JPS61239600A - Inverter type x-ray plant - Google Patents

Abstract

PURPOSE:To obtain a stable tube voltage waveform with small ripple by back- charging the stray capacity of a high tension transformer during an inactive period of an inverter, in order to prevent oscillating current when the inverter is actuated. CONSTITUTION:When transistors 2 and 5 are turned off as base current (a) and (d) are cut off at time t0, load current iI is reduced to zero. Immediately after the load current iI is reduced to zero, at time t1, gate signal (e) is fed to a thyristor 20 to turn on the thyristor. By this, charge of stray capacity CS is discharged through paths CS L1 20 CS to back-charge the stray capacity CS. At time t2, when this vibration is nearly completed, base current (b) and (c) are let to flow, to turn on transistors 3 and 4. As the stray capacity CS is already back-charged by this time, load current iI flows through paths 1 3 12 15 and 16 13 L1 4 1, with almost no oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inverter type X-ray apparatus, and particularly to a technique suitable for reducing the pulsation rate of a tube voltage waveform.

[Background of the invention]

The X-ray device receives commercial power, adjusts the voltage by changing the position of the sliding brush installed on the secondary side of the voltage adjustment transformer, boosts the voltage using a high-voltage transformer, rectifies it, and then outputs the X-rays. Tube-applied configurations have been used.

On the other hand, inverter-type X-ray apparatuses that apply power control technology have been developed using power semiconductors, which have been developed at a remarkable pace in recent years. Since the inverter-type X-ray apparatus uses semiconductor elements for power control, the response of the power control is extremely fast compared to the case where the above-mentioned voltage regulating transformer is used. Therefore, the tube voltage can be easily adjusted during X-ray emission, and the tube voltage can be set accurately.

FIG. 3 shows the configuration of a conventional inverter type X-ray apparatus.

■ is a DC power supply that serves as the input power source for the inverter; 2 to 5 are transistors that are turned on by flowing base current; transistors 3 and 4 are turned on at the same time, and transistors 2 and 5 are turned on at the same time. By repeating the process, DC voltage is converted to AC voltage. Diodes 6 to 9 are connected in antiparallel to the resistors 2 to 5, respectively, and regenerate energy in the circuit to the DC power supply 1. The inverter is thus configured by 2 to 9. 10 is a high voltage transformer that boosts the inverter output voltage;
1 to 14 are diodes constituting a full-wave rectifier, and 15 is a capacitance existing in a high-voltage cable connecting the output of the full-wave rectifier and the X-ray tube 16.

Therefore, the equivalent circuit of the high voltage transformer 10 can be expressed as shown in FIG. Since the transformer ratio of a high-voltage transformer is large, the number of turns of the secondary coil is large, and the number of layers is large. There is a stray capacitance between these layers, which can be expressed as shown in FIG. 4(a). These stray capacitances are expressed as an equivalent circuit,
It may also be used as Fig. 4(b). Well, since the transformer itself can be represented by leakage inductances Lt1 and LL2 and excitation inductance TJe'f, the equivalent circuit together with the stray capacitance C8 is as shown in FIG. 4(C). Furthermore, since LL+<LaX+ LL<Law,
When Lz=LtI+LL2, the equivalent circuit of the high voltage transformer is shown in FIG. 4(d).

FIG. 5 shows an inverter type X-ray apparatus using the equivalent circuit of the high voltage transformer shown in FIG. 4(d). 1 to 9 degrees and 11 to 16 are the same as those shown in FIG. 3, and their explanation will be omitted. The high voltage transformer 10 is illustrated by a leakage inductance Lt and a stray capacitance iCs.

Next, the operation will be explained with reference to FIGS. 5 and 6.

When transistors 2 and 5 are turned on by base currents a and d, the load current 1r becomes 1→2→Lt→11→15 and 1
It flows along the path 6→14→5→1 and supplies power to the load. At this time, the stray capacitance Cs is also charged, and its polarity is as shown in FIG. Next, at time to, base currents a and d stop, transistors 2 and 5 are turned off, and load current ir becomes zero. After a pause period so that transistors 3 and 5 or 2 and 4 do not turn on at the same time, at time t1, the base current and cf flow transistor 3.
and turn on 4. During this period of time 1o-1°, the polarity of the stray capacitance Cs is maintained as shown in FIG. Therefore, when transistors 3 and 4 are turned on at time t, current flows through the path 1→3→C5-Lt→4→1, as shown by the broken line, and the stray capacitance Cse is reversely charged. This reverse charging is performed in a resonant circuit of the leakage inductance TJt and the stray capacitance Cs whose power source is the sum of the voltage of the DC power supply 1 and the voltage of the stray capacitance C8, so that an excessively oscillating DC flows. Therefore, the load current i becomes an oscillating current as shown in FIG. The peak value ixp of this oscillating current is expressed by the following equation, where the voltage of the DC power supply 1 is E1 and the voltage of the stray capacitance Cs is .

