Stackable EMI filter

Abstract

EMI filter comprising a main unit (115) that can be connected to a stackable add-on module (120), the main unit having connectors (51, 52; 53, 54), power conductors (42, 44), and an inductive element (L1-L4) for blocking an unwanted interference signal superimposed on a supply voltage; the stackable add-on module comprising an additional electrical circuit (20) on a printed circuit board (127), the printed circuit board (127) being permanently electrically connected to the power conductors (42, 44) by add-on module connection means (32, 34), such that the stackable add-on module is configured to be stacked on top of the main unit, so that the printed circuit board, when stacked, connects to the add-on module connection means without interrupting the electrical continuity of the power conductors (42, 44). Figure to be published with the abstract: Figure 2

Description

Title of invention: Stackable EMI filter Technical field

[0001] The present invention relates to filters for protection against electromagnetic interference (EMI filters). The concept of EMI filter covers and is, for the purposes of the present invention, synonymous with: electromagnetic compatibility filters (EMC filters), line filters, EMI / EMC chokes and low-pass filters. Prior art

[0002] Most applications of EMI filters involve passive modules that are inserted between a device and its power source, along power conductors that can carry either direct current (DC) or alternating current (AC) power having a mains frequency below 400 Hz, typically 50 / 60 Hz.

[0003] Low-pass filters come in an almost infinite variety of circuits, many of which can be used as EMI filters. A single-phase DC or AC EMI filter typically has two line terminals and two load terminals that are internally connected by a low-resistance path comprising conductors and inductive elements. The filter also has shunt elements, usually capacitive or resistive in nature, so that the supply current passes through the filter with little or no change, and electromagnetic interference, which occurs at higher frequencies, is greatly attenuated. It is common for the path between the line and load terminals to be made of heavy-gauge conductors or solid bus bars, to minimize ohmic losses.

[0004] There are also polyphase alternating current EMI filters, to which the present invention also applies. The number of line and load terminals present in these devices corresponds to the number of phases, to which is optionally added a pair intended for a neutral conductor.

[0005] Although the ports of an EMI filter are conventionally referred to as "line" and "load" or "input" and "output", many filters are actually bidirectional and attenuate interference in both directions. EMI filters are not limited to direct insertion between a power line and a load, but also find their place in more complex equipment, such as in motor drive units.

[0006] In addition to their electrical and filtering characteristics, EMI filters must also meet criteria of dimensions, thermal dissipation, re heat resistance, vibration immunity, and many other parameters. In automotive applications, where electrical components are increasingly common, these criteria are particularly stringent. Therefore, despite the apparent simplicity of the underlying electrical circuit, EMI filters are complex products, difficult to design and adapt to all possible applications. Brief presentation of the invention

[0007] The present invention relates to a stackable filter which can be adapted to different applications by superimposing different additional modules on a base unit.

[0008] According to the invention, these objects are achieved by the subject matter of the appended claims. In particular, the invention relates to an EMI filter comprising a main unit connectable to a stackable add-on module, the main unit comprising connectors for connection between a power source and an electrical load, power conductors electrically connectable by the connectors between the power source and the electrical load, an inductive element for blocking an unwanted interference signal superimposed on a supply voltage;the stackable add-on module comprising an additional electrical circuit on a printed circuit board, the printed circuit board being permanently electrically connected to the power conductors by add-on module connection means, such that the stackable add-on module is configured to be stacked on the main unit, such that the printed circuit board, when stacked, connects to the add-on module connection means without interrupting the electrical continuity of the power conductors.;

[0009] According to other optional features of the method, the latter may optionally include one or more of the following features, alone or in combination: - the power conductors are solid bus bars. - the additional module connection means are conductive pads rising from the bus bars and in electrical contact with them. - the additional module connection means are made in one piece with the bus bars, or brazed to the bus bars, or welded to the bus bars, or force-fitted onto the bus bars, or pressed against the bus bars. - the additional electrical circuit modifies the performance of the main unit, or improves the attenuation in a certain frequency band, or eliminates a resonance, or adds a function. - the additional electrical circuit includes a capacitor between the supply lines and ground, and / or an interline capacitor, and / or re damping resistors, and / or RLC networks, and / or active elements. - the main unit is a single-phase direct current or alternating current unit having a pair of bus bars as power conductors, comprising magnetic cores magnetically coupled to the power bus bars as inductive elements, and line-to-ground capacitors for shunting an unwanted interference component, and the additional stackable unit comprises additional line-to-ground and line-to-line capacitors and snubber resistors in series or parallel. - the main unit is a cable-mounted filter, configured to be mounted on a pair of load-side or line-side cable conductors, in which flexible conductors are magnetically coupled to, and inserted into, a magnetic core of the EMI filter. Brief description of the drawings

