Driver circuit and driver device for lighting sources, and corresponding lighting device and method

Abstract

A driver circuit (Sj) for light sources (LED1, LED2, LED3, LED4), for example LED sources configured to be powered via a supply line at a supply voltage (VBATT), comprises: a first node (Cj-1) and a second node (Cj), configured to have connected therebetween a light source susceptible to flickering in response to variations of the supply voltage (VBATT) transferred to the first node (Cj-1); an electronic switch (Sj1) set between the first node (Cj-1) and the second node (Cj); a shutdown generator (ITOj), coupled (Sj2) to the electronic switch (Sj1) set between the first node (Cj-1) and the second node (Cj); and flicker-detection circuitry (10, 12, 14, 16) coupled (D) to the first node (Cj-1). The flicker-detection circuitry is configured (10, 12, 14, 16) to generate a flicker-detection signal (FS) in response to the aforesaid variations of the supply voltage (VBATT) transferred to the first node (Cj-1). The flicker-detection circuitry (10, 12, 14, 16) is configured to activate the shutdown generator (ITOj) and render conductive the electronic switch (Sj1) in response to the generation of said flicker-detection signal (FS) so that the light source remains off as long as the disturbance that produces the flicker persists.

Description

[0001] "DRIVER CIRCUIT AND DRIVER DEVICE FOR LIGHTING SOURCES , AND CORRESPONDING LIGHTING DEVICE AND METHOD"

[0002] Technical field

[0003] The present disclosure relates to the driving of lighting sources .

[0004] Solutions like those described herein are suited to being used, for example , for driving lighting devices ( in short , lamps ) that use electrically powered light sources , for example solid-state light sources such as LED sources .

[0005] Technological background

[0006] High-brightness LEDs are used to an increasing extent in numerous sectors , such as in the backlighting of liquid-crystal displays ( LCDs ) , in the automotive sector, and in lighting engineering ( for example , for road and street lighting ) thanks to their longer duration, their reduced maintenance requirements , and their better performance in terms of luminance .

[0007] The brightness of LEDs is directly correlated to the current that traverses them .

[0008] An ef fective way to obtain a similar light emission starting from a number of LEDs is to connect them in series . One of the main disadvantages of series connection of a number of LEDs , however, lies in the fact that the cumulative voltage drop ends up setting a limit to the number of LEDs that can be connected in series in a LED string .

[0009] On the other hand, connecting in parallel a number of LEDs or a number of LED strings can cause problems of sharing of the current , linked both to the voltagecurrent characteristic, of an exponential type , and to the negative temperature coef ficient of the forward voltage drop across a LED .

[0010] For this reason, a lamp for motor vehicles ( taken as orientative and non-limiting example ) may comprise a number of LEDs connected in series so that they can be traversed by an identical current and meet given speci fications in terms of light intensity .

[0011] There exist driver circuits or drivers for LEDs both of a constant-voltage type and of a constant-current type .

[0012] A constant-voltage driver facilitates application of a constant voltage for each LED, but the current changes according to the associated load .

[0013] A constant-current driver supplies the LEDs with a current having an "original" value so that this type of driver proves ideal for supplying the current to the LEDs .

[0014] A driver may, however, cause flicker in the case where it is not able to normal i ze and stabili ze the output on the LEDs .

[0015] In particular, it is desirable to be able to counter undesired phenomena of flicker that are liable to arise as a result of a temporary variation of the supply ( on the battery terminal , in the case of a lamp for motor vehicles taken as example ) . An improvement in the performance in terms of flicker ( that it is to prevent ) hence passes through the driver circuit .

