High-voltage transformer

Abstract

A high-voltage transformer 8 comprises a first isolation transformer 81, a second isolation transformer 82, and a wiring board 83 including a coil formed by a wiring pattern. The wiring board 83 has openings (a first opening 83a and a second opening 83b) for inserting a part of a first core 84 and a part of a second core 85 therethrough. The edges of the openings are respectively spaced apart from a part of the first core 84 and a part of the second core 85. The coil 834 is wound around the part of the first core 84 and the part of the second core 85 and thereby forms a secondary winding 81b of the first isolation transformer 81 and a primary winding 82a of the second isolation transformer 82, which are electrically connected to each other.

Description

High Voltage Transformer

[0001] The present disclosure relates to high voltage transformers.

[0002] In high-voltage power supplies that generate high voltages of the order of several hundred kilovolts, high-voltage transformers are used to transmit signals from the low-voltage side to the high-voltage side (see, for example, Patent Document 1). Because a large potential difference occurs between the primary and secondary sides of a high-voltage transformer, the high-voltage transformer is required to have sufficient dielectric strength. The technology described in Patent Document 1 distributes the voltage applied to each transformer by connecting multiple small transformers in series (cascade connection).

[0003] Japanese Patent Application Laid-Open No. 2004-281170

[0004] High-voltage transformers are often required to be compact in addition to having sufficient dielectric strength. To ensure sufficient dielectric strength in a high-voltage transformer, it is possible to isolate the primary or secondary winding from the core, but this increases the diameter of the winding and the overall dimensions of the high-voltage transformer. When multiple high-voltage transformers are connected in series, the impact of increasing the size of each transformer becomes even more pronounced.

[0005] An object of the present disclosure is to provide a high-voltage transformer that is both compact and has a high dielectric strength voltage.

[0006] A high-voltage transformer according to one aspect of the present disclosure is [1] "a high-voltage transformer comprising: a first isolated transformer including a first primary winding, a first secondary winding, and a first core; and a second isolated transformer including a second primary winding, a second secondary winding, and a second core, wherein the first isolated transformer and the second isolated transformer have a common wiring substrate including a coil formed by a wiring pattern, the wiring substrate has an opening for inserting a part of the first core and a part of the second core, the edge of the opening is spaced apart from the part of the first core and the part of the second core, and the coil is wound around the part of the first core and the part of the second core, thereby constituting the first secondary winding and the second primary winding that are electrically connected to each other."

[0007] In the high-voltage transformer described in [1] above, the first secondary winding and the second primary winding are electrically connected to each other, so that the first isolation transformer and the second isolation transformer are connected in tandem. This allows for a smaller potential difference between the primary and secondary sides of each isolation transformer than, for example, when only one isolation transformer is provided. Furthermore, the coil included in the wiring board has a portion constituting the first secondary winding and a portion constituting the second primary winding, and the edges of the opening in the wiring board through which the first core and the second core are inserted are separated from the first core and the second core. This makes it less likely for discharge to occur than, for example, when the first secondary winding and the second primary winding are formed by winding independent conductors. In addition, because the first secondary winding and the second primary winding are formed by coils included in a common wiring board, miniaturization can be achieved. As described above, the high-voltage transformer described above achieves both a small size and a high dielectric strength voltage.

[0008] A high-voltage transformer according to one aspect of the present disclosure may be [2] "the high-voltage transformer according to [1], wherein the wiring board has a plurality of wiring layers each having the wiring pattern surrounding the portion of the first core and the portion of the second core, a resin layer provided between each of the plurality of wiring layers, and an interlayer connector connecting the wiring patterns of adjacent wiring layers among the plurality of wiring layers to each other." In this case, the wiring board including the coil can be easily formed using multilayer printed circuit board technology.

[0009] A high-voltage transformer according to one aspect of the present disclosure may be [3] "the high-voltage transformer according to [1] or [2], wherein at least a portion of the edge of the opening of the wiring board has an arc-shaped shape when viewed in the thickness direction of the wiring board." In this case, a sudden change in the distance between the edge of the opening of the wiring board and the first and second cores is suppressed, thereby suppressing a local increase in electric field strength, and thus further increasing the dielectric strength.

[0010] A high-voltage transformer according to one aspect of the present disclosure may be [4] "the high-voltage transformer according to any one of [1] to [3], wherein the opening of the wiring board includes a first opening and a second opening, the coil includes a portion wound along the edge of the first opening and a portion wound along the edge of the second opening, the portion of the first core passing through the first opening, and the portion of the second core passing through the second opening." In this case, of the coil of the wiring board, the portion wound along the edge of the first opening functions as a first secondary winding, and the portion wound along the edge of the second opening functions as a second primary winding. This allows the second primary winding and the first secondary winding to be arranged separately, allowing the primary winding and the secondary winding to be configured efficiently. For example, energy can be transmitted from the first secondary winding to the second primary winding more efficiently than when the coils are wound collectively along the edges of the first opening and the second opening.

[0011] A high-voltage transformer according to one aspect of the present disclosure may be [5] "the high-voltage transformer according to any one of [1] to [4], wherein the opening includes a first opening, the portion of the first core and the portion of the second core are inserted through the first opening, and the wiring board is not present between the first core and the second core." In this case, the absence of a wiring board between the first core and the second core makes it possible to reduce the distance between the first core and the second core and thereby achieve miniaturization while ensuring a dielectric strength voltage.

[0012] A high-voltage transformer according to one aspect of the present disclosure may be the high-voltage transformer according to any one of [1] to [5], wherein [6] "each of the first core and the second core includes a pair of legs extending in one direction, a first pillar portion connecting the pair of legs at one end of the pair of legs, and a second pillar portion connecting the pair of legs at the other end of the pair of legs, the portion of the first core being included in one of the pair of legs of the first core, and the portion of the second core being included in one of the pair of legs of the second core." In this case, by using a core including a pair of legs extending in one direction, it is easier to maintain a uniform gap between the core and the wiring board compared to, for example, using an annular core, and this makes it possible to suppress uneven distribution of electric field strength and further increase the dielectric strength.

[0013] A high-voltage transformer according to one aspect of the present disclosure may be [7] "the high-voltage transformer according to any one of [1] to [6]," further including: a first opposing electrode in contact with the first core and disposed opposite the wiring board; and a second opposing electrode in contact with the second core and disposed opposite the wiring board." In this case, the potential of the first opposing electrode is the same as the potential of the first core (typically the potential of the first primary winding), and the potential of the second opposing electrode is the same as the potential of the second core (typically the potential of the second secondary winding). Floating capacitances exist between the second opposing electrode and the wiring board, and between the first opposing electrode and the wiring board. Because the voltage between the second secondary winding and the first primary winding is divided by the respective stray capacitances, the potential difference between the second secondary winding and the wiring board and the potential difference between the first primary winding and the wiring board can be stably maintained, thereby further increasing the dielectric strength.

[0014] A high-voltage transformer according to one aspect of the present disclosure may be [8] "the high-voltage transformer according to [7], wherein each of the first opposing electrode and the second opposing electrode has an opposing portion opposing the wiring board and a contact portion connected to the opposing portion and in contact with the first core and the second core, respectively, and wherein at least a portion of the outer edge of the wiring board has an arc-shaped shape, and the opposing portion, when viewed in the thickness direction of the wiring board, has a circular shape including an outer edge that follows the arc described by the outer edge of the wiring board." In this case, the circular shape of the opposing portion can prevent electric field concentration at the outer edge of the opposing portion, thereby further increasing the dielectric strength voltage.

[0015] A high-voltage transformer according to one aspect of the present disclosure may be [9] "the high-voltage transformer according to [8], wherein the facing portion includes a through hole that overlaps with the opening when viewed in the thickness direction of the wiring substrate." In this case, by including the through hole in the facing portion, it is possible to prevent stray capacitance from being generated by elements other than the wiring substrate in the portion facing the opening.

