JP5122778B2 - High voltage circuit and X-ray generator - Google Patents

Description

  The present invention relates to a high voltage circuit, and more particularly to a circuit configuration suitable for an X-ray generator.

  For example, a DC high voltage output circuit includes a Cockcroft-Walton circuit known as a multistage voltage doubler rectifier circuit. This technique is used in many X-ray generators that require DC high voltage.

  Since the X-ray generator needs to output a voltage of several tens of kV to several hundreds of kV, the output terminal, the capacitor of the final stage, and the lead wire of the diode have the same potential of several tens of kV to several tens of kV. Become. A large potential difference occurs between this high-potential part and the housing that houses it, resulting in an extremely uneven electric field in which the electric field is excessively concentrated near the lead wires and terminals, etc., to ensure reliability. In this case, an appropriate insulation distance must be taken so that the maximum electric field strength is less than the allowable value.

However, if the insulation distance is kept large, the size of the device will also increase. Therefore, as a method of shortening the insulation distance, an electric field shield is provided around the high voltage terminal, and the equipotential line spacing is made as uniform as possible. A method is known in which the electric field is relaxed by applying an intermediate potential between the voltage terminal and the casing, and the insulation distance is shortened. (For example, see Patent Document 1)
JP2004-22468

The method of relaxing the electric field by the electric field shield as described above is a useful method for insulating a potential difference of several hundred kV or several thousand kV. However, for a voltage of several tens of kV to several hundreds of kV, the necessary insulation distance is several tens of millimeters or less. Therefore, there is not a sufficient distance for providing the shield, and the provision of the shield may conversely cause electric field concentration between the shield and the high voltage terminal and between the shield and the casing.
In addition, the multistage booster circuit often requires a long mounting space as the number of stages increases, and it is difficult to fit in the target space depending on the specifications of the device.

  An object of the present invention is to provide a high-voltage circuit and an X-ray generator capable of reducing the circuit space by reducing the insulation distance between electrical components and their housings.

  In the high voltage circuit formed by combining a plurality of electrical components including a capacitor and a semiconductor rectifying element, the electrical components between the input end and the output end of the high voltage circuit are arranged in a substantially spiral shape. It is characterized by doing.

  According to the present invention, it is possible to reduce the insulation distance between the electrical components and the casing, and to reduce the circuit space.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration diagram of an X-ray generator using the high voltage output circuit of the present invention. As shown in Fig. 1, rectifier circuit 1 that once rectifies commercial AC voltage, inverter 2 that converts DC voltage obtained by rectifier circuit 1 into high-frequency AC voltage, and the output voltage of inverter 2 is used as the input voltage to boost the voltage. A high-voltage transformer 3 and a Cockcroft-Walton circuit 4 that performs boosting and rectification using the outputs of the high-voltage transformer 3 as inputs are provided, and a DC high voltage that has been boosted and rectified is applied to the anode 5a of the X-ray tube 5. The X-ray tube 5 is a cathode grounding method in which the cathode 5b is grounded, and a direct current high voltage of about 100 kV at the maximum is applied to the anode 5a as a tube voltage. The high voltage transformer 3 and the Cockcroft-Walton circuit 4 are mounted in a high voltage tank 6 filled with insulating oil.

As shown in FIG. 2, the Cockcroft-Walton circuit 4 used in the X-ray high-voltage device has a configuration in which the capacitor 10 and the diode 11 are combined, and is connected in several stages or several tens of stages. By rectifying and boosting, a high DC voltage is generated. This circuit is characterized in that as the number of stages is increased, the potential at that portion also increases.
The output terminal 9 of this Cockcroft-Walton circuit 4, one end of the uppermost capacitor 10a, and one end of the uppermost diode 11a are several tens of kV to hundreds equivalent to the voltage (tube voltage) applied to the X-ray tube. The potential is 10 kV. The Cockcroft-Walton circuit 4 is known in several ways other than that shown in FIG. 2, such as a symmetric shape. In the present invention, any system can be used.

