A double-layer shielding structure for transformer and its application

Abstract

The present invention relates to a double-layer shielding structure for a transformer and its application. The double-layer shielding structure comprises two metal shielding bodies arranged in parallel, a dielectric layer is arranged between the two metal shielding bodies, and the equivalent capacitance of the two metal shielding bodies is changed by changing the distance between the two metal shielding bodies, the dielectric constant of the dielectric layer and the facing area of ​​the two metal shielding bodies. The double-layer shielding structure is arranged inside a magnetic core or coated outside a magnetic core to shield electromagnetic interference. The double-layer shielding structure can effectively reduce the common-mode noise of the transformer, reduce the common-mode noise of the magnetic element to the earth and its electromagnetic radiation characteristics, and effectively reduce the conducted and radiated EMI noise.

Description

Technical Field

[0001] The invention belongs to the field of transformers, and in particular relates to a double-layer shielding structure for a transformer and an application thereof. Background Art

[0002] The common-mode EMI characteristics of the transformer in the isolated switching power supply are key parameters that affect its electromagnetic compatibility characteristics. Especially with the emergence and popularization of SiC devices and power electronic wide bandgap devices, the switching frequency and resonance of the switching power supply have been further improved, and the common-mode EMI characteristics of the transformer directly determine the quality of the electromagnetic compatibility characteristics of the switching power supply. In order to reduce the common-mode noise of the transformer, a metal shield is generally added between the primary and secondary sides of the transformer or outside the winding and the magnetic core of the transformer, hoping to reduce the common-mode noise from the primary to the secondary side of the transformer and the common-mode noise of the magnetic components to the earth. However, these methods can reduce common-mode noise in some applications, but some cannot reduce or even worsen its conducted or radiated EMI noise.

[0003] A single layer shield is set in the transformer windings such as Figure 1 As shown in (a), a metal shield is added between the primary winding layer and the secondary winding layer. If the transformer is a step-down transformer, the copper foil is connected to the static potential of the primary winding. If it is a step-up transformer, the shield is connected to the static potential of the secondary winding. This method can shield the common mode noise of one winding, but has no effect on the common mode noise of the other winding.

[0004] A single-layer shield is set on the outermost winding of the transformer. Figure 1 As shown in (b), the shield is connected to the electrostatic potential of the outermost winding. This can shield the potential jump between the winding and the magnetic core, reducing the external radiation of the transformer core, but it has no shielding effect on the common mode noise between the primary and secondary sides of the transformer.

[0005] Add a single layer of shielding outside the transformer core such as Figure 1 As shown in (c), when the winding is sandwich-wound, a layer of conductive copper foil is wrapped on the surface of the transformer's core, and the copper foil is electrostatically connected to the outermost layer of the core winding, so that the electric field on the core cannot radiate outward. However, this shielding method cannot effectively shield the common-mode noise between the primary and secondary sides.

[0006] like Figure 1 As shown in (d), by adding a partial shielding winding to the transformer winding and adjusting the height of the shielding winding, the induced charge on the secondary side can be minimized, thereby reducing the common-mode noise between the primary and secondary sides. However, in the high-frequency band, the primary-to-secondary voltage does not satisfy the turns ratio, so the fixed structure cannot shield the effect of high-frequency common-mode noise.

[0007] The above-mentioned metal shields are all single-layer shielding structures. Transformers generally have noise sources from the primary and secondary sides. Structure 1 can shield the noise from the primary to the secondary side, but cannot shield the noise from the secondary to the secondary side. Structures 2 and 3 can reduce the electromagnetic radiation generated by the magnetic components to the outside, but will deteriorate the noise from the primary to the secondary side of the transformer. Structure 4 can effectively shield the common mode noise from the primary to the secondary side and from the secondary to the primary side of the transformer in the low frequency band, but in the high frequency band, because the voltage of the primary and secondary sides of the transformer does not meet the turns ratio, it has no shielding effect. The main reason for this is that the existing shielding body has only a single-layer structure and cannot completely shield the noise from the primary and secondary sides. Summary of the invention

[0008] The purpose of the present invention is to provide a double-layer shielding structure for a transformer and its application, which can effectively reduce the common-mode noise of the transformer, reduce the common-mode noise of the magnetic component to the earth and its electromagnetic radiation characteristics, and effectively reduce the conducted and radiated EMI noise.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a double-layer shielding structure for a transformer, comprising two metal shielding bodies arranged in parallel, with a dielectric layer provided between the two metal shielding bodies, and the equivalent capacitance of the two metal shielding bodies is changed by changing the distance between the two metal shielding bodies, the dielectric constant of the dielectric layer and the facing area of ​​the two metal shielding bodies.

