Optoelectronic circuit with light-emitting diodes

Abstract

An optoelectronic circuit for receiving a variable voltage containing alternating increasing and decreasing phases, the optoelectronic circuit including a plurality of assemblies of light-emitting diodes and a switching device for controlling or interrupting the circulation of a current in each assembly and for varying the intensity of the current according to the number of assemblies through which the current passes during at least one increasing or decreasing phase.

Claims

1. An optoelectronic circuit intended to receive a variable voltage containing an alternation of rising and falling phases, the optoelectronic circuit comprising: a plurality of assemblies of light-emitting diodes; a current source configured to supply a current having an intensity depending on at least one control signal, the current source comprising elementary current sources assembled in parallel and configured to be activated and deactivated independently from one another; and a switching device configured to control said current through each assembly of the assemblies of light-emitting diodes, and configured to supply said at least one control signal to vary the intensity of said current according to the number of assemblies conducting said current during at least a rising or falling phase.

2. The optoelectronic circuit of claim 1, wherein the current source is configured to supply a current having its intensity varying among a plurality of different intensity values according to the number of assemblies conducting said current during at least one rising or falling phase.

3. The optoelectronic circuit of claim 1, wherein the elementary current sources are configured to supply currents having the same intensity or different intensities.

4. The optoelectronic circuit of claim 1, wherein the switching device is configured to activate at least one of the elementary current sources during at least one rising phase and is configured to deactivate at least one of the elementary current sources during at least one falling phase.

5. The optoelectronic circuit of claim 1, wherein one of the elementary current sources is configured to supply a current having a given intensity and the other elementary current sources are each configured to supply a current having an intensity equal to a power of two different from said given intensity.

6. The optoelectronic circuit of claim 1, wherein the switching device is configured to connect the assemblies of light-emitting diodes according to a plurality of connection configurations successively according to a first order during each rising phase of the variable voltage and a second order during each falling phase of the variable voltage and is configured to activate the elementary current sources according to a third order during each rising phase of the variable voltage and of deactivating the elementary current sources according to a fourth order during each falling phase of the variable voltage.

7. The optoelectronic circuit of claim 1, comprising a memory having a plurality of values of the control signal of the current source, each corresponding to the provision by the current source of said current having its intensity varying among said plurality of intensity values, stored therein.

8. The optoelectronic circuit of claim 1, comprises means for modifying the variation profile of the intensity of said current according to the number of assemblies conducting said current during at least one rising or falling phase.

9. The optoelectronic circuit of claim 1, wherein the assemblies of light-emitting diodes are series-connected and wherein the switching device comprises, for each assembly of light-emitting diodes, at least one switch connecting said assembly to the current source, the switching device being configured to transmit binary control signals for the turning off or on of the switches according to said connection configurations.

10. The optoelectronic circuit of claim 1, wherein the switching device is configured to control said current at least in part through interrupting flow of the current.

11. A method of controlling a plurality of assemblies of light-emitting diodes of an optoelectronic circuit receiving a variable voltage containing an alternation of rising and falling phases, the optoelectronic circuit further comprising a current source supplying a current having its intensity depending on at least one control signal and a switching device, wherein, during at least one rising or falling phase, the switching device orders or interrupts the flowing of said current through each assembly and supplies said at least one control signal to vary the intensity of said current according to the number of assemblies conducting said current, wherein the current source comprises elementary current sources assembled in parallel and capable of being activated and deactivated independently from one another.

12. The method of claim 11, wherein the current source supplies said current having its intensity varying among a plurality of different intensity values according to the number of assemblies conducting said current during at least one rising or falling phase.

13. The method of claim 11, wherein the current source comprises at least two elementary current sources assembled in parallel and wherein at least one of the elementary current sources is activated during at least one rising phase and at least one of the elementary current sources is deactivated during at least one falling phase.

14. The method of claim 13, wherein the current source comprises at least three elementary current sources assembled in parallel, wherein, for at least successive rising and falling phases, the number of activated elementary current sources increases from the beginning to the end of the rising phase and the number of activated elementary current sources decreases from the beginning to the end of the falling phase or wherein the number of activated elementary current sources increases and then decreases from the beginning to the end of the rising phase and the number of activated elementary current sources increases and then decreases from the beginning to the end of the falling phase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which:

(2) FIG. 1, previously described, is an electric diagram of an example of an optoelectronic circuit comprising light-emitting diodes;

(3) FIG. 2, previously described, is a timing diagram of the power supply voltage and current of the light-emitting diodes of the optoelectronic circuit of FIG. 1;

(4) FIG. 3 shows an electric diagram of an embodiment of an optoelectronic circuit comprising light-emitting diodes and a device for switching the light-emitting diodes;

(5) FIG. 4 shows an electric diagram of an embodiment of the current source of the optoelectronic circuit of FIG. 3;

(6) FIGS. 5A and 5B are timing diagrams of voltages and of currents of the optoelectronic circuit of FIG. 3 for two embodiments of control of the current source of the optoelectronic circuit;

(7) FIGS. 6 to 10 show other embodiments of the current source of the optoelectronic circuit of FIG. 3;

(8) FIG. 11 is an electric diagram of another embodiment of an optoelectronic circuit comprising light-emitting diodes and a device for switching the light-emitting diodes;

(9) FIG. 12 is an electric diagram of a more detailed embodiment of a portion of the optoelectronic circuit of FIG. 11;

(10) FIG. 13 is a timing diagram of voltages and of the current of the optoelectronic circuit of FIG. 11;

(11) FIG. 14 is an electric diagram of another embodiment of an optoelectronic circuit comprising light-emitting diodes and a device for switching the light-emitting diodes;

(12) FIG. 15 is an electric diagram of a more detailed embodiment of a portion of the optoelectronic circuit of FIG. 14;

(13) FIG. 16 is an electric diagram of another embodiment of an optoelectronic circuit comprising light-emitting diodes and a device for switching the light-emitting diodes;

(14) FIGS. 17 and 18 show electric diagrams of embodiments of a current sensor of the electronic circuit of FIG. 16;

(15) FIGS. 19 and 20 show curves of the variation, obtained by simulation, of voltages and of currents of the optoelectronic circuit of FIG. 3 for two embodiments of control of the current source of the optoelectronic circuit; and

(16) FIG. 21 shows an electric diagram of another embodiment of an optoelectronic circuit comprising light-emitting diodes and a device for switching the light-emitting diodes.