[0016] Drivers for driving LEDs form the subj ect of an extensive technical literature , also in relation to the problem of flicker, as witnessed, by way of example , by articles such as the following :

[0017] A. Wilkins , J . Veitch, and B . Lehman : "LED lighting flicker and potential health concerns : IEEE standard PAR1789 update" 2010 IEEE Energy Conversion Congres s and Exposition, Atlanta, GA, USA, 2010 , pp . 171- 178 ;

[0018] Shu Wang, et al . "A Flicker-Free Electrolytic Capacitor-Less AC-DC LED Driver" , IEEE TRANSACTIONS ON POWER ELECTRONICS , vol . 27 , No . 11 , November 2012 , pp . 4540-4548; and

[0019] H. Dong, X. Xie, K. Peng, J. Li, and C. Zhao: "Feedforward dynamic compensation control for single-stage PFC LED driver to eliminate flicker to human eyes during AC input voltage variation" IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, Dallas, TX, USA, 2014, pp . 1460-1465.

[0020] Document US 2023 / 104439 Al is further exemplary of the related art .

[0021] For completeness, it may moreover be noted that: a non-ideal behaviour may also be traced back to the environment of the integrated circuit (IC) for driving of the LEDs, which may suggest implementation of a filtering process using additional components; and the phenomenon of flicker may arise - and the aim is that it should be countered - in electrically powered lighting devices (in short, lamps) of different types: reference, for simplicity, to solid-state light sources, such as LED sources, is hence to be understood in an exemplary and non-limiting sense.

[0022] Object and summary

[0023] The object of the solution described herein is to contribute to overcoming the drawbacks outlined above.

[0024] According to the solution described herein, the above object is achieved thanks to a driver circuit or driver having the characteristics recalled in the ensuing claims.

[0025] The solution described herein also applies to a corresponding driver device, a corresponding lighting device, and a corresponding method.

[0026] The claims form an integral part of the technical teachings provided herein in relation to the solution described .

[0027] The solution described herein envisages a circuit configured for supplying a constant current to a number of LEDs with improved performance in terms of fl icker, in particular in relation to the possible ef fect of transient oscillations induced by an inductive impedance of a cable for connection to a power source ( the battery, in the case of a motor vehicle , taken purely as example ) of a LED module .

[0028] Advantageously, the solution described herein enables , for example , " capture" of possible oscillations of the supply voltage at the drain of a field-ef fect transistor ( for example , a MOSFET ) used as driving switch and driving, on the basis of a corresponding signal , of an additional current generator capable of temporarily switching of f a light source ( for example , a LED) that flickers as long as the cause of the disturbance persists .

[0029] The solution described herein counters the flicker, maintaining a high level of precision in execution of the function of supply as desired by the user, without adding external components coupled to a supply pin ( for example , a battery terminal ) .

[0030] The solution described herein is suited to being implemented at the level of integrated circuit ( IC ) , which renders the solution economically advantageous and configurable .

[0031] The solution described herein is hence advantageous also from the standpoint of costs in so far as it can be integrated in an economically advantageous way from the application standpoint , without af fecting operation of the system .

[0032] Brief description of the drawings

[0033] One or more embodiments will now be described, purely by way of non-limiting example , with reference to the annexed drawings , wherein :

[0034] Figure 1 is a general diagram of a driver device for lighting devices in which a solution as described herein can find application;

[0035] Figure 2 illustrates criteria that can be adopted to obtain a driver device for lighting devices as illustrated in Figure 1 ; and

[0036] Figure 3 is a circuit diagram that illustrates an example of how to obtain a driver device for lighting devices by adopting the solution forming the subj ect of the present application .

[0037] For brevity - except where the context indicates otherwise - parts or elements that are similar are designated in the various figures by the same references , without a corresponding description being repeated for each figure .

[0038] Detailed description

[0039] In the ensuing description, various speci fic details are illustrated in order to enable an in-depth understanding of various examples of embodiments according to the disclosure . The embodiments may be obtained without one or more of the speci fic details , or with other methods , components , materials , etc . In other cases , known structures , materials , or operations are not illustrated or described in detail so that the various aspects o f the embodiments will not be obscured .

