Abstract:
For protection against electromagnetic interference in an apparatus which has a loaded device that can be fed from at least two separate energy sources, an EMC filter is employed with a common-mode inductor arranged to pass through the supply and return line paths which are provided between the energy sources and the load device. This ensures that transition to magnetic saturation is essentially completely precluded even in the case of redundant power supplies to which respectively associated line paths can be routed to and from the load device and, in consequence, with the current being shared differently, since the sum of all the currents passing through the common-mode inductor is approximately zero.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims priority of European Application No. 01302861.8 filed on Mar. 28, 2001.  
         TECHNICAL FIELD  
         [0002]    The invention relates to an EMC filter for apparatuses having a load device which can be fed electrically from at least two separate energy sources.  
         BACKGROUND OF THE INVENTION  
         [0003]    As is generally known, the implementation of and compliance with defined requirements relating to electromagnetic capability and freedom from interference (EMC) of electrical and/or electronic devices is one of the major objects in essentially all fields of electrical engineering.  
           [0004]    Common-mode inductors, as they are referred to, are conventionally used in order to keep interference from external sources away from such devices and/or in order to prevent interference signals caused by devices themselves from being emitted via the power supply lines to the environment.  
           [0005]    Such common-mode inductors are also referred to as current-compensated inductors, when the sum of the magnetic fluxes is approximately zero, because the currents are flowing in opposite directions. In consequence, only a comparatively small magnetic core is required for a large common-mode inductance, without the magnetic saturation region being reached. The transition to magnetic saturation must be prevented since, otherwise, the inductance would be drastically reduced, and the protective effect for electromagnetic freedom from interference would be lost.  
           [0006]    This approach is widely used for mains-powered apparatuses with inductors having two windings normally being used for single-phase AC applications, and inductors having three windings normally being used for 3-phase applications. Furthermore, this procedure is also used in particular for supply lines and/or balanced signal conductors for telecommunication devices and/or systems.  
           [0007]    However, particularly in the case of telecommunications devices, there is also a requirement for redundant supply voltages and/or additional locally required supply voltages. Two mutually independent batteries or rechargeable batteries are frequently used for this purpose.  
           [0008]    The positive and negative terminals of these batteries must be connected via insulated conductors to the supply connections of the telecommunications devices. In addition, the positive terminal of these batteries is conventionally connected to a protective earth. The device receives the necessary supply current from one of the batteries or, depending on the requirement and depending on the individual battery voltages, also from a number of batteries at the same time.  
           [0009]    Furthermore, separate power distribution paths for the separate voltage sources are normally provided within such devices. In this case, the separate supply paths are connected to one another, for example via decoupling diodes, only at replaceable sub-units in the interior of the devices, and supply an internal power supply device in these sub-units. A common-mode inductor can in this case be used between such a connection point and the internal power supply device for the sub-units.  
           [0010]    However, in many cases this procedure has been found to be inadequate since interference can be fed into the mains system via the entire power distribution network inside the device housing. In consequence, additional EMC filters are frequently required for the supply lines, close to the mains or battery connections of such devices. Since the positive lines of the batteries are normally conductively connected or are connected via coupling diodes within the device and are also connected at the batteries via the protective earths, the entire return current can be distributed in an undefined manner between the return conductors. This distribution depends on the resistance of the individual return line paths.  
           [0011]    In particular, it is possible for a current which is being fed back to pass through both return lines, even when the current which is being fed in originates from only one of the two batteries.  
         SUMMARY OF THE INVENTION  
         [0012]    We have recognised the need in the art for a new EMC filter which is improved over the prior art and which ensures reliable protection against electromagnetic interference in a considerably simplified manner when using a number of mutually independent energy sources.  
           [0013]    According to the invention, this object is achieved by an EMC filter, an apparatus and an inductor having the features of claims  1 ,  12  and  14 , respectively. Advantageous and/or preferred embodiments and developments are the subject matter of the dependent claims.  
           [0014]    Thus, for protection against electromagnetic interference for an apparatus which is preferably screened by a metal housing and has a load device which can be fed from at least two separate energy sources, the invention thus provides that an EMC filter with a common-mode inductor be designed such that said inductor is designed for the supply and return line paths which are provided between the energy sources and the load device to pass through jointly.  
           [0015]    It is particularly advantageous in this case that, even in the case of redundant power supplies, those respectively associated line paths are routed to and from the load device separately from the respective other line paths, the transition to magnetic saturation of the inductance is essentially completely precluded independently of any knowledge of the currents which are actually being carried, since the sum of all the currents passing through the common-mode inductor is approximately zero once again.  
           [0016]    One preferred embodiment provides for the inductor to have a number of windings corresponding to the number of line paths, depending on the application. In particular to satisfy different customer requirements and/or Standards that have to be complied with, the invention provides for the common-mode inductor according to the invention to be designed for a communal return line to pass through or for separate return lines to pass through.  
           [0017]    For cost-effective production, and in particular for mass production, it has also been found to be expedient to have an inductor which is produced in a compact manner and is designed with connecting devices to form at least two primaries and two secondaries.  
           [0018]    Depending on the specific field of use, it has furthermore been found in practice to be advantageous to use, in particular, an EMC filter with a common-mode inductor surrounding a magnetic core.  
           [0019]    One preferred development of the EMC filter according to the invention provides for switching between further additional suppression components, in particular in the area of the connecting devices provided for the power supply for the apparatus, for the energy sources, and in particular in the form of batteries. In this case, an arrangement of suppression capacitances and inductances in the form of a low-pass filter between the respective supply and return lines associated with an energy source, and the protective-earth conductors, has been found to be expedient. Furthermore, depending on the specific application, additional inductances, which are provided for current splitting, can also be provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0020]    [0020]FIG. 1 shows a schematic illustration of the circuit diagram of a part of an apparatus with a load which can be fed in a redundant manner from two energy sources. 
