Differential-mode filter

Abstract

A differential-mode filter is intended to attenuate electromagnetic interference between an electricity grid and an electronic device. The differential-mode filter comprises a first inductor (L) and a capacitor (C) forming a second-order filter, and a first resistor (Rd) and a second inductor (Ld) reducing the gain of the second-order filter at the resonant frequency of the second-order filter. The first inductor (L) and the second inductor (Ld) are wound around the same closed magnetic core. In a second example of figure 2b, the filter is a symmetric filter. It consists, in the second example, of a first inductor (L_H), a second inductor (Ld_H), a third inductor (L_L) and a fourth inductor (Ld_L), a first resistor (Rd_H), a second resistor (Rd_L) and a capacitor (C).

Description

[0001] DIFFERENTIAL FASHION FILTER

[0002] TECHNICAL FIELD

[0003] The present invention relates to a differential mode filter.

[0004] STATE OF PRIOR ART

[0005] Electromagnetic interference, or "noise," is a common problem in electrical circuit design. Electromagnetic interference can be generated by components in electronic switching systems, such as switching circuits.

[0006] Filtering circuits are used to reduce the effects of electromagnetic interference. Electromagnetic noise signals are high-frequency signals, so filtering circuits are generally designed as low-pass filters, which allow low-frequency or continuous signals to pass through the electromagnetic filter while filtering out unwanted high-frequency electromagnetic noise signals.

[0007] Filtering circuits prevent electromagnetic interference generated by electronics from reaching the electrical network and affecting other equipment connected to the electrical network, and prevent high-frequency currents on the electrical network from polluting the input voltage of the electronics.

[0008] There are electromagnetic filters that consist of an inductor and a capacitor. These second-order filters have the disadvantage of having a significant gain around the resonant frequency of the second-order filter, and therefore amplifying the noise around the resonant frequency.

[0009] To limit the impact of the gain around the resonant frequency, the use of a damping circuit in parallel with the inductance of the second-order filter can be considered. The damping circuit might consist, for example, of an inductor and a resistor.

[0010] Such circuits are described in the document "Input filter design for switching power supplies" available at the address

[0011] https: / / www.ti.com / lit / an / snva538 / snva538.pdf / tsM733293928902. Weight and size are of crucial importance today in embedded systems in vehicles, portable electronic devices, and aircraft. Therefore, there is a need for an electrical filtering circuit capable of providing sufficient filtering of electromagnetic noise in electronic circuits while reducing the size and weight of the filtering circuit to optimize its use in vehicles, portable electronic devices, and aircraft.

[0012] It is therefore desirable to have a differential mode filter that has only a limited number of components, i.e., is small in size and simple to make.

[0013] DESCRIPTION OF THE INVENTION

[0014] The present invention aims to provide a differential mode filter comprising a limited number of components, resulting in a small size and weight, and ease of manufacture. According to a first aspect, the invention relates to a differential mode filter for attenuating electromagnetic interference between an electrical network and an electronic device. The differential mode filter comprises a first inductor and a capacitor forming a second-order filter, a first resistor, and a second inductor that reduces the gain of the second-order filter to its resonant frequency. The first and second inductors are wound around the same magnetic core.

[0015] The invention also relates to an electrical system comprising a differential mode filter attenuating electromagnetic interference between an electrical network and an electronic device, the differential mode filter comprising a first inductance and a capacitor forming a second-order filter, a first resistor and a second inductance reducing the gain of the second-order filter to the resonance frequency of the second-order filter, characterized in that the first and second inductances are wound around the same magnetic core.

[0016] Thus, the present invention makes it possible to obtain a differential mode filter that comprises only a limited number of components, resulting in reduced size and weight, and is simple to manufacture. Furthermore, by winding the first and second inductors around the same magnetic core, the present invention achieves attenuation equivalent to that of prior art second-order damped filters. The present invention allows the use of a second inductor with a value eight times smaller than that of the prior art, thereby reducing the volume and weight of the differential mode filter, while still achieving equivalent attenuation.

