JPS6217840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a medical or industrial X-ray apparatus, and particularly to a fluoroscopic tube voltage control device for controlling tube voltage during fluoroscopy.

Generally, there are two types of medical X-ray equipment: imaging and fluoroscopy. In the case of fluoroscopy, the tube current is smaller and the time is longer than in the case of radiography, and it is desirable that the tube voltage changes continuously.

Sliding autotransformers, thyristors, transistors, and the like have been used to control the voltage of the viewing tube.

FIG. 1 is an electrical circuit diagram showing an example of a see-through tube voltage control device using a sliding autotransformer.

1 is a sliding autotransformer, 1A is a slider, 2
is a high voltage transformer, 3 is a high voltage rectifier, 4 is an X-ray tube, and Co is a distributed capacitance included in the high voltage cable.

In this case, the tube voltage control is performed by moving the slider 1A to set the input voltage of the high voltage transformer 2. This output voltage is rectified by a high voltage rectifier 3 and applied to an X-ray tube 4. In this method, the input and output waveforms of the high voltage transformer 2 are both sine waves, so problems such as waveform distortion do not occur, but since it is mechanically controlled, response speed and durability are poor, and it is also small and lightweight. difficult to convert. Therefore, recently there has been a tendency to adopt control systems using thyristors or transistors.

Fig. 2 is an electric circuit diagram showing an example of a system using a thyristor, in which 5 is an autotransformer for correcting the power supply voltage, 6 is a thyristor unit, 7 is a phase control unit, and the other parts are the same as in Fig. 1. .

In this method, the tube voltage is controlled by the high voltage transformer 2.
It is set by adjusting the input voltage of the high voltage transformer 2 by controlling the phase of a thyristor unit 6 consisting of two thyristors (or triacs) connected in antiparallel to the primary circuit of the high voltage transformer 2.

FIG. 3 shows the voltage waveforms of each part in FIG. 2, where a is the synchronizing signal from the phase control unit 7, and the shaded part b is the input voltage waveform to the high voltage transformer 2 whose phase is controlled by the thyristor unit 6. , c is a solid tube voltage waveform applied to the X-ray tube 4, and a dotted line is a tube voltage waveform calculated from the turns ratio of the high voltage transformer 2.

Note that since the tube voltage waveform is smoothed by the distributed capacitance Co included in the high voltage cable, it becomes the waveform shown in c in FIG. 3. In this method, the output voltage of the high voltage transformer 2, that is, the phase-controlled tube voltage, is generally higher than the calculated value, and this method also has the troublesome problem that it changes depending on the tube current value. This phenomenon occurs because the stray inductance L and stray capacitance C cause a resonance phenomenon, as shown in the equivalent circuit of the high voltage transformer 2 in FIG.

That is, the waveform shown in FIG. 3b has a steep rising portion and therefore contains many high frequencies.
Therefore, among these, those near the resonant frequency 1/2π√ of the high voltage transformer 2 cause a resonance phenomenon and increase the output voltage.

For this reason, in order to perform accurate voltage control using this method, it is necessary to take very complicated measures to control the output tube voltage by feeding it back to the phase control section.

Fig. 5 is an electric circuit diagram showing an example of a system using a full-wave rectifier circuit and a transistor, and 8 is a transistor unit consisting of a full-wave rectifier circuit 8A with bridge-connected rectifiers and a transistor 8B provided in its output circuit. , 9 is a base control unit.

That is, in FIG. 5, a full-wave rectifier circuit 8A is constructed in which a rectifier is bridge-connected to the primary circuit of the high voltage transformer 2.
is inserted so that direct current is always applied to the transistor 8B of the output circuit, and the transistor 8B is controlled by the base control circuit 9.

In general, transistors can be turned ON/OFF arbitrarily, so only the rising part of the input power supply voltage can be applied to the high voltage transformer 2 as shown in Figure 6, or more than a certain value of the input power supply voltage can be applied as shown in Figure 7. It is easy to think of a method in which the amount is consumed by the transistor 8B, and only the shaded portion is ultimately provided to the high voltage transformer 2.