     
    
     DETAILED DESCRIPTION  
       [0021]    The following merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof.  
         [0022]    Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.  
         [0023]    Thus, for example, it will be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudocode, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.  
         [0024]    The functions of the various elements shown in the FIGS., including any functional blocks labeled as “processors”, may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, conventional and/or custom, may also be included. Similarly, any switches shown in the FIGS. are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the implementor as more specifically understood from the context.  
         [0025]    In the claims hereof any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements which performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. Applicant thus regards any means which can provide those functionalities as equivalent as those shown herein.  
         [0026]    The following text refers to FIG. 1 which shows, schematically, the example of a circuit diagram of a sub-region of a telecommunications apparatus which is screened by a metal housing. The apparatus is designed with connections P 1 _ 1 , P 1 _ 2 , P 1 _ 3 , P 2 _ 1 , P 2 _ 2 , P 2 _ 3  for connection of two energy sources, which are not illustrated, in the form of batteries, P 1  and P 2 , which may have different battery voltages. The connections P 1 _ 1  and P 2 _ 1  are in this case connected to protective-earth conductors, which are connected to earth. The connections P 1 _ 2  and P 2 _ 2  are connected to power supply conductors, and the connections P 1 _ 3  and P 2 _ 3  are connected to the respectively associated current return conductors.  
         [0027]    The respective power supply lines which are connected to the connections P 1 _ 2  and P 2 _ 2  are connected inside the apparatus via respective connecting devices J 1  and J 2  to a load, which is not illustrated, in order to supply it with power. In a corresponding manner, the return lines, which are connected to connections P 1 _ 3  and P 2 _ 3 , are connected to the load via the respective connecting devices J 3  and J 4 . The load is furthermore connected to a protective earth via the connecting device J 5 .  
         [0028]    In consequence, the load is connected to a redundant power supply, thus ensuring that it is still supplied if one energy source fails.  
         [0029]    The supply and return lines which respectively run between the input connections P 1 _ 2  and P 1 _ 3 , as well as P 2 _ 2  and P 2 _ 3  and the respective connecting devices J 1  and J 2  as well as J 3  and J 4  are, as can be seen in FIG. 1, arranged separately, with the respective supply and return lines associated with an energy source conventionally being routed within a multicore cable.  
         [0030]    The EMC filter according to the invention has a common inductor L 9  through which all four separately running line paths are routed. The inductor L 9  which, in practice, is expediently based on a magnetic core, in the present case comprises four windings, that is to say a specific winding is provided for each supply path and for each return path. The inductor is prefabricated as a component in the present exemplary embodiment. Furthermore, for respectively accommodating connecting ends which are designed to be complementary to the conductors, the inductor L 9  has plug-in devices  3 ,  7 ,  12 ,  16 ,  17 ,  4 ,  8  and  11 . The winding ends which merge into the plug-in device thus form two primaries and two secondaries. A cable which can be associated with the energy source P 1  is, in consequence, connected to the conductor L 9  in such a way that the supply conductor is connected to the connection  3  and the return conductor is connected to the connection  12 . The supply and return conductors which continue onwards and are connected between the inductor L 9  and the connecting devices J 1  and J 3  are connected to the inductor connections  17  and  8  respectively. In a corresponding manner, the supply conductor which is connected via the connection P 2 - 2  to the second energy source is routed via the inductor connections  7  and  4  to the connecting device J 2 , and the return conductor which is connected via the connection P 2 - 3  to the same energy source is routed via the inductor connections  16  and  11  to the connecting device J 4 .  
         [0031]    The common inductor L 9  thus ensures that, even without knowing which supply and return lines are actually being used by the load to carry current at that time, the sum of the currents passing through the inductor is always essentially zero. In consequence, magnetic saturation of the inductor, which is thus current-compensated, is precluded.  
         [0032]    To provide a further protective effect, the EMC filter also has inductors L 1  to L 8  as well capacitances C 1  to C 17 . In realistic applications, the inductors must be connected in parallel, for load reasons. The capacitors in the filter thus at the same time reduce the balanced and unbalanced interference signals in the supply lines. These components are arranged close to the connections P 1 _ 1 , P 1 _ 2 , P 1 _ 3 , P 2 _ 1 , P 2 _ 2 , P 2 _ 3  and to the connecting devices J 1  to J 5  between the individual supply and return lines and the protective-earth conductors, for the suppression and decoupling.  
         [0033]    In detail, the respective capacitances C 1  and C 3 , C 2  and C 4 , C 10  and C 12  as well as C 11  and  13  connected between a supply line and a return line and the protective-earth conductors, together with the inductances L 1 , L 4 , L 5  and L 8 , respectively, form a low-pass filter in the form of a π-circuit. Further low-pass filters for suppression are also constructed, in particular using the capacitive components C 1 , C 2  and C 5  in conjunction with the inductance L 1 , as well as the capacitive components C 1 O, C 11 , C 14  together with the inductance L 5 , between the respectively associated supply and return lines.  
         [0034]    Further decoupling capacitances C 6 , C 9  and C 15  are arranged in the area of the connecting devices, J 1  to J 4  between the supply and return lines. Finally, capacitances C 7 , C 8 , C 16  and C 17  are in each case provided for decoupling the lines from the protective earth.  
         [0035]    It should be mentioned that, in the case of a redundant power supply from more than just two energy sources, the filter according to the invention can be appropriately upgraded or adapted within the knowledge and experience of a person skilled in the art in this field, without departing from the protective scope of the invention. The invention furthermore covers embodiments in which return conductors are routed jointly rather than separately.