[0017] According to another aspect of the invention, the first resistor and the second inductor reduce the gain of the second-order filter to the resonant frequency of the second-order filter, are connected in series, and are connected in parallel with the first inductor. According to another aspect of the invention, the closed magnetic core has a closed quadrilateral or torus shape, and part of the turns of the first and second inductors are wound around one side of the quadrilateral or a portion of the torus's circumference, and the other part of the turns of the first and second inductors are wound around the opposite side of the quadrilateral or an opposite portion of the torus's circumference.

[0018] According to another aspect of the invention, the magnetic core is a quadrilateral or a torus, and all the turns of the first and second inductors are wound around the same side of the quadrilateral or the same portion of the torus's circumference. According to another aspect of the invention, all the turns of the second inductor are wound around the turns of the first inductor.

[0019] According to another aspect of the invention, a first termination of the first inductance is intended to be connected to a terminal of the electrical network, a second termination of the first inductance is connected to a power input of the electronic device and to a first termination of the capacitor, a second termination of the capacitor being connected to another terminal of the electrical network and to another power input of the electronic device.

[0020] According to another aspect of the invention, a first termination of the first inductance is intended to be connected to a terminal of the electrical network, a second termination of the first inductance is connected to a power input of the electronic device and to a first termination of the capacitor, a second termination of the capacitor is connected to another power input of the electronic device and to a first termination of a third inductance forming with the first inductance and the capacitor a second-order filter, a second termination of the third inductance being connected to another terminal of the electrical network, a second resistor and a fourth inductor reducing the gain of the second-order filter to the resonant frequency of the second-order filter are connected in series and are connected in parallel with the third inductance.According to another aspect of the invention, the electrical network includes a power supply delivering a direct current voltage and the electronic device is a DC / AC or DC / DC converter.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

[0023] [Fig. 1] represents an example of an electrical network that supplies electrical power to an electronic system and in which a differential mode filter is placed;

[0024] [Fig. 2a] represents a first example of the realization of a differential mode filter according to the present invention;

[0025] [Fig. 2b] represents a second example of the realization of a differential mode filter according to the present invention;

[0026] [Fig. 3a] represents an example of winding the differential mode filter inductances around a magnetic core according to the first embodiment example;

[0027] [Fig. 3b] represents an example of winding the differential mode filter inductances around a magnetic core according to the second embodiment example;

[0028] [Fig. 4] represents a comparative example of the frequency response curve of the differential mode filter according to the first embodiment of the present invention with filters from the prior art.

[0029] DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0030] Fig. 1 represents an example of an electrical network 120 which supplies electrical power to an electronic system 10 and in which a differential mode filter 100 is inserted.

[0031] The electrical network 120 is in the example of Fig. 1 a continuous supply network of which one of its terminals 1 is connected to the differential mode filter 100 and of which another of its terminals 3 is connected to the differential mode filter 100.

[0032] Alternatively, the 120 electrical network is an alternative power supply network.

[0033] In the example of Fig. 1, the differential mode filter 100 is included in an electronic system 10 which comprises an electronic device 110 such as, for example, a DC / DC or DC / AC converter. The differential mode filter is connected to two power supply inputs 2 and 4 of the electronic device 110, which presents an impedance Ze between these two power supply inputs. Fig. 2a shows a first example of an embodiment of a differential mode filter according to the present invention.

[0034] The differential mode filter 100 in the example in Fig. 2a is called an asymmetric filter.

[0035] The differential mode filter 100 consists in the first example of a first inductance L, a second inductance Ld, a first resistance Rd and a capacitor C.

[0036] One terminal of the second inductor Ld is connected to one terminal of the first inductor L and to terminal 1 of the electrical network 120. A second terminal of the first inductor Ld is connected to one terminal of the first resistor Rd. A second terminal of the first resistor Rd is connected to a second terminal of the first inductor L, to one terminal of the capacitor C, and to the power supply input 2 of the electronic device 110.

[0037] A second termination of capacitor C is connected to terminal 3 of the electrical network 120 and to the power input 4 of the electronic device 110.

[0038] The first inductance Ld and the capacitor C form a second-order filter.

[0039] The second inductance Ld and the first resistance Rd form the damping circuit.

[0040] According to the invention, the first inductance L and the second inductance Ld are wound around the same closed magnetic core 30. The surface 20a, delimited by dashed lines, delimits the first inductance L and the second inductance Ld, which are wound around the same closed magnetic core 30.

