JP2017011876A - Switching power source and isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power source and an isolator that can reduce noise while performing miniaturization.SOLUTION: A switching power supply 100 includes a primary coil P1, a secondary coil S1, a primary circuit, a secondary circuit, a multilayer substrate 3, a primary ground conductor 4, and a secondary ground conductor 5. A primary coil P1 is formed on the multilayer substrate 3. The secondary coil S1 is formed on the multilayer substrate 3 and is magnetically coupled to the primary coil P1. The primary ground conductor 4 is formed on the multilayer substrate 3 and serves as a reference potential point of the primary circuit 1. The secondary ground conductor 5 is formed on the multilayer substrate 3 and serves as a reference potential point of the secondary circuit 2. The primary ground conductor 4 is capacitively coupled with the secondary ground conductor 5.SELECTED DRAWING: Figure 1

Description

  The present invention generally relates to a switching power supply and an isolator, and more particularly to a switching power supply and an isolator using a transformer formed on a multilayer substrate.

  Conventionally, a switching power supply using a transformer formed on a substrate is known. Such a switching power supply mounting structure is disclosed in, for example, Patent Document 1. The switching power supply described in Patent Document 1 includes a coil layer, a wiring layer, a shield layer, and a core. The coil layer is configured by stacking a plurality of flat coils having a spiral conductor pattern. A switching transistor, a switching control circuit, a rectifying diode, and the like are mounted on the wiring layer. The shield layer is provided between the coil layer and the wiring layer. The core constitutes a magnetic circuit for the coil layer.

JP-A-6-325949

  By the way, in the insulation type switching power supply as in the above-described conventional example, noise is generated due to the influence of the high frequency current flowing through the transformer and the parasitic capacitance between the primary coil and the secondary coil of the transformer. In the conventional example, when a component such as a capacitor is mounted in order to remove such noise, there is a problem that it is difficult to reduce the size in order to secure a space for mounting the component.

  The present invention has been made in view of the above points, and an object thereof is to reduce noise while reducing the size.

  The switching power supply according to the first aspect of the present invention includes a multilayer substrate, a primary coil formed on the multilayer substrate, a secondary coil formed on the multilayer substrate and magnetically coupled to the primary coil, and the primary A primary circuit having a switching element that is electrically connected to the coil and opens and closes a power feeding path from an external power source to the primary coil; and a rectifier that is electrically connected to the secondary coil and rectifies the output of the secondary coil A secondary circuit having a circuit, a primary ground conductor formed on the multilayer substrate and serving as a reference potential point of the primary circuit, and a secondary ground conductor formed on the multilayer substrate and serving as a reference potential point of the secondary circuit The primary ground conductor is capacitively coupled to the secondary ground conductor.

  A switching power supply according to a second aspect of the present invention further includes a floating conductor that is electrically insulated from both the primary ground conductor and the secondary ground conductor in the switching power supply according to the first aspect, and the floating conductor includes: In the thickness direction of the multilayer substrate, it is preferable that the multilayer substrate is disposed between the primary ground conductor and the secondary ground conductor.

  A switching power supply according to a third aspect of the present invention is the switching power supply according to the second aspect, wherein the multilayer substrate has at least one conductive layer between the primary ground conductor and the secondary ground conductor. The floating conductor is preferably formed on the conductor layer.

  A switching power supply according to a fourth aspect of the present invention is the switching power supply according to the third aspect, wherein a plurality of the conductor layers are provided across an insulating layer, and the floating conductor is formed on the plurality of conductor layers. Is preferred.

  The switching power supply according to a fifth aspect of the present invention is the switching power supply according to any one of the second to fourth aspects, wherein at least one of the primary ground conductor and the secondary ground conductor is formed in different layers. Preferably, the plurality of ground conductors are arranged, and the floating conductor is arranged with at least one of the plurality of ground conductors interposed therebetween.

  The switching power supply according to a sixth aspect of the present invention is the switching power supply according to any one of the second to fifth aspects, wherein the floating conductor is a conductor on which at least one of the primary coil and the secondary coil is formed. It is preferable to have a conductor of the same layer formed in the same layer as the layer, and the conductor of the same layer is disposed so as to surround the coil formed in the same layer as the conductor of the same layer.

  The switching power supply according to a seventh aspect of the present invention is the switching power supply according to any one of the first to sixth aspects, wherein at least one of the primary ground conductor and the secondary ground conductor is formed with the same coil. A ground conductor of the same layer formed in the same layer as the conductor layer, and the ground conductor of the same layer is disposed so as to surround the same-order coil formed in the same layer as the ground conductor of the same layer. It is preferable.

  The switching power supply according to an eighth aspect of the present invention is the switching power supply according to any one of the first to seventh aspects, wherein the primary ground conductor and the secondary ground conductor are electrons of the primary circuit and the secondary circuit, respectively. It is preferable to have a ground conductor formed on the same layer as the land to which the component is attached.

  The switching power supply according to a ninth aspect of the present invention is the switching power supply according to any one of the first to eighth aspects, wherein the multilayer substrate further includes a surface mounting terminal electrically connected to an external substrate. Is preferred.

  An isolator according to a tenth aspect of the present invention includes a switching power supply according to any one of the first to ninth aspects, an input signal input to the primary side, and an output output to the secondary side in accordance with the input signal. An insulation circuit that electrically insulates a signal; and a signal processing circuit that processes the input signal and the output signal, wherein the insulation circuit and the signal processing circuit are each provided in the multilayer substrate. To do.