[0040] Reference to "an embodiment" or "one embodiment" in the framework of the present description is intended to indicate that a particular configuration, structure , or characteristic described in relation to the embodiment is comprised in at least one embodiment . Hence , phrases such as " in an embodiment" or " in one embodiment" that may be present in various points of the present description do not necessarily refer exactly to one and the same embodiment . Moreover, particular conformations , structures , or characteristics may be combined in any adequate way in one or more embodiments .

[0041] The references used herein are provided merely for convenience and hence do not define the sphere of protection or the scope of the embodiments .

[0042] As has been said, in the various figures the same references are used to designate corresponding parts or elements , without the corresponding description being repeated for each figure for reasons of brevity .

[0043] Moreover, for reasons of simplicity and ease of explanation, in the present description the same reference may be used to designate : a given node or line , as well as a signal that is present on that node or line ( for example , the line VBATT ) ; and / or a given component ( such as a capacitor or a resistor ) , as well as the corresponding electrical parameter ( for example , capacitance or resistance / impedance ) .

[0044] Again, the fact that a certain element is said to be "connected" or "coupled" to another element is to be understood either in the sense that no other element is set between these two elements or in the sense that a further element may be set between these two elements . When, instead, an element is said to be "directly connected" or "directly coupled" to another element , this means that no other element is set between these two elements .

[0045] Figure 1 is an overall diagram of a driver device for LED lamps , in which a solution as described herein can find application .

[0046] By way of non-limiting example , a driver device for LED lamps for the automotive sector is discussed herein .

[0047] The above reference is not on the other hand to be understood in a limiting sense . The solutions described herein may, in fact , find use in a wide range of sectors of application : j ust to cite some other examples of possible application, the solutions described herein may be used for the backlighting of liquid-crystal displays ( LCDs ) or in lighting engineering ( for example , in road and street lighting) .

[0048] Again, as already mentioned previously, the phenomenon of flicker may arise - and it is desirable that it should be countered - in electrically powered lighting devices ( lamps ) of di f ferent types .

[0049] Even though the present description will refer for simplicity to solid-state light sources , such as LED sources , the solutions described herein may in general be applied to a wide range of lighting devices susceptible to flickering phenomena according to modalities that are substantially similar to those described herein, by way of example , with reference to solid-state light sources , such as LED sources .

[0050] Albeit developed with reference to possible application to LED lamps (where the flicker phenomenon may arise in a particularly troublesome way) , a solution as described herein is hence suited to being used, in general , combined with electrically powered lighting sources exposed to a phenomenon of flickering of the light emitted, for example following upon temporary variations of a supply voltage and / or on account of a supply line that has an inductive behaviour with consequent momentary triggering of ripple .

[0051] Figure 1 refers to a lighting device ( a lamp ) comprising a plurality of solid-state light sources , for example four LEDs ( this number is not to be understood in a limiting sense ) designated by LED1 , LED2 , LED3 , and LED4 .

[0052] As illustrated, the LEDs in question are cascaded ( in series ) between an electrical supply line or node at a (nominal ) voltage VBATT and ground GND .

[0053] Associated to three out of four of the LEDs illustrated herein ( in the present case , the LEDs denoted as LED2, LED3, and LED4) , i.e., to all the LEDs with the exception of the first LED (namely, LED1, which directly coupled to the line VBATT) is a driver device 100 (which may be implemented in the form of integrated circuit - IC) comprising driver circuits S2, S3, and S4 to which there flow respective currents (designated by 12, 13, and 14) deriving from the supply line VBATT.

[0054] In particular, as illustrated herein: the circuit S2 receives the current 12 and acts between a node Cl (connected to the cathode of the LED denoted by LED1 and to the anode of the LED denoted by LED2) and a node C2 (connected to the cathode of the LED denoted by LED2) ; the circuit S3 receives the current 13 and acts between the node C2 (connected to the cathode of the LED denoted by LED2 and to the anode of the LED denoted by LED3) and a node C3 (connected to the cathode of the LED denoted by LED3) ; and the circuit S4 receives the current 14 and acts between the node C3 (connected to the cathode of the LED denoted by LED3, and to the anode of the LED denoted by LED4) and a node C4 (connected to the cathode of the LED denoted by LED3 and from which a "tail" current I G flows to ground GND) .

