Patent Publication Number: US-2023132668-A1

Title: An isolated primary side switched converter for led loads

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is the U.S. national stage application of international application PCT/EP2021/057289 filed Mar. 22, 2021, which international application was published on Oct. 21, 2021 as International Publication WO 2021/209227 A1. The international application claims priority to European Patent Application No. 20165072.8 filed Mar. 24, 2020. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The invention relates to an isolated primary side switched converter, in particular an LLC converter, for supplying LED (light emitting diode) loads and to a driver comprising such a converter. 
     BACKGROUND OF THE INVENTION 
     Converters, such as LLC converters, are generally known. For instance, such converters can be implemented in LED drivers to provide a stable DC supply voltage for an LED load. 
     LLC converters generally comprise a transformer which is arranged between a primary and a secondary side of the converter, wherein both sides are galvanically isolated from each other. A capacitor is usually provided on the secondary side to convert the AC voltage applied to a secondary side winding into a DC voltage, which is then used to supply the LED load. 
     Different topologies or configurations for the design of the secondary side are known, which differ in the position of the capacitor and the use of rectification circuits on the secondary side. 
     However, the possibilities to connect an LED load to a secondary side of an LLC converter and the voltage range provided to such an LED load is strongly limited by the known LLC designs. 
     Thus, it is an objective of the invention to provide an improved primary side switched converter, which avoids the above-mentioned disadvantages. In particular, it is an object of the invention to provide a converter that offers a higher variability of the output voltage. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims. 
     According to a first aspect, the invention relates to a isolated primary side switched converter, comprising a galvanic isolation stage separating a primary side and a secondary side of the converter, a secondary side winding of the isolation stage, wherein the secondary side winding is coupled to a primary side winding, and wherein the secondary side winding comprises a center tap, a first terminal, a second terminal and a third terminal for connecting an LED load on the secondary side of the converter, a rectification circuit on the secondary side of the converter, wherein the rectification circuit is configured to set the first terminal at a first electrical polarity, and to set the second and the third terminal at a second electrical polarity that is different to the first electrical polarity, wherein the third terminal is electrically connected to the center tap, and wherein a voltage between the second and the first terminal is larger than a voltage between the third and the first terminal. This provides the advantage, that LED loads can be supplied with different voltages by the same secondary side of a converter. 
     For instance, the first polarity is a negative polarity and the second polarity is a positive polarity. 
     In particular, the phrases “voltage between the second and the first terminal” and “voltage between the third and the first terminal” refers to absolute values of said voltages. In other words, the absolute value of the voltage between the second and the first terminal is larger than be absolute value of the voltage between the third and the first terminal. 
     In particular, the absolute value of the voltage between the first and the second terminal is double the voltage between the first and the third terminal. 
     Preferably, the second terminal is a high voltage terminal and the third terminal is a low voltage terminal. 
     Preferably, the second terminal is at a larger electrical potential than the third terminal. In particular, the absolute value of the electrical potential at the second terminal is larger than at the third terminal. 
     Preferably, all terminals of the converter are connected to the secondary side winding via the same electrical power path on the secondary side of the converter. 
     The center tap can be an electrical contact at a point halfway along the secondary side winding. In other words, the secondary side winding can be a single winding with an electrical connection in the center. 
     Alternatively, the secondary side winding can comprise two winding sections with the same number of windings that are connected in series, e.g. via an electrical line, wherein the center tap corresponds to an electrical connection between the two sections. 
     The LED load can comprise an LED, an LED module and/or an LED track. In particular, the LED load connected to the terminal can comprise several LEDs or modules, e.g. a first LED connected between the first and the second terminal and a second LED connected between the first and the third terminal. 
     In an embodiment, the LED load is connectable between the first and the second terminal, between the first and the third terminal and/or between the second and the third terminal. 
     The terminals can be configured to allow connecting more than one LED load to each terminal at the same time. For instance, one LED load can be connected between the first and the second terminal and one additional LED can be connected between the first and the third terminal at the same tame. Likewise, one LED load can be connected between the first and the second terminal and one additional LED load can be connected between the second and the third terminal at the same time. 
     In an embodiment, the secondary side winding comprises no further tapping besides the center tap. This achieves the advantage that the secondary side winding can be a simple center tap winding of low complexity and low cost. 
     Preferably, the secondary side winding comprises electrical connections at both ends, wherein the secondary side winding comprises no further electrical connections besides said electrical connections at both ends and the center tap. 
     In an embodiment, the converter comprises a decoupling circuit for reducing voltage fluctuations between the terminals. This achieves the advantage that the LED load is supplied with a steady DC voltage. 
     In particular, the decoupling circuit is configured to reduce voltage fluctuations between the first and the second terminal, between the second and the third terminal, and/or between the first and the third terminal. 
