Driver circuit for lamps, and corresponding lamp and method

Abstract

A supply circuit (10) that can be integrated in an automotive solid-state lamp (L) for vehicles, for example of a LED-socket type, comprises: an input stage (E) configured to generate a voltage signal (Vbus) starting from a control signal (Vbcm); an electrical dummy load (DL); a driver module (C) for driving light sources configured to supply (ILS) at least one solid-state light source (LS); a comparator (D) coupled to the input stage (E) and configured to make a comparison between the aforesaid voltage signal (Vbus) and a lower threshold level (Vmin); and an enable block (A) for enabling the electrical dummy load (DL) and the module (C) for driving light sources, which is coupled to the comparator (D) and is configured for counting a time-out time (TO). The enable block (A) is configured to: i) in response to the voltage signal (Vbus), enable the electrical dummy load (DL), with the driver module (C) disabled, and activate counting (TC) of the time-out time (TO); and ii) in response to elapsing of the time-out time (TO), disable the dummy load (DL), conditioning enabling of the module (C) for driving light sources (LS) to the outcome of the comparison in the comparator (D).

Description

[0001] "DRIVER CIRCUIT FOR LAMPS, AND CORRESPONDING LAMP AND METHOD"

[0002] Technical field

[0003] The present disclosure relates to driving of lamps, for example for purposes of diagnostic testing.

[0004] One or more embodiments may be applied to LED lamps used for so-called retrofitting or aftermarket equipping, for example in the automotive sector.

[0005] Technological background

[0006] Lamps that use solid-state light generators, for example LED light generators, are used ever increasingly in place of traditional incandescent or fluorescent lamps. This applies, in particular, to the automotive sector .

[0007] LED lamps for vehicles are able to provide characteristics of luminous flow and distribution of light that are compatible with the requirements of use in lights for motor vehicles, where the characteristics of intensity and distribution of the luminous flux assume particular importance.

[0008] The relevant prior art is rather extensive, as documented by EP 3 828 463 Bl and by the extensive review of prior documents contained therein (US 9 677 753 B2; US 10 415 787 B2; US 9 470 391 B2 - corresponding to which is US 2014 / 328079 Al; US 8 118 462 B2; US 8 066 414 B2; US 7 144 140 B2; US 2015 / 0146447 Al; US

[0009] 2011 / 0025211 Al; US 2010 / 0165632 Al; US 2010 / 0027270 Al; EP 3 647 649 Al, IT 102019000010188 Al; CN 109 140 373 A; CN 106 594 627, CN 207 334 634 U) and by the Italian patent 102022000010499.

[0010] Further prior art documents include US 2011 / 062869 Al, US 2019 / 150237 Al and DE 10 2004 045435 B4.

[0011] Many motor vehicles are today equipped with electronic systems capable of carrying out diagnostic testing on different components of the vehicle. Such systems maybe associated to a central control unit of the vehicle electronics, which is frequently referred to as BCM (Body Control Module) .

[0012] A BCM may be configured for carrying out diagnostic testing inherent to the state of the lamps and issuing corresponding signals.

[0013] Conventional lamps (incandescent lamps, i.e., filament lamps) may be subjected, according to the type and model of the vehicle, to various diagnostic tests.

[0014] For instance, a first possible test is a check with DC current: the purpose of this diagnostic test is to check integrity of the filament when the lamp is on (i.e., with the lamp powered) . The filament of the lamp is classified as "failed" when the current consumption drops below a given threshold (indication of the fact that the filament is interrupted or damaged) . The failure is signalled by the BCM unit on the control panel (dashboard) of the vehicle.

[0015] Another possible test is a check with pulsed current (also known as cold lamp check - CLC) : the purpose of this diagnostic test is to check the integrity of the filament with the lamp off (not powered) ; a burst of voltage pulses generated by the BCM unit (approximately 1 ms to 2 ms of duration and 100 ms to 500 ms of period) is applied to the lamp under test. In a filament lamp, on account of the high thermal capacity of the filament of the cold lamp, the pulses applied do not manage to turn on the lamp. The pulsed current that flows through the cold filament is, however, detected by the BCM unit and compared with a given threshold. The filament of the lamp is classified as "failed" when the current detected drops below a given threshold (filament interrupted or damaged) . The failure is signalled by the BCM unit on the control panel of the vehicle. Solid-state retrofit lamps , for example LED lamps , are designed in view of possible direct replacement of traditional filament lamps ( for example , halogen lamps ) both for the main lights and for the auxiliary light sources of the vehicle . In sectors of use such as the automotive sector, LED retrofit lamps have achieved a considerable success for various reasons of advantage over traditional lamps , such as the quality of the light emitted, the long duration, and the ease of installation . LED retrofit lamps may, however, cause problems of compatibility with diagnostic testing : the installation of LED lamps as retrofit to replace traditional filament lamps may cause the diagnostic tests implemented by a BCM unit not to be able to detect properly the state of the lamp or to being subj ect to drawbacks . For instance , in the case of a DC-current test , the high ef ficiency of light emission of the LEDs (number of lumen per watt ) means that retrof it lamps have a low current absorption . The current absorbed may hence drop below the diagnostic threshold established by the BCM unit so that a false failure message is issued .

