JP2004281170A - High voltage device for x-ray tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify and miniaturize an electric insulating structure in an X-ray high voltage generating circuit or the like for a CT of ultra-high voltage and an anode grounded type. <P>SOLUTION: This high voltage device for a bulb is constituted of a high voltage transformer for boosting an input AC voltage, a high voltage rectification circuit connected to its secondary winding wire, a high voltage detecting circuit formed by connecting a plurality of resistors in series, and a filament circuit for supplying the current to the filament of the high voltage bulb. The filament circuit is constituted of filament transformers cascade-connected, and to potential points in which the respectively sharing voltages of these filament transformers are approximately equalized, the cascade-connected points of the respective filament transformers are respectively connected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high voltage generator such as an X-ray apparatus for X-ray or an X-ray apparatus for CT.
[0002]
[Prior art]
A high voltage generator for an X-ray tube, for example, an X-ray apparatus for an X-ray or a high voltage generator for an X-ray apparatus for a CT, is usually of a neutral grounding type, and has a high voltage having two positive and negative outputs of a positive electrode +75 kV and a negative electrode -75 kV. It has a voltage generator. Further, there is an example in which only a negative electrode output of -140 kV is used as in a CT X-ray apparatus having a grounded anode. In any case, since the filament of the X-ray tube is connected to the negative electrode of these high-voltage generators, a filament transformer must be provided. This transformer usually requires a withstand voltage of -75 kV or -140 kV or more, and in the UL standard, it must withstand a voltage of 1.25 times those voltages and a high voltage of -90 kV or -175 kV. Therefore, such a filament transformer becomes large due to electrical insulation, which is a major obstacle to downsizing the high voltage generator.
[0003]
To solve such a problem, the present applicant has already disclosed the technique in Patent Document 1 below. This technology reduces the size of a high-voltage transformer by dividing a conventional large high-voltage transformer into multiple parts, and cascades these small high-voltage transformers to obtain a predetermined high voltage while making the entire device compact. It is.
[0004]
[Patent Document 1] Japanese Patent Publication No. 62-35349 (page 2, FIG. 2)
[0005]
[Problems to be solved by the present invention]
According to the technique disclosed in Patent Document 1, it is possible to reduce the size of the high-voltage transformer, but it has been found that the size cannot be reduced to a satisfactory level. The reason is that when multiple high-voltage transformers are actually connected in series, the voltage shared by each high-voltage transformer may vary considerably due to differences in the size of the stray capacitance depending on their location, manufacturing variations, etc. This is because, unless a sufficient margin is provided, there is a problem that a high-voltage transformer having a large shared voltage causes dielectric breakdown.
[0006]
[Basic concept of the present invention] The basic concept of the electrical insulation structure of the filament transformer according to the present invention is that the dielectric breakdown penetration voltage and the creepage dielectric breakdown voltage are not directly proportional to the insulation distance, but are approximately proportional to 1/2 power. Therefore, the filament transformer is divided into a plurality of cascades and the voltage is equally distributed to the individual filament transformers, thereby simplifying the insulation structure of each transformer and greatly reducing the size.
[0007]
For example, assuming that the insulation distance of 175 kV is L, four filament transformers are connected in cascade, and a means for equalizing the voltage sharing of each filament transformer is provided. .75 kV. Therefore, the insulation distance per filament transformer is (43.75 / 175) squared × L = 0.0625L, and the insulation distance per filament transformer is 0.25L. Will be done.
[0008]
Means and Action for Solving the Problems
In order to solve the above problems, the invention according to claim 1 of the present application provides a high-voltage transformer having a primary winding to which an AC voltage is supplied and a secondary winding that generates a boosted AC voltage;
A high-voltage rectifier circuit connected to the secondary winding, a high-voltage detection circuit formed by connecting a plurality of resistors in series, and a high-voltage for the X-ray tube configured to supply power to a filament of the X-ray tube. In the apparatus, the filament circuit includes a plurality of cascade-connected filament transformers in which a primary winding and a secondary winding of an adjacent filament transformer are connected in series, and each of these filament transformers has a voltage shared by the filament transformers. The present invention provides a high-voltage device for an X-ray tube in which cascade connection points of the respective filament transformers are connected to potential points that substantially equalize.