  According to the present invention, a capacitor can be formed between the reference potential point of the primary circuit and the reference potential point of the secondary circuit by capacitively coupling the primary ground conductor and the secondary ground conductor formed on the multilayer substrate. it can. Therefore, according to the present invention, it is not necessary to secure a space for mounting a noise removing component, so that noise can be reduced while achieving miniaturization.

1 is a schematic cross-sectional view showing a switching power supply according to Embodiment 1. FIG. 1 is a schematic circuit diagram showing a switching power supply according to Embodiment 1. FIG. 3A to 3C are schematic plan views of an insulating layer formed above the core layer in the switching power supply according to the first embodiment. 4A to 4C are schematic plan views of an insulating layer formed below the core layer in the switching power supply according to the first embodiment. FIG. 5A is a schematic plan view showing the isolator according to the embodiment. FIG. 5B is a schematic cross-sectional view showing the isolator according to the embodiment. 6 is a schematic cross-sectional view showing a switching power supply according to Modification 1 of Embodiment 1. FIG. 6 is a schematic cross-sectional view showing a switching power supply according to Embodiment 2. FIG. 8A to 8C are schematic plan views of an insulating layer formed above the core layer in the switching power supply according to the second embodiment. 9A to 9C are schematic plan views of an insulating layer formed below the core layer in the switching power supply according to the second embodiment. 6 is a schematic cross-sectional view showing a switching power supply according to Modification 1 of Embodiment 2. FIG. FIG. 10 is a schematic cross-sectional view showing a switching power supply according to Modification 2 of Embodiment 2.

(Embodiment 1)
As shown in FIGS. 1 to 4C, the switching power supply 100 according to Embodiment 1 of the present invention includes a primary coil P1, a secondary coil S1, a primary circuit 1, a secondary circuit 2, a multilayer substrate 3, A primary ground conductor 4 and a secondary ground conductor 5 are provided. The primary coil P1 is formed on the multilayer substrate 3. The secondary coil S1 is formed on the multilayer substrate 3 and is magnetically coupled to the primary coil P1.

  The primary circuit 1 includes switching elements Q1 and Q2 that are electrically connected to the primary coil P1 and open and close a power feeding path from the external power source PS1 to the primary coil P1. The secondary circuit 2 includes a rectifier circuit 21 that is electrically connected to the secondary coil S1 and rectifies the output of the secondary coil S1.

  The primary ground conductor 4 is formed on the multilayer substrate 3 and serves as the reference potential point RP1 of the primary circuit 1. The secondary ground conductor 5 is formed on the multilayer substrate 3 and serves as the reference potential point RP2 of the secondary circuit 2. The primary ground conductor 4 is capacitively coupled to the secondary ground conductor 5.

  Further, the isolator 200 according to the embodiment of the present invention includes a switching power supply 100, an insulating circuit 7, and a signal processing circuit 6, as shown in FIGS. 5A and 5B. The insulation circuit 7 electrically insulates the input signal input to the primary side and the output signal output to the secondary side according to the input signal. The signal processing circuit 6 processes the input signal and the output signal. The insulating circuit 7 and the signal processing circuit 6 are each provided on the multilayer substrate 3.

<Configuration of switching power supply>
Hereinafter, the switching power supply 100 of this embodiment will be described. In the following description, the thickness direction of the multilayer substrate 3 is assumed to be the vertical direction, the primary coil P1 side as viewed from the secondary coil S1, and the secondary coil S1 side as viewed from the primary coil P1. That is, the upper and lower sides in FIG. Hereinafter, the width direction of the multilayer substrate 3 will be described as the left-right direction. That is, the left and right in FIG. The definition of these directions is not intended to limit the usage pattern of the switching power supply 100 of the present embodiment.

  The switching power supply 100 of this embodiment is a so-called half-bridge type DC / DC converter, and as shown in FIG. 2, a transformer including a primary coil P1 and a secondary coil S1, a primary circuit 1, and a secondary circuit 2 And.

  The primary circuit 1 is electrically connected to the primary coil P1. The primary circuit 1 includes two switching elements Q1 and Q2, a capacitor C1, and a control circuit 11. The switching element Q1 is a p-channel enhancement type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The switching element Q2 is an n-channel enhancement type MOSFET.

  The switching element Q1 has a drain electrically connected to the external power source PS1, which is a DC power source, a gate electrically connected to the control circuit 11, and a source electrically connected to the first end of both ends of the primary coil P1 via the capacitor C1. . The switching element Q2 has a drain electrically connected to the source of the switching element Q1, a gate electrically connected to the control circuit 11, and a source electrically connected to the reference potential point RP1 and the second end of both ends of the primary coil P1. Here, the reference potential point RP1 is the ground of the primary circuit 1.

  The switching elements Q1 and Q2 are turned on / off by a drive signal supplied from the control circuit 11, thereby opening and closing a power feeding path from the external power source PS1 to the primary coil P1. Switching elements Q1 and Q2 may be bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors).

  The capacitor C1 is electrically connected in series with the primary coil P1. The capacitor C1 forms a primary side resonance circuit together with the primary coil P1.

  The control circuit 11 is constituted by a microcomputer (microcomputer), for example. The control circuit 11 supplies a drive signal to each of the switching elements Q1 and Q2, thereby turning on / off the switching elements Q1 and Q2 and driving the primary coil P1.

  The secondary circuit 2 is electrically connected to the secondary coil S1. The secondary circuit 2 includes a rectifier circuit 21 and a low drop-out regulator (LDO) 22.

