i associated with it and that a first connection terminal Bcl; of the resistive component Ri is connected to the second terminal B2; of the conduction component SW; of said linking circuit L; and that a second connection terminal Bc2; of the resistive component Ri is connected to the second reference terminal A2. The optoelectronic circuit 20 includes a control circuit 28 comprising a difference amplifier 30 and as many output stages as there are conduction components SW;which comprises the optoelectronic circuit 20, each of said output stages being connected to the third terminal B3i of one of said conduction components SWi, the control circuit 28 being adapted to provide, for each linking circuit L;, 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 Bel; of the resistive component R; and the second terminal B2; of the conduction component SW; of this linking circuit L;, and the second reference terminal A2, and on the other hand at least a second voltage V REP 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 Voffsetî, different for each output stage of the control circuit 28. ;

[0035] To explain the operation of the optoelectronic circuit 20, we consider an optoelectronic circuit with a simplified structure. Figure 3 represents a particular embodiment of Figure 1 where N is equal to 3. The control circuit 28 comprises three output stages connected to the three conduction components SWb, SW2, and SW3 at the third terminals B3i, B32, and B33, respectively.A capacitor Ci mounted at the input of the optoelectronic circuit 20 between the first supply terminal Ai and the second reference terminal A2 allows the variable voltage Væim to be maintained at a value greater than the threshold voltage of the first set of LEDs Db. This arrangement ensures that the first set of LEDs Di is always conducting and that the optoelectronic circuit emits light continuously, regardless of the variation of the variable voltage Væim. In what follows, the focus is on the operation of the simplified optoelectronic circuit 20 of [Fig.3].

[0036] When the value of the variable voltage Vim is less than the sum of the threshold voltages of the diode sets Di and D2, only the diode set Di is conducting. The The control circuit 28 provides the linking circuit Li (comprising Ri and SWi) with the control signal Si from the comparison between the first voltage Vsource (taken between a first potential between the first connection terminal Bcli and the second terminal B2i and the second reference terminal A2) and the second voltage Vref-The control circuit 28 allows the first voltage Vsource to be locked to the second voltage Vref offset by the third voltage Voffseti- In this case, the three conduction components are conducting.

[0037] When the value of the variable voltage Vim becomes greater than the sum of the threshold voltages of the diode sets Di and D2 but remains less than the sum of the threshold voltages of the diode sets D2 and D3, only the diode sets Di and D2 are conducting. The control circuit 28 provides the linking circuit L2 (comprising Rb, R2, and SW2) with the control signal S2 based on the comparison between the first voltage Vsource (taken between a first potential between the first connection terminal Bcl2 and the second terminal B22 and the second reference terminal A2) and the second voltage Vref. The control circuit 28 allows the first voltage Vsource to be controlled by the second voltage VREf, offset by the third voltage VOffset2. In this case, the conduction components SW2 and SW3 are conducting, and SWi is blocked.

[0038] When the value of the variable voltage Vim is greater than the sum of the threshold voltages of the diode sets Db D2 and D3, all diode sets Db D2 and D3 are conducting. The control circuit 28 provides the linking circuit L3 (comprising Rb, R2, R3, and SW3) with the control signal S3 based on the comparison between the first voltage Vsource (taken between a first potential between the first connection terminal Bcl3 and the second terminal B23 and the second reference terminal A2) and the second voltage Vref. The control circuit 28 allows the first voltage Vsource to be locked to the second voltage VREf offset by the third voltage Voffsets. In this case, the conduction components SWi and SW2 are blocked, and SW3 is conducting.

[0039] Let us now consider again the optoelectronic circuit 20 of [Fig. 1]. Each conduction component SW; is a circuit whose equivalent electrical resistance varies between a maximum 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; is at its maximum value, the conduction component SW; is substantially equivalent to an open switch. According to this embodiment, for i varying from 1 to N, when a conduction component SW; is conducting, the conduction components SW; to SWm are blocked and the conduction components SWi+i to SWN are conducting.

[0040] According to one embodiment, the control signal S; of each component of The conduction signal SW is a signal that can vary continuously between a first and a second value. Depending on the embodiment, the equivalent electrical resistance of the conduction component SW can decrease or increase as the control signal Si varies from the first value to the second value. The first and second values ​​of the control signals S, i, varying from 1 to N, may not be the same for all conduction components SW.

[0041] According to one embodiment, the light-emitting diode assemblies D; are connected together so as to constitute a light-emitting circuit in which the light-emitting diode assemblies D; are in series with each other, the light-emitting circuit having a first end electrically connected to the first supply terminal Ai and a second end connected to a node A3; the optoelectronic circuit 20 comprises as many resistive components R; as light-emitting diode assemblies D;, and said resistive components R; are mounted in series with each other, between the node A3 and the second reference terminal A2.