DETAILED DESCRIPTION

(17) For clarity, the same elements have been designated with the same reference numerals in the various drawings and, further, the various drawings are not to scale. In the following description, unless otherwise indicated, terms substantially, approximately, and in the order of mean to within 10%. In the following description, the ratio of the active power consumed by the electronic circuit to the product of the effective values of the current and of the voltage powering the electronic circuit is called power factor.

(18) FIG. 3 shows an electric diagram of an embodiment of an optoelectronic circuit 20 comprising a light-emitting diode switching device. The elements of optoelectronic circuit 20 common with optoelectronic circuit 10 are designated with the same reference numerals. In particular, optoelectronic circuit 20 comprises rectifying circuit 12 receiving power supply voltage V.sub.IN between terminals IN.sub.1 and IN.sub.2 and supplying rectified voltage V.sub.ALIM between nodes A.sub.1 and A.sub.2. As a variation, circuit 20 may directly receive a rectified voltage, and it is then possible for the rectifying circuit not to be present.

(19) Optoelectronic circuit 20 comprises N series-connected assemblies of elementary light-emitting diodes, called general light-emitting diodes D.sub.i in the following description, where i is an integer in the range from 1 to N and where N is an integer in the range from 2 to 200. Each general light-emitting diode D.sub.1 to D.sub.N comprises at least one elementary light-emitting diode and is preferably formed of the series and/or parallel assembly of at least two elementary light-emitting diodes. In the present example, the N general light-emitting diodes D.sub.i are series-connected, the cathode of general light-emitting diode D.sub.i being coupled to the anode of general light-emitting diode D.sub.i+1, for i varying from 1 to N1. The anode of general light-emitting diode D.sub.1 is coupled to node A.sub.1. General light-emitting diodes D.sub.i, with i varying from 1 to N, may comprise the same number of elementary light-emitting diodes or different numbers of elementary light-emitting diodes.

(20) Optoelectronic circuit 20 comprises a current source 22 having a terminal coupled to node A.sub.2 and having its other terminal coupled to a node A.sub.3. Call I.sub.CS the current flowing between nodes A.sub.1 and A.sub.2. Circuit 20 comprises a device 24 for switching general light-emitting diodes D.sub.i, with i varying from 1 to N. As an example, device 24 comprises N controllable switches SW.sub.1 to SW.sub.N. Each switch SW.sub.i, with i varying from 1 to N, is assembled between node A.sub.3 and the cathode of general light-emitting diode D.sub.i. Each switch SW.sub.i, with i varying from 1 to N, is controlled by a signal S.sub.i supplied by a control unit 26. Current source 22 is also controlled by control unit 26. Control unit 26 may be totally or partly formed by a dedicated circuit or may comprise a microprocessor or a microcontroller capable of executing a series of instructions stored in a memory. As an example, signal S.sub.i is a binary signal and switch SW.sub.i is off when signal S.sub.i is in a first state, for example, the low state, and switch SW.sub.i is on when signal S.sub.i is in a second state, for example, the high state.

(21) Each switch SW.sub.i is, for example, a switch comprising at least one transistor, particularly a field-effect metal-oxide gate transistor or enrichment (normally on) or depletion (normally off) MOS transistor. According to an embodiment, each switch SW.sub.i comprises a MOS transistor, for example, having an N channel, having its drain coupled to the cathode of general light-emitting diode D.sub.i, having its source coupled to node A.sub.3, and having its gate receiving signal S.sub.i.

(22) Optoelectronic circuit 20 comprises one or a plurality of sensors connected to control unit 26. It may be a single sensor, for example, a sensor capable of measuring voltage V.sub.ALIM or the current flowing between terminals IN.sub.1 and IN.sub.2, or a plurality of sensors, where each sensor may be associated with a general light-emitting diode D.sub.i. As an example, a single sensor 28 has been shown in FIG. 3.

(23) Control unit 26 is capable of controlling switches SW.sub.i, with i varying from 1 to N, to the on or off state according to the value of voltage V.sub.ALIM, according to a sequence based on the measurement of a physical parameter, for example, at least a current or a voltage. As an example, the turning off and the turning on of switches SW.sub.i may be controlled by control unit 26 based on the signals supplied by sensor 28 or the sensors. As a variation, the turning off and the turning on of switch SW.sub.i may be controlled based on the measurement of the voltage at the cathode of each general light-emitting diode D.sub.i. The number of switches SW.sub.1 to SW.sub.N may vary according to the turn-off and turn-on sequence implemented by control unit 26. As an example, switch SW.sub.N may not be present.

(24) Current source 22 is a current source controlled by control unit 26 and capable of supplying a current I.sub.CS which remains uninterrupted as long as power supply voltage V.sub.ALIM is greater than the threshold voltage of general light-emitting diode D.sub.1. Current source 22 is capable of supplying a variable current at different levels according to the number of general light-emitting diodes which are conductive. Preferably, current source 22 supplies a current I.sub.CS having its intensity increasing when the number of general light-emitting diodes which are conductive increases. This advantageously enables to increase the power factor of optoelectronic circuit 20 with respect to the case where the current would be constant. Optoelectronic circuit 20 may comprise a circuit, not shown, for supplying a reference voltage, possibly obtained from voltage V.sub.ALIM for the supply of the current source.

(25) FIG. 4 shows an embodiment of current source 22 where current source 22 comprises M elementary controllable current sources CS.sub.1 to CS.sub.M, M being an integer capable of varying from 1 to N. Preferably, M is equal to N. In the present embodiment, elementary current sources CS.sub.j, with j varying from 1 to M, are assembled in parallel between node A.sub.3 and node A.sub.2. Each elementary current source CS.sub.j is activated or deactivated by control unit 26 by means of a control signal C.sub.j. As an example, signal C.sub.j is a binary signal and elementary current source CS.sub.j is off when signal C.sub.j is in a first state, for example, the low state, and current source CS.sub.j is activated when signal C.sub.j is in a second state, for example, the high state. As a variation, signal C.sub.1 may be omitted and current source CS.sub.1 may be automatically activated, that is, it supplies a current as soon as it is powered with a sufficient voltage.