  The rectifier circuit 21 includes four diodes D1 to D4 that constitute a diode bridge, and a capacitor C2. The diodes D1 to D4 perform full-wave rectification on the voltage output from the secondary coil S1. Capacitor C2 smoothes the pulsating voltage output from diodes D1-D4. That is, the rectifier circuit 21 rectifies the output of the secondary coil S1. The output terminal on the low voltage side of the rectifier circuit 21 is electrically connected to the reference potential point RP2. Here, the reference potential point RP2 is the ground of the secondary circuit 2.

  The low-loss regulator 32 operates so that the difference between the voltage input from the input terminal (the voltage across the capacitor C2) and the voltage output from the output terminal becomes small.

  The switching power supply 100 according to the present embodiment outputs a voltage corresponding to the power supply voltage of the external power supply PS1 input to the primary side of the transformer to the secondary side of the transformer by driving the primary coil P1. Note that the switching power supply 100 of the present embodiment only needs to have a function of transmitting power from at least the primary side of the transformer. For example, bidirectional switching having a function of transmitting power also from the secondary side of the transformer It may be a power source.

  In the switching power supply 100 of this embodiment, the primary coil P1 and the secondary coil S1 are formed on the multilayer substrate 3 as shown in FIGS. 1, 3A to 3C, and 4A to 4C. Moreover, in the switching power supply 100 of this embodiment, the primary circuit 1 and the secondary circuit 2 are each arrange | positioned on the upper surface of the multilayer substrate 3 (after-mentioned insulating layer 311). Further, in the switching power supply 100 of the present embodiment, the primary ground conductor 4 that becomes the reference potential point RP1 of the primary circuit 1 is formed on the multilayer substrate 3. In addition, a secondary ground conductor 5 serving as a reference potential point RP <b> 2 of the secondary circuit 2 is formed on the multilayer substrate 3. The primary ground conductor 4 and the secondary ground conductor 5 are electrically insulated from each other.

  Further, the primary ground conductor 4 may be the same potential as the reference potential point RP1 of the primary circuit 1 and may not be included in the primary circuit 1. Similarly, the secondary ground conductor 5 may have the same potential as the reference potential point RP2 of the secondary circuit 2 and may not be included in the secondary circuit 2.

  3A to 3C are schematic plan views of insulating layers 311, 312, and 30, which will be described later, as viewed from above. Moreover, FIG. 4A-FIG. 4C show the schematic plan view which looked at each of the insulating layers 30,322,321 mentioned later from the downward direction, respectively. FIG. 1 is a sectional view taken along line XX in FIG. 3A. In FIG. 1, a conductor formed as a wiring on the upper surface of the insulating layer 311 is not shown.

  The multilayer substrate 3 is a printed circuit board based on, for example, FR4 (Flame Retardant Type 4). The multilayer substrate 3 is formed by stacking a plurality (here, five) of insulating layers 30, 311, 312, 321, 322. The insulating layers 30, 311, 312, 321, 322 are formed by, for example, prepreg. Specifically, the multilayer substrate 3 is formed by stacking insulating layers 312 and 311 on the insulating layer 30 as a core layer, and insulating layers 322 and 321 on the lower side. That is, the insulating layer 30 is located in the middle of the multilayer substrate 3 in the vertical direction.

  Vias H <b> 1 to H <b> 8 are provided at both left and right ends of the multilayer substrate 3. The vias H1, H3, and H4 are electrically connected to the primary circuit 1 via conductors formed as wirings on the upper surface of the insulating layer 311. The vias H5, H7, and H8 are electrically connected to the secondary circuit 2 through conductors formed on the upper surface of the insulating layer 311. The via H2 is electrically connected to the primary ground conductor 4, and the via H6 is electrically connected to the secondary ground conductor 5.

  The vias H1 to H8 are electrically connected to electrodes T1 to T8 formed on the lower surface of the insulating layer 321 (see FIG. 4C). These electrodes T1 to T8 are formed, for example, in a rectangular plate shape with copper (Cu) having a gold (Au) thin film formed on the surface thereof, and are used for bonding to lands provided on an external substrate.

  That is, in the switching power supply 100 of the present embodiment, the multilayer substrate 3 further includes surface mounting terminals (electrodes T1 to T8) that are electrically connected to the external substrate. For this reason, the switching power supply 100 according to the present embodiment can be surface-mounted on an external substrate, improving the reliability of electrical connection with the external substrate and improving the strength of the joint portion with the external substrate. be able to. Note that whether or not to adopt the configuration is arbitrary.

  The primary coil P1 is composed of a plurality (here, two) of coil conductors P11 and P12. The coil conductors P11 and P12 are formed on the upper surfaces of the insulating layers 312 and 30, respectively. The coil conductor P11 has a first end electrically connected to the primary circuit 1 via the via H9 and a second end electrically connected to the first end of the coil conductor P12 via the via H10. The second end of the coil conductor P12 is electrically connected to the primary circuit 1 via the via H11. That is, the primary coil P1 is configured by electrically connecting the coil conductors P11 and P12 in series.

  The secondary coil S1 is composed of a plurality (here, two) of coil conductors S11 and S12. The coil conductors S11 and S12 are formed on the lower surfaces of the insulating layers 322 and 30, respectively. The coil conductor S11 has a first end electrically connected to the secondary circuit 2 via the via H12 and a second end electrically connected to the first end of the coil conductor S12 via the via H13. The second end of the coil conductor S12 is electrically connected to the secondary circuit 2 via the via H14. That is, the secondary coil S1 is configured by electrically connecting the coil conductors S11 and S12 in series.

  These coil conductors P11, P12, S11, and S12 are each formed by winding a conductor such as a copper foil. In addition, the external shape of these coil conductors P11, P12, S11, and S12 is not limited to a rectangular shape as shown in FIG. 3B, and may be another shape such as a circular shape or a polygonal shape. Moreover, the primary coil P1 and the secondary coil S1 may each be comprised by one coil conductor, and may be comprised by the 3 or more coil conductor.