[0042] According to one embodiment, the light-emitting diodes D; are arranged in increasing ranks from a first set of light-emitting diodes D; at the first end of the light-emitting circuit to a last set of light-emitting diodes D; at the second end of the light-emitting circuit; for each linking circuit L; of the optoelectronic circuit 20 excluding the last set of light-emitting diodes DN, the second terminal B2; of the conduction component SW; is connected to an electrical link connecting two resistive components Ri mounted in series with each other.

[0043] According to the present embodiment, the plurality of connecting circuits L; can be presented in the following manner: - The Lb circuit connecting A2 to includes Ri and SWb - the circuit L2, connecting A2 to D2, includes Ri and R2 connected together in a series assembly and SW2, - Circuit L3, connecting A2 to D3, comprises RB, R2 and R3 connected together in a series arrangement and SW3, - the LN circuit, linking A2 to DN, includes RB R2.... RN connected together in a series arrangement and SWN.

[0044] Said resistive components R; are intended to carry a source current I, corresponding to the current supplying the conducting sets of LEDs D;. During an increasing phase of the variable voltage Valim, the number of conducting sets of LEDs D; gradually increases as the value of the variable voltage Valim becomes greater than the threshold voltage of the LED set D; under consideration. Similarly, During the decreasing phase of the variable voltage Valim, the number of conducting LED arrays D gradually decreases as the value of the variable voltage Valim falls below the threshold voltage of the LED array D under consideration. Thus, the number of resistive components R and conducting LED arrays D varies proportionally with the variable voltage Valim. Increasing the number of resistive components R then advantageously limits the value of the source current I when there is an increase in the value of the variable voltage Valim. Consequently, the present arrangement of resistive components R allows the power of the LED arrays D to be maintained at a substantially constant value regardless of the variation in the variable voltage Valim.

[0045] Figure 4 shows timing diagrams, obtained by simulation, of the variable voltage Valim, the current Isource, the currents Ib, I2, I3, and I4 flowing in the conduction components SW, in a particular case where N is equal to 4, and the power P, fd of the LED arrays D. It can be seen that during a falling phase of the variable voltage Valim, the value of the current Isource, flowing in the conducting LED arrays D and in the resistive components R forming part of the considered connecting circuit L, increases progressively. This increase is related to the decrease in the number of resistive components R, which varies proportionally with the variable voltage Valim. Similarly, during a rising phase of the variable voltage Valim, the value of the current Isource, flowing in the conducting LED arrays D and in the resistive components Ri, decreases progressively.This decrease is linked to the increase in the number of resistive components R; which varies proportionally with the variable voltage Valim-This allows to have a power in the light-emitting diode assemblies Di substantially constant independent of the value of variable voltage Valim, as can be seen on the PLEd- power timing diagram.

[0046] According to one embodiment, for each conduction component SW;, the control circuit 28 is adapted to control the first voltage Vsource to the second voltage VREF reduced by the third voltage Voffseti which is decreasing with the rank of the set of light-emitting diodes D; to which the conduction component SW; is connected.

[0047] 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 VRu can also be obtained from a modulation signal supplied to the optoelectronic circuit 20 by an external circuit. The second voltage VRu or the modulation signal can be supplied by a drive, in particular a drive that can be operated by a user or a light sensor. minosity.

[0048] According to one embodiment, the difference amplifier 30 receives at input a differential voltage corresponding to the difference between the first voltage Vsource and the second voltage VREF.

[0049] Figure 2 shows 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 ldi and a second current Id2, the control circuit 28, comprising a first current mirror 32, 34 with multiple outputs adapted to copy, for each conduction component SW, the first current ldi or a third current multiplied by a first copy factor, and a second current mirror 36 with multiple outputs adapted to copy, for each conduction component SW, the second current Id2 or the third current multiplied by a second copy factor, the ratio between the first copy factor and the second copy factor being different for each conduction component SW.

[0050] According to one embodiment, for each conduction component SWi, a capacitor is connected to the conduction component SW; or integrated into the conduction component SWi, the first current mirror 34 comprising a capacitor charging circuit Tsupd and the second current mirror 36 comprising a capacitor discharge circuit Tmr.

[0051] According to one embodiment, the difference amplifier 30 comprises a differential pair including a first transistor T i receiving the first voltage Vsource and a second transistor T2 receiving the second voltage VREF.

