Abstract:
In various embodiments, a method for powering light sources from a input power supply through a converter circuit is provided including a primary side and a secondary side separated by a galvanic barrier, wherein the primary side includes a power factor control block with an output capacitor. The method may include providing save circuitry on said secondary side for saving operational data of the converter upon failure of said input power supply; and powering said save circuitry during saving said operational data with energy derived from said output capacitor of said power factor control block.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Italian Patent Application Serial No. TO2011A000637, which was filed Jul. 15, 2011, and is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to techniques for feeding lighting sources such as, for example, light emitting diode (LED) lighting sources. 
         [0003]    Various embodiments may refer to DC/DC switching converters of the isolated type. 
       BACKGROUND 
       [0004]      FIG. 1  is a general exemplary block diagram showing an isolated DC/DC switching converter, which can be used for example for feeding a LED lighting source. 
         [0005]    The main components of the exemplary diagram in  FIG. 1  are the following:
         1 : mains supply,     2 : Power Factor Correction (PFC) circuit,     3 : output capacitor of PFC circuit,     4 : power stage (primary side),     5 : galvanic barrier (transformer),     6 : power stage (secondary side),     7 : light source (in itself not being part of the feeding device, but shown in dashed lines for completeness of illustration).       
 
         [0013]    The diagram in  FIG. 1 , which is of course wholly exemplary, provides in addition further elements, such as:
         8 : control circuitry (primary side),     9 : control circuitry (secondary side),     10 : auxiliary power stage (primary side),     11 : auxiliary power stage (secondary side),     13 : control board (primary side),     14 : control input,     15 : control board (secondary side),     17 : auxiliary supply towards power stage (primary side)  4 ,     18 : supply of control circuit  8  (primary side),     19 : control line from circuit  8  towards power stage (primary side)  4 ,     20 : supply of control circuit  9  (secondary side),     21 : auxiliary supply towards power stage (secondary side)  6 ,     22 : control line from circuit  9  towards power stage (secondary side)  6 ,     25 : auxiliary supply from stage  10  towards control board (primary side)  13 ,     26 : auxiliary supply from stage  11  towards control board (secondary side)  15 , and     27 : connection between control board (secondary side)  15  and power stage (secondary side)  6 .       
 
         [0030]    The general layout shown in  FIG. 1  is known in itself, which makes it unnecessary to provide a more detailed description both of the structure and of the operation thereof. 
         [0031]    In this respect it will be moreover appreciated that the exemplary embodiment in  FIG. 1  includes various elements (e.g. the elements denoted by references  13 ,  14 ,  15 ,  25 ,  26 ,  27  or others) the presence whereof is wholly optional and/or which are adapted to be replaced, in part or completely, with equivalent elements. 
         [0032]    For what of interest here, in  FIG. 1  it is possible to identify two main parts of the converter circuit, namely a primary side and a secondary side mutually separated by a galvanic barrier  5 , being embodied for example by a transformer and being adapted to ensure safety for a user in case of an accidental contact with the load (light source  7 ). 
         [0033]    In some embodiments, the control circuit can include, on primary side  8  and/or on secondary side  9 , “smart” logical circuits, adapted to control the behaviour of the converter circuit as a function of prescribed operational parameters. 
         [0034]    In some embodiments, this may involve having to “save” data related to the device operation, by storing them in a non volatile memory if a failure of the input power supply  1  takes place (for example in the case of a major or minor voltage drop or of a complete interruption). 
         [0035]    The diagram in  FIG. 1  shows the possibility of providing a control board (essentially elements  13  and  15 ) adapted to interact with the supply unit and, for simplicity of illustration (but by no way as a compulsory condition), the circuitry performing such a saving function can be considered as being included in, or anyway dependent from board  15 . 
         [0036]      FIG. 2  (wherein parts, elements and components identical or equivalent to those described with reference to  FIG. 1  are denoted by the same reference numbers as in that Figure) shows the possibility of providing, on the secondary side, an energy storage element  12 , the function whereof is to supply the save circuitry during saving the data which must be stored. 
