JPH0152880B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an X-ray device equipped with an inverter circuit, particularly an inverter-type It is related to.

[Prior art]

Generally, when applying high voltage to the primary side of a transformer, the direction of the final AC pulse when the previous load was opened is different from the direction of the first AC pulse when the load is next closed. If they are the same (hereinafter referred to as "same direction input"), the excitation direction of the transformer core during circuit closing will be the same as the direction during the previous load opening. Because there is residual magnetization in the transformer core that corresponds to the excitation direction determined by the direction of the AC pulse when the load was previously opened, the core easily becomes saturated with the first AC pulse when the load is closed, and a large excitation current is generated. This may cause damage to the inverter circuit elements on the primary side or a drop in the voltage on the secondary side.

In other words, in the B-H curve of the transformer core in Figure 4a, for example, when the previous load was opened, the residual magnetic flux of the core was at the point in Figure 4a, and the next load is applied in the same direction. For example, the iron core is magnetized through the path of the arrow from point a in Figure 1 to point , where the iron core becomes saturated and a large rush current is generated as seen in the current waveform in Figure 4 b, so the output tube voltage is As shown in Figure 4c, the first
The third and third pulse output tube voltages drop.

In order to prevent such magnetic saturation of the transformer core, conventional equipment sets the closing/opening position so that the direction of the AC pulse when opening and the direction of the AC pulse when closing are opposite. The next load is applied from the excitation direction opposite to the excitation direction of the transformer core when the load is opened, and a memory circuit is provided so that closing and opening can be performed regardless of the direction of the AC pulse. One method is to memorize the load direction and apply the next load from the direction opposite to the memorized load direction, and the other is to set the excitation direction of the iron core in a fixed direction using a DC power source before applying the load. A method has been devised in which the load is applied in the direction of the AC pulse, which is the opposite excitation direction.

[Problem to be solved by the invention]

However, all of the conventional methods for preventing polarized magnetization require a special polarized magnetization prevention circuit, which has the drawback of being complex and increasing the size of the X-ray device. .

It is an object of the present invention to provide an inverter-type X-ray device that takes advantage of the characteristics of the inverter-type X-ray device and suppresses rush currents due to different polarized magnetization of a transformer core with a simple configuration.

[Means to solve the problem]

The present invention provides an inverter type X-ray apparatus in which DC voltage is converted to AC voltage by an inverter circuit driven by an oscillator, and the output pulse voltage is boosted by a high voltage transformer and applied to an X-ray tube. A voltage-controlled oscillation circuit in which the oscillation frequency of the oscillator changes depending on the magnitude of the input voltage, and the voltage changes over time to gradually reduce the oscillation frequency of this oscillation circuit from a frequency higher than the steady frequency to the steady frequency. 1. An inverter-type X-ray apparatus comprising: a gradient voltage generation circuit that supplies a gradient voltage to the oscillation circuit; and a voltage change of the gradient voltage generation circuit is synchronized with X-ray exposure.

[Effect]

The oscillator that drives the inverter circuit is time-controlled so that the oscillation frequency changes from a frequency higher than the steady frequency to the steady frequency due to a change in the input voltage.

Therefore, as shown in the B-H curve of the high voltage transformer in Figure 1, when the previous load was opened and the residual magnetic flux of the iron core was at point a in Figure 1, the next load will be applied in the same direction. In this case, the first pulse magnetizes the iron core from point a in FIG. 1 through the path of the arrow. However, since the first pulse has a high frequency, its pulse width is very small, so the iron core is not saturated and the second pulse
The magnetization direction of the core moves from the point to the point in the opposite direction by the second pulse in the opposite direction, and then as the oscillation frequency decreases from a high frequency to a steady frequency, the core passes through the point →→ Since the iron core is magnetized, it does not become saturated, and as a result, the rush current is suppressed, so that the output tube voltage does not drop as shown in FIG. 1b.

Furthermore, even if the residual magnetic flux of the core is large and the first pulse is in the same direction as the previous magnetization direction, and the core reaches a saturated state, the width of the first pulse is very narrow, and the width of the second pulse following it is very narrow. Since the magnet is magnetized in the opposite direction by the second pulse, the rush current is significantly suppressed.