[0052] The first transistor Ti can be a MOS transistor whose gate receives the first voltage Vsource and whose source is connected to one 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 VR|d and whose source is connected to the current source Idiff. The drain current of transistor Ti corresponds to the first current Id1 and the drain current of transistor T2 corresponds to the second current Id2. In one embodiment, transistors Ti and T2 have the same characteristics, in particular the same W / L aspect ratio. The aspect ratio of a transistor's channel is defined as the ratio of its width to its length.

[0053] The first current mirror 32 may comprise two transistors T3 and T4, for example N-channel MOS transistors. The drain of transistor T3 is connected to the drain of transistor T1, and the source of 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. In one embodiment, the two transistors T3 and T4 have the same characteristics risks, including the same form factor, and the current flowing in transistor T4 is therefore equal to the current ldi flowing in T3.

[0054] The first current mirror 34 may include a transistor T5, for example a P-channel MOSFET, whose drain is connected to the drain of transistor T4, whose source is connected to the source of the high reference potential Von, and whose gate is connected to the drain. The first current mirror 34 may further include, for each conduction component SW, i ranging from 1 to N, one of said circuit Tsup4. The circuit Tsup4 may, for example, be a P-channel MOSFET, whose source 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 B3 of the conduction component SW. In one embodiment, the transistors Tsup4 may not have the same characteristics with respect to each other and with respect to transistor T5. Rsup4 is denoted as the ratio between the channel form factor of transistor Tsup4 and the channel form factor of transistor T5.In particular, Rsup4 can be different from R,upj, with i different from j. IG is called the current at the drain of transistor Tsup4.

[0055] The second current mirror 36 may include a transistor T6, for example an N-channel MOSFET, whose drain is connected to the drain of 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 include, for each conduction component SWi, i ranging from 1 to N, one of said circuit Tinf4. The circuit Tinf4 may, for example, be an N-channel MOSFET, whose source is connected to the source of the low reference potential Voff, whose gate is connected to the gate of transistor T6, and whose drain is connected to the third terminal B3 of the conduction component SWi. In one embodiment, the transistors Tinf4 may not have the same characteristics with respect to each other and with respect to transistor T6. Rinf4 is denoted as the ratio between the channel form factor of transistor Tinf4 and the channel form factor of transistor T6.In particular, Rinf4 can be different from Rinf_j, with i different from j. IG'i is called the drain current of transistor Tsup4.

[0056] In one embodiment, each conduction component SW; comprises a MOS transistor. The control signal Si is the gate potential of the MOS transistor of the conduction component SW; at its third terminal B3;. The drain of the MOS transistor corresponds to the first terminal B1; and the source of the MOS transistor corresponds to the second terminal B2;. In another embodiment, the conduction component SW; may comprise two MOS transistors, which advantageously increases the switching speed of the conduction component SW;. Alternatively, the conduction component SW; may be a transistor other than a MOS transistor, a relay, a microelectromechanical system, and generally any element whose electrical conductivity can be controlled by voltage or current.

[0057] According to one embodiment, the first current mirror 34 comprises, for each conduction component SW;, a first copy block TMI|, connected to the gate of the MOS transistor of the conduction component SW; and adapted to provide the first current ldi multiplied by the first copy factor and the second current mirror 36 comprises, for each conduction component SW;, a second copy block Tinf.i connected to the gate of the MOS transistor of the conduction component SW; and adapted to provide the second current Id2 multiplied by the second copy factor.

[0058] According to one embodiment and in an ascending phase of the variable supply voltage Vsupply, while the light-emitting diode assemblies Di to D4 are conducting, the light-emitting diode assemblies D; to DN are blocked, the control signals Si to Si 2 are at Voff, the signals Si to SN are at Von and the signal Sm is at a voltage value enabling the single conduction component SWi to impose the current Isource in the light-emitting diode assemblies, when the voltage across the light-emitting diode assemblies D; becomes greater than the threshold voltage of the light-emitting diode assemblies D;, the latter becomes conducting and a current begins to flow in the light-emitting diode assemblies D;, the conduction component SW; and the resistive components R;.This results in a temporary decrease in the total equivalent impedance between the first supply terminal Ai and node A3, and therefore a temporary increase in the voltage Vsource. This increase in the voltage Vsource leads to a decrease in the current ldi through the transistor Ti of the differential pair 30. As a result, the current reproduced by each transistor Tsup4 decreases for i varying from 1 to N.Since there is an equivalent capacitance at each third terminal B3, i varying from 1 to N, which could correspond to a separate capacitor or a parasitic capacitance of another electronic component, the voltage at the third terminal B3 decreases until it reaches approximately the off potential, while the voltage at the third terminal B3 also decreases until it reaches its equilibrium point. This allows the conduction component SW to impose the source voltage Vsource on its own. The conduction component SWm therefore opens, and simultaneously the conduction component SW becomes increasingly conductive. All the current then flows through the conduction component SW.The control circuit 28 then regulates the source voltage V to the voltage VRu reduced by Voffsetî by the conduction component SW;, the offset voltage Voffsetï between the source voltage VREf and the output voltage Voffsetï being lower than the offset voltage Voffset-. In the case where each conduction component SW; includes a MOS transistor whose gate receives the signal Si, this means that the voltage at the gate of the transistor SWh decreases and the transistor SW, therefore, conducts less and less until it reaches its non-conducting state. At equilibrium, the potential at the . third terminal B3; is equal to the sum of the voltage Vsource and the gate-source voltage of the transistor SW;.