[0041] It is specified that in this document, the concept of a closed magnetic core refers to the path of the magnetic field lines, and not to the structure itself. In other words, in this document, the concept of a closed magnetic core allows for a core with a small slot or air gap.

[0042] Fig. 2b represents a second example of an embodiment of a differential mode filter according to the present invention.

[0043] The differential mode filter 100 in the example of Fig. 2b is called a symmetric filter. The differential mode filter 100 consists in the second example of a first inductance LH, a second inductance Ld_H, a third inductance LL and a fourth inductance Ld_L, a first resistance Rd_H, a second resistance Rd_L and a capacitor C.

[0044] One terminal of the second inductor Ld_H is connected to one terminal of the first inductor LH and to terminal 1 of the electrical network 120. A second terminal of the second inductor Ld_H is connected to one terminal of the first resistor Rd_H. A second terminal of the first resistor Rd_H is connected to a second terminal of the first inductor LH, to one terminal of capacitor C, and to the power supply input 2 of the electronic device 110.

[0045] A second termination of capacitor C is connected to the power input 4 of the electronic device 110, to a first termination of the third inductance LL and to a first termination of the second resistor Rd_L.

[0046] A second terminal of the second resistor Rd_L is connected to a first terminal of the fourth inductor Ld_L. A second terminal of the fourth inductor Ld_L is connected to a second terminal of the third inductor LL and to terminal 3 of the electrical network 120.

[0047] According to the invention, the first inductance LH, the second inductance Ld_H, the third inductance LL, and the fourth inductance Ld_L are wound around the same closed magnetic core 30. The surface 20b, delimited by dashed lines, delimits the first inductance LH, the second inductance Ld_H, the third inductance LL, and the fourth inductance Ld_L, which are wound around the same closed magnetic core 30.

[0048] The first inductance LH, the third inductance LL and the capacitor C form a second order filter.

[0049] The second inductance Ld_H, the fourth inductance Ld_L, the first resistance Rd_H, and the second resistance Rd_L form the damping circuit.

[0050] Fig. 3a represents an example of winding the differential mode filter inductances around a closed magnetic core 30 according to the first embodiment example.

[0051] The turns marked 301 are the turns of the first inductance L around the core 30 and the turns marked 302 are the turns of the second inductance Ld around the core 30.

[0052] It should be noted here that the turns of the first inductance L and the second inductance Ld are made in two parts, one part at the top of the closed magnetic core and another at the bottom of the closed magnetic core 30 but each inductance can also be made in a single part at the top or bottom of the closed magnetic core.

[0053] In other words, according to this embodiment, the closed magnetic core 30 has a closed quadrilateral or torus shape. According to this embodiment, part of the turns of the first inductance L and the second inductance Ld are wound around one side of the quadrilateral or around a portion of the circumference of the torus, and the other part of the turns of the first inductance L and the second inductance Ld are wound around the opposite side of the quadrilateral or an opposite portion of the circumference of the torus.

[0054] Alternatively, the first inductance L and the second inductance Ld can be wound around each other. In other words, according to this variant, the closed magnetic core 30 has a closed quadrilateral or torus shape. According to this variant, all the turns of the first inductance L and the second inductance Ld are wound around the same side of the quadrilateral or on the same portion of the torus's circumference.

[0055] Fig. 3b represents an example of winding the differential mode filter inductances around a magnetic core according to the second embodiment example.

[0056] The turns labeled 351 are the turns of the first inductor LH around the core 30, the turns labeled 352 are the turns of the second inductor Ld_H around the core 30, the turns labeled 353 are the turns of the third inductor LL around the core 30, and the turns labeled 354 are the turns of the fourth inductor Ld_L around the core 30. It should be noted here that in Fig. 3b, the first inductor LH and the second inductor Ld_H are wound side-by-side. They can be wound one on top of the other, as can the third inductor LL and the fourth inductor Ld_L.

[0057] Similarly, in Fig. 3b, the first inductance LH and the second inductance Ld_H are wound in the same direction. They can be wound in opposite directions.

[0058] In Fig. 3b, the third inductance Ld_H and the fourth inductance Ld_L are wound in the same direction, but they can be wound in the opposite direction.

[0059] Fig. 4 represents a comparative example of the frequency response curve of the differential mode filter 100 according to the first embodiment of the present invention with filters from the prior art.