  The primary ground conductor 4 is composed of a plurality (here, two) of ground conductors 41 and 42. The ground conductors 41 and 42 are formed on the upper surfaces of the insulating layers 311 and 30, respectively. The ground conductors 41 and 42 are electrically connected to each other by a via H2 (see FIG. 1).

  As shown in FIG. 3A, the ground conductor 41 is formed in a region (a left region in FIG. 3A) where the primary circuit 1 is disposed with a center line in the width direction (left-right direction) of the insulating layer 311 as a boundary. . In addition, the ground conductor 41 is formed so as to cover substantially the entire surface of the region excluding the conductor formed as a wiring on the upper surface of the primary circuit 1 or the insulating layer 311. The ground conductor 42 is formed so as to cover substantially the entire upper surface of the insulating layer 30 except for the coil conductor P12 and the vias H9, H11, H12, and H14 (see FIG. 3C).

  The secondary ground conductor 5 is composed of a plurality (here, two) of ground conductors 51 and 52. The ground conductor 51 is formed on the upper surface of the insulating layer 311. The ground conductor 52 is formed on the lower surface of the insulating layer 30. The ground conductors 51 and 52 are electrically connected to each other by a via H6 (see FIG. 1).

  As shown in FIG. 3A, the ground conductor 51 is formed in a region (the right region in FIG. 3A) where the secondary circuit 2 is disposed, with the center line in the width direction (left-right direction) of the insulating layer 311 as a boundary. Yes. The ground conductor 51 is formed so as to cover substantially the entire surface of the region excluding the conductor formed as a wiring on the upper surface of the secondary circuit 2 or the insulating layer 311. The ground conductor 52 is formed so as to cover substantially the entire lower surface of the insulating layer 30 except for the coil conductor S12 and the vias H9, H11, H12, and H14 (see FIG. 4A).

  Each of the primary ground conductor 4 and the secondary ground conductor 5 may be composed of one ground conductor, or may be composed of three or more ground conductors.

<About noise>
Here, in the switching power supply 100 of the present embodiment, high frequency noise may be generated by driving the primary coil P1 with a high frequency current. This high-frequency noise becomes common mode noise that flows to the secondary side (secondary circuit 2 side) via parasitic capacitances CP1 and CP2 (see FIG. 2) formed between the primary coil P1 and the secondary coil S1. . The common mode noise is transmitted to, for example, a metal case that houses the switching power supply 100 of the present embodiment, and may flow out to the outside.

  Common mode noise can generally be reduced by separately providing components such as a choke coil and a chip capacitor. However, in a switching power supply that requires a reduction in size, it is difficult to secure a space for mounting such a noise removing component, and an increase in size is inevitable when attempting to mount.

  Therefore, in the switching power supply 100 of the present embodiment, the primary ground conductor 4 (ground conductor 42) and the secondary ground conductor 5 (ground conductor 52) are capacitively coupled. Specifically, as shown in FIG. 1, the ground conductor 42 of the primary ground conductor 4 and the ground conductor 52 of the secondary ground conductor 5 are arranged in the insulating layer 30 in the thickness direction (vertical direction) of the multilayer substrate 3. Are formed so as to face each other. For this reason, in the switching power supply 100 of this embodiment, between the reference potential point RP1 of the primary circuit 1 (the ground of the primary circuit 1) and the reference potential point RP2 of the secondary circuit 2 (the ground of the secondary circuit 2). A capacitor C3 is formed (see FIGS. 1 and 2).

  In the switching power supply 100 of this embodiment, the capacitor C3 can form a path (that is, a return path) for returning the common mode noise to the primary side (primary circuit 1 side). Thus, in the switching power supply 100 of the present embodiment, the return path is formed by the capacitor C3, so that it is difficult for the common mode noise to flow out, that is, the noise can be reduced.

  As described above, in the switching power supply 100 according to the present embodiment, it is not necessary to separately provide a noise removing component, so that noise (common mode noise) can be reduced while reducing the size.

  In the switching power supply 100 of the present embodiment, the primary ground conductor 4 is composed of a plurality of ground conductors 41 and 42, thereby reducing the impedance of the primary ground conductor 4 and reducing more effective noise (common mode noise). We are trying to reduce it. The secondary ground conductor 5 is also composed of a plurality of ground conductors 51 and 52, thereby achieving more effective noise reduction. Note that whether or not to adopt the configuration is arbitrary.

  By the way, although it is conceivable to form a capacitor between the high voltage side potential point of the primary circuit 1 and the high voltage side potential point of the secondary circuit 2, the ground of the primary circuit 1 and the ground of the secondary circuit 2 are considered. It is preferable to form a capacitor C3 between the two. That is, the high-frequency noise described above is also generated due to a relative fluctuation between the ground potential of the primary circuit 1 and the ground potential of the secondary circuit 2, so that the ground of the primary circuit 1 and the ground of the secondary circuit 2 The method of capacitive coupling between the two is straightforward and effective.

  In the switching power supply 100 of the present embodiment, the ground conductor 42 of the primary ground conductor 4 is formed on the upper surface of the insulating layer 30 so as to surround the coil conductor P12 of the primary coil P1 (see FIG. 3C). Similarly, the ground conductor 52 of the secondary ground conductor 5 is formed on the lower surface of the insulating layer 30 so as to surround the coil conductor S12 of the secondary coil S1 (see FIG. 4A). That is, at least one of the primary ground conductor 4 and the secondary ground conductor 5 is connected to the ground conductors 42 and 52 (in the same layer) formed in the same layer as the conductor layer in which the homogeneous coils (coil conductors P12 and S12) are formed. A ground conductor). The ground conductors 42 and 52 (ground conductors in the same layer) surround the same-order coils (coil conductors P12 and S12) formed in the same layer as the ground conductors 42 and 52 (ground conductors in the same layer). Has been placed.