〔Example〕

Next, the embodiment shown in the drawings will be described.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is an output waveform diagram of this circuit.

The circuit configuration of FIG. 2 will be described below in conjunction with the operation description with reference to the output waveform diagram of FIG. 3. Note that each waveform in FIG. 3 corresponds to a point with the same symbol in FIG. 2.

First, when a pulse voltage e corresponding to the X-ray exposure time is inputted by the X-ray exposure signal, the capacitor
As shown in FIG. 3a, _C1 is charged with a time constant determined by resistor _R1 and capacitor _C1 , and this charging voltage a is input to comparator 1a. On the other hand, the pulse voltage e
is input to the reset terminal of flip-flop 2a, flip-flop 2a is reset, and capacitor _C2 starts to oscillate as shown in FIG. 3b. A pulse voltage C having a frequency synchronized with this oscillation frequency is inputted to the flip-flop 2b via the buffer 3. This oscillation frequency gradually decreases as the charging voltage of capacitor _C1 increases, and becomes a constant frequency (steady frequency) determined by the divided voltage of capacitor _C2 and resistors _R2 to _R5 due to saturation of the voltage of a.
The pulse voltage C is alternately applied to the commutation capacitor _C3 and the inverter circuit I by the flip-flop 2b.
The signal is output so that transistors Tr ₁ and Tr ₂ forming the circuit are driven.

Inverter circuit output voltage V _P is high voltage transformer 4
The output voltage V _T is boosted by the rectifier circuit 5, full-wave rectified by the rectifier circuit 5, and applied to the X-ray tube.

In the above embodiment, a comparator is connected to one input terminal, and a capacitor is connected to the capacitor, which is charged in synchronization with the X-ray exposure signal to generate a ramp voltage that increases over time. A voltage-controlled variable frequency oscillator was constructed by combining a flip-flop and a comparator connected to a capacitor that determines the steady frequency. It may be configured such that a capacitor is provided in the front stage of the converter so that the frequency can be varied.

In this case, a capacitor may be charged to a high voltage in advance and discharged to a voltage that defines a steady frequency in synchronization with X-ray exposure, thereby generating a ramp voltage that gradually decreases over time.

〔effect〕

According to the present invention, it is possible to suppress rush current due to biased magnetization of the transformer core with a simple configuration, taking into account the special characteristics of the inverter type X-ray device. As a result, it is possible to provide an inverter-type X-ray apparatus that can prevent a drop in the X-ray tube voltage and also prevent damage to inverter circuit elements due to rush current.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the operation of this invention, Fig. 2 is a circuit diagram showing the configuration of an embodiment of the invention, Fig. 3 is a waveform diagram for explaining the operation of Fig. 2, and Fig. 4 is a transformer core. It is a diagram for explaining the polarized magnetization state of. 0: Voltage controlled variable frequency oscillator (1a, 1b
...Comparator, 2a, 2b...Flip-flop, 3...Buffer), 4: High voltage transformer,
5: Rectifier circuit, 6: X-ray tube, I: Inverter circuit (Tr ₁ , Tr ₂ , T'r ₁ , T'r ₂ ...transistor,
C ₃ ... Commutation capacitor).

Claims (1)

[Scope of Claims] 1. In an X-ray apparatus in which a DC voltage is converted into an AC voltage by an inverter circuit driven by an oscillator, the output pulse voltage is boosted by a high voltage transformer, and is applied to an X-ray tube. , a voltage-controlled oscillation circuit in which the oscillation frequency of the oscillator changes according to the magnitude of the input voltage, and a voltage control type oscillation circuit in which the oscillation frequency of the oscillator changes depending on the magnitude of the input voltage, and a voltage control type oscillation circuit that changes the oscillation frequency with the passage of time to gradually reduce the oscillation frequency of the oscillation circuit from a frequency higher than the steady frequency to the steady frequency. and a ramp voltage generation circuit that supplies a ramp voltage whose voltage changes to the oscillation circuit,
An inverter-type X-ray apparatus characterized in that voltage changes in the gradient voltage generating circuit are synchronized with X-ray exposure.