     In an embodiment, the decoupling circuit comprises a first capacitor that is connected in parallel between the first and the second terminal or between the second and the third terminal. This achieves the advantage that the LED load is supplied with a steady DC voltage. 
     In an embodiment, the decoupling circuit comprises a second capacitor that is connected in parallel between first and the third terminal. This achieves the advantage that the LED load is supplied with a steady DC voltage. 
     In an embodiment, the first and the second capacitor have the same capacitance. 
     In an embodiment, the rectification circuit comprises a center tap rectifier. This achieves the advantage, that a voltage supplied to the terminals can be rectified efficiently. 
     In particular, the center tap rectifier is connected to the center tap of the secondary side winding. 
     In an embodiment, the rectification circuit comprises a full wave bridge rectifier. This achieves the advantage, that a voltage supplied to the terminals can be rectified efficiently. 
     In particular, the rectification circuit comprises a combination of the center tap rectifier and the full wave bridge rectifier. 
     In an embodiment, the rectification circuit comprises four diodes or four switches, in particular MOSFETs (metal-oxide-semiconductor field-effect transistors). 
     In an embodiment, the isolated primary side switched converter is a resonant converter, preferably an LLC converter, in particular a resonant half bridge LLC converter. 
     According to a second aspect, the invention relates to a driver for light sources, in particular LED or LED modules, comprising the isolated primary side switched converter according to the first aspect of the invention. 
     The above description with regard to the primary side switched converter according to the present invention is correspondingly valid for the driver according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in the followings together with the figures. 
         FIG.  1    shows a schematic diagram of a primary side switched converter according to an embodiment; 
         FIG.  2    shows a schematic diagram of a primary side switched converter according to an embodiment; 
         FIG.  3   a - c    shows schematic diagrams of LED loads connected to the converter of  FIG.  1  or  2    according to further embodiments; and 
         FIG.  4    shows a schematic diagram of a driver for light sources according to an embodiment; and 
         FIG.  5    shows a schematic diagram of a driver comprising a center tap rectifier according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is described more fully hereinafter with reference to the accompanying drawings, in which various aspects of the present invention are shown. This invention however may be embodied in many different forms and should not be construed as limited to the various aspects of the present invention presented through this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. The various aspects of the present invention illustrated in the drawings may not be drawn to scale. Rather, the dimensions of the various features may be expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus. 
     Various aspects of an isolated primary side switched converter will be presented. However, as those skilled in the art will readily appreciate, these aspects may be extended to aspects of converters in general without departing from the invention. 
     The term “LED luminaire” shall mean a luminaire with a light source comprising one or more LEDs and a driver to operate the LEDs as well as a housing. LEDs are well-known in the art, and therefore, will only briefly be discussed to provide a complete description of the invention. 
     It is further understood that the aspect of the present invention might contain integrated circuits that are readily manufacturable using conventional semiconductor technologies, such as complementary metal-oxide semiconductor technology, short “CMOS”. In addition, the aspects of the present invention may be implemented with other manufacturing processes for making optical as well as electrical devices. Reference will now be made in detail to implementations of the exemplary aspects as illustrated in the accompanying drawings. The same references signs will be used throughout the drawings and the following detailed descriptions to refer to the same or like parts. 
       FIG.  1    shows a schematic diagram of a primary side switched converter  100  according to an embodiment. 
     The converter  100  comprises a galvanic isolation stage  105  separating a primary side  101  and a secondary side  103  of the converter  100 , a secondary side winding  107  of the isolation stage  105 , wherein the secondary side winding  107  is coupled to a primary side winding, and wherein the secondary side winding  107  comprises a center tap, a first terminal T 1 , a second terminal T 2  and a third terminal T 3  for connecting an LED load LED 1 , LED 2  on the secondary side  103  of the converter  100 . 
     The converter  100  further comprises a rectification circuit  109  on the secondary side  103  of the converter  100 , wherein the rectification circuit  109  is configured to set the first terminal T 1  at a first electrical polarity, and to set the second terminal T 2  and the third terminal T 3  at a second electrical polarity that is different to the first electrical polarity. 
     The third terminal T 3  is electrically connected to the center tap of the secondary side winding  107 , wherein a voltage between the second terminal T 2  and the first terminal T 1  is larger than a voltage between the third terminal T 3  and the first terminal T 1 . 
     In particular, the first polarity is a negative polarity and the second polarity is a positive polarity. 
     Preferably, the second terminal T 2  is at a larger electrical potential than the third terminal T 3 . In particular, the absolute value of the electrical potential at the second terminal T 2  is larger than that at the third terminal T 3 . 
     As shown in  FIG.  1   , the LED load LED 1 , LED 2  is connectable between the first terminal T 1  and the second terminal T 2  and/or between the first terminal T 1  and the third terminal T 3 . Further, the LED load can also be connected between the second terminal T 2  and the third terminal T 3 . 
