JPH0278196A - X-ray generating device - Google Patents

Abstract

PURPOSE:To enable the manufacture of multiple kinds of X-ray generating device having different capacity with inexpensive cost, by connecting to combine appropriate number of unit transformers having relatively small capacity, and forming a high voltage transformer having the respectively optimum parasitic impedance in response to the output capacity. CONSTITUTION:The output voltage of a DC power source 1 is converted to the AC voltage by a resonance type inverter 2 and is pressure raised up by a high voltage transformer 3, and after converting to the DC voltage by a high voltage rectifier 4, it is applied to an X-ray tube 5 so as to generate the X-ray. The high voltage transformer 3 consists of two unit transformers 3a, 3a having the first coil and the second coil connected in parallel. The marks shows the polarity of the coils. In this case, the composite floating capacity value becomes 2C0, the leakage-reactance value becomes LO/2, and the reference impedance ZP becomes (LO/2/2CO)<1/2>. Consequently, the output power PP becomes PP=k/ZP=k/ZO/2=2PO and it shows that they are twice as large as these of the case that one unit transformer 3a is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an X-ray generator using an inverter, and particularly to an X-ray generator suitable for using a resonant inverter.

[Conventional technology]

Resonant inverters (Japanese Patent Application No. 62-18209, etc.), which have been increasingly used for electric power in recent years, have remarkable features for high performance, such as being able to operate at high frequencies and reducing the burden on switching elements.

However, in this case, the output characteristics are easily affected by the circuit constants of the resonant circuit that serves as the load.For this reason, the load is a complex resonant circuit, such as a high-voltage transformer for an X-ray generator. When operating, it is not easy to obtain the desired output characteristics.

In particular, in an X-ray generator with a wide load range, the load impedance, which is one element of the resonant circuit, changes by about the fourth power of 10, so the parasitic impedance of other circuit elements, that is, the high-voltage transformer, cannot be adjusted to the optimum value. It is known that without this, it is not possible to stably control the device output.

High-voltage transformers for such X-ray generators have a very large number of turns in the secondary winding in order to obtain a high step-up ratio, so the stray capacitance of the secondary winding is large. The insulation distance between the primary and secondary sides is long, and the leakage reactance is large.Originally, these parasitic impedances due to stray capacitance and leakage reactance are not necessarily necessary for the function of the transformer, but are incidental due to production technology. It was just an element that occurs. Therefore, when using a high voltage transformer as a load in a conventional voltage type inverter, this parasitic impedance has been ignored or canceled out.

[Problem to be solved by the invention]

However, in a resonant inverter that uses the impedance of the load as a resonant element, the parasitic impedance of the high voltage transformer cannot be ignored, and this can adversely affect the output waveform and control range, or cause the inability to generate the required output. There are many things. For this reason, high-voltage transformers must be manufactured strictly so that the leakage reactance and stray capacitance are at optimum values, making the structure and materials complex, requiring a great deal of time to design, and requiring manufacturing technology. A high degree of accuracy is also required.

On the other hand, in medical X-ray generators, the output capacity differs depending on the diagnostic use such as circulatory system or gastrointestinal use, and the output capacity also differs depending on the use purpose such as stationary type or portable type.The output capacity is usually 10k14.30kW. , 50kW.

There are many types such as 80kW and 100kln.

Therefore, manufacturing the device requires many types of high voltage transformers.

However, with the transformer-type and voltage-type inverter X-ray generators that are currently widely used, separate high-voltage transformers are designed and manufactured independently of each other for each X-ray generator with a different output capacity. It is manufactured using For this reason, as mentioned above, along with the high level of sophistication required in the manufacturing technology of high voltage transformers, it is extremely uneconomical to manufacture many different types of high voltage transformers, resulting in a significant increase in costs. There was a problem that the X-ray generator was expensive.

An object of the present invention is to manufacture an X-ray generator using a resonant inverter in which the parasitic impedance of a high-voltage transformer acts as a resonant element.
＆ It is possible to manufacture high voltage transformers with suitable parasitic impedance at low cost, and it is possible to manufacture many types of X with different output capacities.
The object of the present invention is to provide a line generator at low cost.

[Means to solve the problem]

The above purpose is to manufacture a relatively small-capacity high-voltage transformer as a unit transformer, which makes it easy to obtain a strict parasitic impedance constant, and then connect the unit transformers in an appropriate number of combinations to achieve the required parasitic impedance and output. This is achieved by simultaneously providing capacity.

[Effect]

In the case of an X-ray generator, the wire diameter of the secondary winding of the high voltage transformer is determined by the tube current. Among Xa generators whose ratings are such that the maximum tube current is n times larger, the cross-sectional area of the secondary winding of the high voltage transformer is also n times larger. This relationship holds true for the primary winding, but from this relationship, by connecting n high voltage transformers of the same rating in parallel, an X-ray generator with n times the output capacity can be configured.