By the way, at time 1o, E' - fV, so at time t2 when the first half cycle of this oscillating current is completed, the voltage of stray capacitance Cs reaches its maximum, and this voltage is higher than the voltage of DC power supply 1. Become. However, the voltage V applied to the capacitance 15 existing in the high-voltage cable and the X-ray tube 16 becomes equal to the voltage V of the stray capacitance Cs, so it reaches its maximum at time t2.

This voltage 8 is the leakage inductance Lt and the stray capacitance Cs
Due to the vibration of the high voltage transformer 100 turns ratio DC power supply 1
becomes larger than the boosted one. After that, the stray capacitance C
The charge at s oscillates along the path Cs→7→1→8→Lt→Cs and returns to the power supply, so no power is supplied to the load. Therefore, power is supplied to the X-ray tube 16 only from the discharge from the capacitance 15 present in the high-voltage cable, and vx decreases as shown in FIG. The vibration gradually decreases, and when transistors 3 and 4 turn on at time t3, the stray capacitance C8
is charged with the polarity opposite to that shown in FIG. 5, and the same operation is repeated thereafter.

As described above, the charge in the stray capacitance of the high voltage transformer is charged to the polarity each time the polarity of the inverter output voltage is reversed. This charging current becomes an oscillating current due to the leakage inductance of the high-voltage transformer, and as a result, the tube voltage becomes larger than the inverter output voltage times the step-up ratio of the high-voltage transformer, and the tube current and oscillating current are superimposed. The DC ratings of the transistors 2 to 5 also need to be selected in consideration of the oscillating current.

Therefore, it is necessary to prevent vibrations caused by the leakage inductance and stray capacitance of the high voltage transformer from adversely affecting the tube voltage waveform.

The above-mentioned vibration prevention method using inductance and capacitance in an inverter type X-ray device Qlx7i1
,1,E6.0□l]? 357531°. 0 □□There is a report. In Japanese Patent Laid-Open No. 57-53100, as a method for preventing vibrations caused by leakage inductance of a high voltage transformer and capacitance of a high voltage cable, a resistor is inserted into the circuit to obtain a damping effect.

[Purpose of the invention]

An object of the present invention is to provide an inverter-type X-ray apparatus that can reduce tube voltage pulsations caused by vibrations due to leakage inductance and stray capacitance of a high-voltage transformer and obtain a stable tube voltage waveform.

[Summary of the invention]

The above problem is that the leakage inductance and stray capacitance of the high voltage transformer cannot be physically reduced to zero, and each time the polarity of the inverter output voltage changes, the stray capacitance of the high voltage transformer changes depending on the polarity of the inverter output voltage and its This occurs because the current polarity of the stray capacitance is charged to the opposite polarity.

The present invention has been achieved by focusing on the above two points, and its outline is to make the timing of charging the stray capacitance and the timing of supplying power from the inverter to the load not equal, and to provide power from the inverter to the load. 0°m"'-i;M""°1
°゛＜y′neepmj″t′Eo.

When the polarity changes, to ~ in Figure 6
A rest period such as [, tl or 13 to t4 is provided, and during this period, the polarity of charging of the floating capacitance is reversed. In this way, in the present invention, j(・ is a floating voltage before the polarity of the output voltage
[By reversing the polarity of the capacitor voltage, when the inverter is turned on and the load current starts flowing, there is no need to reverse charge the stray capacitance, and oscillating current can be prevented, so the tube voltage waveform This was done with a focus on the fact that it is possible to eliminate the negative effects of

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the first practical example of the present invention. 1-9.
f11 to f16 are the same as those in Figure 3, and their explanation will be omitted.
, 1 ctance, C8 is the stray capacitance of the high voltage transformer, 2
0 and 21 turn on when a gate signal is input, and the flowing current is below the predetermined latching current, or is a reverse bias, (1
0) It is a thyristor that turns off by

Next, the operation will be explained using FIGS. 1 and 2.