However, if these methods are directly applied to a fluoroscopic tube voltage control circuit, the following problems will occur.

That is, in the system shown in FIG.
Since the period during which B supplies the input current is short, the ripple in the output tube voltage is large. Further, in FIG. 7, although the ripple is small, the amount of heat generated by the transistor 8B is very large.

Generally, in the case of fluoroscopy, the input voltage of the high voltage transformer 2 must be continuously adjusted within the range of 50-120V and the input current within the range of 3-8A. In this case, the transistor 8B needs to have a very large capacity of maximum (120-50) ^V x 8 ^A = 560W.

Currently, it is impossible to realize such a large-capacity transistor with a single transistor, and several transistors must be used in parallel, but the amount of heat dissipated is also problematic from the standpoint of miniaturizing devices.

As described above, all of the conventional methods have had various problems from a practical standpoint.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide an X-ray tube voltage control device that is capable of accurately controlling the X-ray tube voltage and, in addition, is capable of extremely quick response time.

FIG. 8 is an electric circuit diagram showing an example of a fluoroscopic tube voltage control device according to the present invention, and 11 is a photocoupler for coupling the pulse unit 10 and the transistor unit 8. 10A is a transformer, the input side of which is connected to the power supply side of the transistor unit 8. The output of the transformer 10A is full-wave rectified through the diode bridge 10A and input to the inverting terminal of the 10C comparator. On the other hand, 10D is a variable resistor that provides a constant DC voltage, and this variable output terminal is connected to the non-inverting input terminal of the comparator 10C.

The output of the comparator 10C is passed through the current suppression resistor 10E to the photodiode 11A of the photocoupler 11.
Since the phototransistor 11 is connected to
The transistor 8B can be driven by the voltage B.

FIG. 9 is an explanatory diagram of the operation of FIG. 8, where a is the output of the photodiode 11A, which is turned ON when the power supply voltage is at a phase lower than a predetermined value of the variable resistor 10D, making the transistor 8B conductive. This phase is set by variable resistor 10D. b is the input voltage of the high voltage transformer 2, and c is the tube voltage waveform. That is, the tube voltage is set by the variable resistor 10D.

As described above, according to the present invention, the transistor 8B is brought into conduction twice per 1/2 cycle of the AC power supply voltage, and the ripple in the tube voltage is reduced to 1/2 compared to the conventional method shown in FIG. . Also, since the first rising part is a sine wave and the rising is gradual, I wonder if the tube voltage will rise abnormally.Also, the next rising part is steep, but the stray capacitance C shown in Figure 4 is Since it is already charged by the pulse of
At this time, no abnormal increase in tube voltage occurs, and the input voltage and tube voltage are proportional, so it is extremely accurate.
Moreover, it is possible to control the X-ray tube voltage with a fast response speed.

Furthermore, since the transistor 8B provided in the output circuit of the full-wave rectifier circuit is simply controlled by ON/OFF, it generates very little heat, so it only needs to have a small capacity.

[Brief explanation of the drawing]

1 to 7 are electric circuit diagrams and explanatory diagrams showing the configuration of a conventional fluoroscopic tube voltage control device, and FIG.
The figure is an electric circuit diagram showing one embodiment of the present invention, and FIG. 9 is a waveform diagram for explaining the operation of FIG. 8. 2...High voltage transformer, 3...High voltage rectifier, 4
... 10D...
...Variable resistor (tube voltage setting device), 11...Photocoupler.

Claims (1)

[Claims] 1. A full-wave rectifier circuit is connected to the primary circuit of a high-voltage transformer energized by an AC power supply, and the conduction phase of a transistor provided in the output circuit of this rectifier circuit is controlled to An X-ray apparatus configured to adjust a ray tube voltage, characterized in that the transistor is configured to perform conduction control only during a phase period below a predetermined value corresponding to a set tube voltage of an AC power supply voltage. Control device. 2. The circuit for controlling the conduction of the transistor is a comparator that compares the full-wave rectified output of the AC power supply voltage with the tube voltage setting signal, and the conduction phase of the transistor is controlled by the output of this comparator. An X-ray tube voltage control device according to claim 1.