[0016] Figures 1A, IB , and 1C are timing charts that represent , with respect to a common time scale ( abscissa t ) :

[0017] Figure 1A, possible waveforms of a voltage pulse VP ( for example , of 12 V to 15 V) applied to a lamp for a time interval in the case of a check with pulsed current , namely, a CLC ( Cold Lamp Check) test ; and

[0018] Figures IB and 1C , possible waveforms of the current absorbed by the lamp in the case of a LED lamp ( curves IL1 , IL2 of Figure IB ) and in the case of a filament lamp ( curve I F of Figure 1C ) .

[0019] It may be noted that a LED lamp has a high, but short , absorption peak due to charging of the input capacitance of the driver, and Figure IB highlights undesired side ef fects that may arise in the case of a LED retrofit lamp .

[0020] In the first place , in the case of a filament lamp, the test voltage pulse is not able to activate the lamp in the sense that there is no light emission . Instead, considering the on time of the LED lamp, which is much shorter than for filament or incandescent lamps , in the case of a LED lamp there may be emission of a flash of light LF ( Figure IB ) that is visible .

[0021] Moreover, considering the current absorbed by the LED lamp, which is signi ficantly lower than for filament or incandescent lamps ( curve IL2 in Figure IB ) , and possible switch-on delays of the driver of the LED lamp, in the case of a LED lamp there may be a false signalling of failure .

[0022] Questions of this nature are tackled in EP 4 507 456 Al ( inventor Paolo De Anna ) , a document that was not yet available to the public at the priority date of the present application . The above document describes a driver circuit for lamps that , at least in some cases ( for example , when the si ze of the lamp so permit ) , can be integrated in the lamp, giving rise to a retrofit device that can be directly substituted for a traditional filament lamp .

[0023] It appears in any case desirable to facilitate further integration in a driver for a retrofit LED lamp ( and, more in general , in the lamp itsel f ) with a circuit capable of countering issuing of error messages and / or flashes of light during execution of CLC tests , likewise facilitating operation in pulse-width-modulation ( PWM) at low frequency and performance of a function of thermal foldback ( or thermal derating) in an integrated driver for LEDs not pre-arranged for such purposes .

[0024] Obj ect and summary

[0025] The obj ect of one or more embodiments is to contribute to meeting the expectations outlined previously .

[0026] According to one or more embodiments , the above obj ect is achieved thanks to a circuit having the characteristics recalled in the ensuing claims .

[0027] One or more embodiments refer to a corresponding lamp . A lamp comprising at least one solid-state light source ( for example , a LED source ) integrated together with the supply circuit in the body of the lamp is an example of such a lamp .

[0028] One or more embodiments refer to a corresponding method .

[0029] The claims form an integral part of the technical teachings provided herein in relation to embodiments .

[0030] Solutions like the ones described herein make it possible to avoid the use of dedicated external circuits set in separate boxes between the battery supply and the lamp ( or lamps ) supplied, thus facilitating operation free from error messages and / or flashes during diagnostic testing .

[0031] Solutions like the ones described herein facilitate integration in compact LED lamps , in so-called LED socket lamps with integrated driver circuit .

[0032] Solutions like the ones described herein are likewise able to counter possible phenomena of instability linked to PWM operation and / or undesired shutdown of the lamp in the presence of high temperatures .

[0033] Solutions like the ones described herein envisage the use of logic circuitry that adequately drives a dummy resistive load, managing activation of a driver for LEDs so as to simulate the behaviour of a traditional fi lament lamp .

[0034] Brief description of the drawings

[0035] One or more embodiments will now be described, purely by way of non-limiting example , with reference to the annexed drawings , wherein :

[0036] Figures 1A, IB , and 1C, which represent execution of a check with pulsed current , namely, a CLC ( Cold Lamp Check) test , on a lamp, have already been discussed previously;

[0037] Figure 2 is a block diagram that represents , in general terms , the criteria of use of solutions like the ones described herein in an automotive context ;

[0038] Figure 3 is a functional block diagram of solutions like the ones described herein;

[0039] Figure 4 is a more detailed block diagram of solutions like the ones described herein; and

[0040] Figures 5 , 6 , 7 , and 8 are timing charts exempli fying possible waveforms of signals that may recur in solutions like the ones described herein .

[0041] It will be appreciated that , for clarity and simplicity of illustration, the various figures may not be represented at one and the same scale .

[0042] Moreover, for brevity - unless the context indicates otherwise - parts or elements that are similar are designated in the various figures by the same reference symbol s , without repeating a corresponding description for each figure .