When the transistors 2 and 5 are turned on by the base currents a and d, the load current i flows through the paths 1→2→Lt→11→15 and 16→14→5→1 to supply power to the load. At this time, the stray capacitance C8 is charged with the polarity shown in FIG. Next, time t. When the base current a(!:d stops and transistors 2 and 5 are turned off, the negative 1 positive current 1
■ becomes zero.

Immediately after the load current i becomes zero, a gate signal e is input to the thyristor 20 at a time t1 to turn on the thyristor 20. Then, the charge of the stray capacitance Cs is C8→L t→
20 → Cs, and the stray capacitance C5fi = reverse charge. The peak value iyp of the oscillating current at this time is expressed by the following equation, assuming that the voltage of the stray capacitance C8 is ■.

This is much lower than the value shown in FIGS. 5 and 6 (formula (b)), and the current peak value can also be made smaller.

At time t2 when this vibration is almost completed, base currents b and C are caused to flow, turning on transistors 3 and 4. Then, since the stray capacitance Cs has already been reversely charged, 1→3→
Load current i2 flows through the paths 12→15 and 16→13→L t→4→1, and almost no vibration occurs. Therefore, the capacitance 15 and X
A voltage obtained by boosting the voltage of the DC power supply 1 to a value approximately equal to times the turns ratio of the high voltage transformer is applied to the wire tube 16 . Well, when transistors 3 and 4 turn on, the thyristor 20 becomes reverse biased, so it turns off.

As described in Part 2, in this embodiment, the voltage of the stray capacitance of the high voltage transformer can be reversely charged during the inverter's rest period, and no oscillating current is generated when the inverter is turned on, so a stable tube with small pulsations can be achieved. voltage can be obtained. Since the oscillating current of the leakage inductance Lt and the stray capacitance Cs does not flow to the inverter, the current capacity of the transistors 2 to 5 only needs to take into account the load current.

: FIG. 7 shows a second embodiment of the invention. 1 to 9. 11 to 16 are the same as those in Figure 3,
The explanation will be omitted. TJ t is the leakage inductance of the high voltage transformer, and C8 is the stray capacitance of the high voltage transformer.

1 Next, the operation will be explained using FIG.

When transistors 2 and 5 are turned on by base currents a and d, load current iI flows along the paths 1→2→Lt→11→15 and 16→14→5→1 to supply power to the load. At this time, the stray capacitance Cs is charged with the polarity shown in FIG. Next, at time to, the base currents a and d stop, and the transistors 2 and 5 turn off, and the load current j□ becomes zero. Immediately after the load current ir becomes zero, at time 1, first, when the base current C is caused to flow and the transistor 4 is turned on, the charge on the stray capacitance CB becomes C8→
Lt→4→a-+ Flows along the path shown by the broken line CB, and reversely charges the stray capacitance C8. The peak value irp of the oscillating current at this time is expressed by equation (c) as in the first embodiment shown in FIG.

At time t2 when this oscillation is almost completed, a base current b is caused to flow and the transistor 3 is turned on. Stray capacitance C8 has already been reversely charged, so 1→3→12→15 and 1
The load current iI flows through the path 6→13→L t→4→1, and almost no vibration occurs. Therefore, a voltage obtained by boosting the voltage of the DC power supply 1 to approximately equal to the turns ratio of the high voltage transformer is applied to the capacitance 15 and the X-ray tube 16 existing in the high voltage cable.

As described above, in the embodiment shown in FIG. 7, the voltage of the stray capacitance of the high-voltage transformer can be reversely charged during the inverter's rest period, as in the embodiment shown in FIG. 1, and when the inverter is turned on, the oscillating current Since no oscillation occurs, a stable tube voltage with small pulsations can be obtained. Fortunately, in this embodiment, there is no need to add any new circuit elements, and it can be implemented using the control signal of the inverter.

FIG. 9 shows a third embodiment according to the invention.

This embodiment is an example of application to a push-pull type inverter. 1 to 3, 6 to 7, and 11 to 16 are the same types as those in Figure 3, and 20 and 21 are the same types as in Figure 1, and their explanations will be omitted. 30 is a high voltage transformer having a center tap in the primary winding, and is connected to a push-pull type inverter.

This operation is as follows. Inverter operation is performed by turning on transistors 2 and 3 alternately.

The polarity of the voltage of the stray capacitance of the high voltage transformer 30 is reversed using the thyristors 20 and 21. In other words, before transistor 3 turns off and transistor 2 turns on, the cyrisk 21 is turned on to reverse the polarity of the stray capacitance voltage, and before transistor 2 turns off and transistor 3 turns on, Turn on the Cyrisk 20 to invert the polarity of the stray capacitance voltage.