(26) The larger the number of current sources CS.sub.j which are activated, the higher the intensity of current I.sub.CS. According to an embodiment, the number of elementary current sources CS.sub.j which are activated depends on the number of general light-emitting diodes D.sub.i which are conductive. According to an embodiment, current source 22 is capable of supplying a current I.sub.CS having an intensity at a level among a plurality of constant levels and having its level depending on the number of general light-emitting diodes which are conductive. The currents supplied by elementary current sources CS.sub.j of current source 22 may be identical or different. According to an embodiment, each elementary current source CS.sub.j is capable of supplying a current of intensity I*2.sup.j-1. Current source 22 is then adapted to supply a current having an intensity I.sub.CS which may, according to control signals C.sub.j, take any value k*I, with k varying from 0 to 2.sup.M1.

(27) The sequence of activation of current sources CS.sub.j during the variation of voltage V.sub.ALIM particularly depends on the operating properties of the optoelectronic circuit which are desired to be favored.

(28) FIG. 5A illustrates an embodiment of a sequence of activation of the current sources which enables to increase the power factor of the optoelectronic circuit. FIG. 5A shows curves of the variation of signals S.sub.1, S.sub.2 and S.sub.3, curves of the variations of signals C.sub.1, C.sub.2, C.sub.3 and C.sub.4, and of current I.sub.CS when optoelectronic circuit 20 comprises four general light-emitting diodes and four elementary current sources CS.sub.j in parallel, during a cycle of voltage V.sub.ALIM in the case where voltage V.sub.IN is a sinusoidal voltage. Call a.sub.0 to a.sub.7 successive times and I.sub.1, I.sub.2, I.sub.3 and I.sub.4 increasing intensity values of current I.sub.CS.

(29) According to an embodiment, at the beginning of a rising phase of voltage V.sub.ALIM, signals S.sub.i, with i varying from 1 to N1, are initially at 1 so that switches SW.sub.i are on. Signal C.sub.1 is at 1 so that current source CS.sub.1 is activated. At time a.sub.0, general light-emitting diode D.sub.1 turns on and conducts current I.sub.CS having an intensity equal to I.sub.1. Switches SW.sub.1, SW.sub.2, and SW.sub.3 are successively turned off at times a.sub.1, a.sub.2, and a.sub.3 along the rise of voltage V.sub.ALIM so that general light-emitting diodes D.sub.2, D.sub.3, and D.sub.4 are successively powered with current. In parallel, current sources CS.sub.2, CS.sub.3 and CS.sub.4 are successively activated at times a.sub.1, a.sub.2 and a.sub.3 along the rise of voltage V.sub.ALIM, so that the intensity of power supply current I.sub.CS is successively equal to I.sub.2, I.sub.3 and I.sub.4. During a falling phase of voltage V.sub.ALIM, switches SW.sub.3, SW.sub.2, and SW.sub.1 are successively turned on at times a.sub.4, a.sub.5, and a.sub.6 to successively short-circuit general light-emitting diodes D.sub.4, D.sub.3, and D.sub.2. In parallel, during a falling phase of voltage V.sub.ALIM, current sources CS.sub.4, CS.sub.3 and CS.sub.2 are successively deactivated at times a.sub.4, a.sub.5, and a.sub.6 so that the intensity of power supply current I.sub.CS is successively equal to I.sub.3, I.sub.2 and I.sub.1. At time a.sub.7, when the power supply voltage becomes smaller than the threshold voltage of general light-emitting diode D.sub.1, current I.sub.CS takes a zero value.

(30) In this embodiment, the current sources are activated so that power supply current I.sub.CS follows as best as possible the general shape of a sine wave, that is, the shape of voltage V.sub.ALIM, in phase therewith. Advantageously, the power factor of the optoelectronic circuit is then increased.

(31) FIG. 5B is similar to FIG. 5A and illustrates an embodiment of a sequence of activation of the current sources, which enables to decrease the flickering perceived by an observer. The curves of FIG. 5B have been obtained with the optoelectronic circuit used to obtain the curves of FIG. 5A, with the difference that the current source activation sequence is modified. Indeed, signals C.sub.1 and C.sub.2 are initially at 1 and signals C.sub.3 and C.sub.4 are initially at 0 so that current sources CS.sub.1 and CS.sub.2 are activated and, at time a.sub.0, the intensity of current I.sub.CS flowing through general light-emitting diode D.sub.1 is equal to I.sub.2. At time a.sub.1, signal C.sub.3 is set to 1 so that the intensity of current I.sub.CS flowing through general light-emitting diodes D.sub.1 and D.sub.2 is equal to I.sub.3. At time a.sub.2, signal C.sub.3 is set to 0 so that the intensity of current I.sub.CS flowing through general light-emitting diodes D.sub.1, D.sub.2 and D.sub.3 is equal to I.sub.2. At time a.sub.3, signal C2 is set to 0 so that the intensity of current I.sub.CS flowing through general light-emitting diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 is equal to I.sub.1. A symmetrical activation sequence is carried out at times a.sub.4, a.sub.5, a.sub.6 and a.sub.7. The intensity of the current is controlled so that the emission light power of the optoelectronic circuit is close to the average light power emitted over a halfwave of voltage V.sub.ALIM. The variations of the light power perceived by the observed are then decreased.

(32) According to an embodiment, the values of control signals C.sub.j may be stored in a memory of control unit 26 for each switching configuration of the switches.

(33) According to another embodiment, the control of current source 22 by control unit 26 may be modified during the operation of the optoelectronic circuit, for example, according to whether it is desirable to increase the power factor of the optoelectronic circuit or to decrease the flickering perceived by an observer. In the case where current source 22 comprises elementary current sources CS.sub.j, this means that the sequence of activation of elementary current sources CS.sub.j may be modified during the operation of the optoelectronic circuit. As an example, the optoelectronic circuit may be made in the form of an integrated circuit comprising a dedicated pin having a control signal of control unit 26 representative of the desired control of current source 22 applied thereto. According to another example, control unit 26 comprises a memory programmable by a user, having data used by control unit 26 for the desired control of current source 22 by control unit 26 stored therein.

(34) FIG. 6 shows an electric diagram of another embodiment of current source 22. In the present embodiment, current source 22 comprises a current mirror 30. Current mirror 30 comprises two MOS transistors 32 and 34, for example, having an N channel. The sources of MOS transistors 32 and 34 are connected to node A.sub.2. Transistor 32 is diode-assembled. The gate of MOS transistor 32 is connected to the drain of MOS transistor 32 and to the gate of MOS transistor 34. The drain of MOS transistor 34 is connected to node A.sub.3. Current source 22 further comprises current sources CS.sub.1 to CS.sub.M which are assembled in parallel between a source of a reference potential VREF and the drain of transistor 32. Reference potential VREF may be supplied from voltage V.sub.ALIM. It may be constant or vary according to voltage V.sub.ALIM. As a variation, MOS transistor 34 may be duplicated for each switch SW.sub.i, with i varying from 1 to N.