         [0037]    The energy storage element  12  can be supplied by a charging circuit  23 , which derives from secondary side  6  of the power stage the energy which must be stored in the energy storage element  12 . In various embodiments, element  12  can be a capacitor, which stores the energy that can be used as a power supply when a failure from the power supply  1  from the mains takes place, i.e. when the input power supply from the mains is no longer available or sufficient to ensure the regular operation of the converter device. 
         [0038]    In various embodiments, in the storage element  12  a sufficient amount of energy can be stored as to support the operation of the save circuitry (for example located in board  15 ) for the whole time interval needed to save the parameters, in presence of a failure of primary input power supply  1 . This time interval depends in turn on the amount of data to be saved, also considering the power absorbed by the circuit during such operations. 
         [0039]    The energy that can be stored in a capacitor can be expressed as ½·CV 2  (wherein C is the capacity and V is the charge voltage). In order to keep the output voltage at a suitable low value for a time interval sufficient to save the data, a rather high capacity C is required, which involves the use of a capacitor with large size and high cost. 
         [0040]    For example, if a control system according to the DALI standard (Digital Addressable Lighting Interface) is used, in case of a drop of the input voltage approximately fifty parameters are stored for each channel, i.e. for each independently controlled LED string. The time interval needed for the data save operation can be 200 ms for each channel, so that on the whole, in the presence of N independently controlled LED strings, storage element  12  must be able to store a sufficient amount of energy to support the operation of the data save circuitry for a time interval of approximately N×200 ms. 
         [0041]    In various embodiments, stage  2  (see  FIG. 1 ), which is used for the power factor control (PFC) of input current and to stabilize the output voltage, can be implemented with a boost converter having a supply voltage higher than the maximum peak value of the rated input voltage. For example, in the case of a 200 V alternated input, the PFC stage output can be 400 V DC, applied across capacitor  3 . 
         [0042]    When the input power supply fails, the voltage on capacitor  3  starts dropping and the energy stored in the capacitor itself is absorbed by the main power stage  4 ,  6  (and therefore by load  7 ) and by auxiliary power stage  10 ,  11 . 
         [0043]    For this very reason, in various embodiments the need can be felt of providing energy storage element  12 , adapted to supply the circuit for the remaining time needed to complete the save operations. Such an energy storage element can be arranged proximate to the smart circuit to be fed. 
         [0044]    Generally speaking, the generation of auxiliary voltages within a feeding device in the lighting sector is a topic which has been extensively dealt with, also in patent literature. In this respect it is possible to refer, for example, to document WO-A-2008/128575, to document WO-A-2008/138391 and to European Patent Application EP 11159153.3. 
       SUMMARY 
       [0045]    From the foregoing description the need arises of providing further improved solutions, for example concerning the possibility of reducing the capacity value (and therefore the size and cost) of the capacitor acting as an auxiliary energy storage on the secondary side of the converter, up to the very option to omit such a storage capacitor. 
         [0046]    Various aspects of this disclosure meet such a need. 
         [0047]    According to various aspects of this disclosure, such an object is achieved thanks to a method having the features specifically set forth in the claims that follow. Various aspects of this disclosure also concern a related device. 
         [0048]    The claims are an integral part of the technical teaching of the invention provided herein. 
         [0049]    Various embodiments are based on the acknowledgement that it is possible to reduce the size of the energy storage capacitor arranged on the secondary side (and in some cases to omit it altogether) by deriving, in case of an input supply failure, feeding energy from the output capacitor of the power factor correction (PFC) stage. 
         [0050]    Various embodiments therefore provide savings in terms of space and cost. 