[0016] A high-voltage transformer according to one aspect of the present disclosure may be

[10] "the high-voltage transformer according to [7], wherein each of the first opposing electrode and the second opposing electrode has an opposing portion opposing the wiring board and a contact portion connected to the opposing portion and in contact with the first core and the second core, respectively; at least a portion of an outer edge of the wiring board has an arc-shaped shape; and the opposing portion, when viewed in the thickness direction of the wiring board, has an arc-shaped shape including an outer edge that follows the arc of the outer edge of the wiring board." In this case, since the opposing portion, when viewed in the thickness direction of the wiring board, has an arc-shaped shape including an outer edge that follows the arc of the outer edge of the wiring board, it is easier to adjust the distance between the first opposing electrode and the second opposing electrode than when the opposing portion is circular. This makes it possible to realize a high-voltage transformer with a high breakdown voltage and a small size by, for example, bringing the first opposing electrode and the second opposing electrode as close as possible while maintaining a distance that makes it difficult for discharge to occur between them.

[0017] A high-voltage transformer according to one aspect of the present disclosure may be

[11] "the high-voltage transformer according to any one of [1] to

[10] , wherein, in a cross section of the wiring board, corners of the wiring board are rounded." In this case, by rounding the corners of the wiring board, it is possible to suppress concentration of an electric field at the corners, thereby further increasing the dielectric strength voltage.

[0018] A high-voltage transformer according to one aspect of the present disclosure may be

[12] "the high-voltage transformer according to any one of [1] to

[11] , further comprising a third isolation transformer including a third primary winding, a third secondary winding, and a third core, wherein the second isolation transformer and the third isolation transformer have a common second wiring board including a second coil formed by a wiring pattern, the second wiring board has a second opening for inserting another part of the second core and a part of the third core, an edge of the second opening is spaced apart from the other part of the second core and the part of the third core, and the second coil is wound around the other part of the second core and the part of the third core, thereby constituting the second secondary winding and the third primary winding that are electrically connected to each other." In this case, since the first isolation transformer and the second isolation transformer are connected in tandem and the second secondary winding and the third primary winding are electrically connected to each other, the second isolation transformer and the third isolation transformer are connected in series via the coil on the wiring board. This further reduces the potential difference between the primary and secondary sides of each isolation transformer. Furthermore, the coil included in the wiring board has a portion that constitutes the second secondary winding and a portion that constitutes the third primary winding, and the edges of the opening in the wiring board through which the second core and the third core are inserted are separated from the second core and the third core. This makes it less likely for discharge to occur than, for example, when the second secondary winding and the third primary winding are formed by winding independent conductors. In addition, since the second secondary winding and the third primary winding are formed by the coil included in a common wiring board, it is possible to achieve a compact design.

[0019] According to the present disclosure, it is possible to provide a high-voltage transformer that is both compact and has a high dielectric strength voltage.

[0020] 1 is a circuit diagram showing a high-voltage power supply including a high-voltage transformer according to an embodiment of the present disclosure. FIG. 1 is a perspective view of the high-voltage transformer shown in FIG. 1. FIG. 2 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 3 is a diagram for explaining the shape of each layer of a coil in the wiring board shown in FIG. 2. FIG. 4 is a diagram for explaining two forms of the wiring layer shown in FIG. 3. FIG. 5 is a view of the first opposing electrode shown in FIG. 2 from the side facing the wiring board. FIG. 6 is a view of the second opposing electrode shown in FIG. 2 from the side facing the wiring board. FIG. 7 is an equivalent circuit of the high-voltage transformer shown in FIG. 2. FIG. 8 is an example of analysis of the potentials of the second opposing electrode, wiring board, and first opposing electrode shown in FIG. 2. FIG. 9 is a view of a high-voltage transformer according to a first modified example. FIG. 10 is a view of high-voltage transformers according to second and third modified examples. FIG. 11 is an equivalent circuit of the high-voltage transformer shown in FIG. 11. FIG. 12 is a view of opposing portions according to fourth and fifth modified examples. FIG. 13 is a view of a high-voltage transformer according to a comparative example. FIG. 14 is a cross-sectional view of the high-voltage transformer according to the first modified example. FIG. 15 is a view of a high-voltage transformer according to an embodiment of the present disclosure. FIG. 16 is a cross-sectional view of the wiring board cut along the YZ plane including the center of the wiring board of the high-voltage transformer according to the embodiment.

[0021] Hereinafter, a preferred embodiment of a high-voltage transformer according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0022] 1 is a circuit diagram showing a high-voltage power supply 1 including a high-voltage transformer according to one embodiment of the present disclosure. The high-voltage power supply 1 is applicable to devices that use an input voltage of several hundred volts, such as X-ray tubes and electron beam irradiation devices. In this embodiment, the high-voltage power supply 1 is described as being applied to an X-ray tube. The high-voltage power supply 1 includes an AC input unit 2, a first inverter 3, an output transformer 4, a Cockcroft-Walton circuit 5, a detection circuit 6, a second inverter 7, a high-voltage transformer 8, and a rectifier circuit 9. The load RL is assumed to be an X-ray tube.

[0023] The AC input unit 2 is a functional unit that converts an AC voltage generated in the AC power supply AP into a DC voltage. The AC input unit 2 is, for example, a switching type AC / DC converter.

[0024] The first inverter 3, output transformer 4, Cockcroft-Walton circuit 5, and detection circuit 6 constitute a circuit for generating a voltage to be supplied to the cathode electrode of the X-ray tube (load RL). The first inverter 3 is a functional unit that converts the DC voltage generated by the AC input unit 2 into an AC voltage. The first inverter 3 is a bridge circuit composed of multiple transistors, such as a half-bridge circuit in which the source terminal of a high-side FET and the drain terminal of a low-side FET are connected to each other. The output transformer 4 is a functional unit that boosts the AC voltage generated by the first inverter 3 in accordance with the turn ratio of the primary winding and the secondary winding. The Cockcroft-Walton circuit 5 is a functional unit that boosts and rectifies the AC voltage output from the output transformer 4 to generate a DC voltage. The Cockcroft-Walton circuit 5 boosts and rectifies the AC voltage output from the output transformer 4 to several hundred kilovolts and supplies it to the load RL. The detection circuit 6 is a functional unit that detects the DC voltage generated by the Cockcroft-Walton circuit 5. The detection circuit 6 is, for example, a circuit in which multiple high-voltage resistance resistors are connected in series with each other, and divides the DC voltage generated by the Cockcroft-Walton circuit 5 and feeds it back to the first inverter 3.

[0025] The second inverter 7, high-voltage transformer 8, and rectifier circuit 9 constitute a circuit for generating a current to be supplied to the cathode electrode of the X-ray tube (load RL). The second inverter 7 is a functional unit that converts the DC voltage generated by the AC input unit 2 into an AC voltage. The second inverter 7 is a bridge circuit formed by multiple transistors. The second inverter 7 drives the transistors at a drive frequency different from that of the first inverter 3, for example.

[0026] The high-voltage transformer 8 is a functional unit that transmits the AC voltage generated in the second inverter 7 to the load RL. The high-voltage transformer 8 does not boost the AC voltage according to a turns ratio, but functions as a power transmission transformer such as a pulse transformer. The high-voltage transformer 8 includes a first isolation transformer 81 and a second isolation transformer 82. The first isolation transformer 81 and the second isolation transformer 82 are connected in series. Specifically, the secondary winding 81b of the first isolation transformer 81 is connected to the primary winding 82a of the second isolation transformer 82. The primary winding 81a of the first isolation transformer 81 is connected to the output terminal of the second inverter 7. The secondary winding 82b of the second isolation transformer 82 is connected to the rectifier circuit 9. Furthermore, the secondary winding 82b of the second isolation transformer 82 is connected to the output of the Cockcroft-Walton circuit 5. As a result, a high voltage of several hundred kilovolts is applied to the secondary winding 82b of the second isolation transformer 82.

[0027] The rectifier circuit 9 is a functional unit that converts AC voltage into DC voltage and supplies the DC voltage to the filament of the X-ray tube (load RL). The rectifier circuit 9 includes a rectifier diode unit 9A and a smoothing capacitor 9B. The rectifier diode unit 9A is composed of, for example, four bridge-connected diodes. The AC voltage supplied from the high-voltage transformer 8 is rectified by the rectifier diode unit 9A and smoothed by the smoothing capacitor 9B, thereby being converted into DC voltage.