On the other hand, it is easier to obtain the parasitic impedance value required for a high-voltage transformer when the volume of the high-voltage transformer is small.

This is because the stray capacitance between the secondary windings is a distributed constant, so if the volume of the secondary winding is large, this calculation becomes complicated.

Here, if the equivalent circuit of the high voltage transformer is expressed in terms of stray capacitance JIC, which is parasitic impedance, and leakage inductance, it becomes as shown in FIG. However, the excitation inductance in parallel with the stray capacitance C is ignored here because it has an infinite value.

If n high-voltage transformers shown in this equivalent circuit are connected in parallel, the combined stray capacitance C will be nC, and the combined leakage inductance will be L/n. Similarly, if n pieces are connected in series, the stray capacitance C will be C/n, and the leakage inductance will be nL.
become. From this, it is possible to synthesize a desired parasitic impedance by connecting high voltage transformers in parallel or in series.

When using the parasitic impedance of a high-voltage transformer as the resonant element of a resonant inverter, it is known that the relationship shown in Figure 3 exists between the constants of stray capacitance C and leakage inductance L, and the output voltage P of the high-voltage transformer. . In order to increase the output power (output capacity) P in Fig. 3, the square root of the ratio of L and C (hereinafter referred to as reference impedance Z) must be reduced, and the relationship in Fig. ) can be expressed as

P=ni/Z・・・・・・・・・・・・・・・
・(1) However, k is an arbitrary constant Z=(nu];7teko...(2) From the above equation (1), the following equation (3) holds.

n P = k / n n --(3
) This equation (3) means that, for example, to increase the output power P by n times, C should be multiplied by n and L should be set to L / n. This can be easily achieved by connecting them in parallel. That is, when creating a high-voltage transformer with a large output power, parallel connection of high-voltage transformers is effective in optimizing its parasitic impedance.

If the high-voltage transformer used for the lowest-output X-ray generator is a unit transformer, multiple unit transformers can be connected in parallel and used for other output capacity xH generators. Can be done. For this reason, X of various output capacitances
For the line generator, it is only necessary to manufacture a large number of identical unit transformers. By manufacturing a large number of identical unit transformers, costs can be reduced through mass production, and the manufacturing cost per unit transformer is reduced, which reduces the price of the high voltage transformer itself and reduces the output capacity. Many different types of X-ray generators can be manufactured at low cost.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
The figure is a circuit diagram showing a first embodiment of the X-ray generator according to the present invention. In this figure, the output voltage of a DC power supply 1 is converted into an AC voltage by a resonant inverter 2,
After being boosted by the high-voltage transformer 3, it is converted into a DC voltage by the high-voltage rectifier 4, and applied to the X-ray tube 5 to generate XIl. In this case, the high voltage transformer 3 is comprised of two unit transformers 3a, 3a, and these two unit transformers 3a, 3a are primary windings.

The secondary windings are also connected in parallel. Note that the * mark in the figure indicates the polarity of the winding of each unit transformer 3a, and if a positive voltage is applied to the primary winding on the side marked with *, the polarity of the secondary winding will also change.
The sign side produces a positive voltage.

Since a medical X-ray generator generates a tube voltage of a maximum of 150 kV, it is necessary to prevent discharge within the high voltage transformer 3. Therefore, here we will introduce the grounded casing (in the figure,
The intermediate point of the secondary winding is grounded in order to fix the potential difference generated between the secondary winding (indicated by the dotted chain line) and the secondary winding to a certain value or less. Also, the secondary winding is one winding here,
Although it is shown as a so-called single-legged transformer, it is a so-called two-legged transformer in which the primary winding is split at the midpoint to create two windings, each of which is inserted into a different leg of the same magnetic core. It is possible because

If the leakage inductance of one unit transformer 3a in FIG. 1 is Lo and the stray capacitance is C6, the reference impedance Z0 is - from the above equation (2) at fboreflr. If this one unit transformer 3a is used for a 10kHz X-ray generator, the value of the reference impedance Zo is:
1 in FIG. 3 as the resonant element of the resonant inverter 2.
This value allows an output of 0kHz. In other words, this embodiment uses X! for 20kW. ! The configuration of the generator is shown. If the unit transformers 3a, 3a shown in FIG. 1 are both shown in the equivalent circuit of FIG. 2, the high voltage transformer 3 in this embodiment is one in which two unit transformers 3a are connected in parallel. Therefore, the combined stray capacitance value is 2CO, and the combined leakage reactance value is L0/2. From the above formula (2), the reference impedance Zp of the high voltage transformer 3 is:

0), which is 1/2 of the reference impedance Z0 of the unit transformer 3a. These results
The output power Pp of the high voltage transformer 3 is as follows: Pp=to/Zp=to/Zo/2=2Po・-
--- (4) It can be seen that the high-voltage transformer 3 of this embodiment can generate an output power of 2@ compared to the case where there is only one unit transformer 3a.

