Protection circuit against surges and electrostatic discharges, corresponding lighting system

Abstract

A supply converter (10), for example an AC-to-DC converter for supplying road and street LED lighting apparatuses (12) is configured to be powered at an input (L, N) exposed to surges (Vsurge) and is provided with an output (LED+, LED-) configured to supply to a load (12) a supply voltage (Visol) protected from said surges (Vsurge). The converter has associated a protection network (CP1, R1; CP2, R2; CS, R3) that comprises a divider (CP1, CP2, CS) with: a first capacitive branch (CP1, CP2), with the series connection of a first capacitor (CP1) and a second capacitor, that is coupled between the input (N) and the output (LED-) of the converter (10); and a second capacitive branch (CS), with a third capacitor (CS), that is coupled between the output (LED-) of the converter (10) and a line (EQUI) configured to be earthed or grounded (E). At least the third capacitor (CS), and, in various embodiments, all three capacitors (C1, C2, CS) of the protection network, has / have a respective resistor (R1, R2, R3) in parallel so that the power mains supply affords protection both against surges (Vsurge), for example resulting from lightning, and against electrostatic discharges (ESDs).

Description

[0001] "PROTECTION CIRCUIT AGAINST SURGES AND ELECTROSTATIC DISCHARGES , CORRESPONDING LIGHTING SYSTEM"

[0002] Technical field

[0003] The present disclosure relates to protection against surges and electrostatic discharges .

[0004] One or more embodiments may advantageously be applied to the protection of lighting devices , for example for road and street lighting, against surge phenomena, such as overvoltages and electrostaticdischarge (ESD) phenomena .

[0005] Technological background

[0006] In outdoor lighting applications , such as road and street lighting applications , over the years various solutions have been proposed for protection against ESD or surge phenomena .

[0007] For instance , there has started to spread the use of Class I I ( or Class 2 ) appliances , which are provided with double or reinforced insulation in regard to the electrical line , so that it is possible to avoid the need to carry out a yearly check, which is rather costly, of the earth ( ground) connection that is referred to as protective-earth ( PE ) connection .

[0008] There then exists in general , on the part of the market , a request for ballasts that are robust and reliable , such as to withstand lightning that strikes the appliances , for example of up to 10 kV . Usually, however, it is the weakest insulation barrier ( lamp cable , socket , etc . ) that is struck, with the result that the ballast is destroyed .

[0009] Known from the document US 9705316 B2 is a device for protection from overvoltages comprising a first connection for coupling to a neutral line (N) and at least one voltage-limiting element designed for blocking the current through the voltage-l imiting element itsel f up to a pre-def inable threshold value of the voltage drop across the voltage-limiting element and for conducting current above the aforesaid threshold value . The device may further comprise a second connection for coupling to a metal casing of an electrical apparatus , at least one capacitor, and at least one first non-reactive resistor . The at least one capacitor, the at least one first non-reactive resistor, and the at least one voltage-limiting element are connected in series between the first connection and the second connection .

[0010] The document US 2014 / 268124 Al describes , in particular with reference to Figure 3 , an insulation trans former 11 , 12 with associated two capacitors 21 , 22 connected to earth at a common node .

[0011] The document WO 2015 / 063310 A2 describes a device for protection from overvoltages for an electronic device comprising : at least one high-impedance arrangement connected in series to a load; at least one low- impedance arrangement connected in parallel to the load; and an earth connection pre-arranged for connecting electrically a heat sink and the low- impedance arrangement .

[0012] Other documents of interest for the present disclosure are US 2004 / 169982 Al and US 4 719 403 A.

[0013] Obj ect and summary

[0014] The obj ect of one or more embodiments is to contribute to providing further improvements in solutions for the protection of lighting devices , for example , outdoor lighting devices such as road and street lighting devices .

[0015] According to one or more embodiments , the above obj ect is achieved thanks to a circuit having the characteristics recalled in the ensuing claims .

[0016] One or more embodiments refer to a corresponding lighting system .

[0017] The claims form an integral part of the technical teachings provided herein in relation to embodiments .

[0018] One or more embodiments may af ford advantages such as : protection of the insulation of the lighting module ( for example , of a LED type ) from the heat sink during an overvoltage ; possible tuning of the criteria and of the modalities of intervention; reduced overall dimensions as compared to solutions that envisage the addition of spark gaps ; provision in the same space of a function o f protection against ESD phenomena ; lower cost as compared to solutions with spark gaps and usefulness also for the purposes of reduction of electromagnetic interference (EMI ) .

[0019] It is recalled that by " spark gap" is meant the ensemble of two electrodes set at a distance apart ( so as to form a gap ) with an insulating medium set in between, for example , a gas such as air or a liquid . When the di f ference of potential between the electrodes reaches a given value , referred to as "explosive potential" , spark discharge is triggered .