[0043] Detailed description

[0044] 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 .

[0045] Reference to "an embodiment" or "one embodiment" in the framework of the present description is meant 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 appear 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 .

[0046] The references used herein are provided simply for convenience and hence do not define the sphere of protection or the scope of the embodiments .

[0047] As has been said, in the various figures , the same references are used to designate corresponding parts or elements , without , for reasons of brevity, the corresponding description being repeated for each figure .

[0048] Once again for reasons of simplicity and ease of exposition, in the present description one and the same reference may be used to indicate : a given node or line , as well as a signal that arises on that node or line ; and / or a given component ( like a capacitor or a resistor ) , as well as the corresponding electrical parameter ( e . g . , capacitance or resistance / impedance ) .

[0049] Again, the fact that a certain element is described as being "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, it is stated that an element is "directly connected" or "directly coupled" to another element , this means that no other element is set between these two elements . The block diagram of Figure 2 illustrates , in general terms , a system ( that can be installed on board a vehicle V, for example a motor vehicle such as a car ) comprising : a central control unit (Body Control Module , BCM) of the electronic system of the vehicle V, which is assumed as being supplied with a (battery) voltage Car voltage and is able to supply a (voltage ) signal Vbcm; and a lamp L that is to be supplied via a circuit 10 that is able to supply the lamp with a voltage Vout and perform various functions , as described in what follows .

[0050] Reference , merely by way of non-limiting example , to ( j ust ) one lamp L is aimed at highlighting the fact that solutions like the ones described herein are advantageously suited to providing LED socket lamps ( for example , for retrofitting traditional filament lamps ) with integrated driver circuit , i . e . , lamps comprising at least one solid-state light source ( for example , a LED source ) integrated together with the supply circuit in a lamp body, such as a lamp body that fits in a spatial envelope according to Figure 2 of Addendum 36 of ECE Regulation 37 for H7 lamps ( SAE 9004 or 9007 ) .

[0051] As has already been said in the introductory part of the present description, the BCM unit of an electronic system on board a motor vehicle V may be configured so as to perform diagnostic testing on the vehicle lamps ( for example , traditional filament lamps ) .

[0052] For instance , a BCM unit may conduct a series of diagnostic tests for detecting and signalling the state of the lamps .

[0053] Once again by way of summary of what has already been said in the introductory part of the present description, traditional incandescent lamps may undergo ( according to the model of the vehicle ) diagnostic testing, such as : check with DC current so as to check the integrity of the filament when the lamp is on, i . e . , powered : the lamp filament is classi fied as " failed" when the current absorption drops below a given threshold (which indicates the fact that the filament is broken or damaged) , with the failure signalled on board ( on the instrument panel or dashboard) by the BCM unit ; and / or check with pulsed current , also known as cold lamp check ( CLC ) ; the purpose of this diagnostic test is to check the integrity of the filament when the lamp is of f (not powered) by applying to the lamp a burst of voltage pulses generated by the BCM unit ( for example , with a pulse width of approximately 1 ms to 2 ms and a period of 100 ms to 500 ms ) ; the high thermal capacity of the filament of the cold lamp causes the pulses applied not to be able to turn the lamp on, but the pulsed current that flows through the cold filament , detected by the BCM unit and compared with a given threshold, enables classi fication of the lamp filament as " failed" when the current detected drops below a given threshold (which indicates the fact that the filament is broken or damaged) , with the failure once again signalled on board by the BCM unit .

[0054] The BCM unit of an electronic system on board a motor vehicle V may likewise be configured to regulate the root-mean-square ( rms ) voltage applied to the lamps on board the vehicle to prevent , in traditional incandescent lamps , conditions of overload of the filament . This function is performed via a regulation based upon pulse-width modulation ( PWM) of the voltage . For instance , when the voltage of the vehicle ( Car voltage in Figure 2 ) exceeds 13 V to 13 . 5 V ( for example , when the engine is running and the alternator is active ) , the BCM unit applies to the lamps L a low PWM frequency value (usually in the range between 80 Hz and 200 Hz ) with a duty-cycle such as to bring the rms voltage back to the rated voltage of the lamp ( 13 V to 13 . 5 V) .

[0055] It is recalled that by "duty-cycle" is meant the fraction of time that an entity passes into an active state in proportion to the total time considered . For instance , in the presence of a signal with rectangular waveform, the duty cycle is the ratio between the duration of the "high" or "on" signal and the total period ("on" + "of f" ) of the signal .

[0056] It is desirable for such a function to be extended to driving LED lamps ( for example , retrofit LED lamps ) , with the capacity of handling such a low- frequency PWM supply, being able to manage a prolonged voltage drop, maintaining a fast and precise control of the current during the "on" times of the PWM signal .

[0057] It is found that various existing drivers for LEDs are not able to deal in an adequate way with such conditions of PWM supply at low frequency on account of saturation of the current control loop and the absence of supply during the "of f" times of the PWM signal . This may give rise to instability in light emission (with perceptible flickering ) and to strong overcurrents in the LEDs .