[0009]
In the high voltage apparatus for an X-ray tube configured as described above, a single conventional large filament transformer is divided into a plurality of small filament transformers and connected in cascade, and their shared voltages are equalized. The electrical insulation structure can be simplified and the size can be significantly reduced.
[0010]
According to a second aspect of the present invention, in the first aspect, the high-voltage detection circuit is configured by connecting in series a number of resistor circuits corresponding to the number of the filament transformers in series, and connecting a series connection point of each of the resistor circuits to the filament. An object of the present invention is to provide a high-voltage device for an X-ray tube which is connected to a cascade connection point of a transformer in the order of potential to equally share each voltage of the filament transformer.
[0011]
In the high voltage device for an X-ray tube configured as described above, the shared voltage of a plurality of cascade-connected filament transformers is made uniform by using a high voltage detection circuit indispensable to the device, and a special voltage sharing is performed. There is no need to provide an equalizing means, which is economical and contributes to downsizing of the device.
[0012]
According to a third aspect of the present invention, in the first aspect, the high-voltage rectifier circuit is a multi-stage voltage doubler rectifier circuit including an AC column and a DC column formed by combining a plurality of capacitors and a plurality of diodes. The present invention is to provide a high-voltage device for an X-ray tube in which the doubled voltage potential point is connected to the vertical connection point of the front filament transformer in the order of potential to equally share each voltage of the filament transformer.
[0013]
In the high voltage device for an X-ray tube configured as described above, a multi-stage voltage doubler rectifier circuit is used as a high voltage rectifier circuit indispensable to the device, and the shared voltage is applied to a plurality of cascade-connected filament transformers by using this circuit. Therefore, it is not necessary to provide any special voltage sharing means, which is economical and contributes to downsizing of the device.
[0014]
A fourth aspect of the present invention is to provide a high-voltage device for an X-ray tube in which a discharge protection resistor is connected in series to each capacitor on the AC column side in the third aspect.
[0015]
In the high-voltage device for an X-ray tube configured as described above, a problem arises when a multi-stage voltage doubler rectifier circuit is used as a high voltage rectifier circuit and the shared voltage of a plurality of cascade-connected filament transformers is made uniform by using the same. This solves the problem that a large voltage is applied to the point, that is, the filament transformer connected to the position of the highest potential at the time of discharge of the X-ray tube, thereby causing dielectric breakdown.
[0016]
Claim 5 of the present application provides a high voltage device for an X-ray tube according to claim 3, wherein a discharge protection resistor is connected in series to the high voltage diode.
[0017]
The high voltage device for an X-ray tube configured as described above has the same effect as the fourth aspect.
[0018]
According to a sixth aspect of the present invention, in the third aspect, the plurality of cascade-connected filament transformers are arranged in a columnar shape, and the multistage voltage doubler rectifier circuit having substantially the same potential gradient, or the high voltage detection. An object of the present invention is to provide a high-voltage device for an X-ray tube arranged along the vicinity of a circuit.
[0019]
In the high voltage device for an X-ray tube configured as described above, since the potential gradient between the filament transformer arranged in a columnar shape and the multi-stage voltage doubler rectifier circuit or the high voltage detection circuit is almost equal, the filament transformer is It can be placed along the vicinity of the multi-stage voltage doubler rectifier circuit or the high voltage detection circuit, and this further contributes to miniaturization.
[0020]
[Embodiment of the present invention]
Next, an embodiment of the present invention will be described. FIG. 1 shows a power supply circuit of a grounded anode X-ray CT apparatus according to this embodiment. Basically, an AC power supply 1, a rectifier circuit 2 for rectifying an AC voltage of the AC power supply 1, a high-voltage inverter circuit 3 for converting a DC voltage to a high-frequency AC voltage, and a filament for converting a DC voltage to a high-frequency AC voltage And a high voltage generating circuit 5 for supplying a high voltage and filament power to the cathode of the X-ray tube 6, ie, the filament F. Note that the anode A of the X-ray tube 6 is grounded, and as an example, 175 kV is supplied to the filament F at the time of the withstand voltage test.
[0021]
Here, the high-voltage inverter circuit 3 and the filament inverter circuit 4 are high-frequency inverter circuits that input a three-phase 200 V commercial AC power supply and perform switching operations at several kHz to several tens of kHz. Omitted.