[0020] Brief description of the drawings

[0021] One or more embodiments will now be described, purely by way of non-limiting example , with reference to the annexed drawings , wherein :

[0022] Figure 1 exempli fies a first possible solution of protection against surges that can be used for lighting devices with the use of a spark gap ;

[0023] Figure 2 exempli fies the possibility of replacing with a number of spark gaps a single spark gap as illustrated in Figure 1 ;

[0024] Figure 3 exempli fies a further possible solution of protection against surges that can be used for lighting devices ;

[0025] Figure 4 illustrates possible critical aspects linked to the adoption of the solution of Figure 3 ;

[0026] Figures 5 to 7 exempli fy possible developments of the solution of Figure 3 ;

[0027] Figure 8 exempli fies a possible solution of protection against surges and ESD phenomena according to embodiments of the present disclosure ;

[0028] Figure 9 exempli fies operating criteria of the solution according to Figure 8 ; and

[0029] Figures 10 to 12 exempli fy possible developments of the solution of Figure 8 .

[0030] It will be appreciated that , for clarity and simplicity of illustration, the various figures may not be represented at the same scale .

[0031] For brevity, in the present description one and the same reference may be used to denote : both a certain node or line and a signal that is set up on said node or line ; both a certain component ( for example , a capacitor or a resistor ) and an electrical parameter ( for example , capacitance or resistance / impedance ) .

[0032] Once again for brevity - and unless the context indicates otherwise - parts or elements that are similar are designated in the various figures with the same references , without a corresponding description being repeated for each figure , this also considering the fact that the solutions claimed are basically those exempli fied in Figures 8 to 12 , whereas Figures 1 to 7 have the function of facilitating understanding and implementation of what is claimed .

[0033] In this connection, it may once again be noted that various elements and characteristics of the developments of the solution of Figure 8 exempli fied with reference to Figures 10 to 12 may not be linked in an imperative way to the circuit structure in relation to which these elements or characteristics are presented by way of example .

[0034] Considering two examples to which we will return again in what follows : for continuity of presentation, the structure represented in Figure 11 is described in terms of di f ferences as compared to the structure represented in Figure 10 , but elements and characteristics of the structure represented in Figure 11 may be applied also to the structures represented in Figures 8 and 9 ; and / or once again for continuity of presentation, the structure represented in Figure 12 is described in terms of di f ferences as compared to the structure represented in Figure 11 , but elements and characteristics of the structure represented in Figure 12 may be applied also to the structures represented in the previous figures .

[0035] Detailed description of examples of embodiment

[0036] 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 of the embodiments will not be obscured .

[0037] 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 .

[0038] The references used herein are provided merely for convenience and hence do not define the sphere of protection or the scope of the embodiments .

[0039] As has been said at the outset of the present description, in outdoor lighting applications , such as road and street lighting applications , there have been proposed various solutions for protection against ESD or surge phenomena .

[0040] In addition to the solution proposed in the document US 9705316 B2 ( already mentioned) a conceivable solution in this regard is represented schematically in Figure 1 .

[0041] A current path L1>>N between the casing or reflector of a lighting apparatus (here not represented explicitly and such that it might be touched by an operator ) and earth ( ground) comprises a spark gap SG and two varistors VAR2 , VAR3 set between the lines LI and N and a node A coming under which is the spark gap SG, referenced to earth .

[0042] This approach is in contrast with the concept of safety as pursued in Class I I ( or Class 2 ) appliances . The spark gap SG defines a path from the apparatus to the power mains for high voltages at the casing of the apparatus , but high-voltage spikes on the power-supply line are not trans ferred to the casing (which, as has been said, is such that it might be touched by an operator ) . In addition to this, spark gaps and varistors cannot be considered safety components that can be positioned through safety barriers, except for spark gaps with separation gaps in air greater than the clearance distance (cl) required.

[0043] Class II appliances require a double / reinf orced insulation and are tested at 3750 VAC.

[0044] A solution that can be hypothesized for tackling these aspects is represented schematically in Figure 2.

[0045] This solution takes into account the fact that, according to the safety specifications 61347-1 and 60598-1, the distances cl (clearance distance) and cr (creepage distance) can be divided into a number of sections if the size of the individual section is greater than 1 mm.

[0046] The idea underlying the solution of Figure 2 is to replace a single spark gap with two cutouts of given dimensions on the printed circuit board (PCB) of the appliances, for example, a first cutout of 4 mm that is to form a first spark gap SGI, and a second cutout greater than 2 mm that is to form a second spark gap SG2, thus providing a total clearance distance greater than 6 mm.

[0047] It is, however, noted that with cl = 5 mm and cr = 6 mm the breakdown voltages are too high to enable this solution to function as protection for the ballast .

[0048] A capacitor Y1 may hence be positioned across the smaller spark gap (SG2, in the case illustrated in Figure 2) so as to function as triggering aid upon onset of a high-voltage pulse. In the presence of the capacitor, the high-voltage pulse has to overstep just the barrier provided by the 4-mm spark gap SGI.

[0049] The solution of Figure 2 proves satisfactory from various points of view, in particular when the tracks or traces on the PCB that define the spark gaps terminate with an oval or round shape ( avoiding pointed portions that might be removed as a result of the discharges ) and are of suf ficient si ze / diameter .

[0050] What has proven advantageous is that the tracks or traces of the PCB should be tinplated so as to prevent blasts of the copper material of the tracks or traces .

[0051] For the capacitor Yl , to obtain more reliable results , a value of capacitance higher than 470 pF has been found to be advantageous .

[0052] The value of the smaller gap SG2 greater than 2 mm is advantageously chosen so as to pass the insulation test with 3750 VAC .