     The first terminal T 1 , the second terminal T 2  and/or the third terminal T 3  can be configured to allow connecting multiple LED loads, in particular multiple LED or modules, simultaneously. 
     In other words, the first terminal T 1  and the second terminal T 2  form a first connection for connecting the LED load, and the first terminal T 1  and the third terminal T 3  form a second connection for connecting LED load, wherein the first connection provides larger supply voltage to the LED load than the second connection. Furthermore, also the second terminal T 2  and the third terminal T 3  can form a connection for connecting the LED load. 
     In particular, the first terminal T 1  is connected to ground. 
     In  FIG.  1   , the LED load comprises two LED LED 1 , LED 2 , wherein LED 1  is connected between the third terminal T 3  and the first terminal T 1 , and LED 2  is connected between the second terminal T 2  and the first terminal T 1 . Thus, the LED 2  receives a larger supply voltage than the LED 1 . 
     In  FIG.  1   , the secondary side winding  107  is depicted as two separate winding sections Ls 1 , Ls 2  in series. Both winding sections Ls 1 , Ls 2  comprise the same number of windings. The center tap is formed by an electrical connection between both windings sections Ls 1 , Ls 2 . 
     Preferably, the secondary side winding  107  comprises no additional tapping besides said center tap. 
     In  FIG.  1   , the secondary side winding  107  is connected to the rectification circuit  109  via two resistances R 3 , R 5 . 
     Preferably, the rectification circuit  109  is configured to rectify an AC voltage provided by the secondary side winding  107  to a DC voltage of constant polarity. 
     The rectification circuit  109  comprises a center tap (or middle tap) rectifier having two diodes D 1 , D 2  on its two branches. 
     Preferably, each branch of this center tap rectifier is extended by one additional diode D 7 , D 8 . In particular, the additional diodes D 7 , D 8  are connected antiparallel to the respective diodes D 1 , D 2  of each branch. 
     The so extended rectification circuit  109  with four diodes D 1 , D 2 , D 7 , D 8 , can form a full wave bridge rectifier that connects the secondary side winding  107  to the terminals T 1 , T 2 , T 3 . 
     Instead of diodes D 1 , D 2 , D 7 , D 8 , the rectification circuit  109  can comprise four switches, in particular MOSFETs. 
     The rectification circuit  109  can be configured to rectify the AC voltage provided by the secondary side winding  107  in synchronous fashion, in particular by using synchronously switched switches instead of the diodes D 1 , D 2 , D 7 , D 8 . 
     The converter  100  can further comprise a decoupling circuit for reducing voltage fluctuations, in particular a ripple voltage, on the connected LED load LED 1 , LED 2 . 
     In  FIG.  1   , the decoupling circuit comprises a first capacitor C 1  that is connected in parallel between the second terminal T 2  and the third terminal T 3 , and a second capacitor C 2  that is connected in parallel between the third terminal T 3  and the first terminal T 1 . 
     Preferably, the first capacitor C 1  and the second capacitor C 2  have the same capacitance. 
     In  FIG.  1   , the decoupling circuit is symmetrical, i.e. the first capacitance C 1  is in parallel to the first winding section Ls 1  and the second capacitance C 2  is in parallel to the second winding section Ls 2  of the secondary side winding  107 . 
     This allows several configurations for connecting an LED load of two separate LED LED 1 , LED 2 : 
     If one LED LED 2  is connected between second terminal T 2  and third terminal T 3 , in parallel to the first capacitor C 1 , and a further LED LED 1  is connected between the third terminal T 3  and the first terminal T 1 , in parallel to the second capacitor C 2 , than both LEDs LED 1 , LED 2  are supplied with an identical lower voltage (LV) (this configuration is not shown in  FIG.  1   ). For instance, this lower voltage is between 10V and 20V. Further, the voltage supplied to each LED LED 1 , LED 2  is filtered by the respective capacitor C 1  or C 2 , which is in parallel to the respective LED LED 1 , LED 2 . The first capacitor C 1  is connected between the second and the third terminal (T 2 , T 3 ). 
     If, however, one LED LED 2  is connected between the second terminal T 2  and the first terminal, as shown in  FIG.  1   , than both capacitors C 1 , C 2  act as decoupling filters for this LED LED 2 . In this case, one LED LED 2  bridges both capacitors C 1 , C 2  and is thus supplied with a higher voltage (HV). For instance, this higher voltage is between 30V and 60V. 
       FIG.  2    shows a schematic diagram of the primary side switched converter  100  according to another embodiment. 