         [0051]    In various embodiments, for example if the auxiliary power stage is implemented as a flyback converter, the capacity value (and therefore the size and cost) of the output capacitor can be reduced to a value sufficient to stabilize the output voltage with an acceptable ripple, without having to take into account the needs of energy storage in order to face the input power supply failure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]    In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which: 
           [0053]      FIGS. 1 and 2  have already been described in the foregoing; 
           [0054]      FIG. 3  is a circuit diagram of an embodiment; 
           [0055]      FIG. 4  is a block diagram of an embodiment; 
           [0056]      FIG. 5  shows the pattern of a wave form in an embodiment; 
           [0057]      FIG. 6  is a block diagram of an embodiment; and 
           [0058]      FIG. 7  is a block diagram of an embodiment. 
       
    
    
     DESCRIPTION 
       [0059]    In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or several specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments. 
         [0060]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0061]    The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
         [0062]    In various embodiments, the detailed description in the following may refer to a converter circuit as generally depicted in  FIG. 1 . 
         [0063]    Various presently considered embodiments may therefore refer to specific implementations of a circuit corresponding to the general arrangement of  FIG. 1 . 
         [0064]    To avoid unnecessarily overburdening the present detailed description, parts, elements or components which have been previously described with reference to  FIG. 1  and  FIG. 2  will be denoted in the following by the same references, avoiding a repetition of the related detailed description. 
         [0065]      FIG. 3  shows a first observation by the inventors, i.e. that in various embodiments storage capacitor  12  can be supplied via auxiliary power stage  10 ,  11 . 
         [0066]    To achieve this, referring to the embodiment of  FIG. 3 , it is possible to use a flyback converter including, according to the typical structure of a flyback converter, a diode  12   a  and an output capacitor  12   b,  connected to the secondary winding  11  of the auxiliary supply stage, whose primary winding  10  is subjected to the action of an electronic switch such as, for example, a MOSFET  10   a.    
         [0067]    As for the energy storage, as an alternative to or in conjunction with an additional capacitor  12 , an output capacitor  12   b  of the converter can be used having a capacity value higher than the rated capacity required for the converter operation. For this reason, in the diagram of  FIG. 3  (and in the diagram of  FIG. 6  which will be explained in the following), capacitor  12  (the “additional” capacitor to the flyback arrangement) is shown in dashed lines. 
         [0068]    Various embodiments, as schematically shown in  FIG. 4 , can make use of the possibility for the DC/DC converters, as shown in  FIG. 1 , to include filtering and stabilizing components, arranged upstream of form factor correction stage  2 , including for example a filtering block  30 , a bridge or half-bridge rectifier  31  and a capacitor  32  with a low value. 
         [0069]    By detecting the voltage across capacitor  32  it is therefore possible to spot the possible failure of input power supply  1 . 
         [0070]    The diagram in  FIG. 4  refers as an example to the possible provision of a comparator circuit  33 , adapted to compare a reference voltage value Vref to a voltage corresponding to the voltage across capacitor  32 . 
         [0071]    The latter voltage can for example be detected by resorting to a resistive voltage divider, detecting voltage across capacitor  32 . The divider may include, for example, a first resistor  35  and a second resistor  36 , the latter being interposed between an input of comparator circuit  33  and ground. In such exemplary embodiment, comparator circuit  33  compares the voltage across resistor  36  with the value of reference voltage Vref. 
         [0072]    Whatever the specific embodiment used, the voltage across capacitor  32  can have an alternated pattern, as schematically shown by line V 32  in  FIG. 5 , with a value alternatively higher or lower than a reference voltage Vth, which depends, according to the specific embodiments, on reference voltage Vref. 
         [0073]    In this embodiment, the output voltage from comparator  33 , provided on a line denoted as  34  in  FIG. 4 , can therefore have a “high” value when the voltage across capacitor  32  is higher than threshold value Vth, and a “low” value when (in time intervals such as the interval denoted by t under     —     Vth ) voltage across capacitor  32  is below threshold value Vth. 