[0022]
The high-voltage generating circuit 5 includes a high-voltage transformer 11 connected to the high-frequency output of the high-voltage inverter circuit 3 and a well-known multistage multiplier called a Cockcroft-Walton circuit with a negative output connected to the secondary high-voltage winding 12. A voltage rectifier circuit (hereinafter referred to as a CW circuit) 13, a discharge protection resistor 14 connected to the output of the CW circuit 13, a first-stage filament transformer 15A having a primary winding An1 connected to the filament inverter circuit 4, and Three cascade-connected filament transformers 15B, 15C, 15D, a high-voltage output connector 16 connected to the secondary side of the last-stage filament transformer 15D and the other pole of the discharge protection resistor 14, and a CW circuit 13 High-voltage detector 17 which detects the high-voltage output of the inverter and feeds it back to the high-voltage inverter circuit 2 to stabilize the high-voltage output. Etc. consists of. The high voltage output connector 16 is connected to the filament F of the X-ray tube 6.
[0023]
Here, the cascade connection means that the secondary winding An2 of the filament transformer 15A and the primary winding Bn1 of the filament transformer 15B are connected in series, and the secondary winding Bn2 of the filament transformer 15B and the primary winding Bn1 of the filament transformer 15C are connected. This means that the winding Cn1 is connected in series, and the secondary winding Cn2 of the filament transformer 15C and the primary winding Dn1 of the filament transformer 15D are connected in series. If necessary, a capacitor or a resistor may be interposed between them.
[0024]
The high voltage detector 17 of this embodiment includes four resistor circuits 17A, 17B, 17C, 17D corresponding to the number of filament transformers 15A, 15B, 15C, 15D. Each resistor circuit is shown by a single resistor in the drawing, but in reality, a plurality of resistors are connected in series, or a single high-voltage resistor, or each of the resistor circuits 17A to 17D. It is composed of a capacitor connected in parallel to each of the plurality of resistors for equalizing the voltage. Then, the serial connection points A, B, and C of the series-connected resistance circuits 17A to 17D are arranged in descending order of the potential in the vertical connection point a between the corresponding filament transformers 15A and 15B and the vertical connection point between the filament transformers 15B and 15C. The connection point b is connected to the vertical connection point c between the filament transformers 15C and 15D.
[0025]
The CW circuit 13 has a normal circuit configuration, and includes four DC column capacitors 18A to 18D, four AC column capacitors 19A to 19D, and eight capacitors connected across the capacitors. Of high voltage diodes 20A to 20H. Since this is a conventional technique, detailed description is omitted, but only the capacitor 19A is charged to approximately the peak value E of the voltage of the secondary winding 12 of the high-voltage transformer 11, and the other capacitors 19B to 19D and 18A to 18D The transformer 11 is charged to a voltage 2E almost twice the peak value of the secondary winding voltage of the transformer 11, and outputs a high voltage of 8E as a final output.
[0026]
The discharge protection resistor 14 discharges the charges of the capacitors 18A to 18D and 19A to 19D instantaneously through the high-voltage diodes 20A to 20H due to the discharge accident of the X-ray tube 6, and destroys these high-voltage diodes by overcurrent. This is to limit discharge current in order to prevent and protect the device.
[0027]
In this embodiment, since the filament inverter circuit 4 is at the potential level of an X-ray control device (not shown), that is, at the ground potential level at which a human operates and contacts, substantially all of the four filament transformers 15A to 15D are connected. High voltage is applied.
[0028]
However, as described above, the voltage sharing of one filament transformer is 1/4 of the high-voltage output voltage, about 44 kV, and the insulation distance per filament transformer is 1/16. It can be seen that the overall size is smaller than the filament transformer withstands all voltages.
[0029]
Here, what is important is that in a simple cascade connection of the filament transformers, the filament transformers cannot equally share the high voltage, which is an obstacle to miniaturization. The cascade connection points a, b, and c are connected to the series connection points A, B, and C of the respective resistance circuits 17A to 17D of the high-voltage detector 17 divided into the same number of sets as the number of the filament transformers 15A to 15D. Connect in order from the side. In this case, since the respective resistance circuits 17A to 17D of the high-voltage detector 17 share the same voltage, the filament transformers also share the same voltage, and are arranged close to each other without applying special electric insulation means. Can be done.