[0028] 2 is a perspective view of high-voltage transformer 8. High-voltage transformer 8 has a wiring board 83, a first core 84, a second core 85, a first opposing electrode 86, and a second opposing electrode 87. For ease of explanation, the thickness direction of wiring board 83 is defined as the Z-axis direction, the direction perpendicular to the Z-axis direction is defined as the Y-axis direction, and the direction perpendicular to the Z-axis and Y-axis directions is defined as the X-axis direction.

[0029] The wiring substrate 83 has a main body portion 831, a first fixing portion 832, and a second fixing portion 833. When viewed from the Z-axis direction, the main body portion 831 has an elliptical shape with its major axis extending in the Y-axis direction and its minor axis extending in the X-axis direction. The main body portion 831 includes openings (a first opening 83a and a second opening 83b). In this embodiment, the openings are composed of the first opening 83a and the second opening 83b. The first opening 83a and the second opening 83b are symmetrical with respect to a line A1 that passes through the center 83c of the main body portion 831 and is parallel to the X-axis direction. The first opening 83a and the second opening 83b penetrate the wiring substrate 83 in the Z-axis direction. When viewed from the Z-axis direction, the first opening 83a and the second opening 83b have a perfect circular shape. In other words, the shape of at least a part of the edges of the first opening 83 a and the second opening 83 b is arc-shaped when viewed from the Z-axis direction. The diameter of the first opening 83 a is equal to the diameter of the second opening 83 b. The wiring substrate 83 has a front surface 83 e and a back surface 83 f opposite to the front surface 83 e.

[0030] When viewed from the Z-axis direction, the first fixing portion 832 protrudes in the X-axis direction from the edge of the main body 831 on the first opening 83a side. When viewed from the Z-axis direction, the second fixing portion 833 protrudes in the X-axis direction from the edge of the main body 831 on the second opening 83b side, opposite to the first fixing portion 832.

[0031] The wiring board 83 further includes a wiring pattern. The wiring pattern is layered from the front surface 83e through the interior of the wiring board 83 to near the back surface 83f. The wiring pattern forms a coil 834. In other words, the wiring board 83 further includes a coil 834 formed by a wiring pattern. When viewed from the Z-axis direction, the top layer of the coil 834 is formed on the front surface 83e, from the first fixing portion 832 to the second fixing portion 833, along the outer edge of the main body portion 831. The top layer of the coil 834 is formed in an arc between the outer edge of the main body portion 831 and the edge of the first opening 83a. As will be described in detail later, a portion of the coil 834 formed by the wiring pattern forms the secondary winding 81b of the first isolation transformer 81, and another portion of the coil 834 formed by the wiring pattern forms the primary winding 82a of the second isolation transformer 82. In other words, the first isolation transformer 81 and the second isolation transformer 82 have a common wiring board 83 including a coil 834 formed by a wiring pattern.

[0032] The top layer of coil 834 is formed exposed on surface 83e. When high-voltage transformer 8 is used impregnated with insulating oil, heat dissipation can be improved. Alternatively, the surface of the top layer of coil 834 may be covered with, for example, a film-like resin. When high-voltage transformer 8 is used in a resin-molded state, oxidation of coil 834 can be suppressed.

[0033] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a diagram illustrating the shape of each layer of the coil 834 in the wiring board 83. The wiring board 83 further includes a plurality of wiring layers 836, resin layers 835 provided between each of the plurality of wiring layers 836, and interlayer connectors (first interlayer connectors 837 and second interlayer connectors 838) that connect the wiring patterns of adjacent wiring layers among the plurality of wiring layers 836. The coil 834 is formed by winding the plurality of wiring layers 836 along the Z-axis direction. As shown in FIG. 3, in the cross-section of the wiring board 83, corners E1 of the wiring board 83 are rounded.

[0034] 4A shows the state in which the wiring layer 836 is wound on the surface 83e. The interlayer connection portion includes a first interlayer connection portion 837 and a second interlayer connection portion 838. The first interlayer connection portion 837 is provided along the X-axis direction between the first opening 83a and the first fixing portion 832. The second interlayer connection portion 838 is provided along the X-axis direction between the second opening 83b and the second fixing portion 833. The first interlayer connection portion 837 and the second interlayer connection portion 838 include a plurality of vias aligned along the Y-axis direction. The wiring layer 836 is wound on the surface 83e from one of the plurality of vias in the first interlayer connection portion 837 to one of the plurality of vias in the second interlayer connection portion 838.

[0035] 4B shows the state in which the wiring layer 836 (first wiring layer 836) wound on the surface 83e and the adjacent wiring layer 836 (second wiring layer 836) are wound. The wiring layer 836 includes a portion wound along the edge of the first opening 83a and a portion wound along the edge of the second opening 83b. First, the portion wound along the edge of the second opening 83b will be described. The second wiring layer 836 is connected to the first wiring layer 836 at one of the vias in the second interlayer connection portion 838. The second wiring layer 836 is wound along the edge of the second opening 83b toward one of the vias in the second interlayer connection portion 838. 4(c) shows how the second wiring layer 836 and the adjacent wiring layer 836 (third wiring layer 836) are wound. The third wiring layer 836 is connected to the second wiring layer 836 through one of the multiple vias in the second interlayer connection portion 838. As shown in FIGS. 4(a) to 4(c), when the wiring layer on the front surface 83e side in the Z-axis direction is the upper layer and the wiring layer on the back surface 83f side is the lower layer, the upper layer and the next lower layer are connected through the multiple vias in the second interlayer connection portion 838. A similar winding structure is repeated for the fourth layer and subsequent layers.

[0036] Fig. 4(d) shows how the wiring layer 836 is wound in the layer two layers above the bottom layer. Fig. 4(e) shows how the wiring layer 836 is wound in the layer one layer above the bottom layer. Fig. 4(f) shows how the wiring layer 836 is wound in the bottom layer. In the bottom layer, the wiring layer 836 is wound from one of the vias in the second interlayer connection portion 838 to one of the vias in the first interlayer connection portion 837.

[0037] Next, the portion wound along the edge of the first opening 83a will be described. As shown in (e) of Figure 4, the wiring layer 836 in the upper layer one layer above the bottom layer is connected to the wiring layer 836 in the lowermost layer at one of the vias in the first interlayer connection portion 837. The wiring layer 836 in the upper layer one layer above the bottom layer is wound along the edge of the first opening 83a toward one of the vias in the first interlayer connection portion 837. Thereafter, as shown in (d) to (a) of Figure 4, the wiring layer 836 is wound toward the upper layer along the edge of the first opening 83a.

[0038] 3, the resin layer 835 is provided between adjacent wiring layers 836. Inside the wiring substrate 83, the wiring layers 836 and the resin layers 835 are formed so as to be alternately stacked along the Z-axis direction. The resin layer 835 is, for example, an epoxy resin. Because epoxy resin has electrical insulating properties, it functions as an insulating layer between each layer of the wiring layers 836. Instead of the epoxy resin, a glass cloth may be used, or a combination of epoxy resin and glass cloth may be used.

[0039] 5A and 5B are diagrams illustrating two forms of wiring layers. FIG. 5A illustrates the cross-sectional shapes of multiple wiring layers 836 according to the embodiment. Each wiring layer 836 is composed of a single wire. Each wiring layer 836 is formed by winding a wire having an elongated cross section whose longitudinal direction is along the surface 83e around the Z-axis direction. FIG. 5B illustrates the cross-sectional shapes of multiple wiring layers 836A according to another example. Each wiring layer 836A is formed by winding a wire divided into multiple pieces along the surface 83e around the Z-axis direction. The multiple wires constituting each wiring layer 836A have a smaller cross-sectional area than the wires of the wiring layer 836.

[0040] Referring again to FIG. 2 , the first core 84 and the second core 85 have a closed loop shape. In the example of FIG. 2 , the first core 84 and the second core 85 are UU-shaped ferrite cores. The first core 84 includes a pair of legs 84d, 84c extending in the Z-axis direction, a first pillar portion 84a connecting the legs 84d and 84c at one end thereof, and a second pillar portion 84b connecting the legs 84d and 84c at the other end thereof. The first pillar portion 84a and the second pillar portion 84b have an elongated shape with the Y-axis direction as the longitudinal direction.