[0010] Furthermore, the double-layer shielding structure is applied to a transformer, which includes a magnetic core with a center column and two power windings, wherein a first power winding and a second power winding are sequentially arranged outward from the center column of the magnetic core, and when the first power winding is the primary winding, the second power winding is the secondary winding, and when the first power winding is the secondary winding, the second power winding is the primary winding; the double-layer shielding structure is arranged inside the magnetic core or coated on the outside of the magnetic core to shield electromagnetic interference.

[0011] Furthermore, the double-layer shielding structure is arranged on the outside of the second power winding in the magnetic core, and its wiring method is: the first metal shielding body closer to the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body closer to the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0012] Furthermore, the double-layer shielding structure is arranged between the first power winding and the second power winding in the magnetic core, and its wiring method is: the inner first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the outer second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the connection point between the second power winding and the circuit switch tube; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0013] Furthermore, the double-layer shielding structure is arranged on the inner side of the first power winding in the magnetic core, and its wiring method is: the inner first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the outer second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the connection point between the first power winding and the main circuit switch tube; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0014] Furthermore, the double-layer shielding structure is coated on the outer surface of the magnetic core, and its wiring method is: the inner first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the outer second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0015] Furthermore, the double-layer shielding structure is applied to a transformer, which includes a magnetic core with a center column and three power windings, wherein a first power winding, a second power winding and a third power winding are sequentially arranged outward from the center column of the magnetic core, and when the first power winding and the third power winding are primary windings, the second power winding is a secondary winding, and when the first power winding and the third power winding are secondary windings, the second power winding is a primary winding; the double-layer shielding structure is arranged inside the magnetic core or coated on the outside of the magnetic core to shield electromagnetic interference.

[0016] Furthermore, the double-layer shielding structure is arranged on the outside of the third power winding in the magnetic core, and its wiring method is: the first metal shielding body close to the inside is connected to the positive or negative pole of the bus voltage corresponding to the third power winding, and the second metal shielding body close to the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the third power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0017] Furthermore, the double-layer shielding structure is simultaneously arranged between the first power winding and the second power winding and between the second power winding and the third power winding in the magnetic core, and there are three wiring methods:

[0018] 1) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding;

[0019] 2) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the connection point between the third power winding and the circuit switch tube;

[0020] 3) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the connection point between the second power winding and the circuit switch tube; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the connection point between the third power winding and the circuit switch tube;

[0021] The EMI characteristics of the switching power supply can be improved by adjusting the distance between the two metal shields, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shields.

[0022] Furthermore, the double-layer shielding structure is coated on the outer surface of the magnetic core, and its wiring method is: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; or the first metal shielding body is connected to the connection point of the third power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point of the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0023] Compared with the prior art, the present invention has the following beneficial effects: the present invention proposes a double-layer shielding structure applied to a transformer, which not only has the electric field shielding function of a traditional metal shielding body, but can also effectively reduce the common-mode noise of the transformer, reduce the common-mode noise of the magnetic component to the earth and its electromagnetic radiation characteristics, and can also realize the integration of capacitors. The capacitors can not only serve as compensation capacitors for common-mode noise but also have the function of Y capacitors, thereby effectively reducing conducted and radiated EMI noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of a single-layer shielding body arranged on a transformer in the prior art.

[0025] Figure 2 It is a structural schematic diagram of a double-layer shielding structure in an embodiment of the present invention.

[0026] Figure 3 It is a schematic diagram of the structure in which a double-layer shielding structure is arranged inside a magnetic core in an embodiment of the present invention.

[0027] Figure 4 It is a schematic diagram of the structure in which a double-layer shielding structure is coated on the outside of a magnetic core in an embodiment of the present invention.

[0028] Figure 5 It is a schematic diagram of the wiring circuit of the double-layer shielding structure in the flyback converter in the first embodiment of the present invention.

[0029] Figure 6 yes Figure 5 Alternative circuit diagram.