[0055] It is desired that the LEDs denoted by LED1, LED2, LED3, LED4 should be switched on (only) when the voltage VBATT has reached a threshold provided so as to guarantee a headroom sufficient for a "tail" current generator represented by a current I G cascaded (in series) to the string of LEDs denoted by LED1, LED2, LED3, and LED4.

[0056] For this purpose, the circuits S2, S3, and S4 can be configured so as to act between the pairs of nodes Cl and C2, C2 and C3, C3 and C4 as switches, which, when open (non-conductive ) , enable the LEDs denoted by LED2, LED3, and LED4 to switch on and, when closed (conductive) , short the LEDs denoted by LED2, LED3, and LED4, thus switching them off.

[0057] In a lighting device according to the diagram of Figure 1, it is possible to drive the intensity of the currents 12, 13, 14 (for example, via a voltage-to- current - Vtol or V2I - converter circuit designated by 102) so that the LEDs functioning as light sources are kept turned off as long as the voltage VBATT remains below a threshold level and then switch on, possibly one after another, when the voltage VBATT increases (for example, according to a ramp) above the threshold level.

[0058] One may think that the nominal voltage VBATT can vary in an even rather wide range, for example from 5 V to 20 V, with possible variations with respect to the nominal value.

[0059] To prevent damage caused by short-circuits or other adverse conditions, it is possible to envisage circuits for protection against phenomena such as, precisely, shorting, overheating, undervoltage, and so forth.

[0060] To meet specifications of reference voltage for a wide range of protection circuits, it is desirable for the reference not only to have a precise output voltage and a low temperature coefficient, but also to be able to function over a wide range of supply voltages and be sufficiently stable, with a relatively limited powersupply rejection ratio (PSRR) .

[0061] What has been described so far corresponds to characteristics and criteria of implementation to be deemed in themselves known to persons skilled in the sector and such as not to require any further description herein .

[0062] For completeness, it may again be noted that what has been illustrated herein with reference to the LEDs denoted by LED2, LED3, and LED4 could in principle be applied also with reference to the LED denoted by LED1. The practice of application on the other hand indicates that this extension is not imperative.

[0063] Again, it will be noted that the device 100 is suited to being coupled to the light sources LED1, LED2, LED3, LED4 and to the supply source (line or node VBATT) at the level of final installation. The light sources LED1, LED2, LED3, LED4 and / or the supply source are hence elements distinct from the embodiments.

[0064] Figure 2 illustrates, at a circuit level, the possibility of implementing the principle diagram of Figure 1, envisaging that each driver S2, S3, and S4 (i.e., S j , with j = 2, ..., k, with k here chosen, in a non-limiting way, as equal to 4) in the device 100 comprises a first electronic switch S21, S31, S41 (i.e., Sjl with j = 2, ..., k) such as a MOSFET set in parallel to a respective LED, namely, LED2, LED3, LED4 (i.e., LEDj with j = 2, ..., k) so as to function as switch for each LED.

[0065] The first switches S21, S31, S41 (i.e., Sjl with j = 2, ..., k) are current-driven with a current-mirror structure (n:l) - with gate-to-gate coupling - by respective second electronic switches S22, S32, S42 (i.e., Sj2 with j = 2, ..., k) - such as diode-connected MOSFETs - the input current of which (on the source-to- drain current path) 12, 13, or 14 (i.e., Ij with j = 2, ..., k) comes from the line or node VBATT with an intensity driven by the block 102 (Vtol or V2I converter circuit) so that the LEDs are kept turned off as long as the voltage VBATT remains below a threshold level and then switch on, possibly one after another, when the voltage VBATT rises above the threshold level.

[0066] It is recalled once again that the choice, exemplified herein, of a value of k equal to 4 is not to be understood in a limiting sense.