[0041] The second core 85 includes a pair of legs 85d, 85c extending in the Z-axis direction, a first pillar 85a connecting the legs 85d and 85c at one end thereof, and a second pillar 85b connecting the legs 85d and 85c at the other end thereof. The first pillar 85a and the second pillar 85b have an elongated shape with the Y-axis direction as the longitudinal direction. The first core 84 and the second core 85 are aligned along the Y-axis direction. The position of the first core 84 in the X-axis direction coincides with the position of the second core 85 in the X-axis direction.

[0042] A portion of the leg 84d of the first core 84 is inserted through the first opening 83a. In other words, the portion of the first core 84 that passes through the first opening 83a (a portion of the first core 84) is included in the leg 84d. The leg 84d is spaced from the edge of the first opening 83a. In other words, the leg 84d does not contact the edge of the first opening 83a. The leg 84d, for example, passes through the center of the first opening 83a. In this case, the distance between the leg 84d and the edge of the first opening 83a is uniform along the circumferential direction of the first opening 83a. The primary winding 81a (first primary winding) of the first isolation transformer 81 is wound around the leg 84c of the first core 84. In the example shown in FIG. 2, insulating paper is wrapped around the leg 84c, and the primary winding 81a is wound around the insulating paper.

[0043] A portion of the leg 85d of the second core 85 is inserted through the second opening 83b. In other words, the portion of the second core 85 that is inserted through the second opening 83b (a portion of the second core 85) is included in the leg 85d. The leg 85d is spaced from the edge of the second opening 83b. In other words, the leg 85d does not contact the edge of the second opening 83b. The leg 85d, for example, passes through the center of the second opening 83b. In this case, the distance between the leg 85d and the edge of the second opening 83b is uniform along the circumferential direction of the second opening 83b. The secondary winding 82b (second secondary winding) of the second isolation transformer 82 is wound around the leg 85c. In the example shown in FIG. 2, insulating paper is wrapped around the leg 85c, and the secondary winding 82b is wound around the insulating paper.

[0044] The portion of the coil 834 wound along the edge of the first opening 83a is wound around the leg 84d of the first core 84 and forms the secondary winding 81b (first secondary winding) of the first isolation transformer 81. The portion of the coil 834 wound along the edge of the second opening 83b is wound around the leg 85d of the second core 85 and forms the primary winding 82a (second primary winding) of the second isolation transformer 82. On the surface 83e, the top layer of the coil 834 electrically connects the first interlayer connector 837 and the second interlayer connector 838. As a result, the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are electrically connected to each other.

[0045] Here, we will explain how AC current is transmitted by the high-voltage transformer 8. First, an AC voltage is applied to the primary winding 81a of the first isolation transformer 81, causing an AC current to flow through the primary winding 81a of the first isolation transformer 81. This generates magnetic flux in the leg 84c of the first core 84. The generated magnetic flux interlinks the portion of the coil 834 wound along the edge of the first opening 83a (the secondary winding 81b of the first isolation transformer 81), generating an electromotive force in the secondary winding 81b of the first isolation transformer 81. Next, an AC current generated by the electromotive force generated in the secondary winding 81b of the first isolation transformer 81 flows through the portion of the coil 834 inside the wiring board 83 and then flows through the portion of the coil 834 wound along the edge of the second opening 83b (the primary winding 82a of the second isolation transformer 82). This generates magnetic flux in the leg 85d of the second core 85. The generated magnetic flux interlinks with the secondary winding 82b of the second isolation transformer 82, generating an electromotive force in the secondary winding 82b of the second isolation transformer 82, causing an AC current to flow. In this way, the high-voltage transformer 8 transmits an AC current from the primary winding 81a of the first isolation transformer 81 to the secondary winding 82b of the second isolation transformer 82.

[0046] The first opposing electrode 86 and the second opposing electrode 87 are disposed opposite to the wiring substrate 83. The first opposing electrode 86 is in contact with the first core 84. The second opposing electrode 87 is in contact with the second core 85.

[0047] FIG. 6 is a view of the first opposing electrode 86 as viewed from the side facing the wiring substrate 83. The first opposing electrode 86 has an opposing portion 861 and a contact portion 862. The first opposing electrode 86 has an opposing surface 86a facing the wiring substrate 83. The opposing surface 86a may be coated with, for example, a film-like resin to prevent oxidation. The opposing portion 861 has a circular shape including an outer edge that follows the arc of the outer edge of the wiring substrate 83. The opposing portion 861 includes a third opening 86b (through hole). The third opening 86b has a perfect circular shape. The third opening 86b overlaps with the first opening 83a when viewed from the Z-axis direction. The third opening 86b includes an edge that follows the arc of the edge of the first opening 83a. The diameter of the third opening 86b may be the same as the diameter of the first opening 83a. The contact portion 862 is connected to the facing portion 861 so as to intersect with the facing portion 861 along the Y-axis direction. The area of ​​the contact portion 862 is the same as the area of ​​the upper end surface of the first pillar portion 84a of the first core 84.

[0048] The first opposing electrode 86 is formed on a first support portion 860. The first support portion 860 includes a third fixing portion 863. As shown in FIG. 2, the third fixing portion 863 is connected to the first fixing portion 832 of the wiring substrate 83 by a spacer SP, thereby supporting the wiring substrate 83. The contact portion 862 of the first opposing electrode 86 is in contact with the upper end surface of the first columnar portion 84a of the first core 84. Here, the length of the spacer SP is half the length of the legs 84d and 84c of the first core 84. As a result, the distance between the surface 83e of the wiring substrate 83 and the upper end surface of the first columnar portion 84a is equal to the distance between the back surface 83f of the wiring substrate 83 and the lower end surface of the second columnar portion 84b.

[0049] FIG. 7 is a view of the second opposing electrode 87 as viewed from the side facing the wiring substrate 83. The second opposing electrode 87 has an opposing portion 871 and a contact portion 872. The second opposing electrode 87 has an opposing surface 87a facing the wiring substrate 83. The opposing surface 87a may be coated with, for example, a film-like resin to prevent oxidation. The opposing portion 871 has a circular shape including an outer edge that follows the arc of the outer edge of the wiring substrate 83. The opposing portion 871 includes a third opening 87b (through hole). The third opening 87b has a perfect circular shape. The third opening 87b overlaps with the second opening 83b when viewed from the Z-axis direction. The third opening 87b includes an edge that follows the arc of the edge of the second opening 83b. The diameter of the third opening 87b may be the same as the diameter of the second opening 83b. The contact portion 872 is connected to the opposing portion 871 so as to intersect with the opposing portion 871 along the Y-axis direction. The area of ​​the contact portion 872 is the same as the area of ​​the lower end surface of the second pillar portion 85b of the second core 85.

[0050] The second opposing electrode 87 is formed on a second support portion 870. The second support portion 870 includes a fourth fixing portion 873. As shown in FIG. 2, the fourth fixing portion 873 is connected to the second fixing portion 833 of the wiring substrate 83 by a spacer SP, thereby supporting the wiring substrate 83. The contact portion 872 of the second opposing electrode 87 is in contact with the lower end surface of the second column portion 84b of the second core 85. Here, the length of the spacer SP is half the length of the legs 85d and 85c of the second core 85. As a result, the distance between the surface 83e of the wiring substrate 83 and the upper end surface of the first column portion 85a is equal to the distance between the back surface 83f of the wiring substrate 83 and the lower end surface of the second column portion 85b.

[0051] 8 shows an equivalent circuit of the high-voltage transformer 8. Because the first opposing electrode 86 is in contact with the first pillar portion 84a of the first core 84, the potential of the first opposing electrode 86 can typically be the same as the potential of the primary winding 81a of the first isolation transformer 81. The potential of the primary winding 81a of the first isolation transformer 81 is the potential of the AC voltage generated in the second inverter 7. On the other hand, because the second opposing electrode 87 is in contact with the second pillar portion 85b of the second core 85, the potential of the second opposing electrode 87 can typically be the same as the potential of the secondary winding 82b of the second isolation transformer 82. The potential of the secondary winding 82b of the second isolation transformer 82 is the potential of the DC voltage generated in the Cockcroft-Walton circuit 5, which is a high-voltage potential of several hundred kilovolts.