         [0074]    The duration of the intervals wherein signal  34  is at a “low” level can be transferred, as a read parameter, to control circuit  8 , so that this circuit can identify the supply voltage drop when the duration of such intervals reaches a determined limit value, so as to start the save operations of operational parameters, generating the data save request. 
         [0075]    In various embodiments, it is then possible to implement measures that can interrupt the energy absorption from capacitor  3 , for example:
       deactivate power stage  4  (and stage  6  supplied thereby), and/or   “disconnect” load  7 , i.e. act on stage  6  so as to interrupt its connection to load  7 .       
 
         [0078]    Either measure, or both of them, can be implemented for example through lines  19  and  22 , and/or line  27  ( FIG. 1 ) which connects control board  15  (secondary side) and power stage  6  (secondary side). 
         [0079]    As will be seen in the following, in various embodiments capacitor  3  can be used to feed supply energy to the data save circuitry, during the data saving itself. 
         [0080]    In various embodiments, it may therefore be convenient to save the energy stored on capacitor  3 , preventing this energy from being dispersed onto power stage  4 ,  6  and or onto load  7 . 
         [0081]    If load  7  is disconnected (and therefore the connection thereof to power stage  4 ,  6  is interrupted), it is possible to feed the save circuitry (assumed to be arranged within board  15 ) with the energy stored on capacitor  3 , via power stage  4 ,  6  which in this case is not supplying load  7 . The power stage can now absorb energy from capacitor  3  and transfer it towards the save circuitry; this solution can therefore be implemented also in the absence of auxiliary power stage  10 ,  11 . 
         [0082]    The energy transfer from capacitor  3  towards save circuitry (however it may be accomplished) may take place either through capacitor  12  (i.e. substantially according to an arrangement as in  FIG. 2 , possibly omitting charge circuit  23 ), or directly (in which case capacitor  12  can be omitted). 
         [0083]    The diagram in  FIG. 6  highlights the fact that, in various embodiments, the drop of primary input voltage  1  can be detected by detecting the voltage drop across capacitor  3 , arranged at the output of stage  2 , instead of on capacitor  32  (possibly) provided at the input of stage  2  itself. 
         [0084]    The diagram in  FIG. 6  shows moreover the fact that, in various embodiments, the drop of primary input voltage  1  can be detected on the secondary side of the converter, for example at secondary supply circuit  28  (which is here assumed to be the same as in the exemplary embodiment of  FIG. 3 , i.e. a flyback converter). The arrangement of the detecting circuit may correspond on the whole to what has been shown in document U.S. Pat. No. 6,967,585, which makes it unnecessary to provide a more detailed description herein. 
         [0085]    A detecting function of the supply failure according to a solution which is similar to what shown in  FIG. 6  (i.e., by detecting the voltage across capacitor  3  at the output of power factor correction stage  2 ) can moreover be implemented according to the solution exemplified in  FIG. 7 , i.e. on the primary side of the converter, wherein the comparator circuit  33  is supplied, in addition to reference voltage Vref, with the voltage at the middle point of a resistive divider  135 ,  136  connected across capacitor  3 . 
         [0086]    In this case, the output signal from capacitor  33  is applied onto line  34 , adapted to transfer it towards control  8  (i.e. towards the secondary side of the converter) via an opto-coupler  39 , that embodies a corresponding part of galvanic barrier  5  in order to transfer the alarm signal (a alarm about the failure of input supply  1 ) to the secondary side of the converter. 
         [0087]    In various embodiments, the output voltage of the detecting circuit can be approximately proportional to the input voltage (in practice it is possible to refer to the voltage across capacitor  3 ) so that, if this voltage is sent to a comparator circuit such as circuit  33 , the failure of input power supply  1  can be detected also on the secondary side, starting the data save function by using the energy stored in capacitor  3 . 
         [0088]    Whatever the specific embodiment used to detect the failure of mains supply  1 , when such an event is detected the corresponding alarm signal on line  34  causes the save circuitry of the control circuit (for example on the secondary side denoted by  15 ) to start saving the parameters by using, as a supply, the energy stored in capacitor  3 . 
