JPS614200A - X-ray device - Google Patents

Abstract

PURPOSE:To enable protection against overcurrent and short-circuit current by connecting a couple of primary windings and a resonance capacitor to a rectifier and smoothing means by crossing both terminal sides to a switching means. CONSTITUTION:In normal operating condition, primary current flows in either of primary windings 6a, 6b by repeating plus and minus alternately, but when switching elements 14a, 12b are turned just after turn-off of switching elements 12a, 14b, it is estimated that excessive abnormal current may flow as elements 12a, 14a and 12b, 14b become continued at the same time. While in the case of windings 6a, 6b of a transformer T, winding start is in the identical direction and connecting relation of depolarization is given, then inductive flux of windings 6a, 6b is erased and abnormal voltage will not be generated. Elements 12a, 14a, 12b, 14b will not be broken even if abnormal surge current of some tens as much of rated current flows therein.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an X-ray apparatus used in a series rEt bridge inverter source circuit.

[Technical background of the invention and its problems] As a conventional X-ray device, for example, US Pat. No. 422,578
There is also a so-called series resonant bridge inverter system, as disclosed in No. 8 and the like.

This series resonant bridge inverter type X-ray apparatus rectifies and smoothes an AC voltage supplied from an electric power source (generally a commercial power supply) to obtain a DC voltage, and also connects this DC voltage to each other in series and performs switching. X It is designed to obtain line tube voltage.

In such an X-ray apparatus, there is a problem in that if two switching elements connected in series are turned on at the same time for some reason, an excessive short-circuit current will flow, causing damage to the switching elements.

In addition, large ground fault currents such as the above-mentioned short circuit currents and ground faults in circuit elements of X-ray equipment are also generated in high voltage circuits on the secondary side of transformers, including high voltage generating equipment.

In order to deal with this problem, there is a means for controlling both switching elements so that after the first switching element is turned off, the second switching element is turned on.

However, even with such means, there is no guarantee that the above-mentioned problems will not occur due to variations in the characteristics of the J3 circuit elements, instability of the gate pulses supplied from the switching element control means, etc.

Furthermore, there are means for overcurrent protection using fuses, breakers, etc., but fast-acting fuses are generally expensive, and breakers have the drawbacks of poor responsiveness.

[Object of the Invention] The present invention has been made in view of the circumstances in item 1, and provides one-minute protection against overcurrent and short circuit current with a simple and inexpensive configuration.
The purpose is to provide an X-ray device that can achieve

1 Summary of the Invention] Achieving the above objectives [The summary of this defense is to rectify and smooth input AC voltage to output DC voltage.
a smoothing means, a resonant circuit comprising at least a primary winding of the transformer and a resonant capacitor, and a switching means for applying the DC voltage to the resonant circuit at a predetermined period; In an X-ray apparatus that obtains an i-X-ray tube voltage based on the voltage induced in the A pair of primary windings and a resonance capacitor are connected to the rectifier and the resonance capacitor.
The smoothing means is characterized in that both terminal sides of each are connected to the switching means so as to cross each other.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an X-ray apparatus according to the present invention, in which 1 is a power supply supplying AC voltage to the apparatus;
2, rectifiers 2a, 2b, 2G, and 2ri are bridge-connected, and rectifying means for rectifying the AC voltage supplied from the power source 1J; 3, an 11 capacitor C; This is a smoothing means for smoothing the rectified voltage.

Note that the first rectification stage 2 and the first rectification stage 3 are collectively referred to as a rectification/smoothing means 22.

6 is a resonant circuit, and this resonant circuit 6 has a pair of primary windings F! 16a,
(i 'L) To, that 1 (76 笍(6E), 6[
) are connected in series to 4'1 and 5a for resonance.
, 5b and the first-order winding 6a, 61)
is depolarized↑! The winding starts in the same direction so that the connection relationship of 1 is to the right, and Miki winds 116 rows at the same time.

The winding start side is a switching means 2 which will be described later.
It is connected to 0b °C.

Further, the other terminals of both primary windings 6a and 6b are connected to switching means 20a, which will be described later, via resonance capacitors 5a and 5b, respectively.

The secondary winding 6c of the transformer (2) is connected to a high-voltage rectifying means 7 consisting of four bridge-connected rectifying elements.