[0053] The solution of Figure 2 has proven suitable for being incorporated in a reliable way in a ballast that meets the requirements of the safety speci fications , with the cutouts that define the spark gaps SGI and SG2 and the capacitor Yl si zed on the basis of the characteristics of the ballast .

[0054] As further advantage , the solution of Figure 2 enables replacement of a costly spark gap with a low- cost solution .

[0055] Figures 3 to 7 refer to solutions that stem from the considerations below .

[0056] In the context of power supply there are some applications that require a high immunity on account of the environment in which they are installed; for example , power supplies dedicated to outdoor applications are to be installed outdoors and are liable to be exposed to unforeseeable conditions (wind, lightning, snow, clouds , etc . ) , at the same time having to guarantee a high reliability ( also because they are frequently di f ficult to replace ) .

[0057] Among the multiple sources of risk are overvoltages ( for example , overvoltages due to lightning) and electrostatic discharges (ESD) to which an outdoor driver is exposed, the duration and functionality being markedly af fected . Moreover, connected to the driver is the lighting module ( for example , of a LED type ) and, possibly, a sensor, which is also exposed and needs to be protected .

[0058] A high degree of protection is rather easy to achieve for Class 1 drivers , where the installation envisages speci fically an earth connection, but becomes more di f ficult for Class 2 drivers .

[0059] A Class 2 insulation basically means that all the conductive parts that might be touched are insulated with a double or reinforced insulation with respect to the power-mains input to guarantee a high degree of safety .

[0060] It is possible to consider as example an appliance or device for road and street lighting . This is usually made of metal ; hence , by connecting it to earth, it is possible to obtain a Class 1 configuration .

[0061] The earth connection may, however, end up wearing out unless a periodic check is carried out . This represents a cost for the end user, who usually prefers to install Class 2 drivers even i f the appliance or device is made of metal .

[0062] For a Class 2 driver there exi sts an intrinsic di f ficulty in protecting the driver and the associated module from common-mode surges .

[0063] A common-mode surge ( CMS ) occurs when lightning strikes the line L / N . In this case , the power-mains input increases as exempli fied in Figure 3 , where 10 designates as a whole a Class 2 supply converter ( represented for simplicity as a trans former connected at input to the lines L and N) that applies an output voltage OUTPUT to a lighting source 12 ( for example , a LED module ) mounted on a heat sink 14 with interposition of an insulation 16.

[0064] As a result of the double insulation, denoted by DI, the overvoltage Vsurge is transferred to the module 12 as "insulated" voltage ViSOi, both voltages being referenced to earth E.

[0065] In actual fact, as represented in Figure 4, it should be taken into account that, as a result of the capacitance across the transformer of the converter 10 (capacitance usually present for reasons of suppression of the radiofrequency noise, i.e., of electromagnetic interference - EMI) the voltage ViSOimay become equal to VSUrge (see the charges + and - represented on the converter 10) . Considering a value of Vsurge that reaches, for example, 10 kV, the insulation may fail, also damaging the driver and the module.

[0066] There should then be taken into account also the second dangerous overvoltage source, i.e., electrostatic discharge (ESD) . Considering as example a driver of an apparatus or device mounted on a hill top or a bridge, in the case of wind or clouds C (in a meteorological sense) it is possible for electric charges (++++++) to accumulate across the internal insulation, which also may fail beyond a certain voltage .

[0067] Figure 5 shows how these problems can be tackled with a solution that may basically amount to that of Figure 1.

[0068] In this regard, it is once again recalled that, for brevity - and unless the context indicates otherwise -parts or elements that are similar are designated in the various figures with the same references, without a corresponding description being repeated for each figure.

[0069] Basically, in the solution of Figure 5: the converter 10 and the heat sink 14 are both referenced to earth E via a line EQUI ( equipotential pin) referenced to earth E , and a common-mode-surge suppressor 18 is provided, traversed by the lines L and N and comprising two varistors VAR2 , VAR3 ( for example , two metal-oxide varistors - MOVs ) , each set between one of the lines LI and N and a node A coming under which is a "double" spark gap SGI , SG2 referenced to earth E .

[0070] The double spark gap SGI , SG2 of Figure 5 comprises a first spark gap, SGI ( for supplying a precise minimum triggering voltage ) and a second spark gap SG2 integrated in the medium ( RGB ) to guarantee the safety distances . The varistors prevent the shorting condition when the spark gaps SGI , SG2 are in conduction .

[0071] The solution of Figure 5 takes up a certain amount of space on the medium, i f the aim is to put the various components inside the driver, and has a certain cost . In addition to this , the air spark gap on the RGB is not easy to regulate and may undergo degradation after it has absorbed a few discharges .

[0072] As illustrated in Figure 6 , for ESD protection there may be envisaged resistances Rl , R2 positioned outside the driver, which, however, may prove cumbersome .

[0073] It has been noted that it is possible to protect the LED module 12 from a common-mode overvoltage of up to 10- 14 kV, reducing the stress applied to the converter ( trans former ) 10 and making it possible to have room to house the ESD protection by exploiting some components that may already be present in drivers in order to reduce EMI .