[0059] According to one embodiment and in a falling phase of the variable supply voltage V, while the light-emitting diode assemblies Di to D; are conducting, the light-emitting diodes Di+i to DN are blocked, the signals Si to Sm are at Voff, the signals Si+i to SN are at Von and the signal Si is at a voltage value allowing the only conduction component SWid to impose the current Isource in the light-emitting diode assemblies, when the voltage across the light-emitting diode assembly D; decreases and becomes less than the threshold voltage of the light-emitting diode assembly D;, the latter begins to block.This results in a temporary increase in the total equivalent impedance between the first supply terminal Ai and node A3, and therefore a temporary decrease in the source voltage Vsource. This decrease in the source voltage leads to an increase in the current ldi flowing through transistor Ti of the differential pair 30. Consequently, the current produced by each transistor T,up increases. Since there is an equivalent capacitance at each third terminal B3i, the voltage at the third terminal B3i increases until it reaches approximately the potential Von, while the voltage at the third terminal B3i also increases until it reaches its equilibrium point, allowing the conduction component SWd to impose the source voltage V on its own at Vref - Voffseth. The conduction component SWd therefore closes completely, and the conduction component SWm becomes increasingly conductive. All the current then flows through the conduction component SWm.The control circuit 28 then controls the voltage Vsource to the voltage VREF reduced by Voffseu i by the conduction component SWi, the offset voltage Voffseth being higher than the offset voltage Voffsetî- In the case where each conduction component SW; includes a MOS transistor whose gate receives the signal Si, this means that the voltage at the gate of the transistor SWm increases and that the transistor SW, । becomes more and more conducting and the transistor SW; reaches its fully conducting state. .

[0060] Furthermore, in the embodiments described above, each transistor T,up is adapted to copy the current ldi multiplied by the copy factor Rsup4 and each transistor Tmr is adapted to copy the current Id2 multiplied by the copy factor Rinf. As an alternative, each of the transistors Tmr and TMI|, can be adapted to copy a reference current, for example a constant current.

[0061] According to one embodiment, the optoelectronic circuit 20 comprises a capacitor Ci mounted between the first power supply terminal Ai and the second reference terminal A2, enabling the variable voltage VÆiM to remain above a threshold voltage of the array of light-emitting diodes Di connected to the first power supply terminal Ab. The capacitance Ci at the input of the optoelectronic circuit 20 advantageously avoids the risks of periods of no light emission and therefore avoids any uncomfortable stroboscopic effect.

[0062] According to one embodiment, the third voltage V0FFSETi varies with temperature. The offset voltage V0FFSETi can either increase or decrease as the temperature increases. If the offset voltage V0FFSETi decreases as the temperature increases, an increase in temperature results in a decrease in the current flowing through the resistive components R; and therefore a decrease in the thermal power supplied by the optoelectronic circuit 20. This provides protection of the optoelectronic circuit 20 against thermal runaway.