(35) FIG. 7 shows an electric diagram of another embodiment of current source 22 where current source 22 comprises the same elements as the embodiment shown in FIG. 6 and where each current source CS.sub.j, with j varying from 1 to M, comprises a resistor 35.sub.j series-assembled with a MOS transistor 36.sub.j, for example, with a P channel, between the source of reference potential VREF and the drain of transistor 32. The gate of each transistor 36.sub.j receives control signal C.sub.j or an image of this signal. According to an embodiment, MOS transistor 36.sub.j operates in saturated state and acts as a current source. The current supplied by current source CS.sub.j is then defined by the ratio of the potential difference across resistor 35.sub.j to the value of resistance 35.sub.j. According to an embodiment, each transistor 36.sub.j is located on the side of transistor 32 while each resistor 35.sub.j is located on the side of the source of reference potential VREF.

(36) FIG. 8 shows an electric diagram of another embodiment of current source 22 where current source 22 comprises the same elements as the embodiment shown in FIG. 4 and where each current source CS.sub.j, with j varying from 1 to M, comprises a resistor 37.sub.j series-assembled with a MOS transistor 38.sub.j, for example, having an N channel, between node A3 and node A2. The gate of each transistor 38.sub.j receives control signal C.sub.j or an image of this signal. According to an embodiment, MOS transistor 38.sub.j operates in saturated state and acts as a current source. The current supplied by current source CS.sub.j is then defined by the ratio of the potential difference across resistor 37.sub.j to the value of resistance 37.sub.j. According to an embodiment, each transistor 38.sub.j is located on the side of node A3 while each resistor 37.sub.j is preferably located on the side of node A2.

(37) FIG. 9 shows an electric diagram of another embodiment of current source 22 where current source 22 comprises a MOS transistor 40, for example, with an N channel, having its drain connected to node A3 and having its source connected to a terminal of a resistor 42, the other terminal of resistor 42 being connected to node A2. Current source 22 comprises an operational amplifier 44 having its non-inverting input (+) connected to a terminal of a voltage source 46 controlled by control unit 26 and having its inverting input () connected to the junction point of transistor 40 and of resistor 42. The other terminal of voltage source 46 is connected to node A2. The output of operational amplifier 44 is connected to the gate of transistor 40. Voltage source 46 may be controlled by control unit 26.

(38) FIG. 10 shows an electric diagram of another embodiment of current source 22 where current source 22 comprises a current source 48 having a terminal connected to the source of reference potential VREF. The other terminal of current source 48 is connected to the drain of a diode-assembled MOS transistor 50, for example, having an N channel. The source of MOS transistor 50 is connected to node A.sub.2. The gate of MOS transistor 50 is connected to the drain of MOS transistor 50. Current source 22 further comprises M MOS transistors 52.sub.j, with j varying from 1 to M, for example, having an N channel. The source of each transistor 52.sub.j is connected to node A2. The drain of each transistor 52.sub.j is connected to node A3. The gate of each transistor 52.sub.j is connected to the gate of transistor 50 via a switch 54.sub.j. Each switch 52.sub.j is controlled by control signal C.sub.j supplied by control unit 16. As a variation, switch 54.sub.1 may be omitted. Each transistor 52.sub.j forms a current mirror with transistor 50. The intensity of current I.sub.CS depends on the number of switches 54.sub.j which are on. According to an embodiment, each transistor 52.sub.j is identical to transistor 50. When switch 54.sub.j is on, transistor 52.sub.j conducts a current having the same intensity as the current supplied by current source 48 and is equivalent to elementary current source CS.sub.j. According to another embodiment, the dimensions of transistors 52.sub.j may be different from those of transistor 50 and may be different between transistors 52.sub.j so that the intensity of the current flowing through each transistor 52.sub.j, when the associated switch 54.sub.j is on, is different from the intensity of the current supplied by current source 48.

(39) FIG. 11 shows a more detailed electric diagram of an embodiment of an optoelectronic circuit 60. The elements common between optoelectronic circuit 60 and optoelectronic circuit 20 are designated with the same reference numerals. Call V.sub.Ci the voltage between the cathode of general light-emitting diode D.sub.i and node A.sub.2 and V.sub.CS the voltage between nodes A.sub.3 and A.sub.2. In the following description, unless otherwise mentioned, the voltages are referenced to node A.sub.2.

(40) Optoelectronic circuit 60 further comprises N comparison units COMP.sub.i, with i varying from 1 to N, capable of each receiving voltage V.sub.Ci and of each supplying a signal H.sub.i and a signal L.sub.i. Control unit 26 receives signals L.sub.1 to L.sub.N and H.sub.1 to H.sub.N. Control unit 26 preferably corresponds to a dedicated circuit.

(41) Control unit 26 is capable of controlling switches SW.sub.i, with i varying from 1 to N, to the on or off state according to the value of voltage V.sub.Ci at the cathode of each general light-emitting diode D.sub.i. To achieve this, each comparison unit COMP.sub.i, with i varying from 1 to N, is capable of comparing voltage V.sub.Ci at the cathode of general light-emitting diode D.sub.i with at least two thresholds Vhigh.sub.i and Vlow.sub.i. As an example, signal L.sub.i is a binary signal which is in a first state when voltage V.sub.Ci is smaller than threshold Vlow.sub.i and which is in a second state when voltage V.sub.Ci is greater than threshold Vlow.sub.i. As an example, signal H.sub.i is a binary signal which is in a first state when voltage V.sub.Ci is smaller than threshold Vhigh.sub.i and which is in a second state when voltage V.sub.Ci is greater than threshold Vhigh.sub.i. The first states of binary signals H.sub.i and L.sub.i may be the same or different and the second states of binary signals H.sub.i and L.sub.i may be the same or different.