[0074] Figure 7 represents a conventional solution used to reduce electromagnetic interference in a powersupply unit PSU . In this regard, it is once again recalled that, for brevity - and unless the context indicates otherwise - parts or elements that are similar are designated in the various figures with the same references, without a corresponding description being repeated for each figure.

[0075] In a solution as represented in Figure 7, to reduce EMI two capacitors Cl and C2 are provided, one (Cl) set on the line N as bridge between the input (the primary of the transformer) and the output (the secondary of the transformer) of the converter 10, and the other (C2) set between the output of the converter and the line or pin EQUI referenced to earth E.

[0076] To reduce electromagnetic interference, the two capacitors Cl and C2 usually have approximately the same value. This means that the voltage is divided between the converter 10 and the lighting source (e.g., a LED source) 12, without, however, taking into account the voltage ViSOiacross the insulation 16 of the lighting source 12. Hence, in a solution as represented in Figure 7, the protection may be assumed as being entrusted to a circuit substantially amounting to that of Figure 5.

[0077] Figure 8 represents a solution in which, in the context of a power-supply unit PSU, to reach Class 2, the parts of the converter 10 are with double insulation with respect to the line EQUI (earth E) , and also the output is with double insulation with respect to the input of the converter 10.

[0078] The foregoing provides a solution that is inexpensive, effective, safe, reliable, and compact.

[0079] It is a solution that is able to provide an excellent strength against overvoltages and electrostatic discharges in the framework of power supplies, improving protection of the module and of the power-supply unit , in the context of a circuit comprising a supply converter 10 configured to be powered at an input ( lines L and N) exposed to surges ( see CMS ) and provided with an output LED+ , LED- configured to supply to a load 12 a supply voltage ViSOiprotected in regard to the aforesaid surges ( denoted in what follows also by Vsurge) .

[0080] In the case of the example illustrated here (which is merely an example ) , the converter 10 of the driver PSU is an AC-to-DC converter with an input comprising a phase line L and a neutral line N and an output comprising a first line LED+ at a first voltage and a second line LED- at a second voltage , with the first voltage that is higher ( for example , positive ) than the second voltage ( for example , negative ) .

[0081] As has already been said, for simplicity the converter 10 is here represented schematically in the form of a trans former, without there being represented details of implementation ( additional components , etc . ) that may vary according to the speci fic modes of implementation of the converter 10 .

[0082] It will on the other hand be noted that the embodiments presented herein are to a large extent "transparent" and may vary according to the speci fic modalities of implementation of the converter 10 .

[0083] The embodiments presented herein regard, in fact , primarily criteria such as to enable the converter or driver 10 and the module 12 to be protected against common mode deriving from a surge ( employing some components already used for other purposes , for example , to reduce electromagnetic interference ) , using in a combined way the space to provide also ESD protection .

[0084] Various possible embodiments envisage resorting to an optimi zed network comprising capacitors together with ESD resistances located on the medium or PCB, for example underneath the capacitors, achieving a strength to (common-mode) overvoltages of 10 kV and an ESD protection for outdoor drivers.

[0085] In the solution illustrated in Figure 8, the internal protection is constituted by the following components :

[0086] VR1 : varistor (e.g., made of metal oxide - MOV) set between the lines L and N upstream of the converter 10 with a fuse Fl in series; and

[0087] CPI, CP2, and CS : capacitors with associated (in parallel) respective resistors Rl, R2 (use of the same references as those of Figure 6 is here deliberate) and R3 (for example, an SMD) for ESD protection.

[0088] In the solution illustrated in Figure 8, the capacitors of the protection network are arranged as follows : the capacitors CPI and CP2, on the line N, in series with one another as bridge between the input and the output of the insulation converter 10; and the capacitor CS, between the output of the converter 10 (line LED-) and the pin or line EQUI (earth E) .

[0089] The varistor VR1 facilitates maintenance of a controlled voltage between the input lines L and N of the converter 10 in the event of differential-mode surges deriving from a common mode applied to L. In fact, if the voltage is not clamped, it could increase a great deal and damage the entire device (driver) .

[0090] The capacitors CPI, CP2, and CS may be viewed as defining a protection network comprising a divider with : a first capacitive branch (capacitors CPI and CP2) , with the series connection of a first capacitor CPI and a second capacitor CP2, said first capacitive branch being coupled between the input (line N) and the output (line LED-) of the converter (10) ; and a second capacitive branch, with a third capacitor (the capacitor CS) , that is coupled between the output (line LED-) of the converter 10 and a line (line or pin EQUI) configured to be earthed (grounded) E.

[0091] The capacitors CPI, CP2, and CS set between the input and the output of the converter 10 (lines N and LED- on the primary side and on the secondary side of the corresponding transformer) and between the secondary side of the converter 10 and the line EQUI could be viewed as serving only to reduce EMI, with their values dictated by the electromagnetic interference that it is desired to reduce.

[0092] The solution presented in Figure 8 is in actual fact different from that of Figure 7.

[0093] Figure 7 shows, in fact, two capacitors Cl and C2, one between the line N and the line LED- and the other between the line LED- and the equipotential pin (line EQUI, earthed E) .

[0094] Thanks also to the presence of the resistances in parallel Rl, R2, and R3, the solution of Figure 8 envisages a capacitor-based divider that is able to reduce the stress on the insulation voltage at the source 12 (LED module) , combining also the ESD protection obtained with the resistances Rl, R2, and R3 associated to the capacitors CPI, CP2, and CS .