Claims

Demands

1. An optoelectronic circuit (20) comprising a first power supply terminal (AJ) and a second reference terminal (A2), the first power supply terminal (Ai) 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 (D;) connected together in a series arrangement, which series arrangement being connected to the first power supply terminal (AJ, - a plurality of conduction components (SW;) where each conduction component (SW;) is associated with one unique set of light-emitting diodes (D;), each conduction component (SW;) having a variable electrical conductance depending on a control signal (S;), each conduction component (SW;) having a first terminal (B1;), a second terminal (B2;) and a third terminal (B3;), - a plurality of linking circuits (L;), the second reference terminal (A2) being connected to each set of light-emitting diodes (Di) by one of said linking circuits (L;), each linking circuit (L;) on the one hand comprising one of said conduction components (SW;) and at least one resistive component (R;) mounted in series with said conduction component (SWi) of said linking circuit (L;), on the other hand being configured such that the first terminal (B h) of the conduction component (SWi) is connected to the set of light-emitting diodes (D;) associated with it and that a first connection terminal (Bch) of the resistive component (R;) is connected to the second terminal (B2;) of the conduction component (SW;) of said linking circuit (L;) and that a second connection terminal (Bc2;) of the resistive component (R; ) 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) in the optoelectronic circuit (20), each of said output stages being connected to the third terminal (B3i) of one of said conduction components (SWi), the control circuit (28) being adapted to provide, for each linking circuit (L;), 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 (Bch) of the resistive component (R;) and the second terminal (B2;) of the conduction component (SW;) of this linking circuit (L;), and the second reference terminal (A2), and on the other hand, at least a second voltage (Vref) identical for all the conduction components (SW;), the control circuit (28) being adapted to control the first voltage (Vsource) to the second voltage (Vref) offset by a third voltage (Voffseu), different for each output stage of the control circuit (28), The optoelectronic circuit (20) is characterized in that: - the light-emitting diode assemblies (D;) are connected together so as to constitute a light-emitting circuit in which the light-emitting diode assemblies (Di) are in series with each other, the light-emitting circuit having a first end electrically connected to the first supply terminal (Ai) and a second end connected to a node (A3); - the optoelectronic circuit (20) comprises as many resistive components (R;) as sets of light-emitting diodes (D;); - said resistive components (R;) being mounted in series with each other, between the node (A3) and the second reference terminal (A2); - the sets of light-emitting diodes (D;) 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 link circuit (L;) of the optoelectronic circuit (20) excluding the last set of light-emitting diodes (Dn), the second terminal (B2;) of the conduction component (SWi) is connected to an electrical link connecting two resistive components (R;) mounted in series with each other.

2. Optoelectronic circuit (20) according to claim 1, wherein, for each conduction component (SWi), the control circuit (28) is adapted to control the first voltage (Vsource) to the second voltage (V RFF) less the third voltage (V0FFsetï) which is decreasing with the rank of the set of light-emitting diodes (D;) to which the conduction component (SW;) is connected.

3. Optoelectronic circuit (20) according to any one of claims 1 to 2, wherein the difference amplifier (30) receives at input a differential voltage corresponding to the difference between the first voltage (Vsource) and the second voltage (V^).

4. Optoelectronic circuit (20) according to any one of claims 1 to 3, wherein the difference amplifier (30) is adapted to provide a first current (ldi) and a second current (Id2), the control circuit (28) comprising a first multi-output current mirror (32, 34) adapted to copy, for each conduction component (SWi), the first current (ldi) or a third current multiplied by a first copy factor, and a second multi-output current mirror (36) adapted to copy, for each conduction component (SWi), the second current (Id2) or the third current multiplied by a second copy factor, the ratio between the first copy factor and the second copy factor being different for each conduction component (SWi).

5. Optoelectronic circuit (20) according to claim 4, comprising, for each conduction component (SW;), a capacitor connected to the conduction component (SW;) or integrated into the conduction component (SWi), the first current mirror (34) comprising a circuit (Tsup4) for charging the capacitor and the second current mirror (36) comprising a circuit for discharging (Tinf.i) the capacitor.

6. An optoelectronic circuit (20) according to any one of claims 1 to 5, wherein the difference amplifier (30) comprises a differential pair including a first transistor (TJ) receiving the first voltage (Vsource) and a second transistor (T2) receiving the second voltage (Vref).

7. Optoelectronic circuit (20) according to claim 6, wherein the first transistor (TJ) 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).

8. Optoelectronic circuit (20) according to any one of claims 1 to 7, wherein each conduction component (SW;) comprises a MOS transistor.

9. Optoelectronic circuit (20) according to claim 8 and any one of claims 4 or 5, wherein the first current mirror (34) comprises, for each conduction component (SW;), a first copy block (Tsup i) connected to the gate of the MOS transistor of the conduction component (SW;) and adapted to provide the first current (ldi) multiplied by the first copy factor and wherein the second current mirror (36) comprises, for each conduction component (SWi), a second copy block (Tinf.i) connected to the gate of the MOS transistor of the conduction component (SWi) and adapted to provide the second current (Id2) multiplied by the second copy factor.

10. Optoelectronic circuit (20) according to any one of claims 1 to 9, comprising a capacitor (Ci) mounted between the first supply terminal (AO and the second reference terminal (A2) and enabling the variable voltage (ValimMc) to remain at a value greater than a threshold voltage of the set of light-emitting diodes (DO connected to the first supply terminal (Ai).

11. Optoelectronic circuit (20) according to any one of claims 1 to 10, wherein the third voltage (Vofesetî) varies as a function of temperature.

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