(42) FIG. 12 shows an electric diagram of a more detailed embodiment of a portion of electronic circuit 60. According to the present embodiment, each comparator COMP.sub.i comprises a first operational amplifier 62, operating as a comparator. The inverting input () of operational amplifier 62 is connected to the cathode of general light-emitting diode D.sub.i, for i varying from 1 to N. The non-inverting input (+) of operational amplifier 62 receives voltage threshold Vhigh.sub.i, which is supplied by a unit 64 which may comprise a memory. Operational amplifier 62 supplies signal H.sub.i. Each comparator COMP.sub.i further comprises a second operational amplifier 66 operating as a comparator. The inverting input () of operational amplifier 66 is connected to the cathode of general light-emitting diode D.sub.i, for i varying from 1 to N. The non-inverting input (+) of operational amplifier 66 receives voltage threshold Vlow.sub.i, which is supplied by a unit 68 which may comprise a memory. Operational amplifier 66 supplies signal L.sub.i.

(43) FIG. 13 shows timing diagrams of power supply voltage V.sub.ALIM and of the voltages V.sub.Ci measured by each comparator COMP.sub.i, with i varying from 1 to N, illustrating the operation of optoelectronic circuit 60 according to the embodiment shown in FIG. 11. FIG. 13 corresponds to the case where N and M are equal to 4. Further, each general light-emitting diode D.sub.i comprises the same number of elementary light-emitting diodes arranged in the same configuration, and thus has the same threshold voltage Vled. Further, current source 22 comprises M current sources CS.sub.j in parallel, each current source CS.sub.j being capable, when it is activated, of supplying a constant current of same intensity I. As an example, voltage V.sub.ALIM supplied by rectifying bridge 12 is a rectified sinusoidal voltage comprising a succession of cycles, in each of which voltage V.sub.ALIM increases from the zero value, crosses a maximum value and decreases to the zero value. As an example, two successive cycles of voltage V.sub.ALIM are shown in FIG. 13. Call t.sub.0 to t.sub.20 successive times.

(44) At time t.sub.0, at the beginning of a cycle, switch SW.sub.1 is turned on and all switches SW.sub.i, with i varying from 2 to N, are turned off. Voltage V.sub.ALIM rises from the zero value and distributes between general light-emitting diode D.sub.1, switch SW.sub.1, and current source 22. Voltage V.sub.ALIM being smaller than threshold voltage Vled of general light-emitting diode D.sub.1, there is no light emission (phase P.sub.0) and voltage V.sub.C1 remains substantially equal to zero. Current I.sub.CS is zero.

(45) At time t.sub.1, when the voltage across general light-emitting diode D.sub.1 exceeds threshold voltage Vled, general light-emitting diode D.sub.1 becomes conductive (phase P.sub.1). The voltage across general light-emitting diode D.sub.1 then remains substantially constant and voltage V.sub.C1 keeps on increasing along with voltage V.sub.ALIM. As soon as power supply voltage V.sub.C1 is sufficiently high to allow the activation of current source 22, current I.sub.CS, having an intensity equal to I, flows through general light-emitting diode D.sub.1, which emits light. As an example, voltage V.sub.CS is preferably substantially constant when current source 22 is in operation.

(46) At time t.sub.2, when voltage V.sub.C1 exceeds threshold Vhigh.sub.1, unit 26 successively orders the turning on of switch SW.sub.2 and the activation of current source CS.sub.2, and then the turning off of switch SW.sub.1. Voltage V.sub.ALIM is then distributed between general light-emitting diodes D.sub.1 and D.sub.2, switch SW.sub.2, and current source 22. Preferably, threshold Vhigh.sub.1 is substantially equal to the sum of the threshold voltage of general light-emitting diode D.sub.2 and of operating voltage V.sub.CS of current source 22 so that, at the turning on of switch SW.sub.2, general light-emitting diode D.sub.2 conducts current I.sub.CS having an intensity equal to 2I and emits light. The fact for switch SW.sub.2 to be turned on before the turning off of switch SW.sub.1 ensures that there will be no interruption in the current flow through general light-emitting diode D.sub.1. Phase P.sub.2 corresponds to a phase of light emission by general light-emitting diodes D.sub.1 and D.sub.2.

(47) Generally, during a rising phase of power supply voltage V.sub.ALIM, for i varying from 1 to N1, while switch SW.sub.i is on and the other switches are off, unit 26 successively orders the turning on of switch SW.sub.i+1, the activation of current source CS.sub.i+1, and then the turning off of switch SW.sub.i when voltage V.sub.Ci exceeds threshold Vhigh.sub.i. Voltage V.sub.ALIM is then distributed between general light-emitting diodes D.sub.1 to D.sub.i+1, switch SW.sub.i+1, and current source 22. Preferably, threshold Vhigh.sub.i is substantially equal to the sum of the threshold voltage of general light-emitting diode D.sub.i+1 and of operating voltage V.sub.CS of current source 22 so that, at the turning on of switch SW.sub.i+1, general light-emitting diode D.sub.i+1 conducts current I.sub.CS having an intensity equal to i+1 times I and emits light. Phase P.sub.i+1 corresponds to the emission of light by general light-emitting diodes D.sub.1 to D.sub.i+1. The fact for switch SW.sub.i+1 to be turned on before the turning off of switch SW.sub.i ensures that there will be no interruption in the current flow through general light-emitting diodes D.sub.1 to D.sub.i.

(48) Thus, at time t.sub.3, unit 26 orders the turning on of switch SW.sub.3, the activation of current source CS.sub.3, and the turning off of switch SW.sub.2. Phase P.sub.3 corresponds to the emission of light by general light-emitting diodes D.sub.1, D.sub.2, and D.sub.3. At time t.sub.4, unit 26 orders the turning on of switch SW.sub.4, the activation of current source CS.sub.4, and the turning off of switch SW.sub.3. Phase P.sub.4 corresponds to the emission of light by general light-emitting diodes D.sub.1, D.sub.2, D.sub.3, and D.sub.4.

(49) Power supply voltage V.sub.ALIM reaches its maximum value at time t.sub.5 during phase P.sub.4 in FIG. 13 and starts a falling phase.

(50) At time t.sub.6, when voltage V.sub.C4 decreases below threshold Vlow.sub.4, unit 26 successively orders the turning on of switch SW.sub.3, the deactivation of current source CS.sub.4, and the turning off of switch SW.sub.4. Voltage V.sub.ALIM is then distributed between general light-emitting diodes D.sub.1, D.sub.2, and D.sub.3, switch SW.sub.3, and current source 22. General light-emitting diodes D.sub.1, D.sub.2, and D.sub.3 conduct current I.sub.CS having an intensity equal to 3I. Preferably, threshold Vlow.sub.4 is selected to be substantially equal to the sum of operating voltage V.sub.CS of current source 22 and of the minimum operating voltage of switch SW.sub.4 so that, at the turning on of switch SW.sub.3, there is no interruption in the current flow.