From the above, it can be seen that an X-ray generator capable of generating multiple times as much output power can be constructed simply by connecting a plurality of unit pressure vessels 3a in parallel. Further, in this embodiment, the unit transformer 3a
Although the explanation has been given using an example with an output capacity of 10 km, it is needless to say that the present invention is not limited to this.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention. In this second embodiment, the desired output power is obtained by connecting the secondary windings of two unit transformers 3a, 3a in series. Here, by changing the winding direction at the midpoint of the secondary winding, both ends of the secondary winding have the same polarity, and both ends are connected to form the secondary winding in one unit transformer 3a. By arranging them in parallel, only one unit transformer 3a can obtain the current capacity for two. However, since the turn ratio of the secondary winding to the primary winding is halved, each unit transformer 3a, 3a only needs to share half of the required tube voltage.The midpoint of the secondary winding is Since they are each grounded, the two unit transformers 3a, 3a on the positive side and the negative side are connected in series with respect to the ground potential. In order to reverse the polarity as positive side and negative side transformers, the primary windings of each unit transformer 3a, 3a are connected so as to have opposite polarities. Since the stray capacitance C0 of the unit transformer 3a is connected in series, the stray capacitance C of the high voltage transformer 3 of this second embodiment is 2C in the equivalent circuit converted to the primary side.
It is expressed as Similarly, the leakage inductance is L o /
2, and as a result, the parasitic impedance itself of the high voltage transformer 3 is the same as in the first embodiment, and an output power of 20 kHz is possible. According to this second embodiment, half the voltage applied to the Xi tube 5 only needs to be shared by one unit transformer 3a, so that the withstand voltage design is easy and downsizing is also possible.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

This third embodiment has one high voltage rectifier 4 for each output of the two unit transformers 3a, 3a of the first embodiment.
are connected, rectified into DC voltage, and then added in parallel, and the power that can be generated is the same as in the first embodiment. In this third embodiment, twice the number of high voltage rectifiers 4 is required as in the first embodiment, but the current capacity of the rectifying elements constituting the high voltage rectifier 4 may be half. In the embodiment, if there are manufacturing variations in the unit transformers 3a and transformers with different turns ratios and parasitic impedances are connected in parallel, a circulating current flows between the secondary windings and the tube voltage waveform changes. Abnormalities may appear, but this third
According to the embodiment, the circulating current is blocked by the high-voltage rectifier 4, so that it does not adversely affect the tube voltage waveform. Therefore, the high voltage transformer 3 does not require strict production control, which has the advantage of reducing manufacturing costs.

〔Effect of the invention〕

According to the present invention, when manufacturing an X-ray generator using a resonant inverter that uses the parasitic impedance of a high-voltage transformer as a resonant element, each high-voltage transformer has an optimal parasitic impedance depending on its output capacity. This has the advantage that it can be manufactured at low cost, and therefore, many types of X-ray generators with different output capacities can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the device of the present invention;
The figure is an equivalent circuit diagram of a high voltage transformer used in an X-ray generator, Figure 3 is a characteristic diagram showing the relationship between reference impedance and output power of the same high voltage transformer, and Figure 4 is a second implementation of the device of the present invention. FIG. 5 is a circuit diagram showing a third embodiment of the device of the present invention. 1... DC power supply, 2... Resonant inverter, 3...
- High voltage transformer, 3a... unit transformer, 4... high voltage rectifier, 5... Xll tube. Patent applicant Hitachi Medeico Co., Ltd. Agent Patent attorney Masami Akimoto and 1 other person 2nd diagram 3rd figure T

Claims (1)

[Claims] 1. A DC power supply, a resonant inverter that converts the DC voltage from the DC power supply into an AC voltage, and a resonant inverter that acts as a resonant element of the resonant inverter and boosts the output voltage of the resonant inverter. In the X-ray generator, the high-voltage transformer has a predetermined parasitic impedance. 1. An X-ray generator characterized in that a desired parasitic impedance and output capacitance are provided by connecting an appropriate number of unit transformers. 2. The X-ray generator according to claim 1, wherein the high voltage transformer is formed by connecting a plurality of unit transformers in parallel. 3. The high voltage transformer includes a first unit transformer in which the winding direction is reversed at the middle point of the secondary winding, the middle point is grounded, and both ends are short-circuited; The unit transformer consists of a second unit transformer whose primary winding has opposite polarity, and the first unit transformer and the second unit transformer have their primary windings connected in parallel. The X-ray generator according to claim 1, comprising a secondary winding connected in series. 4. The high voltage transformer comprises a plurality of unit transformers, the primary windings of which are connected in parallel, the secondary windings of each of which are connected to separate high voltage rectifiers, and the output ends of each high voltage rectifier are connected in parallel. TeX
The X-ray generator according to claim 1, which is connected to a ray tube.