[0058] Another aspect considered in the solutions described herein is the function known as "thermal foldback" ( or "thermal derating" ) that , in the case of circuits for driving LEDs , or LED drivers , is to reduce gradually the power of the LED when a dedicated thermistor sensor set on the LED lamp indicates reaching of a critical temperature .

[0059] In the maj ority of cases , the integrated circuits ( ICs ) of LED drivers envisage at most thermal protections of an ON / OFF type that force shutdown in the case where j unction temperatures are reached that are considered as being indicative of overheating.

[0060] More in general, it may be noted that a fair share of integrated circuits of LED drivers available today on the market use DC-DC switching converter circuits of a buck type operating in the frequency ranges of from 100 kHz to 200 kHz, with the use of external freewheeling diodes in a package of an SO8 type.

[0061] Being able to reduce the size of the electronics of a LED driver is an important factor for the purpose of obtaining compact LED lamps.

[0062] To reduce the size of such a driver one may think of implementing various measures, such as: resorting to converters (e.g., buck converters) with synchronous rectification so as to avoid the use of external power diodes, such as freewheeling diodes, thus also reducing the power losses; using miniaturized power packages (for example, 2x2-mm ones) ; or using higher switching frequencies (100 kHz to 1MHz) .

[0063] Integrated drivers (for example, the product SGM3770 manufactured by SGMICRO) capable of operating at a frequency of 790 kHz are today available on the market.

[0064] However, the above high-performance components are not in themselves able to meet fully the requirements outlined previously (management of CLC tests, anti-flash function, thermal foldback, low-frequency operation) .

[0065] Figure 3 is a functional block diagram of solutions like the ones described herein, which is to be read in conjunction with Figure 2.

[0066] The above functional diagram highlights the possible integration in a lamp L (a lamp with solid- state light sources LS, such as LED sources, for example, a retrofit lamp for the automotive sector) of a circuit 10 capable of facilitating driving of the aforesaid sources by a BCM unit that delivers a supply voltage .

[0067] The above solution is aimed at providing a lamp L that integrates , in the lamp body, not only the light sources ( for example , LED sources ) but also the corresponding supply / driver circuit , in an ensemble that can be simply substituted ( as "retrofit" ) for a traditional ( incandescent ) lamp, complying with the overall dimensions laid down by the speci fications and at the same time facilitating achievement of performance of light emission fully in conformance with the standards ( at the level of " street legal" solutions ) .

[0068] Solutions like the ones described herein aim at overcoming the limitations of the integrated circuits described above by facilitating execution of functions such as the CLC test via a circuit 10 capable of achieving driving of solid-state light sources ( LED sources ) , countering the undesired phenomenon of flashing in response to the CLC test , likewise facilitating both PWM operation at low frequency and thermal foldback via an optimi zed dedicated electronic circuit that can be integrated in the driver of a LED lamp and, better still , in the LED lamp itsel f , thus making it possible to obtain, for example , retrofit LED lamps of a LED-socket type , which can be simply substituted for traditional incandescent lamps , complying with the overall dimensions laid down by the speci fications and at the same time facilitating achievement of performance of light emission fully in conformance with the standards ( at the level of " street legal" solutions ) with the body of the retrofit lamp that fits , for example , in a spatial envelope according to Figure 2 of Addendum 36 of ECE Regulation 37 for H7 1 amp s ( S AE 9004 or 9007 ) .

[0069] For instance , the aim is that a circuit like the one designated herein by 10 will be able , during a CLC test , to absorb high current pulses ( for example , of between 1 A and 2 A) for intervals of 10 ms to 15 ms after application of the voltage of the BCM unit , preventing any false detection ( and signalling) of failures of the lamp by the BCM unit .

[0070] The aim is likewise that the circuit 10 should be able to keep the LED driver of f for the first 10 ms to 15 ms subsequent to application of the voltage by the BCM unit so as to prevent the lamp from flashing during the CLC test .

[0071] Again, the aim is that the circuit 10 should be able to force a gradual reduction of the current of the LED driver ( thermal foldback ) in the presence of conditions of overheating detected via a thermistor ( for example , a PTC - Positive Temperature Coef ficient - thermistor ) .

[0072] An aspect that is certainly advantageous is then represented by the fact that the circuit should be able to " freeze" the feedback loop of the driver during the of f times of the low- frequency PWM signal generated by the BCM unit .

[0073] It is desirable that the foregoing can be obtained at contained costs , with reduced dimensions , and a minimum number of components , avoiding the need to resorting to separate circuits arranged between the BCM unit and the lamp L and overcoming the limitations of solutions that present , for example , a dedicated input for an external thermistor and are not suited to being integrated in compact LED lamps .