[0060] The x-axis represents the frequency and the y-axis represents the attenuation of the differential mode filter expressed in dB. Curve 41 represents the attenuation of an unattenuated second-order filter, curve 42 represents the attenuation of an attenuated second-order filter according to the prior art, and curve 43 represents the attenuation of the differential mode filter according to the present invention.

[0061] The results of curves 42 and 43 are very similar. The mechanical implementation of the damped filter in the prior art requires one more component than the mechanical implementation of the differential mode filter according to the present invention.

[0062] Moreover, for equivalent attenuations, the second inductance Ld has a smaller value with a ratio of the order of 8 for the differential mode filter according to the present invention compared to the filter of the prior art and makes it possible to reduce the volume and weight of the differential mode filter.

Claims

DEMANDS 1. A differential mode filter (100) intended to attenuate electromagnetic interference between an electrical network and an electronic device, the differential mode filter (100) comprising a first inductance (L, LH) and a capacitor (C) forming a second order filter, a first resistance (Rd, Rd_H) and a second inductance (Ld, Ld_H) reducing the gain of the second order filter to the resonance frequency of the second order filter, characterized in that the first inductance (L, LH) and the second inductance (Ld, Ld_H) are wound around the same closed magnetic core (30).

2. The differential mode filter (100) according to claim 1, characterized in that the first resistance (Rd, Rd_H) and the second inductance (Ld, Ld_H) reducing the gain of the second order filter at the resonance frequency of the second order filter are connected in series and are connected in parallel with the first inductance (L, LH).

3. The differential mode filter (100) according to claim 1 or 2, characterized in that the closed magnetic core (30) has a closed quadrilateral or torus shape and in that part of the turns of the first inductance (L, LH) and of the second inductance (Ld, Ld_H) are wound around one side of the quadrilateral or around a portion of the circumference of the torus and the other part of the turns of the first inductance and of the second inductance are wound around the opposite side of the quadrilateral or an opposite portion of the circumference of the torus.

4. The differential mode filter (100) according to claim 1 or 2, characterized in that the closed magnetic core has a closed quadrilateral or torus shape and in that the set of turns of the first inductance (L, LH) and of the second inductance (Ld, Ld_H) is wound around the same side of the quadrilateral or the same portion of the circumference of the torus.

5. The differential mode filter (100) according to claim 1 or 2 or 4, characterized in that all the turns of the second inductance (Ld, Ld_H) are wound around the turns of the first inductance (L, LH).

6. The differential mode filter (100) according to any one of claims 1 to 5, characterized in that a first termination of the first inductance (L, LH) is intended to be connected to a terminal (1) of the electrical network, a second termination of the first inductance (L, LH) is connected to a power supply input of the electronic device (10) and to a first termination of the capacitor (C), a second termination of the capacitor (C) being connected to another terminal of the electrical network and to another power supply input of the electronic device (10).

7. The differential mode filter (100) according to claim 1 or 2, characterized in that a first termination of the first inductance (LH) is intended to be connected to a terminal of the electrical network (1), a second termination of the first inductance (LH) is connected to a power supply input of the electronic device and to a first termination of the capacitor (C), a second termination of the capacitor (C) is connected to another power supply input of the electronic device (10) and to a first termination of a third inductance (LL) forming with the first inductance (LH) and the capacitor (C) a second-order filter, a second termination of the third inductance (LL) being connected to another terminal of the electrical network,A second resistor (Rd_L) and a fourth inductor (Ld_L), reducing the gain of the second-order filter to the resonant frequency of the second-order filter, are connected in series and in parallel with the third inductor (LL).

8. An electrical system (10) comprising a differential mode filter (100) attenuating electromagnetic interference between an electrical network and an electronic device (110), the differential mode filter comprising a first inductance (L, LH) and a capacitor (C) forming a second-order filter, a first resistor (Rd, Rd_H) and a second inductance (Ld, Ld_H) reducing the gain of the second-order filter to the resonant frequency of the second-order filter, characterized in that the first inductance (L, LH) and the second inductance (Ld, Ld_H) are wound around the same closed magnetic core (30).

9. The system (10) according to claim 8, characterized in that the electrical network comprises a power supply delivering a DC voltage and the electronic device (110) is a DC / AC or DC / DC converter.

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