The DC output of the high-voltage rectifying means 7 is applied to the filament, anode, and 9b of the X-ray tube 9 via the smoothing conte, the connector 8, the high-voltage cable 10a, and the 'I Ob, and is connected to the output side of the high-voltage rectifying means 7. The voltage is detected by a voltage detection section 11 consisting of voltage dividing resistors 11a and 11b.

20a and 20b are switching means, and this switching means 20a includes a first rectifying element 13a and a first switching element (thyristor) 1 connected in parallel.
2a, a second rectifying element 15a and a second switching element (thyristor) 14a which are also connected in parallel, and the switching means 20b has a third rectifying element 13b and a third rectifying element (thyristor) which are also connected in parallel. A switching element (thyristor) 12b, a fourth rectifying element 15b, and a fourth switching element (thyristor) 14b. Here, the first rectifying element 1
The anode of the second rectifying element 15a and the cathode of the second switching element 14a are connected to the resonance output 5a at the connection point d, and the anode of the second rectifying element 15a and the cathode of the second switching element 14a are 7C%. The anodes are respectively connected to the resonance terminals 1 and 5b at connection points e.

On the other hand, the cathodes of the first and third rectifying elements 13a and 13[) and the anodes of the first and third switching elements 12a and 12b are connected to one of the rectifying and smoothing means 22 via connection points f and a. At the connection point, there are also second and fourth rectifying elements 15.
a, 15b anodes and second and fourth switching elements 1/1. The cathodes of a and 14[) are respectively connected to the other connection point of the rectifying/smoothing means 22 via connection points (c and b).

The anode of the third rectifying element 13b and the cathode of the third switching element 12b are connected to the transformer 1-
- connected to the next winding 6b, the cathode of the fourth rectifying element 15b and the fourth switching element 14
Node 7 of b is connected to the primary winding 6a of the transformer T at a connection point i.

19 is a control means for the switching means 20a, and this control means 19 includes a current detection means (for example, a variable current detection means) interposed between the connection point i and the primary windings 5a, 6b. The output of an I/V (current/voltage) converting means 17 that converts the detected current by a current converter (CT) 16 into a voltage signal and the output of the voltage detecting means 11 are input, and the first, fourth, and 2. Gate pulses (
Timing signals) GPI and GP2 are supplied.

Note that the transformer T, high-voltage rectifier 7, smoothing capacitor 8, X-ray tube 9, and high-voltage cable 10a110b are applied with a high voltage with a ground voltage of 75 KV, so electricity is generated inside the housing of the X-ray apparatus. Immersed in insulating oil.

Next, the operation of the X-ray apparatus with the above configuration is shown in Figures 2(a) and (b).
The explanation will also be given with reference to the waveform showing the transmission current of the transformer and the timing chart of the gate pulses GPI and GP2 shown in FIG.

The alternating current voltage supplied from the power source 1 is applied to the rectifying/smoothing means 22 via the switching means 21, rectified by the rectifying means 2, and then smoothed by the smoothing means 3. Applied between b and f, 9.

In this state, the first and fourth switching elements 12a, 1
A gate pulse G P is applied from the control means 19 to the gate of /lb.
1 is applied to the first and fourth switching elements 12a,
14b is turned on.

At this time, when the - sending current 1a is transferred from connection point a → connection point f - → connection point d → capacitor 5a → - next winding 6a → connection point i → connection point, as shown in Fig. 2 (a), between F 1tlJ j.

~ t1 flows.

Here, the primary winding 1 of the resonant circuit 6? Since the constants of +6a and the resonance capacitor 5a are selected in advance to satisfy the resonance conditions, when the half cycle of the -transmission current 1a is completed, the primary winding 1i+6a is stored in the primary winding 1i+6a. 1a flows in the opposite direction of the current path and via the rectifying elements 13 El and 13b, accompanied by damped oscillation.

At this time, the resonance capacitor 5a is negatively charged, and when the reverse direction transmission current 1a decreases below the holding current of the first and fourth switching elements 12a and 14b, the first and fourth switching elements 12a, 14b is turned off.

Next, the 21st. Third switching element 14a112b
To explain the timing of turning on the primary current 1a, as shown in FIG. , [/V converter 17, and the control means 19 applies a gate pulse G P 2 to the gates of the second and third switching elements 14a and 12b.

Further, when turning on the second and third switching elements 14a and 12b at a low frequency as shown in FIG. 2(b), the input phase of the gate pulse GE]2 by the control means 19 may be delayed.