[0010] Exemplary embodiments of the invention are presented in the description and illustrated by the drawings, in which:

[0011] [Fig. 1a] schematically illustrates the electrical circuit of an EMI filter,

[0012] [Fig.lb] and [Fig. le] illustrate a filter whose electrical characteristics are different from those of [Fig.la], thanks to the addition of additional components,

[0013] [Fig.2] illustrates the stackable filter of the invention.

[0014] Exemplary embodiments of the present invention

[0015] [Fig. 1a] shows a direct current or single-phase EMI filter 15. The present disclosure will refer to this type of device for the sake of brevity, it being understood that the invention also covers polyphase filters. The filter has line terminals 51, 52 for connection to a supply line, and load terminals 53, 54 for delivering filtered power to a load not shown. The line and load are connected by bus bars 42, 44, or other suitable power conductors, with inductive elements L1-L4 interposed.

[0016] Capacitors C1, C2 provide the bypass to ground of unwanted interference currents. They are connected between the power conductors 42, 44 (eg bus bars) and ground, or another node having a sufficiently low impedance at the frequencies at which interference occurs.

[0017] The EMI filter 15 may be part of a base unit of the filter of the invention, as will be described in the following.

[0018] [Fig.lb] illustrates a filter which comprises all the elements of the filter 15, as well as additional circuits 20 (eg additional shunt components). The shunt components comprise two additional shunt elements between the bus bar and ground: R2, C4, respectively R3, C5, and a line-to-line shunt composed of RI and C3.

[0019] In the example shown, the additional elements are each composed of a capacitor and a resistor in series, in order to improve attenuation and damping, but this is not essential, and the invention is not limited to this. In other variants not shown, the additional circuits 20 may comprise damping resistors in parallel with the reactive components rather than in series as shown, or simply consist of damping resistors, connected between the lines or between the lines and ground, which are electrically connected in parallel with the capacitors of the main circuit, or simply of capacitors, between the lines and ground or between the lines. The additional components may also comprise an RLC network of any topology, and active elements.

[0020] Adding additional circuits 20, such as shunt components, to the EMI filter 15 modifies the transfer function of the filter and / or modifies its performance, possibly by improving attenuation in a certain desired frequency band, by suppressing resonance, or by adding some function by means of active elements.

[0021] The additional circuits 20 may be part of a stackable additional module according to the invention, as will be explained later.

[0022] [Fig. 1c] illustrates how the additional circuits 20 can be added to the original EMI filter 15 without compromising the continuity of the bus bars (i.e., power conductor 42, 44). The additional circuits 20 and the original EMI filter 15 can conveniently be maintained at different levels, the connection being provided by two conductive elements 32, 34 which connect the bus bars (i.e., power conductor 42, 44) to suitable nodes of the additional circuit 20. The conductors 32, 34 must have a low impedance at the frequency at which interference occurs, but they do not carry the DC or low frequency load current and do not contribute substantially to power losses. Electrical continuity between the ground points of the original circuit and the additional circuit 20 is implied.

[0023] [Fig.2] illustrates the stackable filter of the invention with a base element which includes connectors for line and load terminals, bus bars, inductive elements, and possibly shunt elements, and an additional stackable module 120 on the main element, with an electrical circuit comprising an additional electrical component mounted on a printed circuit board 127, such as for example the additional circuit 20 shown above. The assembly also includes two conductive elements 132, 134 which are connected to the bus bars or connectors on the side of the base element 15 and connect to the printed circuit board of the additional stackable element. A third electrical connection for grounding can be obtained using dedicated conductors or a metal chassis of the base element. In the example shown, the ground connectors 138 are soldered into corresponding holes 128 of the printed circuit board 127 and screwed to a suitable grounding point of the main filter unit 115.