[0095] Advantageously, the divider is built so as to present the maximum voltage between the line N and the line LED-. For this reason, two capacitors CPI, CP2 are inserted, whereas just one capacitor CS is present between the line LED- and the equipotential pin EQUI.

[0096] Two capacitors CPI, CP2 make it possible to take into account overvoltages of up to 14 to 15 kV. Various commonly used capacitors are able to withstand 5 to 8 kV (according to the brand) . Therefore, assuming that we have not more than 1-2 kV across the insulation module from the line LED- to the pin EQUI, there remain up to 13kV to 14kV for the series of the capacitors CPI and CP2.

[0097] From the standpoint of the specifications, at least two resistances are used between the line N and the line LED-. Hence, at least two capacitors (with a respective resistance for each capacitor) facilitate achievement of compliance with the specifications (standards) .

[0098] The parts separated by an insulation can, in fact, be bridged with resistances, for example with a single resistor in the case of a basic and supplementary insulation. To provide the bridge on a double or reinforced insulation at least two separate resistors connected in series are used, having the same nominal resistance, each being sized for the total operating voltage so that their impedance is likely not to change appreciably during the service life of the control circuitry .

[0099] The sharing described above is, on the other hand, given merely as an example: in fact, it depends upon the maximum voltage allowed through the insulation between the lighting source (e.g., LED source) 12 and the module.

[0100] The resistances Rl, R2 (as has been said, the use of the same references as those of Figure 6 is deliberate) and R3 are suited to being positioned underneath the respective capacitors CPI, CP2, and CS to which they are associated (in parallel) . Hence, the space is well exploited with the combination of both protections: surge and ESD protection.

[0101] A further advantage is that of sharing the voltage between the capacitors: the leakage of the capacitors CPI and CP2 is not easy to control so that the resistance can help to balance the voltage.

[0102] A further component is the fuse Fl added in series to the varistor VR1. The fuse Fl is not an effective part of the protection against overvoltages, but serves in the case of damage to prevent shorting between the lines L and N.

[0103] As regards the possible (at least approximate) sizing of the components illustrated in Figure 8, it is possible to consider an overvoltage (Vsurge) applied between the line N and the pin EQUI, as represented in Figure 9.

[0104] On account of the high value of variation (dV / dt) of the voltage in question, the latter is divided by the network constituted by the capacitances of the capacitors CPI, CP2, and CS .

[0105] Considering the maximum current allowed for 700-pA Class 1 drivers with an input at 265V / 60Hz, an approximate calculation for the parameters may be performed considering:

[0106] 400 pA absorbed by the capacitances; the value is conservative if the self-leakage resistance, the tolerances, and the capacitance of the transformer 10, which can be viewed as a parallel capacitance, are considered; and

[0107] 100 pA absorbed by the resistances.

[0108] In this regard, it is once again recalled that in the present disclosure one and the same reference can be used for brevity to indicate both a certain component (for example, a capacitor or a resistor) and an electrical parameter thereof (for example, the capacitance or the resistance / impedance ) .

[0109] Starting from

[0110] CSUM = CPI + CP2 + CS

[0111] CS = (400 pA X Vsurge) / [VllneMax X Vlsol X (6.28 X 60 H z) ] then CSUM = 400 pA / [ViineMax x (6.28 x 60 Hz) ] where (6.28 = 2n) and VuneMax is the expected maximum value for the voltage Viineof the neutral line, with the touch current that is the current at output from the capacitors to the pin EQUI (or else also EE) .

[0112] Usually the neutral at the electric-power station is connected to earth, but, in the case where in use the wires are reversed, it is necessary to be sure that the current is not dangerous, i.e., less than 0.7 mA; hence, the maximum voltage applied will be the voltage L - N.

[0113] It will be noted that, even though in the present description reference is made for simplicity to a protection on the line N, the same criteria may be adopted on the line L, the foregoing taking into account the fact that, in a way independent of the marking L / N applied on the power-supply unit PSU, the user can change the lines L and N around, and it is desired that the driver will preserve, also in this case, the desired safety characteristics.

[0114] In this regard, it will be noted once again that the references appearing in brackets in the claims and in the abstract have the sole purpose of facilitating reading of the patent document, and hence in no way limit the sphere of protection.

[0115] Consequently, the fact that, for example, a first capacitive branch CPI, CP2 has been described and illustrated herein as having a series connection of a first capacitor CPI and a second capacitor coupled [between the input N and the output LED+ of the converter 10, is merely of an exemplary nature. In various possible embodiments, the aforesaid first capacitive branch CPI, CP2, with a series connection of a first capacitor CPI and a second capacitor, may be coupled to the input of the converter 10 on the lines L and LED+ and not , instead, on the lines N and LED- ( as illustrated in the figures purely by way of example ) .