  FIG. 3 shows a mounting format of the high voltage generator in the present invention. Here, the high voltage transformer 3 and the Cockcroft-Walton circuit 4 are mounted in a high voltage tank 6 in which insulating oil is sealed. In this embodiment, the Cockcroft-Walton circuit 4 has 20 stages, the first stage to the fourth stage 15 are arranged along the left surface of the high voltage tank 6, and the fifth stage to the eighth stage 16 are parallel to the lower surface of the high voltage tank 6. Is arranged. Similarly, the 9th to 12th stages 17 are arranged in parallel to the right surface of the high voltage tank 6, and the 13th to 16th stages 18 are arranged in parallel to the upper surface of the high voltage tank 6. Next, the 17th to 18th stages 19 are arranged in parallel to the first stage to the 4th stage 15 as shown in the figure, and the 19th stage to the last stage (20th stage) 20 are arranged in parallel to the 5th to 8th stages 16. In this way, as the number of stages increases, the capacitor and the diode of the Cockcroft-Walton circuit 4 are arranged in order while drawing a spiral trajectory in order. The insulation distance between the adjacent locations in the Cockcroft-Walton circuit 4, for example, the first stage to the fourth stage 15 and the 17th stage to the 18th stage 19 is provided with an appropriate insulation distance according to the potential difference generated therebetween.

  FIG. 4 shows an example of an analysis result of the maximum electric field strength Emax [kV / mm] −insulation distance l [mm] between a flat plate and a parallel cylinder as electrodes. Here, the analysis results are obtained by modeling the inner wall surface of the high voltage tank as a flat plate and the lead wire of the diode or capacitor as a parallel cylinder. Accordingly, for example, if the allowable value of the maximum electric field strength is 10 [kV / mm] or less, an insulation distance of about 5 mm is required when the potential difference is 20 kV. When the potential difference is 40 kV, an insulation distance of about 35 mm or more is required. This shows that when the potential difference is doubled, an insulation distance of 7 times or more is required, and reducing the potential difference greatly contributes to shortening the insulation distance.

  For comparison, FIG. 5 shows an implementation example of a conventional Cockcroft-Walton circuit. Conventionally, in many cases, the first stage is arranged side by side as described above, which is vertically long, and the final stage of the Cockcroft-Walton circuit is arranged at the end. For this reason, the output stage of the Cockcroft-Walton circuit, which has the highest voltage, and the inner wall surface of the high-voltage tank 6, which is the ground potential, face each other directly (as shown in the results shown in FIG. 4). A very large insulation distance 23 had to be maintained in three directions from one end of the capacitor and one end of the diode to the inner wall surface of the high voltage tank 6.

  Compared to this, in the configuration of the present invention, the portions from the first stage to the 16th stage are arranged at a location near the inner wall surface of the high voltage tank 6 (earth potential). In the Cockcroft-Walton circuit, the potential of components increases as the number of stages increases, so the potential difference between the high-voltage tank 6 and the capacitor and diode is smaller than in the conventional mounting method. Therefore, the insulation distance 21 between them can be shortened. In addition, since the highest potential portion of the high voltage terminal 9 and one end of the uppermost capacitor 10a and one end of the uppermost diode 11a are arranged in the center, the insulation distance 22 from the inner wall surface of the high voltage tank 6 must be kept sufficiently. Can do.

According to the above configuration, particularly in the Cockcroft-Walton circuit 4, the insulation distance from the circuit portion to the inner wall surface of the high-voltage tank 6 including the first stage to the fourth stage 15 can be shortened, and the entire apparatus can be reduced in size.
In addition, according to the present invention, the length of the four sides of the Cockcroft-Walton circuit 4 that has been apt to be long on one side in the past can be made substantially the same, so that it can be freely mounted to meet the requirements of the device. The effect of increasing the degree is obtained.

  FIGS. 6, 7 and 8 show implementation examples of the Cockcroft-Walton circuit 4 according to the second embodiment. The second embodiment is also used for the X-ray generation device in the same manner as the first embodiment. The difference from the first embodiment is that a protective resistor 24 is provided between the cockcroft-Walton circuit 4 and the X-ray tube 5 and a method for arranging the cockcroft-Walton circuit 4.

For example, when the X-ray tube 5 is discharged in the tube, the protective resistor 24 is provided to suppress the discharge current and protect the X-ray tube and peripheral circuits. When a discharge occurs in the X-ray tube 5, the voltage (tube voltage) applied to the X-ray tube 5 is applied to the protective resistor 24. Therefore, the protective resistor 24 is the same number as the tube voltage applied to the X-ray tube 5. It is necessary to have a high voltage resistance of 10 kV to several hundreds kV. Since such a high withstand voltage resistor is increased in size, a mounting method has been a problem in order to reduce the size of the entire apparatus. It is also necessary to maintain an appropriate insulation distance from the high voltage tank 6.
As shown in FIG. 7, the arrangement method is a structure 25 in which each face of the quadrangle is spiraled toward the apex. As the number of stages rises from the input terminals 7 and 8 of the Cockcroft-Walton circuit at the lower part of the quadrangle, it is arranged at the upper part of the quadrangle. This configuration is a configuration in which the central portion is pulled out in the configuration of the first embodiment.