[0030] Figure 7 yes Figure 6 Equivalent circuit diagram of .

[0031] Figure 8 It is a schematic diagram of the wiring circuit of the double-layer shielding structure in the flyback converter in the second embodiment of the present invention.

[0032] Fig. 9 yes Figure 8 Equivalent circuit diagram of .

[0033] In the figure: 101-magnetic core, 102-first power winding, 103-second power winding, 104-shielding winding, 105-partially shielded winding; 201-metal shielding body, 202-dielectric layer, 203-metal shielding body; 301-magnetic core, 302-first power winding, 303-second power winding, 304-first metal shielding body, 305-dielectric layer, 306-second metal shielding body; 401-magnetic core, 402-third power winding, 403-second power winding, 404-first metal shielding body, 405-dielectric layer, 406-second metal shielding body, 407-first power winding. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] like Figure 2 As shown, the present invention provides a double-layer shielding structure for a transformer, including two layers of metal shielding bodies arranged in parallel, which can generally be copper foil or aluminum foil, and a dielectric layer is arranged between the two metal shielding bodies. The equivalent capacitance of the two metal shielding bodies is changed by changing the distance between the two metal shielding bodies, the dielectric constant of the dielectric layer, and the facing area of ​​the two metal shielding bodies. Changing the distance between the two metal shielding bodies is achieved by changing the thickness of the dielectric layer. The dielectric constant of the dielectric layer can be changed by using materials with different dielectric constants. Changing the facing area between the two metal shielding bodies can be achieved by changing the size of the metal shielding bodies used; the width sh of the double-layer shielding body is determined according to the core height, core thickness or winding window height of the transformer, and the facing area is controlled by controlling the length sl of the double-layer shielding.

[0036] Will Figure 2 The double-layer shielding structure shown is applied to a transformer to achieve electromagnetic interference shielding. It can be divided into two categories according to the setting position of the double-layer shielding structure: one is to set the double-layer shielding structure inside the magnetic core of the transformer, and the other is to cover the double-layer shielding structure outside the magnetic core of the transformer.

[0037] There are mainly two structures of transformers using the double-layer shielding structure.

[0038] like Figure 3 As shown, one transformer structure is: the transformer includes a magnetic core with a center column and two power windings, the first power winding and the second power winding are sequentially arranged outward from the center column of the magnetic core, when the first power winding is the primary winding, the second power winding is the secondary winding, when the first power winding is the secondary winding, the second power winding is the primary winding. For a transformer with this structure:

[0039] like Figure 3 As shown in (a), the double-layer shielding structure can be arranged on the outside of the second power winding in the magnetic core, and the wiring method is: the first metal shielding body close to the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body close to the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply can be improved.

[0040] like Figure 3 As shown in (b), the double-layer shielding structure can be arranged between the first power winding and the second power winding in the magnetic core, and the wiring method is: the first metal shielding body closer to the inside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body closer to the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the connection point between the second power winding and the circuit switch tube; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply can be improved.

[0041] like Figure 3As shown in (c), the double-layer shielding structure can be arranged on the inner side of the first power winding in the magnetic core, and the wiring method is: the first metal shielding body closer to the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body closer to the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the connection point between the first power winding and the main circuit switch tube; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply can be improved.

[0042] The double-layer shielding structure can be coated on the outer surface of the magnetic core, and its wiring method is: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0043] like Figure 4 As shown, another transformer structure is: the transformer includes a magnetic core with a center column and three power windings, the first power winding, the second power winding and the third power winding are sequentially arranged outward from the center column of the magnetic core, when the first power winding and the third power winding are primary windings, the second power winding is a secondary winding, when the first power winding and the third power winding are secondary windings, the second power winding is a primary winding. For a transformer of this structure:

[0044] The double-layer shielding structure can be arranged on the outside of the third power winding in the magnetic core, and its wiring method is: the first metal shielding body close to the inside is connected to the positive or negative pole of the bus voltage corresponding to the third power winding, and the second metal shielding body close to the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the third power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

[0045] The double-layer shielding structure can be simultaneously arranged between the first power winding and the second power winding and between the second power winding and the third power winding in the magnetic core, and there are three wiring methods: 1) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the inner first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the outer second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; 2) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding. The corresponding bus voltage positive or negative pole; the double-layer shielding structure arranged between the second power winding and the third power winding is connected in the following way: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the connection point between the third power winding and the circuit switch tube; 3) The double-layer shielding structure arranged between the first power winding and the second power winding is connected in the following way: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the connection point between the second power winding and the circuit switch tube; the double-layer shielding structure arranged between the second power winding and the third power winding is connected in the following way: the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the connection point between the third power winding and the circuit switch tube; the EMI characteristics of the switching power supply are improved by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies.