[0116] Hence , considering design of the network for a voltage Vsurge of 10 kV and a voltage ViSOi( reasonably) of approximately 1 kV, the maximum values for the parameters are approximately the following :

[0117] CS = 47 nF

[0118] CPI = 10 nF

[0119] CP2 = 10 nF

[0120] For the resistances , given that :

[0121] RSUM = R1 + R2 + R3

[0122] RSUM = VlineMax / 1 00 pA

[0123] R3 = (Vlsoi / Vsurge) x RSUM

[0124] R1 = R2 = (RSUM - R3 ) / 2 then

[0125] R1 = R2 = 1300 kQ and R3 = 260 kQ

[0126] With the parameters referred to above , by stimulating the network with 10 kV, the pulse through the insulation is approximately 1 kV .

[0127] With the circuit topologies exempli fied in Figure

[0128] 8 and in the subsequent figures ( for example , with the quantitative values referred to above , which, on the other hand, are not to be understood in a limiting sense ) it is possible to proceed in such a way that the cascaded connection ( ideally in series ) of the capacitor CPI and the capacitor CP2 will give rise to an equivalent capacitance that is (much) lower ( for example , at least ten times lower ) than the capacitance of the capacitor CS .

[0129] The corresponding division ratio enables , for example in the case of a common-mode peak of 10 kV, the voltage across the insulation of the LED to be approximately 1 kV, while there is a voltage drop of

[0130] 9 kV across the trans former 10 or the series connection of the capacitors CPI and CP2.

[0131] For this reason, it is advantageous to use two capacitances such as CPI and CP2 in series.

[0132] Since rather small values of capacitance are envisaged for the capacitors CPI and CP2, these capacitors may present leakages that, in the case of overvoltage, may unbalance the voltage.

[0133] It has been noted that this problem can be tackled using resistors that, in a synergistic way, also provide ESD protection in stationary operation, for example, envisaging that at least the third capacitor (i.e., CS) has a respective resistor (R3) coupled in parallel between the output LED+, LED- of the converter 10 and the line EQUI configured to be earthed (grounded) E.

[0134] In particular, as exemplified in Figures 8 to 11, it is possible to envisage the use of three resistances Rl, R2, and R3, set in parallel, respectively, to the capacitors CPI, CP2, and CS .

[0135] The ESD-protection resistances Rl, R2 may also be shifted as RN1, RN2 into a position corresponding to the capacitors CN1 and CN2, as illustrated in Figure 12, to which reference will again be made in what follows .

[0136] To reduce the conducted emission noise, the structure represented in Figures 8 and 9 can be in fact integrated by adding between the line N and the pin / line EQUI two further capacitors CN1, CN2 that improve the performance at the level of EMI, as illustrated in Figure 10.

[0137] In this case, a further capacitive branch is hence envisaged, that comprises the series connection of a first further capacitor CN1 and a second further capacitor CN2.

[0138] For calculation of the network comprising the capacitors CPI, CP2, and CS in the terms outlined above, the further current path created between the line N and the pin / line EQUI by the capacitors CN1 and CN2 is in this case considered.

[0139] In parallel with the varistor VR1 (with its fuse Fl in series) in the event of very high expected voltage peaks starting from the input a further varistor VR2 (with a fuse F2 thereof in series) may be added .

[0140] Figure 11 represents a structure that may be applied to provide solutions with a number of outputs, for example with two outputs.

[0141] For continuity and simplicity of treatment, Figure 11 is here described as regards the differences from Figure 10, but the same may apply also to the structure represented in Figures 8 and 9.

[0142] Figure 11 exemplifies a solution with two outputs: in this case, the unit or driver PSU comprises, in addition to the converter 10 considered previously, a further converter 10' .

[0143] For instance, the first converter 10 may be used for supplying the lighting source (e.g., LED source) 12, and the second converter 10' may be used for supplying a sensor 120 (for example, a sensor of ambient light) .

[0144] The sensor 120 may have an insulation different from that of the pin or line EQUI. Hence, the value of the capacitances / resistances used may differ from that used for the LED sources 12 so as to obtain a value of insulation voltage ViSOi' different from ViSOi.

[0145] In various embodiments, the protection network of the further converter 10' (i.e., for example, the elements CP1A, RIA; CP2A, R2A; CSA, R3A) is homologous to the protection network of the first converter 10 (i.e., the network formed, for example, by the elements CPI, Rl; CP2, R2; CS, R3) .

[0146] The term "homologous" (not to be confused with "homogeneous") is used herein with its current meaning that identifies an element corresponding to another, in so far as it is of the same kind, and has the same qualities, properties, etc., as another.

[0147] This fact is highlighted in Figure 11 by adopting for the components associated to the converter 10' references CP1A, CP2A, CSA and RIA, R2A, R3A that are distinct from those of the homologous elements CPI, CP2, CS and Rl, R2, R3 associated to the converter 10.

[0148] As illustrated in Figure 12, in the case where the leakage for the capacitances is negligible, the ESD- protection resistances Rl, R2 (and RIA, R2A) can be shifted as RN1, RN2 into a position corresponding to the capacitors CN1, and CN2, for example underneath them.

[0149] In this case, it is advantageous for the resistances R3 / R3A to be considered negligible as regards the effect on CS and CSA, with a high value of resistance (for example, 10 MQ) for R3 / R3A.

[0150] For continuity of treatment, the example of Figure 12 is here described as regards the differences from Figure 11 (circuit with a number of outputs / loads ) , but the same may apply also for the structures with a single output / load represented in the previous figures.