         [0089]    In conventional solutions, such as the one shown in  FIG. 1 , in order to save the operational data as soon as a supply voltage drop is detected, only the energy stored in capacitor  12  is used. To such a purpose, it is therefore detected that the supply voltage is no longer present, and a data save request is generated towards the secondary side, which keeps on being fed thanks to the energy stored in capacitor  12 , while the energy stored in capacitor  3  is used to feed the load. In solutions such as shown in  FIG. 1 , capacitor  3  is therefore present because it is useful for the PFC block and, when supply voltage  1  drops, the capacitor discharges rather rapidly, because the energy stored therein is absorbed by load  7  via power circuit  4 ,  6 . 
         [0090]    The solutions according to the embodiments, on the contrary, make use of capacitor  3  during the data save process, performed in case of failure of supply voltage  1 , in order to preserve the supply of the save circuitry (e.g. board  15 ), so that capacitor  12  can be implemented with reduced size and capacity, or even omitted completely (in any case obtaining savings in terms of space and cost). 
         [0091]    In various embodiments it is therefore possible to operate by detecting a supply voltage drop and by generating a data save request. 
         [0092]    This can be accomplished, for example, with the circuits of  FIG. 4 ,  FIG. 6  or  FIG. 7 , each by itself or in mutual combination: for example, in various embodiments it is possible to use a detector acting on capacitor  32  (see  FIG. 4 ) and also a detector acting on capacitor  3  (see for instance  FIG. 6 ), this being a combination which allows for a longer time to save data. 
         [0093]    In various embodiments, the same circuits can be used both to detect the failure of the supply voltage and to generate a request of data saving. 
         [0094]    For example, in various embodiments, it is possible to use only the circuit of  FIG. 7 , while at the same time switching off main supply stage  4 ,  6  and requesting a data saving to the secondary side as soon as a signal transition is generated which indicates the alarm situation due to the input supply failure. 
         [0095]    It will be appreciated, moreover, that the circuit in  FIG. 4  compares a voltage which is proportional to input voltage with a reference threshold Vref, while the circuits of  FIG. 6  and  FIG. 7  operate by comparing Vref with a voltage proportional to the voltage of capacitor  3 , and not with the input voltage, although in any case they are mutually connected values. 
         [0096]    Moreover, the circuits in  FIG. 4 ,  FIG. 6  and  FIG. 7  include a comparator with a different function. 
         [0097]    The circuit in  FIG. 4  generates a signal: the time is measured during which this signal is high vs low, while in the circuits of  FIG. 6  and  FIG. 7  a transition from high to low or vice versa is sufficient to trigger the alarm signal. 
         [0098]    In the circuit of  FIG. 4  the operating principle involves therefore measuring the time during which the signal is below a predetermined reference threshold (see diagram in  FIG. 5 ), in order to determine the occurrence of a voltage drop. 
         [0099]    The circuits in  FIG. 6  and in  FIG. 7  operate by measuring indirectly ( FIG. 6 ) or directly ( FIG. 7 ) the voltage of capacitor  3 , in order to generate the data save request because the power supply has failed. 
         [0100]    Moreover, the circuit in  FIG. 4  can operate on the primary side of the converter, both for detecting and for acting to switch off primary side  4  of power stage  4 ,  6 . 
         [0101]    The circuit in  FIG. 6  is on the secondary side (on the right of galvanic bather  5  in the Figures) and therefore performs an indirect measure of the voltage across capacitor  3 , operating in a similar way on the secondary side in order to output the alarm signal. 
         [0102]    The circuit in  FIG. 7  is on the primary side (on the left of galvanic barrier  5  in the Figures) and therefore performs a direct detection (measure) of the voltage across capacitor  3 , but operates on the secondary side (via opto-coupler  39 ) in order to output the alarm signal. 