[0046] like Figure 4 As shown, the double-layer shielding structure can be coated on the outer surface of the magnetic core, and its wiring method is: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; or the first metal shielding body is connected to the connection point of the third power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point of the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply can be improved.

[0047] like Figure 3 As shown, there are three structures for setting the double-layer shielding structure inside the magnetic core. The key to the three structures being able to shield electromagnetic interference is the connection method of the shielding body. Different connection methods have different effects on electromagnetic shielding. Figure 4 As shown, a double-layer shielding body is wrapped on the surface of the magnetic core. In order to play a good shielding role, the double-layer shielding body needs to be connected to the corresponding winding electrostatic potential phase according to the winding structure, among which the connection of the first metal shielding body wrapped around the outside of the magnetic core of the transformer needs to be connected according to the winding that causes the potential change of the magnetic core.

[0048] The equivalent capacitance of the two shielding bodies can be adjusted by adjusting the height H of the shielding body, the dielectric constant of the dielectric layer between the two shielding layers, or increasing or decreasing the number of turns of the shielding layer. This capacitance can not only serve as a compensation capacitor for common mode noise, but also has the function of a Y capacitor to reduce conducted and radiated EMI noise.

[0049] In the first embodiment, Figure 3 The structure of (a) is applied to the flyback converter. The double-layer metal shielding structure acts as a compensation capacitor for common-mode noise. Its wiring structure in the flyback converter is as follows: Figure 5 shown.

[0050] Among them, shielding layers 1 and 2 are connected to Figure 5 Point A and B correspond to the points in the flyback converter, where point A is the positive pole of the bus voltage and point B is the connection point between the secondary power winding and the diode. C add is the equivalent capacitance between the two shielding layers 1 and 2, and C add The size of is related to the facing area between the two shielding layers, the distance between the two shielding layers, and the dielectric constant of the dielectric layer between the shielding layers. Figure 5 The conducted common-mode noise source of the flyback converter is mainly caused by the jump voltage across the switch tube S and the secondary rectifier diode D. V ds and voltage source V d Instead, we can get Figure 6 As shown in the alternative circuit diagram, according to the circuit theorem, it can be concluded that the currents driven by the two common-mode noise voltage sources on the LISN resistor are in opposite directions. Therefore, the common-mode current on the LISN can be adjusted by adjusting the impedance on the common-mode current conduction path to minimize the voltage drop on the LISN.

[0051] The present invention introduces an equivalent capacitance between the shielding layers C add , adjusted by Vd The impedance of the common mode noise current path caused by C add , so that the current Id and the current Ids cancel each other out. Figure 6 The simplified equivalent circuit diagram is as follows Figure 7 Therefore, the common mode current in the conduction frequency band will be suppressed.

[0052] In the second embodiment, Figure 4 The structure shown is applied to the flyback converter, and the double-layer metal shielding structure acts as a Y capacitor for common mode noise. The wiring structure in the flyback converter is as follows: Figure 8 As shown, shield layer 1 is connected to the primary electrostatic potential, and shield layer 2 is connected to the secondary electrostatic potential. V p is the primary voltage, V s is the secondary voltage, V ds is the voltage across the switch tube S, C Yadd is the equivalent capacitance between the two shielding layers.

[0053] The common mode radiation equivalent circuit after adding a shielding layer to the transformer is as follows Fig. 9 As shown in the figure Z T1 , Z T2 , Z T3 is the equivalent impedance of the transformer, the equivalent capacitance between the shielding layers C Yadd Equivalent to connecting in parallel with the cable impedance Z conv and antenna impedance Z atenna Therefore, this can reduce the common mode radiation current flowing through the antenna impedance, thereby reducing the radiated electromagnetic interference on the antenna. After adding a double-layer shielding body outside the magnet, since the shielding body is connected to the static potential, it will also shield the external radiation of the transformer core.