[0030]
In other words, the high voltage detector 17, which is indispensable in this embodiment, performs the original high voltage detection, and at the same time, equalizes the shared voltage of the plurality of cascade-connected filament transformers. Since it is not necessary to add, the size of the entire apparatus can be reduced.
[0031]
All of the filament transformers 15A to 15D may be the same, but since only the filament transformer 15A is driven by the filament inverter circuit 4, the filament transformers 15B to 15C are different in the number of turns and the like. It is advantageous in manufacturing that the filament transformers 15B to 15C have the same structure and the same number of turns.
[0032]
Next, FIG. 2 shows a mounting example of the CW circuit 13, the filament transformers 15A to 15D, and the high voltage detector 17 in the high voltage generating circuit 4 having the circuit configuration shown in FIG. The same symbols as those shown in FIG. 1 indicate corresponding members.
[0033]
Since the filament transformer has almost the same structure, the filament transformer 15A will be described. The primary winding is wound around one leg of the UU-type ferrite core 31 and is electrically insulated. The secondary winding 32 is wound concentrically thereon. Therefore, the primary winding is not visible on the drawing. The filament transformer in which the small filament transformers 15A to 15D are connected in cascade does not become one large filament transformer as in the related art, but has an elongated columnar structure.
[0034]
The filament transformers 15A to 15D are substantially equal to each other so that the potential gradient of the filament transformers 15A to 15D is substantially equal to the potential gradient of the voltage detection resistors 17A to 17D arranged in a single bar or the DC column of the CW circuit 13. They are arranged in columns of height. By arranging them in this manner, they can be arranged along the voltage detection resistors 17A to 17D or in the vicinity of the DC column of the CW circuit 13, and there is an advantage that the whole can be downsized.
[0035]
FIG. 3 shows another embodiment of the present invention. The same symbols as those used in FIG. 1 indicate corresponding members. The number of subordinately connected filament transformers 17 is set to 1 / m (m is a natural number) of the number n of stages of the CW circuit 13. That is, when the four filament transformers 15A to 15D are cascaded, the CW circuit 13 has an integer multiple of four. In this embodiment, a four-stage CW circuit 13 and four filament transformers 15A to 15D are used, and their cascade connection points a, b, and c are connected to a capacitor 18A constituting a DC column of each stage of the CW circuit 13. To 18D corresponding to the series connection points A, B, and C in order of decreasing potential.
[0036]
As a result, the potential sharing of the filament transformer becomes the same as that of the series connection points A, B, and C of the CW circuit 13, and is substantially uniform. Therefore, each of the filament transformers 15A to 15D has a withstand voltage of about 2E, which is substantially equal to twice the peak value E of the secondary winding 12 of the high-voltage transformer 11, so as to have a withstand voltage between the primary winding and the secondary winding. Design insulation. However, in practice, the voltage of the capacitors 18A to 18D decreases with the regulation of the CW circuit 13 as it goes to the higher voltage portion. However, since the voltage is usually 10% or less, there is no problem, and it can be said that the voltage is shared almost uniformly.
[0037]
In this embodiment, the discharge protection resistors are not connected to the point P as in the first embodiment, but the four discharge protection resistors 21A to 21D are used. Each is connected in series and arranged separately.
[0038]
The reason will be described. If the discharge protection resistors are collectively connected to the high voltage output at point P in FIG. 3 as in the embodiment of FIG. 1, the primary winding Dn1 and the secondary winding Dn2 of the final stage filament transformer 15D are connected. Is connected across the discharge protection resistor. As a result, when the X-ray tube 6 is discharged, all the voltages of the capacitors 19A to 19D of the AC arm are applied to the collective discharge protection resistor through the high-voltage diode 20H, and at the same time, the primary winding Dn1 of the filament transformer 15D of the final stage. And the secondary winding Dn2, all the high voltage is applied, so that the filament transformer 15D causes dielectric breakdown.