[0067] A device 100 as illustrated in Figure 2 is able to operate in the presence of a generic linear ramp of the voltage on the line or node VBATT .

[0068] However, in the presence of possible disturbance ( consider, once again by way of example , use in a "noisy" context , as in the case of use on board a motor vehicle and / or with oscillations of the supply induced by a finite impedance of the cable for connection to a powersupply source ) , the voltage on the line or node VBATT may vary around its desired DC value , oscillating at a frequency of up to some tens of kilohertz with a peak- to-peak amplitude of from 500 mV to 1 V .

[0069] In many cases , the above disturbance does not create any problem of flicker . However, when the variations come close to the threshold level , the switches S22 , S32 , S42 can open and close repeatedly - i . e . , become alternately non-conductive and conductive - with a flicker of the associated LED ( i . e . , LEDj ) , which can be perceived by the human eye , proving troublesome or in any case undesired .

[0070] The level of disturbance due to a possible flicker correlated to a possible variation of the supply voltage VBATT can be estimated starting from detection of the supply voltage VBATT by determining an index of seriousness of the flicker correlated to the human perception of the disturbance .

[0071] To prevent this ef fect one may think of intervening around the frequency of the disturbance , without interfering with the desired DC behaviour .

[0072] Figure 3 illustrates a possible embodiment , implemented according to the solution described herein, of the generic circuit Sj ( j = 1 , ..., k) illustrated in Figure 1 , which is to receive a current Ij from the line VBATT and to operate between the nodes Cj-i and Cj .

[0073] The solution exempli fied in Figure 3 may hence be applied to : the circuit S2 of Figure 1 (i.e., S j , with j = 2) , which receives the current 12 and acts between two nodes Cl (connected to the cathode of the LED designated by LED1 and to the anode of the LED designated by LED2) and C2 (connected to the cathode of the LED designated by LED2 ) ; the circuit S3 of Figure 1 (i.e., S j , with j = 3) , which receives the current 13 and acts between the node C2 (connected to the cathode of the LED designated by LED2 and to the anode of the LED designated by LED3) and a node C3 (connected to the cathode of the LED designated by LED3 ) ; and the circuit S4 of Figure 1 (i.e., S j , with j = 4) , which receives the current 14 and acts between the node C3 (connected to the cathode of the LED designated by LED3 and to the anode of the LED designated by LED4) and a node C4 (connected to the cathode of the LED designated by LED3 and from which a "tail" current I G flows to ground GND) .

[0074] It may be noted that, also in this case, what has been illustrated herein with reference to the LEDs denoted by LED2, LED3, and LED4 could in principle be applied also with reference to the LED denoted by LED1. The practice of application on the other hand indicates that this extension is not imperative.

[0075] Basically, Figure 3 illustrates an example of a driver circuit Sj for light sources (for example, LED sources such as LED1, LED2, LED3, LED4) configured to be powered via a supply line at a supply voltage VBATT.

[0076] The driver circuit Sj of Figure 3 comprises: a first node Cj-i and a second node Cj that are configured to have connected therebetween a light source susceptible to flickering in response to variations of the supply voltage VBATT transferred to the first node Cj-i; and an electronic switch Sjl set between the first node Cj-i and the second node Cj .

[0077] In this regard, it will be noted that (also in relation to what is explained in what follows) the distinction between "first" node and "second" node (with reference to Cj-i and Cj ) is made merely for the purposes of simplicity of explanation in so far as in practice all that is said in what follows with reference to the node Cj-i can apply to the node C , and vice versa: just to provide an example, also the connection to ground of the node C4 (Cj with j = 4) could - at least in principle - be the cause of flicker as a result of the inductance of a cable for connection to ground.