[0052] A first stray capacitance Cf1 exists between the first opposing electrode 86 and the wiring board 83. The first stray capacitance Cf1 constitutes stray capacitance between the primary winding 81a and the secondary winding 81b of the first isolation transformer 81. The magnitude of the first stray capacitance Cf1 is proportional to the surface area of ​​the first opposing electrode 86 and the surface area of ​​the portion of the wiring board 83 that faces the first opposing electrode 86. A second stray capacitance Cf2 exists between the second opposing electrode 87 and the wiring board 83. The second stray capacitance Cf2 constitutes stray capacitance between the primary winding 82a and the secondary winding 82b of the second isolation transformer 82. The magnitude of the second stray capacitance Cf2 is proportional to the surface area of ​​the second opposing electrode 87 and to the surface area of ​​the portion of the wiring board 83 that faces the second opposing electrode 87. The voltage between the secondary winding 82b of the second isolation transformer 82 and the primary winding 81a of the first isolation transformer 81 is divided by the first stray capacitance Cf1 and the second stray capacitance Cf2. This divides the voltages applied to the first isolation transformer 81 and the second isolation transformer 82. As a result, the potential near the wiring board 83 becomes intermediate between the potential near the second opposing electrode 87 and the potential near the first opposing electrode 86.

[0053] FIG. 9 shows an example of an analysis of the potentials of the second opposing electrode 87, the wiring board 83, and the first opposing electrode 86. In FIG. 9, the horizontal axis represents the position in the X-axis direction, and the vertical axis represents the position in the Z-axis direction. In FIG. 9, lighter colors represent higher potentials, and darker colors represent lower potentials. As shown in FIG. 9, the potential near the second opposing electrode 87 is highest, and the potential near the first opposing electrode 86 is lowest. It can be seen that the potential near the wiring board 83 is intermediate between the potential near the second opposing electrode 87 and the potential near the first opposing electrode 86. This indicates that the voltage between the secondary winding 82b of the second isolation transformer 82 and the primary winding 81a of the first isolation transformer 81 is divided by the first stray capacitance Cf1 and the second stray capacitance Cf2. [Operation and Effects]

[0054] In the high-voltage transformer 8, the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are electrically connected to each other, so that the first isolation transformer 81 and the second isolation transformer 82 are connected in tandem. This allows for a smaller potential difference between the primary and secondary sides of each isolation transformer than, for example, when only one isolation transformer is provided. Furthermore, the coil 834 included in the wiring board 83 has a portion that constitutes the secondary winding 81b of the first isolation transformer 81 and a portion that constitutes the primary winding 82a of the second isolation transformer 82. The edges of the openings (first opening 83a and second opening 83b) of the wiring board 83 through which the first core 84 and the second core 85 are inserted are separated from the first core 84 and the second core 85. This makes it less likely for discharge to occur than, for example, when the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are formed by winding independent conductors. In addition, the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are configured by the coil 834 included in the common wiring board 83, which contributes to miniaturization. As described above, the high-voltage transformer 8 can achieve both a small size and a high dielectric strength voltage.

[0055] In the high-voltage transformer 8, the coil 834 included in the wiring board 83 has a portion that constitutes the secondary winding 81b of the first isolation transformer 81 and a portion that constitutes the primary winding 82a of the second isolation transformer 82. In other words, the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are embedded in the wiring board 83. This eliminates unevenness between the wiring, and suppresses electric field concentration on the unevenness, compared to when, for example, the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are configured with wiring wound around a core material. In addition, when the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 are configured with wiring wound around a core material, variations in the winding finish, such as wiring spacing and wiring density, can occur. In contrast, the high-voltage transformer 8 prevents variations in the winding finish. Furthermore, the secondary winding 81b of the first isolation transformer 81 and the primary winding 82a of the second isolation transformer 82 may be configured with wires wound around a core material and buried in resin. In this case, too, unevenness between the wires is eliminated, and electric field concentration on the unevenness can be suppressed.

[0056] The wiring board 83 has a plurality of wiring layers 836 each having a wiring pattern surrounding a part of the first core 84 and a part of the second core 85, a resin layer 835 provided between each of the plurality of wiring layers 836, and a first interlayer connector 837 and a second interlayer connector 838 that connect the wiring patterns of adjacent wiring layers 836 to each other among the plurality of wiring layers 836. In this case, the wiring board 83 including the coil 834 can be easily formed using multilayer printed circuit board technology.

[0057] When viewed in the thickness direction (Z-axis direction) of the wiring board 83, at least a part of the edge of the openings (first opening 83 a and second opening 83 b) of the wiring board 83 has an arc shape. In this case, a sudden change in the distance between the edge of the opening of the wiring board 83 and the first core 84 and the second core 85 is suppressed, and a local increase in electric field strength is suppressed, thereby further increasing the dielectric strength.

[0058] The opening of the wiring board 83 includes a first opening 83a and a second opening 83b. The coil 834 includes a portion wound along the edge of the first opening 83a and a portion wound along the edge of the second opening 83b. A portion of the first core 84 passes through the first opening 83a, and a portion of the second core 85 passes through the second opening 83b. In this case, the portion of the coil 834 of the wiring board 83 wound along the edge of the first opening 83a functions as the secondary winding 81b of the first isolation transformer 81, and the portion wound along the edge of the second opening 83b functions as the primary winding 82a of the second isolation transformer 82. This allows the primary winding 82a of the second isolation transformer 82 and the secondary winding 81b of the first isolation transformer 81 to be arranged separately, thereby efficiently configuring the primary winding 82a and the secondary winding 81b. For example, compared to when the coil 834 is wound collectively along the edge of the first opening 83a and the edge of the second opening 83b, energy can be transmitted more efficiently from the secondary winding 81b of the first isolation transformer 81 to the primary winding 82a of the second isolation transformer 82, and in addition, magnetic flux leakage can be made less likely.

[0059] The first core 84 includes one leg 84d and the other leg 84c of a pair of legs 84d, 84c extending in the Z-axis direction, a first pillar 84a connecting the legs 84d and 84c to each other at one end of the legs 84d and 84c, and a second pillar 84b connecting the legs 84d and 84c to each other at the other end of the legs 84d and 84c. The second core 85 includes one leg 85d and the other leg 85c of a pair of legs 85d, 85c extending in the Z-axis direction, a first pillar 85a connecting the legs 85d and 85c to each other at one end of the legs 85d and 85c, and a second pillar 85b connecting the legs 85d and 85c to each other at the other end of the legs 85d and 85c. A portion of the first core 84 is included in a leg portion 84d of the first core 84, and a portion of the second core 85 is included in a leg portion 85d of the second core 85. In this case, by using the first core 84 and the second core 85, it becomes easier to maintain a uniform gap between the first core 84 and the second core 85 and the wiring board 83 compared to, for example, when an annular core is used, and it is possible to suppress bias in the electric field strength and further increase the dielectric strength voltage.

[0060] The high-voltage transformer 8 further includes a first opposing electrode 86 in contact with the first core 84 and disposed opposite the wiring board 83, and a second opposing electrode 87 in contact with the second core 85 and disposed opposite the wiring board 83. In this case, the potential of the first opposing electrode 86 is the same as the potential of the first core 84 (typically the potential of the primary winding 81 a of the first isolation transformer 81), and the potential of the second opposing electrode 87 is the same as the potential of the second core 85 (typically the potential of the secondary winding 82 b of the second isolation transformer 82). A first stray capacitance Cf1 and a second stray capacitance Cf2 exist between the second opposing electrode 87 and the wiring board 83, and between the first opposing electrode 86 and the wiring board 83, respectively. Because the voltage between the secondary winding 82b of the second isolation transformer 82 and the primary winding 81a of the first isolation transformer 81 is divided by the first stray capacitance Cf1 and the second stray capacitance Cf2, it is possible to stably maintain the potential difference between the secondary winding 82b of the second isolation transformer 82 and the wiring board 83, and the potential difference between the primary winding 81a of the first isolation transformer 81 and the wiring board 83. This makes it possible to further increase the dielectric strength voltage.

[0061] In order to regulate the potential of the wiring board 83, it is conceivable to supply a voltage to the wiring board 83 from another power source, for example. In that case, it is necessary to provide connection terminals on the wiring board 83, and there is a risk that an electric field will concentrate at such connection terminals, causing discharge. In contrast, the high-voltage transformer 8 is provided with a first opposing electrode 86 and a second opposing electrode, so that the intermediate potential of the wiring board 83 can be regulated in a non-contact manner. This makes it possible to prevent an electric field from concentrating at the connection terminals provided on the wiring board 83.