[0039]
In order to prevent this, the above-described collective discharge protection resistor is divided into four, and each of the discharge protection resistors 21A to 21D is connected in series to the capacitors 19A, 19B, 19C and 19D of the AC arm, and a high voltage diode is connected. The current flowing through 20H is limited. Therefore, even when the X-ray tube 6 is discharged, equalization of the voltage sharing of the filament transformers 15A to 15D does not deteriorate. When the capacitance of the capacitor is small and there is no risk of damaging the high-voltage diode, the discharge protection resistor itself is unnecessary.
[0040]
Further, the position of the discharge protection resistor does not necessarily have to be in series with the AC capacitors 19A to 19D, but may be connected in series to each of the high voltage diodes 20A to 20H.
[0041]
The high-voltage generating circuit 5 is usually mounted in insulating oil or an insulating medium such as silicon rubber. Further, the multistage voltage doubler rectifier circuit 13 has been described as a Cockcroft-Walton circuit, but may have a similar circuit configuration such as a Schenkel circuit.
[0042]
In each of the above embodiments, the number of stages of the multistage voltage doubler rectifier circuit and the number of cascade connection stages of the filament transformer have been described as four, but other numbers of stages may be used. For example, when the number of stages of the multistage voltage doubler rectifier circuit is eight and the number of filament transformers is four, each filament transformer is substantially equal to four times the peak value E of the secondary winding 12 of the high voltage transformer 11. The voltage 4E is shared, and the insulation between the primary winding and the secondary winding is designed so as to have a withstand voltage equal to or higher than the voltage 4E.
[0043]
【The invention's effect】
As described above, according to the present invention, the insulation structure of a filament transformer in a high-voltage device for an X-ray tube, in particular, an X-ray high-voltage generation circuit for an ultra-high voltage CT of an anode grounded type is simplified and the size is greatly reduced. Can be.
[Brief description of the drawings]
FIG. 1 shows an embodiment of a circuit configuration of a high-voltage device for an X-ray tube according to the present invention.
FIG. 2 shows an example of the arrangement of circuit components of a high-voltage generator according to the present invention.
FIG. 3 shows another embodiment of the circuit configuration of the high-voltage device for an X-ray tube according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... High voltage inverter circuit 3 ... Filament inverter circuit 4 ... High voltage generation circuit 5 ... X-ray tube 6 ... Rectifier circuit 11 ... High voltage transformer 13 ... Multi-stage double voltage rectifier circuits 15A, 15B, 15C, 15D: Filament transformer 17: High voltage detection circuits 17A, 17B, 17C, 17D: Resistance circuit of high voltage detection circuit 17

Claims (6)

A high voltage transformer having a primary winding to which an AC voltage is supplied and a secondary winding for generating a boosted AC voltage;
A high voltage rectifier circuit connected to the secondary winding;
A high voltage detection circuit formed by connecting a plurality of resistors in series,
A filament circuit for feeding a filament of the X-ray tube;
In the high voltage device for an X-ray tube constituted by
The filament circuit is composed of a plurality of cascade-connected filament transformers in which primary windings and secondary windings of adjacent filament transformers are connected in series, and these filament transformers substantially equalize the voltage sharing. A high voltage device for an X-ray tube, wherein a vertical connection point of each of the filament transformers is connected to a potential point to be used. In claim 1,
The high voltage detection circuit is configured by serially connecting a number of resistor circuits corresponding to the number of the filament transformers in series, and connecting a series connection point of each of the resistance circuits to a vertical connection point of the filament transformer in order of potential. A high-voltage device for an X-ray tube, wherein each voltage of the filament transformer is shared equally. In claim 1,
The high-voltage rectifier circuit is a multi-stage voltage doubler rectifier circuit composed of an AC column and a DC column formed by combining a plurality of capacitors and a plurality of diodes. A high-voltage device for an X-ray tube, wherein the high-voltage devices are connected to the metal connection points in the order of potential so that the voltages of the filament transformer are shared equally. In claim 3,
A high-voltage device for an X-ray tube, wherein a discharge protection resistor is connected in series to each capacitor on the AC column side. In claim 3,
A high-voltage device for an X-ray tube, wherein a discharge protection resistor is connected in series to the high-voltage diode. In any one of claims 3 to 5,
A plurality of cascade-connected filament transformers are arranged in a columnar shape and are arranged along a multi-stage voltage doubler rectifier circuit having a substantially equal potential gradient or near the high voltage detection circuit. apparatus.

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