[0078] The circuit exemplified in Figure 3:

[0079] "captures" the oscillations of the voltage on VBATT on the source-to-drain current path of the switch S l (for example on the drain of the MOSFET Sjl - node D in Figure 3 ) ; and drives, in response to (and as a function of) the aforesaid oscillations of the voltage on VBATT, a further current generator ITOj that operates in a way substantially similar to the current generator Ij on the source-to-drain current path of the switch Sjl (for example, on the drain of the MOSFET Sj2 - node K in Figure 3) so as to switch off the LED that is flickering on account of the disturbance as long as the disturbance (which is assumed as being temporary) is present.

[0080] The circuit exemplified in Figure 3 hence comprises : a shutdown generator ITOj (for example, a shutdown current generator) coupled (via the MOSFET Sj2) to the electronic switch Sjl set between the first node Cj-i and the second node (Cj) ; and flicker-detection circuitry coupled (in a node D) to the first node Cj-i. The aforesaid flicker-detection circuitry is configured to generate a flicker-detection signal FS on a homologous line in response to the aforesaid variations of the supply voltage VBATT transferred to the first node Cj-i.

[0081] The flicker-detection circuitry is configured to activate the shutdown generator ITOj and render the electronic switch Sjl conductive in response to generation of the flicker-detection signal FS so that the light source coupled between the two nodes Cj-i and Cj remains off as long as the disturbance that produces the flicker persists.

[0082] For instance, the current generator ITOj is suited to being implemented in the form of a voltage-driven transistor (i.e., as a transconductance module) capable of varying the current through the MOSFET S 2, thus causing, via the current-mirror coupling, the MOSFET Sjl to act as electronic switch that switches off the corresponding LED denoted by LEDj (i.e., LED2, LED2, or LED4) in so far as by closing, i.e., becoming conductive, the MOSFET Sjl shorts the corresponding LED.

[0083] In this way, the source concerned (e.g., LED2, LEDS, LED4) can be switched off and kept deactivated for the time - which is likely to be short - during which flickering is present: it is found, in fact, that the aforesaid possible switching-off (more often than not, a slightly delayed switching-on) proves less troublesome - and frequently not even perceived - as compared to flickering .

[0084] The behaviour of the line or node VBATT is exempt from hysteresis in the sense that the achievement of a high threshold precision is facilitated in the presence of both ascending ramps and descending ramps of the voltage on the line or node VBATT.

[0085] To sum up, the solution exemplified in Figure 3 envisages : connecting - between a first node (here Cj-i) and a second node (here Cj ) that have an electronic switch Sjl set therebetween- a light source susceptible to flickering in response to variations of a supply voltage VBATT transferred to the first node; generating, via flicker-detection circuitry (here the elements 10, 12, 14, 16) coupled (at the node D) to the first node, a flicker-detection signal FS in response to variations of the supply voltage VBATT transferred to the first node; and activating, via the flicker-detection circuitry, a shutdown generator as ITOj, coupled (here, in a way in itself known, via the MOSFET Sj2) to the electronic switch Sjl, rendering the electronic switch Sjl conductive in response to the generation of the flickerdetection signal FS .

[0086] The circuit exemplified in Figure 3 detects an undesired oscillation on VBATT thanks to a voltagesensing circuitry that is coupled to the node D and drives the shutdown generator ITOj accordingly.

[0087] In the example presented in Figure 3, the above voltage-sensing circuitry generates the flickerdetection signal FS via a high-pass filter (HPF) 10 coupled to the node D, i.e., - in the example presented herein - to the drain of the MOSFET Sjl, with the signal filtered by the filter 10 supplied to an amplifier 12, the gain of which affects the level of the flickerdetection signal FS and determines the degree of accuracy of the action of reaction to the disturbance.

[0088] By way of non-limiting example, it has been found that a (lower) cut-off frequency in the region of 1 kHz for the high-pass filter 10 and a gain of 10 dB of the stage 12 prove advantageous choices in the context exemplified herein. In other words, in the example presented herein, the flicker-detection circuitry: comprises a high-pass filter 10 coupled (in D) to the first node (here Cj-1) ; and / or is coupled to the shutdown generator ITOj through a gain stage 12; and / or is coupled to the shutdown generator ITOj through an envelope detector (14, 16) .