         [0103]    The circuit in  FIG. 6  is arranged according to a flyback topology (elements  10 ,  10   a,    11 ,  12 ,  12   a,    12   b ) with a circuit that performs an indirect detection of voltage across capacitor  3  which comprises elements  38 ,  33 ,  34 . The mains  38  supplies a voltage proportional to the voltage on the capacitor and, when such a voltage goes below a predetermined threshold (Vref), the comparator generates a alarm signal, i.e. a data save request. In this case, unlike the case in  FIG. 4 , times are not measured. 
         [0104]    The circuit in  FIG. 7  is based on the same operating principle which has been previously described referring to the circuit in  FIG. 6 ; the difference is that, in the case of  FIG. 7 , the measure is applied directly across capacitor  3  by using resistors  135  and  136 , through a comparison with a suitable predetermined threshold Vref and by transferring to the secondary side, by using opto-coupler  39 , the alarm signal and the data save request. 
         [0105]    Specific implementation details of the various embodiments of  FIG. 4 ,  FIG. 6  and  FIG. 7  can be anyway freely transferred from one to another embodiment (for example the circuits which operate on capacitor  32  could act on capacitor  3 , and the circuits which operate on capacitor  3  could act on capacitor  32 ). 
         [0106]    Whatever the measures adopted to detect a failure of power input supply  1  and to generate the data save request, the save circuitry (which for simplicity is assumed to be arranged within board  15 , but in various embodiments can also be implemented in different ways according to criteria known in themselves) is powered during data saving thanks to the energy stored in capacitor  3 . 
         [0107]    With such an aim, in order to transfer the energy stored on capacitor  3  towards the save circuitry (both in the presence of storage capacitor  12 , whose size can be reduced, and in the absence of capacitor  12 ), it is possible to follow different methods. 
         [0108]    For example, as exemplified in  FIG. 6 , in various embodiments it is possible to use auxiliary power stage  10 ,  11 , so that the energy of capacitor  3  is transferred from primary side  10  to secondary side  11 , and therefrom towards the save circuitry. 
         [0109]    In this case, in various embodiments, it is possible to switch off (for example through lines  19  and  22 ) the main power stage, avoiding the unnecessary absorption thereby of useful energy stored in capacitor  3 . At this point, in practice, only the auxiliary power stage  10  and  11  will absorb energy from capacitor  3 , and it will be possible to use that energy to power the save circuitry of the operational data of the converter. 
         [0110]    In various embodiments, this can virtually allow to dispense with storage capacitor  12 , or at least to reduce its capacity value (and therefore its size and cost) to minimum values. 
         [0111]    An auxiliary power stage with a flyback arrangement offers the possibility to use flyback capacitor  12   b  in order to perform, at least partly, the storage function of capacitor  12 . However, the auxiliary power stage needs not be a flyback stage. 
         [0112]    As has already been previously stated, in various embodiments, for example in the absence of auxiliary power stage  10 ,  11 , the data save circuitry can be supplied with energy drawn from capacitor  3  through the main power stage  4 ,  6 . 
         [0113]    In this case, in various embodiments, it is possible to act on stage  6  (for example via line  27 ) in such a way as to disconnect load  7  (light source) from power stage  4 ,  6 , so that stage  4 ,  6  transfers energy from capacitor  3  (only) towards save circuitry (e.g.  15 ) and not towards load  7 , avoiding therefore a waste of the energy needed to save the data. In this case, actually, power stage  4 ,  6  is not feeding load  7 , and can then transfer power from capacitor  3  to the save circuitry. 
         [0114]    In various embodiments, the energy transfer from capacitor  3  towards the save circuitry can take place either via capacitor  12  or directly (in which case capacitor  12  may be omitted). 
         [0115]    Various embodiments can therefore power the circuits for data saving by using the energy stored in output capacitor  3  of PFC stage denoted by  2 . 
         [0116]    While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.