[0074] It will again be appreciated that , as regards what is of interest here , the BCM unit may be of any known type configured to perform CLC tests with pulsed-current check on the lamp L, this rendering superfluous any further more detailed description herein .

[0075] Figure 4 is a more detailed block diagram of a circuit solution like the one described herein, articulated in various blocks , which are denoted by letters from A to F and provide the following functions : block A - CLC and anti- flash functions ; block B - functions of PWM signal generation and thermal foldback; block C - integrated circuit ( IC ) for driving the LED sources of the lamp L ; block D - detection of the level o f a supply voltage Vbus , here exempl i fied as referenced to ground GND, with a comparator configured to detect the possible decrease in the voltage Vbus below a minimum threshold Vmin of the supply voltage ; block E - bridge recti fier that produces the voltage Vbus starting from the voltage coming from the BCM unit ; block F - capacitance of the DC link for trans fer of the voltage Vbus .

[0076] Likewise visible in Figure 4 are : a thermistor TH ( for example , a PTC thermistor ) , an electrical dummy load DL, for example a resistive load, as well as a feedback line FB used for adding an of fset value on the current- feedback path of the driver of the light sources of the lamp L .

[0077] As illustrated in Figure 4 , the outcome of the comparison of the voltage Vbus with the voltage Vmin by the comparator of block D causes the latter to intervene (via an enable signal Enable ) on block A and on block B .

[0078] As illustrated in Figure 4 , block A is configured so as to be able to intervene on the dummy load DL, connected to the line ( DC link) at the voltage Vbus , causing activation or else deactivation thereof according to the criteria described in what follows .

[0079] As illustrated in Figure 4 , block A is likewise configured so as to be able to intervene also on block C ( LED driver, identi fied hereinafter also as driver module) via an enable input designated by ICEN, enabling or else disabling driving of the light sources according to the criteria described in what follows.

[0080] Block A incorporates a time counter TC, which, by operating in a way in itself known, implements a function of counting the time, being able, in particular, to detect and signal reaching of a count value that corresponds to a time limit (time-out time TO) that, as described more fully in what follows, can be fixed at a value of (by way of non-limiting example) 10 ms tol5 ms.

[0081] The block or module (IC) designated by C is coupled to the line (DC link) at the voltage Vbus, with the capacity of performing a function of driving the light sources LS of the lamp L with a closed-loop currentcontrol function (IC current loop) as a function of: a signal indicating the intensity of the current ILS through the light sources LS of the lamp L, represented in Figure 3 with the graphic symbol of a LED; the signal ILS can be obtained, in a way in itself known, via an amperometric sensor (such as a shunt) ; and the signal supplied on the line FB by block B that superintends the PWM and thermal-foldback functions.

[0082] Block C may advantageously be constituted by an integrated driver of a type in itself known, for example the integrated circuit available under the brand name GM3770 manufactured by SGMICRO capable of operating at a frequency of 790 kHz.

[0083] In view of the fact that such a working frequency may be the source of electromagnetic interference (EMI) , block C may have associated to it (advantageously in conditions of strict adjacency to such a high-frequency driver) a radiofrequency filter RE with the function of countering electromagnetic interference.

[0084] As illustrated in Figure 4, block B receives, in addition to the signal Enable of the comparator of block D, a signal ( applied on an input TI ) indicating the value of resistance of the thermistor TH, which in turn is indicative of the ( j unction) temperature of the light sources LS of the lamp L, thus being able to detect increase of the aforesaid temperature towards a threshold value to be considered critical , such as to suggest an intervention of thermal foldback, which block B can command block C ( LED driver ) to perform via the line FB .

[0085] Figure 4 highlights the fact that solutions like the ones described herein are suited to being used without modi fications to the BCM unit , which ( it will be appreciated) constitutes an element distinct from the embodiments .

[0086] Figure 4 , viewed in conj unction with Figure 3 , highlights the fact that a circuit 10 according to the solutions described herein is suited to being completely integrated into a lamp L such as a retrofit LED lamp of a LED-socket type , which can be simply substituted for a traditional incandescent lamp , duly complying with the overall dimensions laid down by the speci fications and at the same time facilitating achievement of performance of light emission fully in conformance with the standards ( at the level of " street legal" solutions ) .

[0087] This result may advantageously be achieved by organi zing the above circuitry into two sections housed on two supports arranged within the body of the lamp L according to the criteria described in a PCT application filed by the present applicant and claiming the same priority date of the present application .

[0088] The reader is consequently referred to the aforesaid parallel application for a complete description of possible criteria for mounting the components of the circuitry of which Figure 4 illustrates a possible architecture and Figures 5 to 8 exempli fy possible criteria of operation.

[0089] In summary, the circuit 10 illustrated in Figures 4 comprises: an input stage (block E) configured to generate a voltage signal Vbus starting from a control signal Vbcm coming from a BCM unit (see Figure 2) ; an electrical dummy load (DL) and a driver module (integrated circuit of block C) for driving the light sources LS configured to supply a current ILS to one or more solid-state light sources LS (for example, LED sources ) ; and a comparator (block D) , which is coupled to the input stage (block E) and is configured to make a comparison between the voltage signal Vbus and a lower threshold level Vmin.