[0062] Each of the first opposing electrode 86 and the second opposing electrode 87 has an opposing portion 861 opposing the wiring substrate 83 and a contact portion 862 connected to the opposing portion 861 and in contact with the first core 84 and the second core 85, respectively. At least a portion of the outer edge of the wiring substrate 83 has an arc shape, and the opposing portion 861, when viewed in the thickness direction of the wiring substrate 83, has a circular shape including an outer edge that follows the arc described by the outer edge of the wiring substrate 83. In this case, the circular shape of the opposing portion 861 can prevent electric field concentration at the outer edge of the opposing portion 861, thereby further increasing the dielectric strength voltage.

[0063] The facing portion 861 includes a through hole (third opening 86b) that overlaps with the first opening 83a when viewed in the thickness direction of the wiring substrate 83. In this case, by including the third opening 86b in the facing portion 861, it is possible to prevent stray capacitance from being formed by elements other than the wiring substrate 83 in the portion facing the first opening 83a.

[0064] The facing portion 871 includes a through hole (third opening 87b) that overlaps with the second opening 83b when viewed in the thickness direction of the wiring substrate 83. In this case, by including the third opening 87b in the facing portion 871, it is possible to prevent stray capacitance from being formed by elements other than the wiring substrate 83 in the portion facing the second opening 83b.

[0065] In the cross section of the wiring board 83, the corner E1 of the wiring board 83 is rounded. In this case, it is possible to prevent the electric field from concentrating at the corner E1, and therefore it is possible to further increase the dielectric strength. [First Modification]

[0066] FIG. 10 is a diagram showing a high-voltage transformer 8A according to a first modification. Only differences from the high-voltage transformer 8 according to the embodiment will be described. When viewed from the Z-axis direction, the main body 831A has an elliptical shape with its major axis extending in the Y-axis direction and its minor axis extending in the X-axis direction. Instead of the first opening 83a and the second opening 83b, the main body 831A has a single opening 83g (first opening). When viewed from the Z-axis direction, both ends of the opening 83g in the Y-axis direction have an elliptical shape with its major axis extending in the Y-axis direction and its minor axis extending in the X-axis direction. When viewed from the Z-axis direction, a portion of the edge of the opening 83g is arc-shaped. The width between the outer edge of the main body 831A and the edge of the opening 83g is constant along the circumferential direction of the main body 831A.

[0067] One leg 84d of the pair of legs 84d, 84c of the first core 84 and one leg 85d of the pair of legs 85d, 85c of the second core 85 both pass through the opening 83g. There is no area of ​​the wiring board 83A between the legs 84d and 85d. The leg 85d of the second core 85 is provided with a first gap d1 from the leg 84d of the first core 84. The leg 84d of the first core 84 is provided with a second gap d2 from the edge of the opening 83g. The leg 85d of the second core 85 is provided with a second gap d2 from the edge of the opening 83g opposite the edge on the first core 84 side. In other words, the leg 84d of the first core 84 and the leg 85d of the second core 85 do not contact the edge of the opening 83g. In the example of FIG. 10, the length of the first gap d1 is longer than the length of the second gap d2.

[0068] In the first modified example, coil 834 is wound so as to straddle leg 84d and leg 85d. As a result, the winding diameter of coil 834 in high-voltage transformer 8A is larger than the winding diameter of coil 834 in high-voltage transformer 8. When viewed from the Z-axis direction, the top layer of coil 834 is formed over the entire surface 83e. Specifically, the top layer of coil 834 is formed on surface 83e between the outer edge of main body 831A and the edge of opening 83g, so as to wrap around the outer edge of main body 831A.

[0069] In the first modified example, the wiring board 83A includes one interlayer connection portion 839 instead of the first interlayer connection portion 837 and the second interlayer connection portion 838. One interlayer connection portion 839 includes a plurality of vias aligned along the Y-axis direction. An upper layer and a lower layer one level below are connected by one of the plurality of vias in one interlayer connection portion 839.

[0070] 10 does not show the first opposing electrode 86 and the second opposing electrode 87, but as in the embodiment, the first opposing electrode 86 and the second opposing electrode 87 may be provided. The first opposing electrode 86 may be connected to the first fixing portion 832, and the second opposing electrode 87 may be connected to the second fixing portion 833. Alternatively, when the high-voltage transformer 8A is placed on the floor, spacers SP may be provided between the floor and the first fixing portion 832 and the second fixing portion 833, and the wiring board 83A may be supported by the spacers SP.

[0071] The openings in the high-voltage transformer 8A include a first opening (opening 83g). A portion of the first core 84 and a portion of the second core 85 are inserted through the opening 83g, and the wiring board 83 is not present between the first core 84 and the second core 85. In this case, the absence of the wiring board 83A between the first core 84 and the second core 85 ensures the dielectric strength, and the distance between the first core 84 and the second core 85 can be reduced, thereby achieving miniaturization. [Second Modification and Third Modification]

[0072] The high-voltage transformer 8 may be configured by connecting three or more isolation transformers. Fig. 11 shows an example of a high-voltage transformer including a first isolation transformer 81, a second isolation transformer 82, and a third isolation transformer 88.

[0073] FIG. 11A illustrates a high-voltage transformer 8B according to a second modification. Only differences from the high-voltage transformer 8 according to the embodiment will be described. The high-voltage transformer 8B includes a first wiring board 83B and a second wiring board 83C. The high-voltage transformer 8B includes a first core 84, a second core 85, and a third core 89. The second wiring board 83C includes second openings (first opening 83a and second opening 83b). The second wiring board 83C includes a first opening 83a for inserting another portion (leg portion 85c) of the second core 85 and a second opening 83b for inserting a portion (leg portion 89d) of the third core 89. The edge of the first opening 83a is spaced apart from the leg portion 85c of the second core 85. The edge of the second opening 83b is spaced apart from the leg portion 89d of the third core 89. The high-voltage transformer 8B does not include a counter electrode. The primary winding 82a (second primary winding) of the second isolation transformer 82 is formed by a portion of the coil 834 included in the first wiring board 83B that is wound along the edge of the second opening 83b of the first wiring board 83B. The portion wound along the edge of the second opening 83b is also wound around one leg 85d of the pair of legs 85d, 85c of the second core 85. The secondary winding 82b (second secondary winding) of the second isolation transformer 82 is formed by a portion of the coil 834 included in the second wiring board 83C that is wound along the edge of the first opening 83a of the second wiring board 83C. The portion wound along the edge of the first opening 83a is also wound around the leg 85c of the second core 85. The primary winding 88a (third primary winding) of the third isolation transformer 88 is formed by a portion of the coil 834 included in the second wiring board 83C that is wound along the edge of the second opening 83b of the second wiring board 83C. The portion that is wound along the edge of the second opening 83b is also wound around the leg 89d of the third core 89. The secondary winding 88b (third secondary winding) of the third isolation transformer 88 is formed by wrapping insulating paper around the leg 89c of the third core 89 and winding a conductor over the insulating paper.

[0074] FIG. 11B illustrates a high-voltage transformer 8C according to a third modification. Only differences from the high-voltage transformer 8B according to the second modification will be described. The high-voltage transformer 8C includes a pair of first opposing electrodes 86A, 86B, a pair of second opposing electrodes 87A, 87B, a pair of third opposing electrodes 87A, 87B, and a pair of third opposing electrodes 91A, 91B, a pair of third opposing electrodes 91A, 91B. The first opposing electrode 86A contacts the first column portion 84a of the first core 84. The first opposing electrode 86B contacts the second column portion 84b of the first core 84. The second opposing electrode 87A contacts the first column portion 85a of the second core 85. The second opposing electrode 87B is in contact with the second pillar portion 85b of the second core 85. The third opposing electrode 91A is in contact with the first pillar portion 89a of the third core 89. The third opposing electrode 91B is in contact with the second pillar portion 89b of the third core 89.