[0151] In other words, the ESD-protection resistances Rl, R2 may be shifted as RN1, RN2 into a position corresponding to the capacitors CN1 and CN2, also in the case of structures with a single output / load as represented in Figures 8 to 10.

[0152] Consequently, in the various embodiments exemplified herein (at least) the third capacitor CS (and CSA, if present) of the protection network has a respective resistor R3 (and R3A, if present) coupled in parallel between the output LED-, VS- of the converter 10 or 10' and the line EQUI configured to be earthed E.

[0153] In some embodiments, also the first capacitor CP1 / CP1A and the second capacitor CP2 / CP2A (and hence all three capacitors of the protection network) have a respective resistor R1 / R1A coupled in parallel to the first capacitor CP1 / CP1A and a second respective resistor R2 / R2A coupled in parallel to the second capacitor CP2 / CP2A.

[0154] In some embodiments (see, for example, Figures 11 and 12) , the circuit may comprise a further capacitive branch CN1, CN2 coupled between the input (line N) of the converter 10 / 10' and the line EQUI configured to be earthed E.

[0155] The above further capacitive branch comprises the series connection of a first further capacitor CN1 and a second further capacitor CN2.

[0156] In some embodiments (see, for example, Figure 12) the first further capacitor CN1 and the second further capacitor CN2 have a first respective resistor RN1 coupled in parallel to the first further capacitor CN1 and a second respective resistor RN2 coupled in parallel to the second further capacitor CP2. In this case, in the protection network only the third capacitor CS / CSA has a respective resistor R3 / R3A coupled in parallel.

[0157] Various embodiments presented herein are suited to providing a lighting system comprising one or more lighting sources 12 (for example, LED sources) coupled as load to the output LED+, LED- of a supply converter 10 of a circuit as described herein, i.e., a driver protected against surges (e.g., against overvoltages) and ESD phenomena.

[0158] In some embodiments (see, for example, Figures 11 and 12) , the circuit comprises at least one further supply converter 10 ' , and the system comprises at least one further load 120 , advantageously a sensor, coupled to the output VS+ , VS- of the further supply converter 10 ' .

[0159] Once again it is recalled that , even though in the present description reference will be made for simplicity to a protection on the line N, the same criteria may be adopted on the line L . Consequently, the fact that , for example , a first capacitive branch CPI , CP2 has been described herein as having a series connection of a first capacitor CPI and a second capacitor coupled between the input N and the output LED- of the converter 10 is merely of an exemplary nature in so far as , in various possible embodiments , the aforesaid first capacitive branch CPI , CP2 , with a series connection of a first capacitor CPI and a second capacitor, may be coupled to the input L and to the output LED+ of the converter 10 ( and not , instead, to the lines N and LED- , as illustrated in the f igures purely by way of example ) .

[0160] In a similar way, the fact that , for example , a second capacitive branch CS has been described and illustrated herein as having a third capacitor CS coupled between the output LED- of the converter 10 and a line EQUI configured to be earthed E is merely of an exemplary nature in so far as in various possible embodiments , it is possible for the aforesaid second capacitive branch CS with a third capacitor CS to be coupled to the output LED+ of the converter 10 , and not , instead, to the output LED- ( as illustrated in the figures purely by way of example ) .

[0161] To provide another example , the fact that the description and the f igures present a further capacitive branch CN1 , CN2 coupled between the input N of the converter 10 and the line EQUI is merely of an exemplary nature in so far as , in various embodiments , the aforesaid further capacitive branch CN1 , CN2 (which optionally comprises a series connection of a first further capacitor CN1 and a second further capacitor CN2 ) may be coupled between the input L of the converter 10 and the line EQUI configured to be earthed .

[0162] In other words , the converter 10 illustrated herein comprises an AC-to-DC converter with an input L, N having a phase line L and a neutral line N, and an output having a first line LED+ at a first voltage and a second line LED- at a second voltage , the first voltage being higher than the second voltage .

[0163] Optionally, as illustrated herein by way of example , the first capacitive branch CPI , CP2 o f the protection network is coupled between the neutral line N and the second line LED- , whereas the second capacitive branch CS is coupled between the aforesaid second line LED- and the line EQUI configured to be earthed E .

[0164] In various embodiments , the first capacitive branch CPI , CP2 of the protection network may, instead, be coupled between the phase line L and the first line LED+ , with the second capacitive branch CS coupled between the aforesaid first line LED+ and the line EQUI configured to be earthed E .

[0165] The foregoing of course applies also to the various other embodiments exempli fied herein, such as the solutions comprising an auxiliary load 120 as illustrated in Figures 10 and 11 .

[0166] The presence of varistors such as VR1 and / or VR2 (with optionally associated fuses like Fl and / or F2 ) is advantageous in so far as it makes it possible to take into account the fact that the overvoltage may occur on the line L or the line N so as to present always one and the same voltage across the capacitive divider .

[0167] Without prej udice to the underlying principles , the details of construction and the embodiments may vary, even signi ficantly, from 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 .