The terminals of the capacitors and diodes in the final stage are arranged near the apex of the quadrangle and are connected to the output terminal 9 of the Cockcroft-Walton circuit.
The output terminal 9 is connected to the protective resistor 24. The protective resistor 24 is disposed inside the Cockcroft-Walton circuit 4. The other terminal of the protective resistor 24 is connected to the anode 5a of the X-ray tube 5 via a cable.

FIG. 8 shows a state where the configuration of FIG. 7 is stored in the high voltage tank 6 when viewed from above. According to such a configuration of FIG. 7, since the relatively low potential portion is arranged outside as in the first embodiment, the insulation distance between the Cockcroft-Walton circuit 4 and the high voltage tank 6 is around the high potential portion. Can be shorter than when placed. In addition, since the highest potential portion in the final stage is arranged at the apex of the square, the insulation distance between the high potential portion and the high voltage tank 6 can be sufficiently maintained. Since the protective resistor 24 is also arranged at the center of the Cockcroft-Walton circuit, the insulation distance between the protective resistor 24 and the high voltage tank 6 can be kept sufficiently.
In this way, since the insulation distance from the high voltage tank 6 can be shortened while making the most effective use of the space including the protective resistor 24, the entire apparatus can be downsized.

  A third embodiment is shown in FIG. 9, FIG. 10, and FIG. This embodiment is basically the same as the first embodiment. 9 and FIG. 11, the difference is that the X-ray tube 5 is an integrated X-ray generator in which the X-ray tube 5 is placed in the high voltage tank 6 and the arrangement method. In the case of such an integrated X-ray generator, the proportion of the X-ray tube 5 in the high-voltage tank 6 increases, and when the shape of the Cockcroft-Walton circuit 4 is the first embodiment, it may not enter.

  As shown in FIG. 10, the configuration of this embodiment is such that the substrate 26 is set sideways and can be arranged by processing one substrate. Similar to FIG. 3, the first to 16th stages are arranged near the high voltage tank 6, and the 17th to 20th stages are arranged inside thereof.

  As in the first embodiment, the distance between the Cockcroft-Walton circuit 4 and the high voltage tank 6 can be shortened. Considering the shape and size of capacitors and diodes, placing a low potential part near the high voltage tank 6 and arranging it to draw a spiral orbit inside as the stage rises is suitable. The device can be mounted in a shape and the size of the device can be reduced.

  In Embodiments 1 to 3, the Cockcroft-Walton circuit is configured to be mounted in insulating oil, but the same effect can be obtained when mounted in an insulating material other than insulating oil, such as resin-molding the Cockcroft-Walton circuit. can get.

  The multistage switch circuit used in the present embodiment is used in a pulse fluoroscopy device. Pulse fluoroscopy is a device used to view high-quality real-time images during X-ray diagnosis. An overall configuration diagram of the pulse fluoroscope is shown in FIG. As shown in FIG. 12, a converter 27 that once rectifies a commercial AC voltage, an inverter 28 that converts a special-current voltage obtained by the converter 27 into a high-frequency AC voltage, and an output from the inverter 28 is an input, and a high-voltage transformer that boosts the voltage. The rectifier 30 that rectifies by using the output of the voltage generator 29 and the high voltage transformer as an input, and two rectifiers 30 are provided, and are rectified to obtain a DC high voltage. The two rectifiers 30 are applied as tube voltages to the anode 31a and the cathode 31b of the X-ray tube 31 by a neutral point grounding method. In pulse fluoroscopy, this tube voltage is turned on and off in pulses.