By the above operation, as in the previous embodiment, the voltage of the stray capacitance of the high-voltage transformer can be reverse charged during the inverter's rest period, and when the inverter is turned on, no oscillating current is generated, so the voltage is stable with little pulsation. Tube voltage can be obtained.

FIG. 10 shows a fourth embodiment according to the invention.

This embodiment is an example of application to a push-pull type inverter, similar to FIG. 9. All parts shown in Figure 10 are
It is the same as the figure. The difference between FIG. 10 and FIG. 9 lies in the way the cyrisks 20 and 21 are connected. In FIG. 9, the thyristors 20 and 21 are connected in antiparallel between both poles of the primary winding of the high voltage transformer 30, but in FIG. are connected separately between them.

This operation is exactly the same as the embodiment of the single-ten diagram, and the same effect can be obtained. However, the voltage applied to thyristors 20 and 21 in FIG. 9 is twice the voltage applied to thyristors 20 and 21 in FIG. 10.

On the other hand, the current flowing through the thyristors 20 and 21 in FIG. 10 is twice the current flowing through the thyristors 20 and 21 in FIG.

Note that the present invention is not limited to the above embodiments,
Implementation 1 regardless of the difference in inverter method etc.
It is possible and similar effects can be obtained.

! [Effects of the Invention] According to the present invention, in an inverter-type X-ray apparatus, the voltage of the stray capacitance of the high-voltage transformer can be reversely charged during the inverter's rest period, and no oscillating current is generated when the inverter is turned on. , it is possible to obtain a stable tube voltage waveform with small pulsations.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the first embodiment of the present invention, Fig. 2 is a time chart explaining the operation of Fig. 1, Fig. 3 is a configuration diagram of an inverter type X-ray device, and Fig. 4 is a high voltage An equivalent circuit diagram of a transformer, Figure 5 is a configuration diagram of a conventional device, and Figure 6 is a time chart explaining the operation of Figure 5. 7ElIJ
'M' Ji. □Eng. A., 1□□Route diagram, Fig. 8 is a time chart explaining the operation of Fig. 7, Fig. 9 is a circuit diagram showing the third embodiment of the present invention, Fig. 10 is the fourth embodiment of the present invention. It is a circuit diagram showing an example of. 1...DC power supply, 2-5...Transistor, 6-9
...Diode, 11-14...Diode, 15
...High voltage cable capacitance, 16...X-ray tube, C
s... Stray capacitance of high voltage transformer, Lt... Leakage inductance of high voltage transformer, 20.21... Thyristor. d, ・-J > □, Niechi 71

Claims (1)

[Claims] 1. An inverter that receives DC power and converts it into AC;
A transformer for boosting the output voltage of the inverter, a rectifier for converting the output voltage of the transformer into direct current, and a cable having a first capacitance between the rectifier output end and the X-ray tube and the ground. In an inverter-type X-ray apparatus that is connected or provided with a smoothing capacitor between the rectifier output end and the X-ray tube, the inverter output voltage is connected in parallel to the rectifier input side before the polarity of the inverter output voltage changes. An inverter-type X-ray apparatus characterized by having means for changing the polarity of the voltage of the second capacitance. 2. The means for changing the polarity of the voltage of the second capacitance is a switch having a load connected in parallel to the output side of the inverter, and the switch changes the polarity of the voltage of the second capacitance. The inverter-type X-ray apparatus according to claim 1, wherein the inverter-type X-ray apparatus is turned off when the inverter-type X-ray apparatus is turned off. 3. The inverter type X-ray apparatus according to claim 2, wherein the switch is a thyristor connected in antiparallel. 4. The inverter is connected in series with a first switch element connected to the positive pole of the DC power supply and a second switch element connected to the negative pole of the DC power supply, and connected in antiparallel to the first and second switch elements, respectively. A first arm consisting of a diode, a third switch element connected to the positive pole of the DC power supply, and a fourth switch element connected to the negative pole of the DC power supply are connected in series, and the third and fourth switch elements are connected, respectively. a second arm consisting of diodes connected in antiparallel, and between a connection point between the first switch element and the second switch element and a connection point between the third switch element and the fourth switch element. The flip-rich type inverter is connected to a transformer, and the means for changing the polarity of the voltage of the second capacitance is when the first switch element and the third switch are turned on, or when the second switch element is turned on. 2. The inverter type X-ray apparatus according to claim 1, wherein when turning on the first and third switching elements, one of the switching elements is turned on earlier than the other.