(51) Generally, during a falling phase of power supply voltage V.sub.ALIM, for i varying from 2 to N, when voltage V.sub.Ci decreases below threshold Vlow.sub.i, unit 26 successively orders the turning on of switch SW.sub.i1, the deactivation of current source CS.sub.i, and the turning off of switch SW.sub.i. Voltage V.sub.ALIM is then distributed between general light-emitting diodes D.sub.1 to D.sub.i1, switch SW.sub.i1, and current source 22. General light-emitting diodes D.sub.1 to D.sub.i1 conduct current I.sub.CS having an intensity equal to i1 times I. Preferably, threshold Vlow.sub.i is selected to be substantially equal to the sum of operating voltage V.sub.CS of current source 22 and of the minimum operating voltage of switch SW.sub.i so that, at the turning on of switch SW.sub.i1, there is no interruption in the current flow.

(52) Thus, at time t.sub.7, unit 26 orders the turning on of switch SW.sub.2, the deactivation of current source CS.sub.3, and the turning off of switch SW.sub.3. At time t.sub.8, unit 26 orders the turning on of switch SW.sub.1, the deactivation of current source CS.sub.2, and the turning off of switch SW.sub.2. At time t.sub.9, voltage V.sub.C1 becomes zero so that general light-emitting diode D.sub.1 is no longer conductive and current I.sub.CS is zero. At time t.sub.10, voltage V.sub.ALIM becomes zero and a new cycle starts again. Times t.sub.11 to t.sub.20 are respectively similar to times t.sub.1 to t.sub.10. In the present embodiment, comparator COMP.sub.1 can have a simpler structure than comparators COMP.sub.i, with i varying from 2 to N, since threshold Vlow.sub.1 is not used.

(53) According to another embodiment of optoelectronic circuit 60, each comparator COMP.sub.i of optoelectronic circuit 60 only supplies signal L.sub.i. An advantage of this embodiment is that the structure of comparator COMP.sub.i can be simplified. Indeed, it is possible for comparator COMP.sub.i not to comprise operational amplifier 62.

(54) The operation of the optoelectronic circuit according to this other embodiment is then identical to what has been previously described, with the difference that switches SW.sub.i, with i varying from 1 to N1, are initially on and that, in a rising phase of power supply voltage V.sub.ALIM, switch SW.sub.i1 is turned off and current source CS.sub.i is activated when voltage V.sub.Ci is greater than threshold Vlow.sub.i. Indeed, this means that current starts flowing through switch SW.sub.i.

(55) More specifically, in a rising phase of power supply voltage V.sub.ALIM, for i varying from 1 to N1, while light-emitting diodes D.sub.1 to D.sub.i1 are conductive and light-emitting diodes D.sub.i and D.sub.N are non-conductive, when voltage V.sub.Ci rises above threshold Vlow.sub.i, unit 26 orders the turning off of switch SW.sub.i1 and the activation of current source CS.sub.i. Indeed, a rise in voltage V.sub.Ci means that the voltage across light-emitting diode D.sub.i becomes greater than the threshold voltage of light-emitting diode D.sub.i and that the latter becomes conductive.

(56) The operation of the optoelectronic circuit according to this other embodiment in a falling phase of power supply voltage V.sub.ALIM may be identical to that which has been previously described for optoelectronic circuit 60.

(57) FIG. 14 shows an electric diagram of another embodiment of an optoelectronic circuit 70. All the elements common with optoelectronic circuit 60 are designated with the same reference numerals. Conversely to optoelectronic circuit 60, optoelectronic circuit 70 does not comprise switch SW.sub.N. Further, conversely to optoelectronic circuit 60, for i varying from 1 to N1, optoelectronic circuit 70 comprises a resistor 72.sub.i provided between node A.sub.3 and switch SW.sub.i, and optoelectronic circuit 70 comprises a resistor 72.sub.N provided between node A.sub.3 and the cathode of general light-emitting diode D.sub.N. Call B.sub.i a node between resistor 72.sub.i and switch SW.sub.i, for i varying from 1 to N1, and B.sub.N a node between resistor 72.sub.N and the cathode of general light-emitting diode D.sub.N. Further, each comparator COMP.sub.i, with i varying from 1 to N, receives the voltage at node B.sub.i. Signal H.sub.i then is a binary signal which is in a first state when the voltage at node B.sub.i is smaller than a threshold MIN.sub.i and which is in a second state when the voltage at node B.sub.i is greater than threshold MIN.sub.i.

(58) FIG. 15 shows an electric diagram of a more detailed embodiment of a portion of optoelectronic circuit 70. In the present embodiment, comparator COMP.sub.i comprises all the elements of comparator COMP.sub.i shown in FIG. 12, with the difference that operational amplifier 66 is replaced with a hysteresis comparator 74 receiving the voltage across resistor 72.sub.i and supplying signal H.sub.i.

(59) The operation of optoelectronic circuit 70 may be identical to the operation of previously-described optoelectronic circuit 60, with the difference that, in a rising phase of power supply voltage V.sub.ALIM, switch SW.sub.i is turned off and current source CS.sub.i+1 is activated when current starts flowing through resistor 72.sub.i+1.

(60) More specifically, switches SW.sub.i, with i varying from 1 to N1, are initially on. In a rising phase of power supply voltage V.sub.ALIM, for i varying from 2 to N1, while light-emitting diodes D.sub.1 to D.sub.i1 are conductive and light-emitting diodes D.sub.i to D.sub.N are blocked, when the voltage across light-emitting diode D.sub.i becomes greater than the threshold voltage of light-emitting diode D.sub.i, the latter becomes conductive and a current starts flowing through resistor 72.sub.i. This results in a rise in the voltage at node B.sub.i. As soon as the voltage at node B.sub.i rises above threshold MIN.sub.i, unit 26 orders the turning off of switch SW.sub.i1 and the activation of current source CS.sub.i.

(61) The operation of optoelectronic circuit 70 in a falling phase of power supply voltage V.sub.ALIM may be identical to that which has been previously described for optoelectronic circuit 60.

(62) Optoelectronic circuit 70 has the advantage that thresholds MIN.sub.i and Vlow.sub.i can be independent from the characteristics of light-emitting diodes D.sub.i. In particular, they do not depend on the threshold voltage of each light-emitting diode D.sub.i.