When a tube voltage is applied to the X-ray tube 5, a high voltage cable is used, so that there is a stray capacitance 32 due to the high voltage cable, and this capacitor is charged. A multi-stage switch circuit 33 is provided for the purpose of accelerating the discharge of the electric charge accumulated in the capacitor when the application of the tube voltage is stopped, and the fall of the tube voltage. The multistage switch circuit 33 is accommodated in the high voltage tank 40.
In such a multistage switch circuit, a maximum voltage of +75 kV is applied to the anode side 31a and a minimum voltage of −75 kV is applied to the cathode side 31b. Therefore, it has a configuration in which hundreds of semiconductor switches are connected in series to each of the anode side 31a and the cathode side 31b.

  FIG. 13 shows a mounting diagram of the multistage switch circuit in this embodiment. The arrangement method on the anode side 34 is the same as in the first and third embodiments. As the potential increases from the ground potential portion 35, the anode side 34 is arranged so as to draw a spiral orbit on the inside, and the maximum potential is almost at the center. Place portion 36. As a different point, since this apparatus is a neutral point grounding system, the cathode side 37 is arranged in the center of the vortex as the potential decreases from the ground potential portion 38. The lowest potential portion 39 is disposed substantially at the center. Further, a portion close to the ground potential on the anode side 34 and the cathode side 37 is arranged adjacently.

  According to this configuration, also in the multistage switch circuit, the insulation distance 41 from the high voltage tank 40 can be shortened as compared with the case where the maximum potential is arranged in the vicinity of the high voltage tank 40, as in the first to third embodiments. Can be miniaturized.

The figure which shows the whole structure of the X-ray generator which utilizes this invention. The figure which shows a Cockcroft-Walton circuit. The figure which shows the mounting format of the Cockcroft-Walton circuit of this invention. The figure which shows the example of an analysis result of maximum electric field strength-insulation distance. The figure which shows the conventional Cockcroft-Walton circuit implementation example. The figure which shows the circuit example of the Cockcroft-Walton circuit and X-ray tube which added protection resistance. The figure which shows the example of mounting arrange | positioned spirally. The figure which looked at FIG. 7 from the top. The figure which shows the whole structure of an integrated X-ray generator. FIG. 10 is a diagram showing a mounting arrangement in FIG. The figure which looked at FIG. 10 from the side (right). The figure which shows the whole structure of a pulse fluoroscopy apparatus. The figure which shows the example of mounting of a multistage switch circuit.

Explanation of symbols

  1 Rectifier, 2 Inverter, 3 High-voltage transformer, 4 Cockcroft-Walton circuit, 5 X-ray tube, 5a X-ray tube anode, 5b X-ray tube cathode, 6 High-voltage tank, 7, 8 Cockcroft-Walton Circuit (input terminals 1 and 2), 9 Cockcroft-Walton circuit (output terminal), 10 capacitors, 10a last stage capacitor, 11 diode, 11a last stage diode, 12 1st stage (first stage), 13 2nd stage, 14 nth, 15 1st to 4th, 16 5th to 8th, 17 9th to 12th, 18 13th to 16th, 19 17th, 18th, 20 19th, 20th, 21 Insulation distance , 22 Final stage, High voltage tank 6 insulation distance, 23 Insulation distance, 24 Protection resistance, 25 Mounting area, 26 Substrate, 27 Converter, 28 Inverter, 29 High voltage transformer, 30 Rectifier circuit, 31 X-ray tube, 32 Stray capacitance, 33 Multistage switch, 34 Anode side, 35 Earth potential, 36 Maximum potential, 37 Sword side, 38 ground potential, 39 lowest potential, 40 high voltage tank, 41 insulation distance

Claims (3)

In a high voltage circuit that is formed by combining a plurality of electrical components including a capacitor and a semiconductor rectifier, and becomes a high voltage as it goes from the input terminal portion to the output terminal portion,
The high voltage circuit is arranged in a spiral shape from the vicinity of the inner wall surface of the high voltage tank grounded to the ground potential toward the center of the high voltage tank, and the input terminal portion is located near the inner wall surface, The high-voltage circuit according to claim 1, wherein the output terminal portion is located at the central portion . The high voltage circuit is disposed so as to be positioned in the height direction as it goes to the central portion, and the output terminal portion is provided between an X-ray source that generates X-rays and the high voltage circuit. The high-voltage circuit according to claim 1, wherein a protective resistor is connected, and the protective resistor is disposed along the height direction. 3. An X-ray generator including an X-ray source for generating X-rays and a high voltage circuit connected to supply power to the X-ray source, wherein the high voltage circuit is defined in claim 1 or 2. An X-ray generator characterized in that a part of a high voltage circuit is included.

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