  Here, the conductor layer refers to a layer formed of a conductor such as metal on the upper surface (or lower surface) of the insulating layer (for example, the insulating layer 30). This conductor layer is provided in a plane direction substantially perpendicular to the thickness direction (vertical direction) of the multilayer substrate 3. That is, in the multilayer substrate 3, the insulating layers and the conductor layers are alternately arranged along the thickness direction.

  In this configuration, the ground conductors 42 and 52 function as electromagnetic shields. That is, an eddy current flows through the ground conductors 42 and 52 due to the magnetic flux generated by the primary coil P1 and the secondary coil S1. And the magnetic flux which generate | occur | produces by this eddy current mutually cancels with the magnetic flux which primary coil P1 and secondary coil S1 generate | occur | produce, and the noise radiated | emitted outside is shielded. Note that whether or not to adopt the configuration is arbitrary.

  Here, in the switching power supply 100 of the present embodiment, a part of the ground conductor 42 is notched and has a gap G1. Thus, by providing the gap G1 in the ground conductor 42, the impedance of the path through which the eddy current flows is increased, thereby reducing the loss due to the eddy current. Similarly to the ground conductor 42, the ground conductor 52 has a gap G2, thereby reducing loss due to eddy current. Note that whether or not to adopt the configuration is arbitrary.

  In the switching power supply 100 of the present embodiment, the ground conductor 41 of the primary ground conductor 4 and the ground conductor 51 of the secondary ground conductor 5 are formed on the upper surface of the same insulating layer 311 (see FIG. 3A). In addition to the ground conductors 41 and 51, the land to which the electronic component constituting the primary circuit 1 is attached and the land to which the electronic component constituting the secondary circuit 2 is attached are formed on the upper surface of the same insulating layer 311. Yes. That is, the primary ground conductor 4 and the secondary ground conductor 5 have ground conductors 41 and 51 formed on the same layer as the land to which the electronic components of the primary circuit 1 and the secondary circuit 2 are attached, respectively.

  In this configuration, the ground conductor 41 of the primary ground conductor 4, the ground conductor 51 of the secondary ground conductor 5, the land of the primary circuit 1, and the land of the secondary circuit 2 can be arranged on the same layer. Therefore, this configuration has an advantage that mounting of electronic components and processing of the multilayer substrate 3 are facilitated. Note that whether or not to adopt the configuration is arbitrary.

<Configuration of isolator>
Next, the isolator 200 of this embodiment will be described. As shown in FIGS. 5A and 5B, the isolator 200 of the present embodiment includes a switching power supply 100 (in FIG. 5A and FIG. 5B, the reference numerals are omitted), a signal processing circuit 6, and an insulating circuit 7. ing. Further, in the isolator 200 of this embodiment, the switching power supply 100, the signal processing circuit 6, and the insulating circuit 7 are each mounted on the multilayer substrate 3. The insulating circuit 7 may be formed on the surface (for example, the upper surface) of the multilayer substrate 3 or may be provided inside the multilayer substrate 3.

  The signal processing circuit 6 is composed of a first processing circuit 61 on the primary side and a second processing circuit 62 on the secondary side. The first processing circuit 61 processes an input signal input to each of the three input terminals 611 to 613 and outputs the processed signal to the insulating circuit 7. Here, the input signal is a digital signal. The input terminals 611 to 613 are lands formed on the multilayer substrate 3 respectively. In the isolator 200 of the present embodiment, the primary circuit 1 is included in the signal processing circuit 6 (first processing circuit 61) as shown by the broken line in FIG. 5A, but other configurations may be used. That is, the primary circuit 1 and the signal processing circuit 6 may be configured separately.

  The second processing circuit 62 processes a signal transmitted from the first processing circuit 61 via the insulating circuit 7 and outputs it as an output signal to each of the three output terminals 621 to 623. The output signals output to each of these output terminals 621 to 623 correspond one-to-one with the input signals input to each of the input terminals 611 to 613. Here, the output signal is a digital signal. The output terminals 621 to 623 are lands formed on the multilayer substrate 3 respectively. In the isolator 200 of the present embodiment, the secondary circuit 2 is included in the signal processing circuit 6 (second processing circuit 62) as shown by the broken line in FIG. 5A, but other configurations may be used. . That is, the secondary circuit 2 and the signal processing circuit 6 may be configured separately. The second processing circuit 62 may be configured to be supplied with operating power from an external power supply, but may be configured to be directly supplied with operating power as output power of the secondary coil S1, for example.

  The insulation circuit 7 is configured to electrically insulate the input signal input to the primary side from the output signal output to the secondary side in response to the input signal. The insulating circuit 7 is configured to electrically insulate the primary side and the secondary side by magnetic coupling using, for example, a microcoil formed by a semiconductor process. Further, the insulating circuit 7 may be configured to electrically insulate the primary side and the secondary side by, for example, capacitive coupling using a capacitor. In addition, the insulating circuit 7 may be configured to electrically insulate the primary side and the secondary side by optical coupling using, for example, a photocoupler.

