Device for EMC filtering on a printed circuit

An EMC filtering device comprises a printed circuit comprising at least two parallel layers of a high-permittivity material, which are positioned between two layers of an insulating material that are parallel to one another and to the high-permittivity material layers. A core made of a magnetic material comprises three cylindrical arms passing perpendicularly through the high-permittivity and insulating material layers. At least two windings winding around the first arm of the magnetic material core, the windings and the first arm forming a first coil. At least two windings winding around the second arm of the magnetic material core, the windings and the second arm forming a second coil. The two coils being coupled coils.

RELATED APPLICATIONS

This application is a §371 application from PCT/EP2012/071518 filed Oct. 30, 2012, which claims priority from French Patent Application No. 11 60030 filed Nov. 4, 2011, each of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The invention relates to the electronics domain.

The invention more specifically relates to an EMC (“Electromagnetic Compatibility”) filtering device on a printed circuit.

The applications of the invention are notably those of power electronics, specifically power converters, and those of analog and digital electronics.

PRIOR ART

The inflow of net semiconductor technologies has made it possible to work at high temperatures, reduce the size of heat dissipation elements, and raise switching frequencies.

The increase in switching frequencies has led to a deployment of the spectrum of conducted and radiated frequencies at higher frequencies.

Standards such as the DO160 standard in the aerospace sector, the CISPR25 standard in the automotive sector, and the MILSTD standard in the military sector, require conducted emissions to be below a threshold of 10 kilohertz to 100 megahertz, or 150 megahertz.

It is therefore necessary to produce filtering devices that reduce the spectrum of conducted and radiated emissions to below 100 megahertz. In addition, it is necessary to reduce the volume occupied by filtering devices and to reduce the parasitic elements of said filtering devices, as well as the inductance series created with the condensers and the capacitance created in parallel with the coils.

There are filtering devices, with a reduced volume, that make it possible to reduce the spectrum of conducted emissions to frequencies of between 10 megahertz and 100 megahertz, whose discreet filtering elements often underperform due to previously mentioned parasitic elements, while limiting the parasitic elements of the filtering elements.

FIGS. 1a, 2ashow such a filtering device that makes it possible to limit the series creation of inductance with the condensers, andFIGS. 1b, 2bshow a filtering device that does not make it possible limit the series creation of inductance with the condensers.

The filtering device shown inFIG. 1acomprises the conductive paths101,102each comprising a via hole103,104and a dielectric film105with a thickness between 8 micrometers and 32 micrometers interlayered between two copper metal electrodes with a thickness between 15 micrometers and 35 micrometers. The positioning of these elements101-105makes it possible to have an equivalent arrangement shown inFIG. 2a. This equivalent arrangement has two coils110,111and a condenser112connected to the mass113that has a common core120with the two coils110,111.

The filtering device shown inFIG. 1bcomprises a conductive path106comprising a via hole107and a dielectric film105with a thickness between 8 micrometers and 32 micrometers interlayered between two copper metal electrodes with a thickness between 15 micrometers and 35 micrometers. The positioning of these elements105-107makes it possible to have an equivalent arrangement shown inFIG. 2a. This equivalent arrangement has two coils110,111and a condenser112connected to the mass113and in series with a coil114that has a common core120with the two coils110,111.

Comprising two conductive paths101,102and two via holes103,104instead of one conductive path106and one via hole107, like the filtering device shown inFIG. 2a, the filtering device shown inFIG. 1athus makes it possible to obtain a condenser112without series creating parasitic inductance114with the condenser112. The capacitance of the condenser112depends on the permittivity and the thickness of the dielectric film105. The thinner the dielectric film105, the greater the capacitance of the condenser112, the greater the permittivity of the dielectric film105, and the greater the capacitance of the condenser112.

FIG. 3is a chart showing the current level |I| in decibel microamperes based on the frequency in Hertz. The current level |I| is measured with a spectrum analyzer and under normal test conditions. Curve130indicates the limit of the current level |I| based on the frequency imposed by the DO160 standard; curve140shows the current level |I| of a condenser for switching without a filtering device fromFIG. 1abased on the frequency; and curve150shows the current level |I| of a condenser for switching with a filtering device fromFIG. 1abased on the frequency. Curve150remains globally for the entire frequency range shown below curve130, while curve140surpasses curve130starting at a frequency of 1 megahertz. The filtering device inFIG. 1athus makes it possible to remain below the current level |I| limit imposed by the DO160 standard over a range of frequencies, while a simple passive filter makes it possible to reduce the first harmonic to 200 kilohertz.

However, integrating said filtering device into the integrated circuit does not make it possible to obtain the high inductance coils110,111.

To resolve this problem, there are filtering devices integrated into printed circuits comprising layers comprised of magnetic materials, but such devices are costly, difficult to manufacture, and unreliable.