[0024] The contact elements 134, 132 may be an integral part of the bus bar structure (from the same piece of copper) or may be separate elements soldered to the bus bar, brazed to it, or fixed to the bus bar by interaction and friction (press-fitting). The contact elements may also be a separate part that is pressed against the bus bar. The contact between the contact elements 134, 132 and the corresponding tracks of the printed circuit board 127 is preferably soldered or fixed by press-fitting. The example of [Fig. 2] has holes 122, 124 in the printed circuit board 127 for receiving and soldering the contact elements 134, 132.

[0025] The main unit of [Fig. 2] is a cable-mounted EMI filter for automotive applications, which is configured to be coupled to a pair of flexible conductors on either the load side or the line side. The conductors pass through the center hole of the magnetic core 137 and are attached to screw terminals (not visible in the figure) of the main unit 115. The main unit 115 has access openings 139 for inserting a screwdriver, or other suitable tool, and tightening the screw terminals. Similarly, the printed circuit board of the stackable add-on module 120 has openings 129 aligned with the corresponding access openings 139 of the main unit 115 to allow insertion of the screwdriver.

[0026] The stackable filter shown in [Fig. 2] is a highly integrated and compact device and it would be difficult to redesign it to change its performance. The present invention provides an assortment of filters having different performances, in the same assembly or in compatible assemblies, by combining the same base unit with different additional stackable modules.

[0027] In addition, the addition of the stackable add-on module 120 desirably improves the characteristics of the main unit 115, without influencing the design of the bus bars, mechanical interfaces, connectors and magnetic core design. The invention therefore makes it possible to improve the performance of EMI filters and provide customized filters, with less design and engineering effort.

[0028] Reference symbols in the figures [Tables 1] 15 Main circuit 20 Additional circuit 32 Conductor 34 Conductor 42 Bus bar type power conductor 44 Bus bar type power conductor 51 Line terminal 52 Line terminal 53 Load terminal 54 Load terminal 115 Main unit 120 Stackable add-on module 122 PCB hole 124 PCB hole 127 PCB 128 PCB hole 129 Screwdriver access openings 132 Conductor, connecting pin 134 Conductor, connecting pin 137 Magnetic core 138 Ground conductor 139 Screwdriver access openings

Claims

Claims

1. An EMI filter comprising a main unit (115) connected to a stackable add-on module (120), the main unit having connectors (51, 52; 53, 54) connectable between a power source and an electrical load, power conductors (42, 44) electrically connectable by the connectors between the power source and the electrical load, an inductive element (L1-L4) for blocking an unwanted interference signal superimposed on a power supply voltage;the stackable additional module comprising an additional electrical circuit (20) on a printed circuit board (127), the printed circuit board (127) being permanently electrically connected to the power conductors (42, 44) by additional module connection means (32, 34), so that the stackable additional module is stacked on the main unit, so that the printed circuit board connects to the additional module connection means without interrupting the electrical continuity of the power conductors (42, 44).;

2. The EMI filter of claim 1, wherein the power conductors (42, 44) are solid bus bars.

3. An EMI filter according to claim 2, wherein the additional module connection means (32, 34) are conductive pads rising from and in electrical contact with the bus bars.

4. Cl. EMI filter according to claim 3, wherein the additional module connection means (32, 34) are integral with the bus bars, or brazed to the bus bars, or welded to the bus bars, or press-fitted onto the bus bars.

5. The EMI filter of claim 1, wherein the additional electrical circuit (20) modifies the performance of the main unit (115), or improves attenuation in a determined frequency band, or suppresses resonance.

6. An EMI filter according to claim 1, wherein the additional electrical circuit (20) comprises a capacitor between the supply lines and ground, and / or an interline capacitor, and / or damping resistors, and / or RLC networks, and / or active elements.

7. The EMI filter of claim 1, wherein the main unit (115)

8. is a single-phase direct current or alternating current unit having a pair of bus bars as power conductors (42, 44), comprising magnetic cores magnetically coupled to the power bus bars as inductive elements, and line-to-ground capacitors for shunting an unwanted interference component, and the additional stackable unit comprises additional line-to-ground and line-to-line capacitors and damping resistors in series or parallel. The EMI filter of claim 7, wherein the main unit (115) is a cable-mounted filter, configured to be mounted on a pair of load-side or line-side cable conductors, wherein flexible conductors are magnetically coupled to, and inserted into, a magnetic core of the EMI filter.

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