  In the isolator 200 of this embodiment, the upper surface of the multilayer substrate 3 is covered with a sealing material 201 made of a resin material such as an epoxy resin, as shown in FIG. 5B. The sealing material 201 protects circuits such as the primary circuit 1 and the insulating circuit 7, and electrically insulates the primary circuit and the secondary circuit mounted on the upper surface of the multilayer substrate 3 from each other. Is provided.

  The isolator 200 according to the present embodiment includes a communication isolator composed of a signal processing circuit 6 and an insulating circuit 7 and a switching power supply 100 having a power transmission transformer (primary coil P1 and secondary coil S1). It is configured integrally with the substrate 3. Therefore, the isolator 200 of the present embodiment can be configured in a small size while including the switching power supply 100 having a function of reducing noise.

  The isolator 200 according to the present embodiment is configured to output an input signal that is a digital signal to an electrically isolated secondary side, but may have other configurations. For example, the isolator 200 of this embodiment may be configured to output an input signal that is an analog signal to an electrically isolated secondary side.

<Modification 1>
Hereinafter, the switching power supply 100 of the modification 1 of Embodiment 1 is demonstrated. However, since the basic configuration of the switching power supply 100 of the present modification is common to the switching power supply 100 of the first embodiment, common portions are denoted by the same reference numerals and description thereof is omitted.

  In the switching power supply 100 of this modification, as shown in FIG. 6, the multilayer substrate 3 includes the insulating layer 30 as a core layer, the insulating layers 313, 312, 311 above the insulating layer 30, and the insulating layers 323, 322, 321 below. It is formed by stacking. Further, in the switching power supply 100 of this modification, the ground conductor 51 of the secondary ground conductor 5 is formed on the lower surface of the insulating layer 321. Furthermore, in the switching power supply 100 of this modification, the primary coil P1 is comprised by the four coil conductors P11-P14. Similarly, the secondary coil S1 is composed of four coil conductors S11 to S14.

  The coil conductors P11 to P14 are respectively formed on the upper surfaces of the insulating layers 311, 312, 313 and 30. The primary coil P1 is configured by electrically connecting coil conductors P11 to P14 in series by a plurality of vias. The coil conductors S11 to S14 are formed on the lower surfaces of the insulating layers 321, 322, 323, and 30, respectively. The secondary coil S1 is configured by electrically connecting the coil conductors S11 to S14 in series by a plurality of vias.

  Also in the switching power supply 100 of the present modification example, the ground conductor 42 and the ground conductor 52 sandwich the insulating layer 30 in the thickness direction (vertical direction) of the multilayer substrate 3 as in the switching power supply 100 of the first embodiment. Are formed to face each other. Therefore, also in the switching power supply 100 of this modification, by forming the capacitor C3 between the ground of the primary circuit 1 and the ground of the secondary circuit 2, noise (common mode noise) is reduced while achieving miniaturization. can do.

(Embodiment 2)
Hereinafter, the switching power supply 100 according to Embodiment 2 of the present invention will be described. However, the basic configuration of the switching power supply 100 of the present embodiment is common to the switching power supply 100 of the first embodiment.

  As shown in FIGS. 7, 8A to 8C, and 9A to 9C, the switching power supply 100 according to the present embodiment is a floating conductor that is electrically insulated from both the primary ground conductor 4 and the secondary ground conductor 5. 8 is further provided. In the switching power supply 100 of the present embodiment, the ground conductor 42 of the primary ground conductor 4 is formed on the upper surface of the insulating layer 312. The ground conductor 52 of the secondary ground conductor 5 is formed on the lower surface of the insulating layer 322.

  8A to 8C are schematic plan views of the insulating layers 311, 312, and 30 as viewed from above. 9A to 9C are schematic plan views of the insulating layers 30, 322, and 321 viewed from below, respectively. FIG. 7 is a sectional view taken along line XX in FIG. 8A. In FIG. 7, illustration of a conductor formed as a wiring on the upper surface of the insulating layer 311 is omitted.

  The floating conductor 8 is composed of a plurality (here, two) of floating conductors 81 and 82. The floating conductor 81 is formed on the upper surface of the insulating layer 30. The floating conductor 82 is formed on the lower surface of the insulating layer 30. The floating conductors 81 and 82 are electrically connected to each other by a plurality of vias 9 (see FIG. 7). Further, the floating conductors 81 and 82 are not electrically connected to the primary ground conductor 4 and the secondary ground conductor 5. Note that the floating conductors 81 and 82 are not electrically connected to the primary coil P1 and the secondary coil S1.

  As shown in FIG. 7, the floating conductor 8 is disposed between the primary ground conductor 4 and the secondary ground conductor 5 in the thickness direction (vertical direction) of the multilayer substrate 3. In particular, in the switching power supply 100 of the present embodiment, the multilayer substrate 3 has at least one conductor layer between the primary ground conductor 4 and the secondary ground conductor 5, and the floating conductor 8 is the conductor. Formed in layers.

  The floating conductor 8 is formed in the same layer as the conductor layer on which the coil conductors P11 and P12 of the primary coil P1 or the coil conductors S11 and S12 of the secondary coil S1 are formed. Of course, the floating conductor 8 may be formed in a conductor layer different from the conductor layer in which the primary coil P1 or the secondary coil S1 is formed.

  In the switching power supply 100 of the present embodiment, between the primary ground conductor 4 and the secondary ground conductor 5, there are two conductor layers, a layer in which the coil conductor P12 is formed and a layer in which the coil conductor S12 is formed. Is provided. The floating conductor 81 is formed in the same layer as the conductor layer where the coil conductor P12 is formed, and the floating conductor 82 is formed in the same layer as the conductor layer where the coil conductor S12 is formed.