(63) FIG. 16 shows an electric diagram of another embodiment of an optoelectronic circuit 80. All the elements common with optoelectronic circuit 60 are designated with the same reference numerals. Conversely to optoelectronic circuit 60, optoelectronic circuit 80 does not comprise comparators COMP.sub.i. Further, optoelectronic circuit 80 does not comprise switch SW.sub.N. However, switch SW.sub.N may be present. Further, unlike optoelectronic circuit 60, for i varying from 1 to N1, optoelectronic circuit 80 comprises a current sensor 82.sub.i provided between node A.sub.3 and switch SW.sub.i, supplying a signal CUR.sub.i to control unit 26, and optoelectronic circuit 80 comprises a current sensor 82.sub.N provided between node A.sub.3 and the cathode of general light-emitting diode D.sub.N and delivering a signal CUR.sub.N to control unit 26. Optoelectronic circuit 80 further comprises a voltage sensor 84 provided between current source 22 and node A.sub.3 and delivering a signal VOLT to control unit 26. Current source 22 may be formed according to any of the previously-described embodiments.

(64) According to an embodiment, each current sensor 82.sub.i is capable of supplying control unit 26 with a signal CUR.sub.i representative of the intensity of the current flowing through general light-emitting diode D.sub.i. According to another embodiment, each current sensor 82.sub.i is capable of supplying control unit 26 with a signal CUR.sub.i indicating whether the intensity of the current flowing through general light-emitting diode D.sub.i is greater than a current threshold.

(65) According to an embodiment, voltage sensor 84 is capable of supplying a signal VOLT to control unit 26 representative of voltage V.sub.CS. According to another embodiment, voltage sensor 84 is capable of transmitting a signal VOLT to control unit 26 indicating whether voltage V.sub.CS is greater than a threshold voltage. Voltage sensor 84 may then comprise an operational amplifier assembled as a comparator supplying signal VOLT, having its non-inverting input connected to node A.sub.3 and having its inverting input receiving the threshold voltage.

(66) Optoelectronic circuit 80 may operate as follows. At the beginning of a rising phase of voltage V.sub.ALIM, switches SW.sub.i, with i varying from 1 to N1, are turned on. In a rising phase, for i varying from 2 to N1, while general light-emitting diodes D.sub.1 to D.sub.i1 are conductive and general light-emitting diodes D.sub.i to D.sub.N are non-conductive, when the voltage across general light-emitting diode D.sub.i becomes greater than the threshold voltage of general light-emitting diode D.sub.i, the latter becomes conductive and a current starts flowing through general light-emitting diode D.sub.i. The flowing of the current is detected by current sensor 82.sub.i. Unit 26 then controls switch SW.sub.i1 to the off state.

(67) At the beginning of a falling phase of power supply voltage V.sub.ALIM, switches SW.sub.i, with i varying from 1 to N1, are turned off and when voltage V.sub.CS decreases below a voltage threshold, switch SW.sub.N1 is turned on. Generally, in a falling phase, switches SW.sub.i to SW.sub.N1 being on while switches SW.sub.1 to SW.sub.i1 are off, when voltage V.sub.CS decreases below a voltage threshold, switch SW.sub.i1 is turned on. In the case where each switch SW.sub.i is formed of an N-channel MOS transistor having its drain connected to the cathode of general light-emitting diode D.sub.i and having its source connected to current sensor 82.sub.i, when power supply voltage V.sub.ALIM decreases, the voltage between the drain of switch SW.sub.i and node A.sub.2 decreases. Transistor SW.sub.i is initially in saturation state. During the decrease of the voltage between the drain of switch SW.sub.i and node A.sub.2, transistor SW.sub.i switches from the saturation state to the linear state. This causes an increase of the voltage between the gate and the source of transistor SW.sub.i and thus a decrease of voltage V.sub.CS. When voltage V.sub.CS decreases below a voltage threshold, switch SW.sub.i1 is turned on.

(68) Current source 22 may be controlled according to any of the previously-described embodiments.

(69) FIG. 17 shows an embodiment of current sensor 82.sub.i where current sensor 82.sub.i comprises a resistor 86.sub.i series-assembled between node A.sub.3 and switch SW.sub.i, shown in FIG. 17 as a MOS transistor, and an operational amplifier 88.sub.i assembled as a comparator supplying signal CUR.sub.i, having its non-inverting input (+) connected to a terminal of resistor 86.sub.i and having its inverting input () connected to the other terminal of resistor 86.sub.i. Amplifier 88.sub.i comprises a terminal for setting offset voltage V.sub.offset of the amplifier. Amplifier 88.sub.i supplies signal CUR.sub.i in a first state when the voltage across resistor 86.sub.i is greater than offset voltage V.sub.OFFSET and in a second state when the voltage across resistor 86.sub.i is smaller than offset voltage V.sub.OFFSET.

(70) FIG. 18 shows another embodiment of current sensor 82.sub.i, where current sensor 82.sub.i comprises a resistor 90.sub.i and a diode 92.sub.i series-assembled between node A.sub.3 and switch SW.sub.i, shown in FIG. 18 by a MOS transistor, the cathode of diode 92.sub.i being connected to resistor 90.sub.i. Current sensor 82.sub.i further comprises a bipolar transistor 94.sub.i having its base connected to the anode of diode 92.sub.i, having its collector supplying signal CUR.sub.i, and having its emitter connected to node A.sub.3 by a resistor 96.sub.i. The collector of bipolar transistor 94.sub.i is connected to a terminal of a source of a reference current CREF having its other terminal connected to a source of a reference voltage VREF.

(71) Advantageously, in the embodiments previously described in relation with FIGS. 16 to 18, the maximum voltages applied to the electronic components, particularly transistors MOS, of current sensors 82.sub.i and of current sensor 84 remain small as compared with the maximum value that voltage V.sub.ALIM can take. It is then not necessary to provide, for current sensors 82.sub.i and current sensor 84, electronic components capable of withstanding the maximum voltage that voltage V.sub.ALIM can take.

(72) FIGS. 19 and 20 show curves of the variation, obtained by simulation during a cycle of voltage V.sub.ALIM in the case where voltage V.sub.IN is a sinusoidal voltage, of power supply voltage V.sub.ALIM, of current I.sub.CS, and of a voltage V.sub.DEL equal to the sum of the voltages across the general light-emitting diodes which are conductive, when optoelectronic circuit 20 comprises eight general light-emitting diodes and eight elementary light-emitting diodes CS.sub.j in parallel. Each elementary current source CS.sub.j is capable of supplying a constant current of same intensity.