[0089] Advantageously, driving of the generator ITOj starting from the output of the gain stage 12 is implemented via a peak detector comprising a rectifier diode 14 (for example, with the anode connected to the output of the amplifier 12 and the cathode connected to the generator ITOj) and a capacitor 16 connected between the cathode of the diode 14 and the node Cj .

[0090] The peak detector, and in particular its capacitive components 16, have an advantageous integrating effect on the flicker-detection signal FS used for driving the generator ITOj .

[0091] Advantageously, the shutdown generator ITOj is set at the input of the current mirror, i.e., on the (source- to-drain) current path, for example on the drain of the MOSFET Sj2.

[0092] As illustrated herein by way of example, the electronic switch comprises a transistor (i.e., Sjl) , connected in current-mirror arrangement to a further transistor (i.e., Sj2) , associated to which is a shutdown generator ITOj configured to inject a shutdown current into a current path ( source-to-drain current path, in the case of a field-effect transistor such as a MOSFET) through the further transistor Sj2 in response to the generation of the flicker-detection signal FS .

[0093] As illustrated, the electronic switch Sjl, which is to short (and hence temporarily switch off) the source that is subject to flicker, and the further transistor Sj 2 are field-effect transistors, connected gate-to-gate in current-mirror arrangement.

[0094] Observed in a co-ordinated way along with Figure 1 (and Figure 2) , Figure 3 exemplifies the possibility of providing a driver device 100 for light sources LED1, LED2, LED3, LED4 that are configured to be powered via a supply line at a supply voltage VBATT, where the driver device 100 comprises a plurality of driver circuits Sj obtained according to Figure 3, which each have the first node Cj-i and the second node Cj that can be arranged in a current-flow line between the supply line VBATT and ground GND so that variations of the supply voltage VBATT are transferred to the first node (here Cj-i) of each of the circuits S .

[0095] Such a device 100 is suited to being used for driving a lighting device comprising a plurality of light sources LED2, LED3, LED4 set in series with one another (as exemplified in Figure 1 and Figure 2) , each connected between the first node Cj-i and the second node Cj of a respective driver circuit Sj comprised in the device 100.

[0096] As exemplified in Figure 1 and Figure 2, such a lighting device may comprise a further light source (LED1 in Figure 1 and Figure 2) connected in series to the other series-connected light sources (i.e., LED2, LEDS, LED4) , but the aforesaid further light source (i.e., LED1) may be uncoupled from the driver device 100 (i.e., not have associated a respective driver circuit like the circuit Sj of Figure 3) , thus achieving an advantageous reduction in terms of overall dimensions, considering the reduced exposure of the aforesaid further source to the flicker phenomenon.

[0097] Without prejudice to the underlying principles, the details of construction and the embodiments may vary, even significantly, with respect to what has been illustrated herein purely by way of non-limiting example , without thereby departing from the sphere of protection of the invention, as this is speci fied in the annexed claims .