[0090] Figure 4 also illustrates the two other blocks denoted by A and B.

[0091] Block A is a block for enabling the dummy load DL and the driver module C.

[0092] The enable block A is coupled to the comparator D and is configured for counting TC a time-out time, denoted in what follows by TO.

[0093] The enable block A is configured to: in response to the voltage signal Vbus (i.e., upon reception of this signal) , enable the dummy load DL with the driver module C disabled, activating counting TC of the time-out time TO; and in response to elapsing of the time-out time TO, disable the dummy load DL, conditioning enabling the driver module 0 to the outcome of the comparison between the voltage signal Vbus and the lower threshold level Vmin made by the comparator D, i.e., deciding whether to enable or not the driver module 0 on the basis of the outcome of the above comparison.

[0094] Figures 5, 6 and 7 illustrate, with reference to a common time scale t , appearing on the abscissa, pos sible waveforms of the following signals , here presented in the order from top down, as viewed in the figures : voltage Vbcm applied at input to block E (bridge recti fier ) coming from the BCM unit ; bus voltage Vbus generated by block E and present across the capacitance denoted by F; in addition to being detected by the comparator of block D for its comparison with the lower threshold Vmin, the voltage Vbus may be applied ( as DC link) both to the dummy load DL and to block C ( light-source driver ) ; count value TC of the time counter comprised in block A, which can reach the time-out value TO; current I DL in the dummy load; enable signal I CEN of the integrated circuit for driving the LEDs ( LED driver ) , with the driver respectively disabled or enabled according to whether I CEN is " low" or "high" .

[0095] In particular, the waveforms of Figure 5 correspond to conditions where , in the presence of "normal" switching-on of the lamp L : the lamp L is supplied in a stable way by the BCM unit ; the Vbus comparator enables block A in response to the fact that Vbus > Vmin; block A enables the dummy load DL, currently keeping disabled the integrated circuit ( IC ) for driving the LED sources , and the counter TC of block A starts to count and then reaches the time-out value TO set ( for example , 10 ms to 15 ms ) ; and once block A has veri fied that Vbus has remained above Vmin when the time-out time TO has elapsed, it disconnects ( disables ) the dummy load DL and the integrated circuit ( IC of block C ) for driving the LED sources is enabled so that the sources LS are supplied with the nominal current I LS .

[0096] In summary, Figure 5 exempli fies a situation in which the enable block A coupled to the comparator D detects permanence of the voltage signal Vbus above the lower threshold level Vmin upon elapsing of the time-out time TO and, in response to elapsing of the time-out time TO, disables the dummy load DL and enables the driver module 0 ( and hence the light sources LS ) .

[0097] The waveforms of Figure 6 correspond, instead, to conditions where , for the purposes of execution of a CLC test : the lamp L is supplied by the BCM unit with a short pulse , i . e . , with the BCM unit that suspends the supply before the count value TC of the time counter reaches the time-out value TO; the Vbus comparator enables block A in response to the fact that Vbus > Vmin; block A enables the dummy load, keeping the integrated circuit IC for driving the LED sources disabled; the counter TC of block A starts to count , but reaches the time-out value TO set ( for example , 10 ms tol 5 ms ) only after suspension of the supply voltage by the BCM; and block A keeps the dummy load DL enabled until the comparator D signals that the voltage Vbus reaches the threshold value Vmin and disconnects it when Vbus drops below Vmin, once again keeping the integrated circuit ( IC ) for driving the LED sources disabled .

[0098] The fact that the dummy load DL is still connected until Vbus reaches Vmin counters any undesired flashing that might derive from the energy stored in the capacitance of the DC link (block F in Figure 4 ) in so far as this capacitance is discharged below the voltage threshold of the LEDs . In summary, Figure 6 exempli fies a situation in which the enable block A coupled to the comparator D detects that the voltage signal Vbus has dropped below the lower threshold level Vmin prior to elapsing of the time-out time TO, and disables the dummy load DL, without enabling the driver module C .

[0099] The waveforms of Figure 7 correspond to conditions where the solid-state light sources ( LED sources ) L are subj ect to a PWM supply, so that the count TO of the time-out time TO is represented on a time scale dilated with respect to that of Figures 5 and 6 .