[0054] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. An application of a double-layer shielding structure in a transformer, characterized in that: The double-layer shielding structure comprises two metal shielding bodies arranged in parallel, a dielectric layer is arranged between the two metal shielding bodies, and the equivalent capacitance of the two metal shielding bodies is changed by changing the distance between the two metal shielding bodies, the dielectric constant of the dielectric layer and the facing area of ​​the two metal shielding bodies; The transformer comprises a magnetic core with a central column and two power windings, wherein a first power winding and a second power winding are sequentially arranged outward from the central column of the magnetic core, when the first power winding is a primary winding, the second power winding is a secondary winding, and when the first power winding is a secondary winding, the second power winding is a primary winding; the double-layer shielding structure is arranged inside the magnetic core or coated on the outside of the magnetic core to shield electromagnetic interference; the double-layer shielding structure is arranged on the outside of the second power winding in the magnetic core, between the first power winding and the second power winding in the magnetic core, inside the first power winding in the magnetic core, or coated on the outer surface of the magnetic core; The double-layer shielding structure is arranged on the outside of the second power winding in the magnetic core. The wiring method is as follows: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved; The double-layer shielding structure is arranged between the first power winding and the second power winding in the magnetic core, and the wiring method is as follows: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point of the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the connection point of the second power winding and the circuit switch tube; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved; The double-layer shielding structure is arranged on the inner side of the first power winding in the magnetic core. The wiring method is as follows: the first metal shielding body close to the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body close to the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the connection point between the first power winding and the main circuit switch tube; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved; The wiring method of the double-layer shielding structure wrapped around the outer surface of the magnetic core is: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; the EMI characteristics of the switching power supply are improved by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies.

2. Application of a double-layer shielding structure in a transformer, characterized in that: The double-layer shielding structure comprises two metal shielding bodies arranged in parallel, a dielectric layer is arranged between the two metal shielding bodies, and the equivalent capacitance of the two metal shielding bodies is changed by changing the distance between the two metal shielding bodies, the dielectric constant of the dielectric layer and the facing area of ​​the two metal shielding bodies; The transformer comprises a magnetic core with a central column and three power windings, wherein a first power winding, a second power winding and a third power winding are sequentially arranged outward from the central column of the magnetic core, and when the first power winding and the third power winding are primary windings, the second power winding is a secondary winding, and when the first power winding and the third power winding are secondary windings, the second power winding is a primary winding; the double-layer shielding structure is arranged inside the magnetic core or coated on the outside of the magnetic core to shield electromagnetic interference; the double-layer shielding structure is arranged on the outside of the third power winding in the magnetic core, and between the first power winding and the second power winding and between the second power winding and the third power winding in the magnetic core, or coated on the outer surface of the magnetic core; The double-layer shielding structure is arranged on the outside of the third power winding in the magnetic core. The wiring method is as follows: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the third power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; or the first metal shielding body is connected to the connection point between the third power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved; The double-layer shielding structure is simultaneously arranged between the first power winding and the second power winding and between the second power winding and the third power winding in the magnetic core, and there are three wiring methods: 1) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body on the inside is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body on the outside is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; 2) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body is connected to the connection point between the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the second power winding, and the second metal shielding body is connected to the connection point between the third power winding and the circuit switch tube; 3) The double-layer shielding structure arranged between the first power winding and the second power winding is wired as follows: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the connection point between the second power winding and the circuit switch tube; the double-layer shielding structure arranged between the second power winding and the third power winding is wired as follows: the first metal shielding body is connected to the connection point between the second power winding and the circuit switch tube, and the second metal shielding body is connected to the connection point between the third power winding and the circuit switch tube; By adjusting the distance between the two metal shields, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shields, the EMI characteristics of the switching power supply can be improved. The wiring method of the double-layer shielding structure coated on the outer surface of the magnetic core is: the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; or the first metal shielding body is connected to the connection point of the third power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the first power winding; or the first metal shielding body is connected to the connection point of the first power winding and the circuit switch tube, and the second metal shielding body is connected to the positive or negative pole of the bus voltage corresponding to the third power winding; by adjusting the distance between the two metal shielding bodies, changing the dielectric constant of the dielectric layer, and changing the facing area of ​​the two metal shielding bodies, the EMI characteristics of the switching power supply are improved.

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