[0168] LIST OF REFERENCE SIGNS

[0169] Input LI, L, N

[0170] Varistor VAR2, VAR3

[0171] Node A Spark gap SG, SGI, SG2

[0172] Capacitor Y1

[0173] Common-mode surge CMS

[0174] Surge voltage Vsurge

[0175] Converter 10, 10' Output OUTPUT

[0176] LED+, LED- VS+, vs-

[0177] Insulation voltage ViSOi, ViSOi'

[0178] Double insulation DI (LED) lighting source 12

[0179] Heat sink 14

[0180] Insulation 16

[0181] Earth E

[0182] Clouds C Common-mode-surge suppressor 18

[0183] Power-supply unit PSU

[0184] Varistor VR1, VR1'

[0185] Fuse Fl, Fl'

[0186] Resistors Rl, R2 Capacitors Cl, C2

[0187] Capacitors CPI, CP2, CS

[0188] CP1A, CP2A, CSA Resistors Rl, R2, R3

[0189] RIA, R2A, R3A Capacitors CN1, CN2

[0190] Sensor 120

Claims

CLAIMS1. A circuit, comprising: a supply converter (10) configured to be powered at an input (L, N) exposed to surges (Vsurge) and comprising an output (LED+, LED-) configured to supply a load (12) with a supply voltage (ViSOi) protected against said surges (Vsurge) , a protection network (CPI, Rl; CP2, R2 ; CS, R3) comprising a divider (CPI, CP2, CS) with: a first capacitive branch (CPI, CP2) with a series connection of a first capacitor (CPI) and a second capacitor coupled between the input (L, N) and the output (LED-) of the converter (10) , and a second capacitive branch (CS) with a third capacitor (CS) coupled between the output (LED+, LED-) of the converter (10) and a line (EQUI) configured to be grounded (E) .

2. The circuit of claim 1, wherein the first capacitor (CPI) and the second capacitor (CP2) of the protection network (CPI, Rl; CP2, R2 ; CS, R3) have a first respective resistor (Rl) coupled in parallel to the first capacitor (CPI) and a second respective resistor (R2) coupled in parallel to the second capacitor (CP2 ) .

3. The circuit of claim 1, comprising a further capacitive branch (CN1, CN2) between the input (L, N) of the converter (10) and the line (EQUI) configured to be grounded (E) .

4. The circuit of claim 3, wherein the further capacitive branch (CN1, CN2) comprises the series connection of a first further capacitor (CN1) and of a second further capacitor (CN2) .

5. The circuit of claim 4, wherein: the first further capacitor (CN1) and the second further capacitor (CN2) have a first respectiveresistor (RN1) coupled in parallel to the first further capacitor (CN1) and a second respective resistor (RN2) coupled in parallel to the second further capacitor (CP2 ) , and in the protection network (CPI; CP2; CS, R3) only the third capacitor (CS) has a respective resistor (R3) coupled in parallel.

6. The circuit of any of the preceding claims, comprising at least one varistor (VR1, VR2 ) arranged across the input (L, N) of the converter (10) .

7. The circuit of claim 6, wherein the at least one varistor (VR1, VR2 ) has a fuse (Fl, F2 ) coupled in series therwwith.

8. The circuit of any of the preceding claims, wherein : the converter (10) comprises a converter with an input (L, N) with a phase line (L) and a neutral line (N) and an output with a first line (LED+) at a first voltage and a second line (LED-) at a second voltage, the first voltage being higher than the second voltage.

9. The circuit of claim 8, wherein the first capacitive branch (CPI, CP2) of the protection network is coupled between said neutral line (N) and said second line (LED-) and the second capacitive branch (CS) is coupled between said second line (LED-) and said line (EQUI) configured to be grounded (E) .

10. The circuit of any of the preceding claims, comprising : at least one further supply converter (10' ) configured to be supplied at said input (L, N) exposed to surges (Vsurge) and provided with a respective output (Vs+, Vs-) configured to supply a further load (120) with a further supply voltage (ViSOi' ) protected against surges (Vsurge) , and a respective protection network (CP1A, RIA; CP2A,R2A; CSA, R3A) comprising a respective divider (CP1A, CP2A, CSA) with: a respective first capacitive branch (CP1A, CP2A) with a series connection of a respective first capacitor (CP1A) and a respective second capacitor (CP2A) coupled between the input (L, N) and the output (Vs+, Vs-) of the converter (10) , and a respective second capacitive branch (CSA) with a respective third capacitor (CSA) coupled between the output (Vs+, Vs-) of the further converter (10' ) and the line (EQUI) configured to be grounded (E) , wherein at least the respective third capacitor (CS) of the respective protection network (CP1A, RIA; CP2A, R2A; CSA, R3A) has a respective resistor (R3A) coupled in parallel between the output (LED+, LED-) of the converter (10) and the line (EQUI) configured to be grounded (E) .

11. A lighting system, comprising at least one lighting source (12) and the circuit of any one of the preceding claims, the at least one lighting source (12) being coupled as load to the output (LED+, LED-) of said supply converter (10) .

12. The lighting system of claim 11, wherein the circuit is according to claim 10 and comprises said at least one further supply converter ( 10 ’ ) , and the system comprises at least one further load (120) , coupled to the output (VS+, VS-) of said at least one further supply converter (10' ) .

13. The lighting system of claim 12, wherein said further load (120) coupled to the output (VS+, VS-) of said at least one further supply converter (10' ) comprises a sensor.

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