[0100] Figure 7 regards a condition of operation where : the lamp L is supplied by the BCM unit with a PWM signal , the "on" time of which terminates before the count value TO of the time counter reaches the time-out value TO; the Vbus comparator enables block A in response to the fact that Vbus > Vmin; block A enables the dummy load, keeping the integrated circuit ( TO ) for driving the light sources LS disabled; the counter TO of block A starts to count , but reaches the time-out value TO set ( for example , 10 ms tol 5 ms ) only after some PWM cycles ; the dummy load DL is still connected until Vbus reaches Vmin, and is then disconnected; the cycle described above is repeated, but with the counter TO that is not at zero ; and the dummy load DL is permanently disconnected in response to reaching of the time-out TO threshold ( 10 ms tol 5 ms ) , while the integrated circuit ( TO ) for driving the light sources LS ( LED driver - block C ) is enabled to function in PWM mode with the dummy load DL that is no longer activated .

[0101] In summary, Figure 7 regards a condition where the input stage E is configured to generate a voltage signal Vbus that drops below the lower threshold level Vmin in an alternated manner in response to a pulse-width- modulated control signal Vbcm .

[0102] In such conditions , block A coupled to the comparator D : disables in an alternated manner the dummy load DL in response to the voltage signal Vbus that drops below the lower threshold level Vmin in an alternatd manner prior to elapsing of the time-out time TO, keeping the module C for driving the light sources LS disabled; and upon elapsing o f the time-out time TO, stably disables the dummy load DL, enabling the module 0 for driving the light sources LS to operation driven by the voltage signal Vbus in response to a pulse-width- modulated control signal Vbcm .

[0103] Figure 8 illustrates , instead, once again with reference to a common time scale t , appearing on the abscissa, and with regard to PWM operation, possible waveforms of the following signals , here presented in the order from top down, as viewed in the figures : output voltage of the BCM unit , Vbcm; bus voltage Vbus ( referenced to a minimum value Vmin) ; and signal on the feedback line FB .

[0104] The waveforms of Figure 8 exempli fy the role of block B in handling the PWM and thermal- foldback functions : block B, in fact , manages both of the aforesaid functions , and Figure 8 highlights , in particular, a possible way for handling the PWM function .

[0105] When the voltage Vbus drops below Vmin, the feedback signal FB goes to the "high" level ( in practice , simulating a high current flow towards the LEDs starting from the driver ) , causing the current control loop of the driver C to remain of f , thus preventing the integral component of the current loop from accumulating and giving rise to the phenomenon commonly known as " integrator wind-up" .

[0106] In general , for the purposes of thermal foldback, when the lamp L reaches the critical temperature detected by the thermistor TH, block B intervenes gradually on the signal on the feedback line FB, thus generating a gradual decrease in the current delivered by the driver C of the LED sources .

[0107] In summary, Figure 8 hence refers to the fact that the driver module C is coupled to a feedback line FB and is configured to reduce supply I LS of the light sources LS as a function of a signal present on this feedback line FB .

[0108] Speci fically, Figure 8 refers to a situation where it is assumed that the input stage E generates a voltage signal Vbus drops below the lower threshold level Vmin in an alternated manner in response to a pulse-width- modulated control signal Vbcm, and where the enable block B coupled to the comparator D applies to the feedback line FB a signal for disabling the driver module C in response to the fact that said voltage signal Vbus drops below the lower threshold level Vmin .

[0109] More in general , Figure 4 exempli fies the possible presence of a thermal sensor TH ( for example , a PTC thermistor ) that generates a signal indicative of the ( j unction) temperature of the solid-state light source LS . The aforesaid thermal sensor TH is coupled ( for example , via block B ) to the feedback line FB, and the driver module C is configured to reduce ( optionally, in a gradual way) supply of the light source LS in response to the ( optionally gradual ) increase of the signal present on the feedback line FB .

[0110] Without prej udice to the underlying principles , the details of construction and the embodiments may vary, even signi ficantly, with respect to what has been illustrated herein purely by way of non-limiting example , without thereby departing from the sphere of protection, as this is speci fied in the annexed claims .

[0111] LIST OF REFERENCE SIGNS

[0112] Voltage pulse VP Current of solid-state lamp IL1 , IL2 Current of filament lamp I F Vehicle V Control unit or module BCM Lamp L Light source / sources ( LED / LEDs ) LS Circuit 10 Vehicle (battery) voltage Car voltage Input (voltage ) signal Vbcm (Voltage ) signal on lamp Vout Block for CLC and anti flash functions A Block for PWM and thermal- foldback functions B Block for driving LEDs C Comparator block D Recti fier block E DC-link capacitance F Recti fier voltage Vbus Lower voltage threshold Vmin Ground GND Thermistor TH Thermistor signal TI Dummy load DL Feedback line / signal FB RF filter RF