[0075] Even if there are no opposing electrodes, stray capacitance exists between the first core 84, the second core 85, and the third core 89 and the first wiring board 83B or the second wiring board 83C. For example, in FIG. 11A, stray capacitance exists between the second core 85 and the first wiring board 83B and the second wiring board 83C. However, since the magnitude of stray capacitance is proportional to the surface area of ​​the opposing electrodes, providing the second opposing electrodes 87A and 87B can increase the magnitude of stray capacitance. In other words, the second opposing electrodes 87A and 87B serve to reinforce the stray capacitance between the second core 85 and the first wiring board 83B and the second wiring board 83C. This reinforces the stray capacitance between the second core 85 and the first wiring board 83B and between the second core 85 and the second wiring board 83C, and makes it possible to more stably maintain the potential difference between the secondary winding 82b of the second isolation transformer 82 and the second wiring board 83C, and the potential difference between the primary winding 82a of the second isolation transformer 82 and the first wiring board 83B.

[0076] 12 is an equivalent circuit diagram of the high-voltage transformer 8B and the high-voltage transformer 8C. A third stray capacitance Cf3 existing between the first core 84 and the first wiring board 83B constitutes a third stray capacitance Cf3 between the primary winding 81a and the secondary winding 81b of the first isolation transformer 81. A fourth stray capacitance Cf4, which is the sum of the stray capacitance existing between the second core 85 and the first wiring board 83B and the stray capacitance existing between the second core 85 and the second wiring board 83C, constitutes a fourth stray capacitance Cf4 between the primary winding 82a and the secondary winding 82b of the second isolation transformer 82. A fifth stray capacitance Cf5 existing between the third core 89 and the second wiring board 83C constitutes a fifth stray capacitance Cf5 between the primary winding 88a and the secondary winding 88b of the third isolation transformer 88. High-voltage transformer 8C has first opposing electrodes 86A and 86B, second opposing electrodes 87A and 87B, and third opposing electrodes 91A and 91B, thereby reinforcing each stray capacitance compared to high-voltage transformer 8B. In high-voltage transformers 8B and 8C, the voltage between secondary winding 88b of third isolation transformer 88 and primary winding 81a of first isolation transformer 81 is divided by third stray capacitance Cf3, fourth stray capacitance Cf4, and fifth stray capacitance Cf5. ​​This divides the voltages applied to first isolation transformer 81, second isolation transformer 82, and third isolation transformer 88, respectively. Therefore, compared to high-voltage transformer 8, the magnitude of the voltage applied to each isolation transformer can be reduced.

[0077] The high-voltage transformers 8B and 8C further include a third isolation transformer 88 including a primary winding 88a, a secondary winding 88b, and a third core 89. The second isolation transformer 82 and the third isolation transformer 88 share a second wiring board 83C including a coil 834 (second coil) formed by a wiring pattern. The second wiring board 83C has a first opening 83a for inserting another portion (leg 85c) of the second core 85 and a second opening 83b for inserting a portion (leg 89d) of the third core 89. The edge of the first opening 83a is spaced apart from the leg 85c of the second core 85. The edge of the second opening 83b is spaced apart from the leg 89d of the third core 89. The second coil includes a portion wound around the leg 85c of the second core 85 and the leg 89d of the third core 89, thereby constituting the secondary winding 82b of the second isolation transformer 82 and the primary winding 88a of the third isolation transformer 88, which are electrically connected to each other.

[0078] In the high-voltage transformers 8B and 8C, the first isolation transformer 81 and the second isolation transformer 82 are connected in tandem, and the secondary winding 82b of the second isolation transformer 82 and the primary winding 88a of the third isolation transformer 88 are electrically connected to each other. Therefore, the second isolation transformer 82 and the third isolation transformer 88 are connected in tandem. This further reduces the potential difference between the primary and secondary sides of each isolation transformer. Furthermore, the coil 834 in the second wiring board 83C includes a portion that constitutes the secondary winding 82b of the second isolation transformer 82 and a portion that constitutes the primary winding 88a of the third isolation transformer 88. The edge of the first opening 83a of the second wiring board 83C is separated from the second core 85. The edge of the second opening 83b of the second wiring board 83C is separated from the third core 89. This makes it less likely for discharge to occur than when, for example, the secondary winding 82b of the second isolation transformer 82 and the primary winding 88a of the third isolation transformer 88 are formed by winding independent conductors. Furthermore, because the secondary winding 82b of the second isolation transformer 82 and the primary winding 88a of the third isolation transformer 88 are formed by the coil 834 included in the common second wiring board 83C, miniaturization can be achieved. [Fourth Modification and Fifth Modification]

[0079] The shapes of the first opposing electrode 86 and the second opposing electrode 87 are not limited to those of the first opposing electrode 86 and the second opposing electrode 87 according to the embodiment. (a) of FIG. 13 is a diagram illustrating a first opposing electrode 86C and a second opposing electrode 87C according to a fourth modified example. As shown in (a) of FIG. 13, the opposing portion 861C of the first opposing electrode 86C may have an arc shape including an outer edge along the arc described by the outer edge of the wiring substrate 83 when viewed from the Z-axis direction. The opposing portion 861C may include a notch 86c. The opposing portion 861C may have a shape like a semicircular substrate including an outer edge along the arc described by the outer edge of the wiring substrate 83, cut out by the notch 86c. The notch 86c may include an edge along the arc described by the edge of the first opening 83a.

[0080] 13A, when viewed from the Z-axis direction, the opposing portion 871C of the second opposing electrode 87C may have an arc shape including an outer edge that follows the arc described by the outer edge of the wiring substrate 83. The opposing portion 871C may include a notch 87c. The opposing portion 871C may have a shape like a semicircular substrate that includes an outer edge that follows the arc described by the outer edge of the wiring substrate 83, and that is cut out by the notch 87c. The notch 87c may include an edge that follows the arc described by the edge of the second opening 83b.

[0081] The arc-shaped opposing portions 861C and 871C make it easier to adjust the distance between the first opposing electrode 86C and the second opposing electrode 87C compared to when the opposing portions 861C and 871C are circular. This allows, for example, a high-voltage transformer with high breakdown voltage and small size to be realized by bringing the first opposing electrode 86C and the second opposing electrode 87C as close as possible to each other while maintaining a distance that makes it difficult for discharge to occur between them. In the fourth modification, the wiring board 83A of the first modification may be used instead of the wiring board 83. In this case, the first opposing electrode 86C and the second opposing electrode 87C may be brought as close as possible to form the main body portion 831A in a shape close to a perfect circle.

[0082] FIG. 13B is a diagram illustrating a first opposing electrode 86D and a second opposing electrode 87D according to a fifth modification. As shown in FIG. 13B, the opposing portion 861D of the first opposing electrode 86D has a circular shape including an outer edge that follows the arc of the outer edge of the wiring substrate 83D when viewed from the Z-axis direction, and may not include the third opening 86b. That is, the opposing portion 861D may have a shape that does not include the third opening 86b, as the opposing portion 861 according to the embodiment does. Similarly, the opposing portion 871D of the second opposing electrode 87D has a circular shape including an outer edge that follows the arc of the outer edge of the wiring substrate 83D when viewed from the Z-axis direction, and may not include the third opening 87b. In this case, the circular shapes of the opposing portions 861D and 871D can prevent electric fields from concentrating at the outer edges of the opposing portions 861D and 871D. In (b) of Figure 13, the shape of the wiring board 83D is curved along the X-axis direction. This shows a case where, for example, the housing that stores the high-voltage transformer 8 is curved and the shape is made to match the shape of the housing.

[0083] Various experiments conducted to evaluate the high-voltage transformer 8 according to the embodiment or the high-voltage transformer 8A according to the modified example will be described below. The experiments described below do not limit the present disclosure.

[0084] (First Experiment) In the first experiment, the dielectric strength voltage between the primary winding 82a of the second isolation transformer 82 and the secondary winding 82b of the second isolation transformer 82 was measured in the high-voltage transformer 8 according to the embodiment. A high voltage was applied between the secondary winding 82b of the second isolation transformer 82 and the outer edge of the main body 831, and the voltage value at the time of discharge was measured together with that of a comparative example. FIG. 14 is a perspective view of a high-voltage transformer 8D according to the comparative example. The high-voltage transformer 8D includes a core 91, an annular member 92, and a fixing member 93 that fixes the core 91 and the annular member 92. In the example shown in FIG. 14, the core 91 is a U-shaped ferrite core. The core 91 includes a pillar portion 91a and a pair of legs 91b. The primary winding 81a of the high-voltage transformer 8D is wound around the pillar portion 91a. The secondary winding 81b of the high-voltage transformer 8D is wound around the annular member 92. Although not shown in FIG. 14, the gap between the primary winding 81a and the secondary winding 81b is resin-molded with insulating resin.