  In the switching power supply 100 of the present embodiment, the capacitor C3 formed between the primary ground conductor 4 and the secondary ground conductor 5 includes a capacitor C31 and a capacitor C32 as shown in FIG. The capacitor C31 is formed between the primary ground conductor 4 (ground conductor 42) and the floating conductor 8 (floating conductor 81). The capacitor C32 is formed between the secondary ground conductor 5 (ground conductor 52) and the floating conductor 8 (floating conductor 82). Therefore, in the switching power supply 100 of the present embodiment, by providing the floating conductor 8, the capacitance value of the capacitor C3 can be increased as compared with the switching power supply 100 of the first embodiment. For this reason, in the switching power supply 100 of this embodiment, compared with the switching power supply 100 of Embodiment 1, it is possible to further reduce noise (common mode noise).

  In the switching power supply 100 of the present embodiment, a plurality of conductor layers are provided with the insulating layer 30 interposed therebetween. The floating conductor 8 is formed in a plurality of conductor layers. Here, as described above, the plurality of conductor layers are two layers of the conductor layer in which the coil conductor P12 is formed and the conductor layer in which the coil conductor S12 is formed.

  For this reason, in the switching power supply 100 of the present embodiment, by appropriately adjusting the thickness dimension (vertical dimension) of the insulating layer (for example, the insulating layers 30, 312, and 322), The capacitance value of the capacitor C3 can be easily changed. Note that whether or not to adopt the configuration is arbitrary.

  In the switching power supply 100 of the present embodiment, the floating conductor 81 is formed on the upper surface of the insulating layer 30 so as to surround the coil conductor P12 of the primary coil P1 (see FIG. 8C). Similarly, the floating conductor 82 is formed on the lower surface of the insulating layer 30 so as to surround the coil conductor S12 of the secondary coil S1 (see FIG. 9A). That is, the floating conductor 8 has floating conductors 81 and 82 (conductors in the same layer) formed in the same layer as the conductor layer in which at least one of the primary coil P1 and the secondary coil S1 is formed. The floating conductors 81 and 82 (conductors in the same layer) are arranged so as to surround coils (coil conductors P12 and S12) formed in the same layer as the floating conductors 81 and 82 (conductors in the same layer).

  In this configuration, the floating conductors 81 and 82 function as electromagnetic shields in the same manner as the ground conductors 42 and 52 in the switching power supply 100 of the first embodiment. Note that whether or not to adopt the configuration is arbitrary. Further, in the switching power supply 100 of the present embodiment, the floating conductors 81 and 82 are partially cut away to have gaps G3 and G4. For this reason, in the switching power supply 100 of this embodiment, the loss by an eddy current can be reduced similarly to the gaps G1 and G2 in the switching power supply 100 of the first embodiment. Note that whether or not to adopt the configuration is arbitrary.

<Modification 1>
Hereinafter, the switching power supply 100 of the modification 1 of Embodiment 2 is demonstrated. However, since the basic configuration of the switching power supply 100 of this modification is common to the switching power supply 100 of the second embodiment, common portions are denoted by the same reference numerals and description thereof is omitted.

  In the switching power supply 100 of this modification, as shown in FIG. 10, the multilayer substrate 3 has an insulating layer 30 as a core layer, insulating layers 313, 312, 311 above it and insulating layers 323, 322, 321 below. It is formed by stacking. Moreover, in the switching power supply 100 of this modification, the primary ground conductor 4 is comprised by the three ground conductors 41-43. The secondary ground conductor 5 is composed of three ground conductors 51 to 53. Further, the primary coil P1 is composed of four coil conductors P11 to P14. Similarly, the secondary coil S1 is composed of four coil conductors S11 to S14.

  The ground conductors 41 to 43 are formed on the upper surfaces of the insulating layers 311, 312, and 313, respectively. The ground conductors 51 to 53 are formed on the lower surfaces of the insulating layers 321, 322 and 323, respectively. The coil conductors P11 to P14 are respectively formed on the upper surfaces of the insulating layers 311, 312, 313 and 30. The primary coil P1 is configured by electrically connecting coil conductors P11 to P14 in series by a plurality of vias. The coil conductors S11 to S14 are formed on the lower surfaces of the insulating layers 321, 322, 323, and 30, respectively. The secondary coil S1 is configured by electrically connecting the coil conductors S11 to S14 in series by a plurality of vias.

  In the switching power supply 100 of the present modification, the capacitor C31 is formed between the primary ground conductor 4 (ground conductor 43) and the floating conductor 8 (floating conductor 81). The capacitor C32 is formed between the secondary ground conductor 5 (ground conductor 53) and the floating conductor 8 (floating conductor 82).

  Similarly to the switching power supply 100 of the first embodiment, the switching power supply 100 of the present modification also includes the floating conductor 8 to increase the capacitance value of the capacitor C3 compared to the switching power supply 100 of the first embodiment. Can do. For this reason, in the switching power supply 100 of this modification, it is possible to further reduce noise (common mode noise) compared to the switching power supply 100 of the first embodiment.

<Modification 2>
Hereinafter, the switching power supply 100 of the modification 2 of Embodiment 2 is demonstrated. However, since the basic configuration of the switching power supply 100 of this modification is common to that of the switching power supply 100 of Modification 1 of Embodiment 2, the same reference numerals are given to common parts and description thereof is omitted.

  In the switching power supply 100 of this modification, as shown in FIG. 11, the primary ground conductor 4 is composed of two ground conductors 41 and 42. The secondary ground conductor 5 is composed of two ground conductors 51 and 52. The floating conductor 8 includes four floating conductors 81 to 84.