     In  FIG.  2   , the second capacitor C 2  is connected between the second terminal T 2  and the first terminal T 1  and in parallel to the entire secondary side winding  107 . The first capacitor C 1  is connected in parallel to the second winding section LS 2  only. The first capacitor C 1  is connected between the first and the second terminal T 1 , T 2 . 
     Hence, the decoupling circuit in  FIG.  2    is asymmetrical. 
     In this case, the higher voltage (HV) is present at the first capacitor, while the lower voltage (LV) is present at the second capacitor. Hence, an LED load that requires a higher voltage can be connected to the second terminal T 2  (and the first capacitor C 1 ). 
     In contrast to the circuit in  FIG.  1   , for an LED LED 2  that is connected between the second terminal T 2  and the first terminal T 1 , only the first capacitor C 1  acts as a decoupling filter. The second capacitor C 2  acts as decoupling filter for an LED LED 1  that is connected between the third terminal T 3  and the first terminal T 1 . 
     The converter  100  in  FIG.  1    and/or  FIG.  2    can be a resonant converter, e.g. an LLC converter, in particular a resonant half bridge LLC converter. 
       FIG.  3   a - c    shows schematic diagrams of LED loads connected to the converter  100  of  FIG.  1  or  2    according to further embodiments. 
     In  FIG.  3   a   , a high voltage LED module  301  is connected between the second terminal T 2  and the first terminal T 1 . In this configuration, the LED module  301  is supplied with the high voltage HV. 
     The high voltage LED module  301  can comprise a plurality of individual LEDs D 5 , D 6 , D 9 , D 10 , D 11 , D 12 , in particular an LED track. 
     In  FIG.  3   b   , a low voltage LED module  303  is connected between the third terminal T 3  and the first terminal T 1 . In this configuration, the LED module  303  is supplied with the low voltage LV. 
     The low voltage LED module  303  can be designed to receive a lower supply voltage than the high voltage module  301  in  FIG.  3   a   . For instance, the low voltage LED module  303  comprises a smaller number of individual LEDs D 10 , D 11 , D 12 . 
     The connections shown in  FIGS.  3   a  and  3   b    can be realized with the converter  100  from  FIG.  1  or  2   . 
       FIG.  3   b    shows two low voltage LED modules  305 ,  307  that are connected between the third terminal T 3  and the second terminal T 2  and the second terminal T 2  and the first terminal T 1 , respectively. 
     In this configuration, both LED modules  305 ,  307  are supplied with the low voltage LV. 
     Each of the low voltage LED modules  305 ,  307  in  FIG.  3   c    can corresponds to the low voltage LED module shown in  FIG.  3   b   , or to a module, which comprising half of the LEDs of the high voltage module  301  in  FIG.  3     a.    
     The converter  100  shown in  FIG.  1    is better suited for the configuration shown in  FIG.  3   b   . Due to the symmetrical distribution of decoupling capacitors C 1 , C 2  in  FIG.  3   b   , both LED modules  305 ,  307  can be connected to a filter with identical capacitance. 
       FIG.  4    shows a schematic diagram of a driver  400  for light sources according to an embodiment. The light sources can comprise LED or LED modules, in particular the LED load LED 1 , LED 2 . 
     The driver  400  can comprise an electromagnetic interference (EMI) filter  401  that forwards an input voltage, e.g. a mains voltage, to a PFC circuitry  403 , in particular a boost PFC circuit. The PFC circuitry  403  can in turn supply an LLC transformer  407  with a bus voltage via a half bridge  405 . The voltage that is generated in the LLC transformer  407  can be forwarded to an LED load  411  via a rectification and filter unit  409 . 
     The half bridge  405 , the LLC transformer  407  and the rectification and filter unit  409  can form the converter  100  as shown in  FIGS.  1  and  2   . 
     The driver  400  can further comprise a controller  413 , e.g. an ASIC. The controller  413  can be configured to control the PFC circuitry  403  and the half bridge  405 . Furthermore, the controller can be connected to the LLC transformer  407  via an output current sensing unit  415 , to monitor an output voltage of the driver  400 . 
     The driver can further comprise an interface  417 , e.g. a DALI interface, for communicating with the controller  413 . 
       FIG.  5   . shows a converter based on center tap comprising two diodes D 1  and D 2  in it as well as a center tapped transformer along with that a load R is connected across it. The rectification circuit  109  comprises a center tap rectifier comprising two diodes D 1  and D 2 . 
     The invention further related to a lighting system, in particular a LED luminaire, comprising a driver according to the invention and a light source operated by the driver. 
     All features of all embodiments described, shown and/or claimed herein can be combined with each other. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit of scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalence. 
     Although the invention has been illustrated and described with respect to one or more implementations, equivalent alternations and modifications will occur to those skilled in the art upon the reading of the understanding of the specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of the several implementations, such features may be combined with one or more other features of the other implementations as may be desired and advantage for any given or particular application.