Note that a shunt resistor may be used as the current detection means 16, but in this case, there is a concern that the temperature -F will rise, so it is preferable to use a through-type current transformer.

At the timing mentioned above, the gate pulse G P 2 is the second,
When applied to the third switching elements 14a and 12b, the -order current 1b changes from the connection point a→the connection point h→the -order winding 6b→
Flow occurs when capacitor 5b → connection point e → connection point g -> connection point.

The constants of the primary winding 6b and the resonant capacitor 5b are selected in the same manner as those of the primary winding 6a and the resonant capacitor 5a described above, so that the constants of the primary winding 6b and the resonant capacitor 5b are selected in the same manner as the primary winding 6b and the resonant capacitor 5a, respectively, and are equal to or less than half of the negative current lb. , ]
l! IF is I” '7' t Rudo・Next volume rA6 b
Due to the accumulated magnetic energy, the primary current 1b flows in the opposite direction of the current path and is accompanied by damped oscillation via the combing elements 15a and 13b.

In the same manner as above, a primary current (resonant current) alternately flows through the primary windings 6a and 6b of the resonant circuit 6, and a high voltage is induced in the secondary winding 6C of the transformer T. X-ray 1 after being rectified and smoothed by rectifier 7 and smoothing capacitor 8
To the filament of 9, an anode (applied between the poles 9a and 9b. However, a large current of several hundred amperes (peak value) is applied to the X-ray exposure vA@ of the X-ray tube 9 at 11 o'clock. .

In the following description of V, the resonant frequency f (=1/2π LO) is a number k ll
y is "2".

When the X-ray apparatus is operating normally, the primary current flows through either the primary windings 6a, 6b alternately in positive and negative directions as described above.

However, U,S,PAI-,4225788(S
ep, 30.1980) and 4295049 (OCt
, 13.1981'), as shown in FIG. 2(a), the first and fourth switching elements 12a, 14b
Immediately after turning off the second and third switching elements 14
When turning on the first, second, third, and fourth switching elements 12a, 14a, and 12b,
It is assumed that 2b114b become conductive at the same time, causing an excessive abnormal current to flow.Also, if a short circuit occurs in the secondary high voltage section of the transformer T, the primary circuit of the transformer T There is a possibility that an excessive abnormal current will flow to the side as well.

On the other hand, according to the present invention, both primary windings 6a of the transformer T
, 61) have a depolarizing coupling relationship with the winding starts in the same direction, so the abnormal currents flow in opposite directions. Therefore, the magnetic flux induced in both primary windings 6a and 6b is canceled and the normal voltage There is no risk of occurrence.

Furthermore, generally the switching elements 12a114a, 12
The surge current of b, 14b is several times ten times the rated current,
These switching elements 12a, 14a, 12[), and 14b will not be damaged even in the state where the above-mentioned abnormal current flows.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the invention.

For example, the switching element may be a gate turn-off thyristor (GTO) or a giant-transistor (G-TR) in addition to a normal thyristor.

Also, both and the next winding! It goes without saying that the winding start position is not limited to the advanced embodiment as long as it has a coupling relationship that cancels out the magnetic flux generated at the end of the winding.

Furthermore, the resonant capacitor may be inserted at the winding start side of both primary windings.

[Effects of the Invention] According to the present invention described in detail above, damage to circuit elements due to abnormal currents such as excessive currents and short-circuit currents is prevented by a simple and inexpensive circuit configuration, and an X-ray apparatus with excellent safety can be provided. can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2(a),
(b> is an explanatory diagram showing the waveform of the primary current of transformer (1) and the timing of the gate pulse applied to the switching element, respectively.

Claims (1)

[Claims] A rectifying/smoothing means for rectifying and smoothing an input AC voltage to output a DC voltage; a resonant circuit comprising at least a primary winding of a transformer and a resonant capacitor; In the X-ray apparatus, the resonant circuit includes a pair of switching means that periodically applies voltage, and obtains the X-ray tube voltage based on the voltage induced in the secondary winding of the transformer. It is composed of a primary winding and a pair of resonant capacitors respectively connected to both primary windings, with the pair of primary windings and the resonant capacitor serving as the rectifying/smoothing means, and both terminal sides of each as the switching means. An X-ray apparatus characterized in that the X-ray apparatus is connected to each other so as to intersect with each other.