(73) Calling P.sub.lum the instantaneous light power supplied by the optoelectronic circuit and P.sub.lumMOY the average of the light power over a cycle of voltage V.sub.ALIM, flicker index FI is defined by the following relation (1):

(74) $\begin{array}{cc}FI=\frac{{}_{\mathrm{cycle}}^{}\left(P_{\mathrm{lum}}\left(t\right)-P_{\mathrm{lumMOY}}\right)\mathrm{dt}}{{}_{\mathrm{cycle}}^{}{P}_{\mathrm{lum}}\mathrm{dt}}& \left(1\right)\end{array}$

(75) FIG. 19 has been obtained with a sequence of activation of the elementary current sources of current source 22 similar to what has been previously described in relation with FIG. 5A. The average active power consumed by the optoelectronic circuit is 10.55 W, the power factor is substantially equal to 1 and flicker index IF is substantially equal to 33. Advantageously, the optoelectronic circuit further fulfills the constraints relative to harmonic currents provided for class-D and class-C lighting equipment by standard NF EN 61000-3-2, November 2014 version, regarding electromagnetic compatibility.

(76) FIG. 20 has been obtained for a sequence of activation of the elementary current sources of current source 22 similar to what has been previously described in relation with FIG. 5B. The average active power consumed by the optoelectronic circuit is 10.58 W, the power factor is substantially equal to 0.89, and flicker index IF is substantially equal to 22. The flicker index is decreased with respect to the case illustrated in FIG. 19. The optoelectronic circuit further fulfills the constraints relative to harmonic currents provided for class-D lighting equipment, that is, equipment receiving an active power smaller than 25 W, by standard NF EN 61000-3-2, November 2014 version, regarding electromagnetic compatibility.

(77) FIG. 21 shows an electric diagram of another embodiment of an optoelectronic circuit 100. All the elements common with optoelectronic circuit 20 are designated with the same reference numerals. Optoelectronic circuit 100 comprises, for each general light-emitting diode D.sub.i, a current source 102.sub.i, with i varying from 1 to N, associated with general light-emitting diode D.sub.i. A terminal of current source 102.sub.i, with i varying from 1 to N, is connected to node A.sub.2 and the other terminal is connected to the cathode of general light-emitting diode D.sub.i. Each current source 102.sub.i, with i varying from 1 to N, is controlled by a signal S.sub.i supplied by control unit 26. As an example, signal S.sub.i is a binary signal and current source 102.sub.i is activated when signal S.sub.i is in a first state and current source 102.sub.i is deactivated when signal S.sub.i is in a second state. The intensities of the currents supplied by current sources 102.sub.i are different. Optoelectronic circuit 100 further comprises N comparison units COMP.sub.i, with i varying from 1 to N, capable of each receiving the voltage at the cathode of general light-emitting diode D.sub.i and of each supplying a signal H.sub.i and a signal L.sub.i to control unit 26. Control unit 26 is capable of controlling switches SW.sub.i to the on or off state, with i varying from 1 to N, according to the value of the voltage at the cathode of each general light-emitting diode D.sub.i. To achieve this, each comparison unit COMP.sub.i, with i varying from 1 to N, is capable of comparing the voltage at the cathode of general light-emitting diode D.sub.i with at least two thresholds Vhigh.sub.i and Vlow.sub.i. As an example, signal L.sub.i is a binary signal which is in a first state when voltage V.sub.Ci is smaller than threshold Vlow.sub.i and which is in a second state when voltage V.sub.Ci is greater than threshold Vlow.sub.i. As an example, signal H.sub.i is a binary signal which is in a first state when voltage V.sub.Ci is smaller than threshold Vhigh.sub.i and which is in a second state when voltage V.sub.Ci is greater than threshold Vhigh.sub.i. The first states of binary signals H.sub.i and L.sub.i may be the same or different and the second states of binary signals H.sub.i and L.sub.i may be the same or different.

(78) The operation of optoelectronic circuit 100 may be identical to the operation of previously-described optoelectronic circuit 20, with the difference that the steps of turning off and turning on of switches SW.sub.i of optoelectronic circuit 20 are respectively replaced with steps of activation and of deactivation of current sources 102.sub.i.

(79) More specifically, in a rising phase of power supply voltage V.sub.ALIM, for i varying from 1 to N1, while current source 102.sub.i is activated and the other current sources are deactivated, unit 26 successively orders the activation of current source 102.sub.i+1 and the deactivation of current source 102.sub.i when voltage V.sub.Ci exceeds threshold Vhigh.sub.i. Voltage V.sub.ALIM is then distributed between general light-emitting diodes D.sub.1 to D.sub.i+1 and current source 102.sub.i+1. Preferably, threshold Vhigh.sub.i is selected to be substantially equal to the threshold voltage of general light-emitting diode D.sub.i+1 so that, on activation of current source 102.sub.i+1, general light-emitting diode D.sub.i+1 conducts current I.sub.CS and emits light. The fact for current source 102.sub.i+1 to be activated before current source 102.sub.i is deactivated ensures that there is no interruption in the current flow through general light-emitting diodes D.sub.1 to D.sub.i.

(80) Generally, in a falling phase of power supply voltage V.sub.ALIM, for i varying from 2 to N, when voltage V.sub.Ci decreases below threshold Vlow.sub.i, unit 26 successively orders the activation of current source 102.sub.i1 and the deactivation of current source 102.sub.i. Voltage V.sub.ALIM is then distributed between general light-emitting diodes D.sub.1 to D.sub.i1 and current source 102.sub.i1. The fact for current source 102.sub.i1 to be activated before current source 102.sub.i is deactivated ensures that there is no interruption in the current flow through general light-emitting diodes D.sub.1 to D.sub.i1.

(81) Preferably, each current source 102.sub.i is capable of supplying a current having an intensity which can be modified so that the variation profile of the intensity of the current flowing through general light-emitting diodes D.sub.i during successive rising and falling phases can be modified.

(82) Various embodiments with various variations have been described hereabove. It should be noted that those skilled in the art may combine these various embodiments and variations without showing any inventive step. In particular, the embodiments of current source 22 previously described in relation with FIGS. 4 and 6 to 10 may be implemented with each of optoelectronic circuits 20, 60, and 70.