There are also, for example by the scientific publication “Estimation des pertes cuivre dans des composants magnetiques planar—Application au LCT—LAI DAC Kien—JCGE '08 Lyon—16 et 17 décembre 2008” [“Estimation of copper losses in planar magnetic components—pplication to LCT—LAI DAC Kien—JCGE '08 Lyon—Dec. 16-17, 2008”], “planar” magnetic components comprising a transformer, coils, and condensers, integrated into a printed circuit comprising ferrite elements, for which the manufacture of the printed circuit is disassociated from the manufacture of the ferrite elements. However, the application of said magnetic components is not filtering, but rather a transformer.

PURPOSE OF THE INVENTION

The purpose of the invention is namely to propose an EMC filtering device that is reliable, easy to manufacture, and of a reduced volume, making it possible to lower the spectrum of conducted and radiated emissions to below 100 megahertz due to the reduction of parasitic elements of the filtering elements.

For this purpose, the invention relates to an EMC filtering device, characterized in that it comprises:a printed circuit comprising at least two parallel layers of a high-permittivity material, which are positioned between two layers of an insulating material that are parallel to one another and to the layers of a high-permittivity material,a core made of a magnetic material comprising three cylindrical arms passing perpendicularly through the layers,at least two windings winding around the first arm of the magnetic material core, said windings and the first arm forming a first coil,at least two windings winding around the second arm of the magnetic material core, said windings and the second arm forming a second coil,

the two coils being coupled coils.

According to one embodiment,the core made of a magnetic material comprises the three arms and two plates, each positioned at one end of the three arms,the layers each comprising three circular openings, such that when all of the layers are stacked, the circular openings form three cylindrical openings in which are positioned the three arms of the core.

According to one embodiment,the first winding of each coil is positioned on the top face of the first layer of a high-permittivity material, which is in contact with the first layer of an insulating material,the second winding of each coil is positioned on the bottom face of the second layer of high-permittivity material, which is in contact with the second layer of insulating material.

According to one embodiment, the windings of the two coils are flat.

According to one embodiment, the windings of the two coils are wound in the same direction, making it possible to create common coupled windings.

According to one embodiment, the windings of the first coil are wound in the opposite direction of the winding of the windings of the second coil, making it possible to create differential coupled coils.

According to one embodiment, the core made of a magnetic material comprises an air gap.

According to one embodiment, the layers of a high-permittivity material are made of a carbon material.

According to one embodiment, the core made of a magnetic material is made of ferrite.

According to one embodiment, the layers of dielectric material are made of a type FR4 material.

According to one embodiment, the printed circuit and the arms of the core are between one millimeter and three millimeters high.

Identical, similar, or analogous elements maintain the same reference from one figure to the next.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

FIG. 4shows an EMC filtering device1comprising a printed circuit5and a core10made of a magnetic material.

The printed circuit5comprises three parallel layers20,21,22of insulating material and two layers25,26of a high-permittivity material, that are parallel to one another and to the layers20,21,22.

More specifically, the layer25of high-permittivity material is positioned between the layers20and21of insulating material and the layer26of high-permittivity material is positioned between the layers21and22of insulating material.

More specifically, the layer25of high-permittivity material comprises on its top face, meaning the face that is in contact with the layer20, a negative plane80and a positive plane81and comprises on its bottom face, meaning the face that is in contact with the layer21, a mass plane70. Similarly, the layer26of high-permittivity material comprises on its bottom face, meaning the face that is in contact with the layer22, a positive plane82and a negative plane83and comprises on its top face, meaning the face that is in contact with the layer21, a mass plane71.

According to one embodiment, the printed circuit is of a height H1 between one millimeter and three millimeters. In one embodiment, the layers20-22are of a width E1 between 80 micrometers and 200 micrometers, and the layers25,26are of a thickness E2 between 8 micrometers and 32 micrometers.

The structure of the printed circuit5is symmetrical relative to a plane P1 that is parallel to the layers20,21,22,25,26and passes through the middle of the height H1 of the printed circuit5to be compatible with the requirements for manufacturing the printed circuits5, namely at the level of mechanical resistance.

In one embodiment, the layers20,21,22,25,26each comprise three circular openings, with a diameter D1 between two millimeters and a few centimeters, depending on the power of the equipment to be filters, such that when all of the layers20,21,22,25,26are stacked, the circular openings form three cylindrical openings26,27,28with a diameter D1 and a height H1.

The core10made of a magnetic material comprises two plane-parallel plates11,12that are parallel to the layers20,21,22,25,26and three cylindrical arms13,14,15with a diameter D2 that is slightly less than D1 and with a height H1, such that the three arms13,14,15are positioned inside of the three cylindrical openings26,27,28. The plate11is in contact with the top face of the layer20that is not in contact with the layer25and is bound to a first end of each arm13-15. The plate12is in contact with the face of the layer22that is not in contact with the layer26and is bound to a second end of each arm13-15.