[0085] (First Experimental Results) When 105 kV was applied to the high-voltage transformer 8, a discharge occurred between the primary winding 82a of the second isolation transformer 82 and the secondary winding 82b of the second isolation transformer 82. On the other hand, when 70 kV was applied to the high-voltage transformer 8D, a discharge occurred between the primary winding 81a and the secondary winding 81b. This experiment revealed that the withstand voltage of the high-voltage transformer 8 according to the embodiment was greater than the withstand voltage of the high-voltage transformer 8D according to the comparative example.

[0086] (Second Experiment) In the second experiment, an electric field strength analysis was performed on a cross section of wiring board 83A. FIG. 15 is an example of a model for the electric field strength analysis. FIG. 15 shows a cross section of wiring board 83A cut along the YZ plane from center 83c of wiring board 83A for high-voltage transformer 8A according to a modified example. An electric field strength analysis was performed on corner E2 on the outer edge side of wiring board 83A in the cross section of wiring board 83A. For the analysis, two wiring boards were prepared: one in which corner E2 in the cross section of wiring board 83A was a right angle, and another in which corner E2 in the cross section of wiring board 83A was curved.

[0087] (Second Experimental Results) Figure 16(a) shows the results of an electric field strength analysis performed on a wiring board 83A in which the corner E2 in the cross section of the wiring board 83A is a right angle. Figure 16(b) shows the results of an electric field strength analysis performed on a wiring board 83A in which the corner E2 in the cross section of the wiring board 83A is curved. It can be seen that the electric field strength generated in the wiring board 83A in which the corner E2 is curved is smaller than the electric field strength generated in the wiring board 83A in which the corner E2 is a right angle. This is presumably because the curved corner E2 reduces the local distribution of the electric field at the corner E2.

[0088] (Third Experiment) In the third experiment, the dielectric strength voltage between the edge of the second opening 83b of the wiring board 83 and the leg 85d of the second core 85 was measured. FIGS. 17A to 17C show cross-sectional views of the wiring board 83 cut along the YZ plane including the center 83c of the wiring board 83 of the high-voltage transformer 8 according to the embodiment. FIGS. 17A to 17C show enlarged views of the vicinity of the leg 85d of the second core 85. In FIGS. 17A to 17C, the shape of the corner of the wiring board 83 and the distance d3 between the edge of the second opening 83b and the leg 85d of the second core 85 were varied. In FIG. 17A, the corner of the wiring board 83 was a right angle, and the distance d3 was 11.0 mm. 17B, ​​the corners of the wiring board 83 are curved to a radius of curvature of 1 mm, and the distance d3 is 10.0 mm. In FIG. 17C, the corners of the wiring board 83 are curved to a radius of curvature of 2.3 mm, and the distance d3 is 8.7 mm.

[0089] 17(a) to 17(c), it was confirmed that a withstand voltage of 200 kV or more was ensured between the edge of the second opening 83 b and the leg portion 85 d of the second core 85. From this result, it was found that the greater the degree of curvature of the corners of the wiring board 83, the more the withstand voltage can be ensured even if the distance d3 from the leg portion 85 d is small.

[0090] 8, 8A, 8B, 8C...High voltage transformer, 81...First isolation transformer, 82...Second isolation transformer, 88...Third isolation transformer, 81a...Primary winding of first isolation transformer (first primary winding), 81b...Second isolation transformer secondary winding (first secondary winding), 82a...Primary winding of second isolation transformer (second primary winding), 82b...Second isolation transformer secondary winding (second secondary winding), 88a...Primary winding of third isolation transformer (third primary winding), 88b...Second isolation transformer secondary winding (third secondary winding), 83...Wiring board, 83a...First opening (opening), 83 b...second opening (opening), 84...first core, 85...second core, 89...third core, 84a...first pillar portion of first core, 84b...second pillar portion of first core, 85a...second pillar portion of second core, 85b...second pillar portion of second core, 84d...leg portion of first core (part of first core), 85d...leg portion of second core (part of second core), 86...first opposing electrode, 87...second opposing electrode, 834...coil, 835...resin layer, 836, 836A...wiring layer, 837...first interlayer connection portion, 838...second interlayer connection portion, 861, 871...opposing portion, 862, 872...contact portion.

Claims

1. A high-voltage transformer comprising: a first isolated transformer including a first primary winding, a first secondary winding, and a first core; and a second isolated transformer including a second primary winding, a second secondary winding, and a second core, wherein the first isolated transformer and the second isolated transformer have a common wiring board including a coil formed by a wiring pattern, the wiring board has an opening for inserting a part of the first core and a part of the second core, the edges of the opening are spaced apart from the part of the first core and the part of the second core, and the coil is wound around the part of the first core and the part of the second core, thereby constituting the first secondary winding and the second primary winding that are electrically connected to each other.

2. A high-voltage transformer as described in claim 1, wherein the wiring board has: a plurality of wiring layers each having a wiring pattern surrounding the portion of the first core and the portion of the second core; a resin layer provided between each of the plurality of wiring layers; and an interlayer connection portion that connects the wiring patterns of adjacent wiring layers among the plurality of wiring layers to each other.

3. A high-voltage transformer according to claim 1 or 2, wherein at least a portion of the edge of the opening of the wiring board has an arc shape when viewed in the thickness direction of the wiring board.

4. A high-voltage transformer as claimed in any one of claims 1 to 3, wherein the opening of the wiring board includes a first opening and a second opening, the coil includes a portion wound along the edge of the first opening and a portion wound along the edge of the second opening, the portion of the first core passes through the first opening, and the portion of the second core passes through the second opening.

5. A high-voltage transformer according to any one of claims 1 to 4, wherein the opening includes a first opening, the portion of the first core and the portion of the second core are inserted through the first opening, and the wiring board is not present between the first core and the second core.

6. A high-voltage transformer as claimed in any one of claims 1 to 5, wherein each of the first core and the second core comprises a pair of legs extending in one direction, a first pillar portion at one end of the pair of legs connecting the pair of legs, and a second pillar portion at the other end of the pair of legs connecting the pair of legs, and wherein the portion of the first core is included in one of the pair of legs of the first core, and the portion of the second core is included in one of the pair of legs of the second core.

7. A high-voltage transformer according to any one of claims 1 to 6, further comprising: a first opposing electrode in contact with the first core and disposed opposite the wiring board; and a second opposing electrode in contact with the second core and disposed opposite the wiring board.

8. A high-voltage transformer as claimed in claim 7, wherein each of the first opposing electrode and the second opposing electrode has an opposing portion opposing the wiring board and a contact portion connected to the opposing portion and in contact with each of the first core and the second core, at least a part of the outer edge of the wiring board is arc-shaped, and when viewed in the thickness direction of the wiring board, the opposing portion presents a circular shape including an outer edge that follows the arc described by the outer edge of the wiring board.

9. The high-voltage transformer according to claim 8, wherein the facing portion includes a through-hole that overlaps with the opening when viewed in the thickness direction of the wiring board.

10. A high-voltage transformer as claimed in claim 7, wherein each of the first opposing electrode and the second opposing electrode has an opposing portion opposing the wiring board and a contact portion connected to the opposing portion and in contact with each of the first core and the second core, at least a part of the outer edge of the wiring board has an arc shape, and when viewed in the thickness direction of the wiring board, the opposing portion has an arc shape including an outer edge that follows the arc described by the outer edge of the wiring board.

11. A high-voltage transformer according to any one of claims 1 to 10, wherein corners of the wiring board are rounded in a cross section of the wiring board.

12. The high-voltage transformer according to any one of claims 1 to 11, further comprising a third isolation transformer including a third primary winding, a third secondary winding, and a third core, wherein the second isolation transformer and the third isolation transformer have a common second wiring board including a second coil formed by a wiring pattern, the second wiring board has a second opening for inserting another part of the second core and a part of the third core, an edge of the second opening is spaced apart from the other part of the second core and the part of the third core, and the second coil is wound around the other part of the second core and the part of the third core, thereby constituting the second secondary winding and the third primary winding that are electrically connected to each other.

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