[0113] Current control loop IC current loop

[0114] Time counter of block A TC

[0115] Time-out time TO

[0116] Enable signal Enable

[0117] Enable signal of block C I CEN

[0118] Dummy-load current I DL

Claims

CLAIMS1. A supply circuit (10) for automotive solid-state lamps (L) for vehicles, the circuit comprising: an input stage (E) configured to produce a voltage signal (Vbus) from a control signal (Vbcm) , an electrical dummy load (DL) , a light-source driver module (C) configured to supply (ILS) at least one solid-state light source (LS) , a comparator (D) coupled to the input stage (E) , the comparator (D) configured to perform a comparison between said voltage signal (Vbus) and a lower threshold level (Vmin) , and an enable block (A) of the electrical dummy load (DL) and of the light-source (LS) driver module (C) , the enable block (A) coupled to the comparator (D) and configured to count (TC) a time-out time (TO) , wherein the enable block (A) is configured to: i) in response to said voltage signal (Vbus) , enable the electrical dummy load (DL) with the light-source (LS) driver module (C) disabled and activate the count (TC) of the time-out time (TO) , and ii) in response to the elapsing of said time-out time (TO) , disable the electrical dummy load (DL) and condition enabling the light-source (LS) driver module (0) on the outcome of the comparison between said voltage signal (Vbus) and said lower threshold level (Vmin) in said comparator (D) .

2. The circuit (10) of claim 1, wherein the enable block (A) coupled to the comparator (D) is configured to detect the voltage signal (Vbus) remaining above the lower threshold level (Vmin) upon elapsing of said timeout time (TO) and, in response to elapsing of said timeout time (TO) , disable the electrical dummy load (DL) and enable the light-source (LS) driver module (0) .

3. The circuit (10) of claim 1 or claim 2, whereinthe enable block (A) coupled to the comparator (D) is configured to detect the voltage signal (Vbus) decreasing below the lower threshold level (Vmin) prior to elapsing of said time-out time (TO) and, in response to said time-out time (TO) elapsing, disable the electrical dummy load (DL) without enabling the lightsource (LS) driver module (0) .

4. The circuit (10) of any of the previous claims, wherein : the input stage (E) is configured to produce a voltage signal (Vbus) that alternately decreases below the lower threshold level (Vmin) in response to a pulsewidth modulated control signal (Vbcm) , and the enable block (A) coupled to the comparator (D) is configured to: i) prior to elapsing of said time-out time (TO) , disable alternately the electrical dummy load (DL) in response to the voltage signal (Vbus) alternately decreasing below the lower threshold level (Vmin) keeping the light-source (LS) driver module (C) disabled; and ii) in response to elapsing of said time-out time (TO) , steadily disable the electrical dummy load (DL) and enable the light-source (LS) driver module (0) to operation driven by said voltage signal (Vbus) that alternately decreases below the lower threshold level (Vmin) in response to a pulse-width modulated control signal (Vbcm) .

5. The circuit (10) of any of the previous claims, wherein the light-source (LS) driver module (0) is coupled to a feedback line (FB) and is configured to reduce supply (ILS) of said at least one solid-state light-source (LS) as a function of a signal on said feedback line (FB) .

6. The circuit (10) of claim 5, wherein:the input stage (E) is configured to produce a voltage signal (Vbus) that alternately decreases below the lower threshold level (Vmin) in response to a pulsewidth modulated control signal (Vbcm) , and the enable block (A) coupled to the comparator (D) is configured (B) to apply to the feedback line (FB) a disable signal of the light-source (LS) driver module (C) in response to said voltage signal (Vbus) decreasing below the lower threshold level (Vmin) .

7. The circuit (10) of claim 5 or claim 6, comprising a thermal sensor (TH) configured to generate a thermometric signal (TI) indicative of the temperature of said at least one solid-state light source (LS) , wherein the thermal sensor (TH) is coupled (B) to said feedback line (FB) and the light-source (LS) driver module (C) is configured to reduce supply (ILS) of said at least one solid-state light source (LS) , in response to an increase of the thermometric signal on said feedback line (FB) .

8. An automotive solid-state lamp (L) for vehicles, comprising : at least one solid-state light source (LS) , and a supply circuit (10) according to any of the previous claims arranged with the light-source (LS) driver module (C) therein coupled to the at least one solid-state light source (LS) .

9. The automotive lamp (L) of claim 8, wherein the at least one solid-state light source (LS) and the supply circuit (1) are integrated in a lamp body, preferably a lamp body fitting a spatial envelope according to Figure 2 of Addendum 36 of ECE Regulation 37 for H7 lamps (SAE 9004 or 9007) .

10. A method of supplying automotive solid-state lamp (L) for vehicles via a light-source (LS) driver module (C) configured to supply (ILS) at least one solid-state light source (LS) , the method comprising: producing a voltage signal (Vbus) from a control signal (Vbcm) , performing a comparison between said voltage signal (Vbus) and a lower threshold level (Vmin) , and i) in response to said voltage signal (Vbus) , enable the electrical dummy load (DL) with the light-source (LS) driver module (C) disabled and activating a count (TC) of a time-out time (TO) , and ii) in response to the elapsing of said time-out time (TO) , disable the electrical dummy load (DL) and condition enabling the light-source (LS) driver module (0) (LS) on the outcome of the comparison between said voltage signal (Vbus) and said lower threshold level (Vmin) in said comparator (D) .

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