The filtering device1further comprises two coupled coils30,31each comprising two flat windings35,36,37,38and having three arms13,14,15made from a magnetic material in common.

More specifically, the first winding35of the first coil30is positioned on the top face of the layer25, meaning the face of the layer25that is in contact with the layer20, and the second winding36of the first coil30is positioned on the bottom face of the layer26, meaning the face of the layer26that is in contact with the layer22. Similarly, the first winding37of the second coil31is positioned on the top face of the layer25, meaning the face of the layer25that is in contact with the layer20and the second coiling38of the second coil31is positioned on the bottom face of the layer26, meaning the face of the layer26that is in contact with the layer22.

The windings35,36wind around the arm13while the windings37,38wrap around the arm15.

Windings35,36,37,38comprise a width between one millimeter and one centimeter. The number of windings of the windings35,36,37,38varies between one winding and ten windings.

The positioning of the windings35,36,37,38of the planes70,71,80-83and the layers20-22,25,26make it possible to obtain two “pi filtering” cells50,51, each comprising two condensers60-63and one coil30,31, as shown inFIGS. 6a-6b. The two coils30,31are coupled.

More specifically, a first terminal60.1of the first condenser60of the first cell50is connected to the mass113; a second terminal60.2of the first condenser60of the first cell50is connected to a first terminal30.1of the coil30of the first cell50; a second terminal30.2of the coil30of the first cell50is connected to a first terminal62.2of the second condenser62of the first cell50; and a second terminal62.1of the condenser62of the first cell50is connected to the mass113. Similarly, a first terminal61.2of the first condenser61of the second cell51is connected to the mass113; a second terminal61.1of the first condenser61of the second cell51is connected to a first terminal31.1of the coil31of the second cell51; a second terminal31.2of the coil31of the second cell51is connected to a first terminal63.1of the second condenser63of the second cell51; and a second terminal63.2of the condenser63of the second cell51is connected to the mass113.

According to one embodiment, the inductance created by the filtering device1is a few microhenries.

In a variant, as shown inFIG. 5, the structure10made of a magnetic material does not comprise an arm14, but rather two arms14.1,14.2with a diameter D2 positioned inside of the opening27. The part of the opening27positioned between the two arms14.1,14.2is called an air gap16. Said air gap16makes it possible to prevent the saturation of the core10made of a magnetic material and to preserve a sufficient inductance to ensure the filtering. The thickness of the air gap16is between 100 micrometers and one millimeter.

The position of the windings35,36,37,38relative to the mass planes70,71make it position to reduce the capacitive couplings of the windings30,31such that the filtering device1is effective over the highest range of frequencies of the spectrum of conducted and radiated emissions.

The windings35,36,37,38are in the directions that make it possible to obtain two coupled coils30,31in common mode and in differential mode. If the windings35,36of the coil30and the windings37,38of the coil31are wound in the same direction, for example in a clockwise direction, the two coupled coils30,31are in common mode. If the windings35,36of the coil30and the windings37,38of the coil31are wound in opposite directions, for example the windings35,36are wound in a clockwise direction and the windings37,38are wound in a counterclockwise direction, the two coupled coils30,31are in differential mode.

When the coupled coils30,31are in common mode, the filtering device1filters the parasites in common mode. When the coupled coils30,31are in differential mode, the filtering device1filters the parasites in differential mode.

FIG. 7shows the filtering device1shown from above, when said filtering device is positioned between a power converter, next to the power supply and a LISN (Line Impedance Stabilization Network) or an electric distribution network. The disturbances present in the power converter are filtered in order to be below the threshold defined by the standards, by the filtering device1, and therefore do not penetrate the LISN.

Planes80,81are respectively positive and negative planes that are connected on the side of the power supply, and planes82,83are respectively positive and negative planes that are connected to the LISN or to the electric distribution network. Planes80-83are positioned outside of the area delimited by the core10.

The positioning of the planes80-83relative to the mass planes70-71make it possible to create a greater capacitance than the capacitance created by the positioning of the windings35-38relative to the mass planes70,71.

The printed circuit5of the filtering device1does not integrate magnetic material, which facilitates the manufacture of the printed circuit5, reduces costs, and ensures reliability in accordance with industry requirements.

As a variant, the number of layers of insulating material and high-permittivity material is significant. The symmetry of the printed circuit5and the alternation between a layer of high-permittivity material and a layer of insulating material are respected.

As a variant, an additional layer of insulating material is interlayered between the layers20,25and between the layers26,22. The windings35,37are then positioned between the first additional layer of insulating material and the layer30and the windings36,38are then positioned between the second additional layer of insulating material and the layer22.

In one example, the layers20-22are made of FR4, the layers25,26are made of carbon material, and the core10is made of ferrite. The relative permittivity εrof the carbon material is eight of 16.