  The ground conductors 41 and 42 are formed on the upper surfaces of the insulating layers 311 and 313, respectively. The ground conductors 51 and 52 are formed on the upper surfaces of the insulating layers 321 and 323, respectively. The floating conductor 83 is formed on the upper surface of the insulating layer 312. The floating conductor 84 is formed on the lower surface of the insulating layer 322. The floating conductors 81 to 84 are electrically connected to each other by a plurality of vias 9.

  In the switching power supply 100 of this modification, the capacitor C31 is formed between the ground conductor 41 and the floating conductor 83, between the ground conductor 42 and the floating conductor 83, and between the ground conductor 42 and the floating conductor 81, respectively. Is done. The capacitor C32 is formed between the ground conductor 51 and the floating conductor 84, between the ground conductor 52 and the floating conductor 84, and between the ground conductor 52 and the floating conductor 82. That is, at least one of the primary ground conductor 4 and the secondary ground conductor 5 is composed of a plurality of ground conductors 41, 42, 51, 52 formed in different layers. The floating conductors 81 and 83 (floating conductors 82 and 84) are arranged with at least one ground conductor 42 (ground conductor 52) among the plurality of ground conductors 41 and 42 (ground conductors 51 and 52) interposed therebetween. .

  Therefore, in the switching power supply 100 of this modification, the capacitance value of the capacitor C3 can be further increased as compared with the switching power supply 100 of the second embodiment. For this reason, in the switching power supply 100 of this modification, it is possible to further reduce noise (common mode noise) compared to the switching power supply 100 of the second embodiment.

  As described above, the switching power supply 100 according to the first embodiment of the present invention and the modification 1 thereof, the switching power supply 100 according to the second embodiment and the modifications 1 and 2 and the isolator 200 according to the embodiment of the present invention have been described in detail. However, the configuration described above is merely an example of the present invention, and the present invention is not limited to each of the above-described embodiments, and the technical idea according to the present invention is not limited to these embodiments. Various changes can be made according to the design or the like as long as they do not deviate. For example, the multilayer substrate 3 may be formed by stacking insulating layers only on one side in the thickness direction of the insulating layer 30 (core layer).

DESCRIPTION OF SYMBOLS 1 Primary circuit 2 Secondary circuit 21 Rectifier circuit 3 Multilayer substrate 30,311-313,321-323 Insulation layer 4 Primary ground conductor 41-43 Ground conductor 5 Secondary ground conductor 51-53 Ground conductor 6 Signal processing circuit 7 Insulation circuit 8, 81-84 Floating conductor 100 Switching power supply 200 Isolator P1 Primary coil P11-P14 Coil conductor PS1 External power supply Q1, Q2 Switching element RP1, RP2 Reference potential point S1 Secondary coil S11-S14 Coil conductor T1-T8 Electrode (terminal)

Claims (10)

A multilayer substrate;
A primary coil formed on the multilayer substrate;
A secondary coil formed on the multilayer substrate and magnetically coupled to the primary coil;
A primary circuit electrically connected to the primary coil and having a switching element that opens and closes a power feeding path from an external power source to the primary coil;
A secondary circuit electrically connected to the secondary coil and having a rectifier circuit for rectifying the output of the secondary coil;
A primary ground conductor formed on the multilayer substrate and serving as a reference potential point for the primary circuit;
A secondary ground conductor formed on the multilayer substrate and serving as a reference potential point for the secondary circuit;
The switching power supply, wherein the primary ground conductor is capacitively coupled to the secondary ground conductor. A floating conductor that is electrically insulated from both the primary ground conductor and the secondary ground conductor;
The switching power supply according to claim 1, wherein the floating conductor is disposed between the primary ground conductor and the secondary ground conductor in a thickness direction of the multilayer substrate. The multilayer substrate has at least one conductor layer between the primary ground conductor and the secondary ground conductor,
The switching power supply according to claim 2, wherein the floating conductor is formed in the conductor layer. A plurality of the conductor layers are provided across an insulating layer,
The switching power supply according to claim 3, wherein the floating conductor is formed in the plurality of conductor layers. At least one of the primary ground conductor and the secondary ground conductor is constituted by a plurality of ground conductors respectively formed in different layers,
The switching power supply according to any one of claims 2 to 4, wherein the floating conductor is disposed with at least one of the plurality of ground conductors interposed therebetween. The floating conductor has a conductor in the same layer formed in the same layer as a conductor layer in which at least one of the primary coil and the secondary coil is formed,
The switching power supply according to any one of claims 2 to 5, wherein the conductor of the same layer is disposed so as to surround the coil formed in the same layer as the conductor of the same layer. At least one of the primary ground conductor and the secondary ground conductor has a ground conductor in the same layer formed in the same layer as the conductor layer in which the homogeneous coil is formed,
The ground conductor of the same layer is disposed so as to surround the same-order coil formed in the same layer as the ground conductor of the same layer. Switching power supply.   The said primary ground conductor and the said secondary ground conductor have a ground conductor formed in the same layer as the land to which the electronic component of the said primary circuit and the said secondary circuit is each attached, The 1st thru | or 7 characterized by the above-mentioned. The switching power supply according to any one of the above.   The switching power supply according to any one of claims 1 to 8, wherein the multilayer board further includes a surface mounting terminal electrically connected to an external board. The switching power supply according to any one of claims 1 to 9,
An insulating circuit that electrically insulates an input signal input to the primary side and an output signal output to the secondary side according to the input signal;
A signal processing circuit for processing the input signal and the output signal;
The isolator, wherein the insulating circuit and the signal processing circuit are provided on the multilayer substrate, respectively.

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