[0098] LIST OF REFERENCE SIGNS

[0099] Supply line or node VBATT

[0100] Voltage-to-current converter Vtol

[0101] Light sources (LEDs) LED1, LED2, LED3, LED4

[0102] Currents I G, 12, 13, 14

[0103] Driver device 100

[0104] Driver circuits S2, S3, S4

[0105] Node Cl, C2, C3, C4

[0106] Ground GND

[0107] Current mirror S21, S22; S31, S32; S41, S42

[0108] Shutdown generator ITOj

[0109] Node Cj-i, Cj, D, K

[0110] Current mirror Sjl, Sj2

[0111] Highpass filter 10

[0112] Gain stage 12

[0113] Envelope-detector diode 14

[0114] Envelope-detector capacitor 16

[0115] Flicker-detection signal FS

Claims

CLAIMS1. A driver circuit (Sj) for light sources (LED1, LED2, LED3, LED4 ) configured to be powered via a supply line at a supply voltage (VBATT) , the driver circuit (Sj) comprising: a first node (Cj-1) and a second node (Cj) configured to have connected therebetween a light source susceptible to flickering in response to variations in the supply voltage (VBATT) transferred to said first node (C -1 ) ; an electronic switch (Sjl) arranged between the first node (Cj-1) and the second node (Cj) ; a shutdown generator (ITOj) coupled (Sj2) to the electronic switch (Sjl) arranged between the first node (Cj-1) and the second node (Cj) , and flicker-detection circuitry (10, 12, 14, 16) coupled (D) to the first node (Cj-1) , wherein the flicker-detection circuitry is configured (10, 12, 14, 16) to generate a flicker-detection signal (FS) in response to said variations in the supply voltage (VBATT) transferred to the first node (Cj-1) , the flickerdetection circuitry (10, 12, 14, 16) being configured to activate the shutdown generator (ITOj) and render the electronic switch (Sjl) conductive in response to the generation of said flicker-detection signal (FS) .

2. The driver circuit (Sj) of claim 1, wherein the flicker-detection circuitry (10, 12, 14, 16) includes a high-pass filter (10) coupled (D) to said first node (Cj- 1) .

3. The driver circuit (Sj) of claim 1 or claim 2, wherein the flicker-detection circuitry (10, 12, 14, 16) is coupled to the shutdown generator (ITOj) via a gain stage ( 12 ) .

4. The driver circuit (Sj) of any of claims 1 to 3, wherein the flicker-detection circuitry (10, 12, 14, 16)is coupled to the shutdown generator (ITOj) via an envelope detector (14, 16) .

5. The driver circuit (Sj) of any of the previous claims, wherein: the electronic switch (Sjl) includes a transistor connected in a current-mirror arrangement with a further transistor (Sj2) ; and the shutdown generator (ITOj) is configured to inject a shutdown current into a current path through said further transistor (Sj2) in response to the generation of said flicker-detection signal (FS) .

6. The driver circuit (Sj) of claim 5, wherein the electronic switch (Sjl) and the further transistor (Sj2) are field effect transistors coupled gate-to-gate in a current mirror arrangement.

7. The driver circuit (Sj) of any of the previous claims, wherein the shutdown generator (ITOj) comprises a transconductance module driven via said flickerdetection signal (FS) .

8. A driver device (100) for light sources (LED1, LED2, LEDS, LED4 ) configured to be powered via a supply line at a supply voltage (VBATT) , wherein the driver device (100) comprises a plurality of driver circuits (Sj) according to any of the previous claims wherein the driver circuits (Sj) in the plurality of driver circuits (Sj) each have the first node (Cj-1) and the second node (Cj) arranged in a current flow line between said supply line and ground (GND) .

9. A lighting device comprising: a driver device (100) according to claim 8, and a plurality of series-connected light sources (LED2, LEDS, LED4 ) , each light source (LED2, LEDS, LED4) connected between the first node (Cj-1) and the second node (Cj) of one of the driver circuits (Sj) in said driver device (100) .

10. The lighting device of claim 9, comprising a further light source (LED1) connected in series to said plurality of series-connected light sources (LED2, LED3, LED4) , the further light source (LED1) being uncoupled from said driver device (100) .

11. A method, including: connecting between a first node (Cj-1) and a second node (Cj) having an electronic switch (Sjl) arranged therebetween a light source susceptible to flickering in response to variations in a supply voltage (VBATT) transferred to said first node (Cj-1) ; generating via flicker-detection circuitry (10, 12, 14, 16) coupled (D) to the first node (Cj-1) a flickerdetection signal (FS) in response to said variations in the supply voltage (VBATT) transferred to said first node (Cj -1 ) , and activating, via the flicker-detection circuitry (10, 12, 14, 16) , a shutdown generator (ITOj) coupled (Sj2) to the electronic switch (Sjl) , rendering the electronic switch (Sjl) conductive in response to the generation of said flicker-detection signal (FS) .

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