JPH0146999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an inverter-type X-ray apparatus that can effectively suppress overshoot of a high-voltage output section applied to an X-ray tube.

(Prior Art) As an inverter type X-ray apparatus, an apparatus having a circuit configuration as shown in FIG. 1 has been proposed. That is,
This device basically includes two switching transistors 1 and 1', a DC power source 2, a choke transformer 3, an inverter transformer 6, a rectifier circuit 7, and the output of the rectifier circuit 7 is applied. X-ray tube 1
0. When the switching transistors 1 and 1' are alternately switched at a duty rate of 50%, a current flows from the power source 2 through the primary coil of the choke transformer 3 and the inverter transformer 6. At this time, an alternating voltage is generated on the secondary side of the inverter transformer 6. After this alternating voltage is rectified by a rectifier circuit 7, a high voltage is applied to the X-ray tube 10 to emit X-rays. By the way, during the switching operation of the switching transistors 1 and 1', the energy accumulated in the leakage inductance of the inverter transformer 6 is released, but if this released energy is large (that is, the leakage inductance is large), the switching This may destroy the switching transistors 1, 1'. Therefore, an energy absorption circuit consisting of a resistor 4 and a capacitor 5 connected in series is inserted and connected to prevent destruction. When determining the constants of the resistor 4 and capacitor 5, they are selected so that the leakage inductance and minimum load impedance of the inverter transformer 6 and the current flowing through this energy absorption circuit do not oscillate. In this case, if the value of the resistor 4 is too large, a spike voltage that exceeds the maximum rating may be temporarily applied to the switching transistors 1 and 1'. ′
This is prevented by providing a non-linear element (not shown) for absorbing surge voltage. In an inverter type circuit that takes these considerations into account,
On the secondary side of the inverter transformer 6, a square wave alternating voltage with steep rise and fall characteristics determined by the choke transformer 3 and the load impedance is obtained.

By the way, a shielded cable is used in the path for supplying the high voltage, which is the rectified output of the rectifier circuit 7, to the X-ray tube 10, but this shielded part is grounded, and there is a gap between this shielded part and the core wire. There is a capacitance 11, and as a result, the load seen from the inverter becomes a capacitive load. Therefore, at the start of inverter operation, this capacitance 11 and each transformer 3
Vibration occurs in relation to the leakage inductance of 6 and 6, and this vibration becomes noticeable when the load impedance is large. Here, the conditions for preventing the vibration from occurring are expressed by the following equation (1).

L>4CR2...(1) Here, L is the sum of the leakage inductances of transformers 3 and 6, C is the capacitance of the cable, and R is the load impedance. As is clear from this equation (1), vibration can be prevented by increasing the leakage inductance L as much as possible, and for this purpose, the chiyoke transformer 3 is inserted and connected. If vibration cannot be prevented even after taking such considerations, vibration can be prevented by providing an energy absorption circuit in which a resistor 9 and a capacitor 8 are connected in series on the output side of the rectifier circuit 7. obtain. This is mainly because the energy stored in the leakage inductance is converted into heat by the resistor 9, reducing the Q of the circuit system.

(Problem to be Solved by the Invention) In such a conventional device, the feedback circuit detects the secondary voltage of the inverter transformer and controls the chopper transistor.
Since the secondary voltage is stabilized, an overshoot occurs when the secondary voltage rises. Typically, the feedback circuit
The secondary voltage value is compared with a predetermined reference voltage value, and the chopper transistor is controlled according to the difference value so that the secondary voltage value becomes a predetermined value. When the difference with the secondary voltage value is extremely large, the difference value also becomes large, resulting in an overshoot exceeding a predetermined secondary voltage value. Vibrations caused by such overshoot cause the X-ray tube voltage to fluctuate during X-ray imaging, making it impossible to obtain an X-ray image with stable image quality. Moreover, such an overshoot may even cause glow discharge to occur in the X-ray tube by temporarily increasing the X-ray tube voltage.

The present invention has been developed based on the above circumstances, and aims to prevent overshoot from occurring when the secondary voltage rises during X-ray photography, suppress fluctuations in the X-ray tube voltage, and achieve stable image quality. An object of the present invention is to provide an X-ray device that can obtain an X-ray image.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention includes an input power source, a stepping circuit that tips the input power source, and an output of the stepping circuit that is connected to the primary side train. an inverter transformer that performs an inverter operation and generates a high voltage output to the secondary side track by applying voltage; and an X to which the high voltage output is applied.
A wire tube, a smoothing circuit inserted and connected between the input power source and the inverter transformer, and duty control means for controlling the chopping circuit by gradually increasing the duty from the time when the operation starts. The present invention provides an X-ray device.

(Function) In the X-ray apparatus configured as above,
The duty of the chopping pulse when the secondary voltage of the inverter transformer rises is controlled so as to gradually increase. This prevents the difference value between the reference voltage value and the secondary voltage value from becoming extremely large even when the secondary voltage rises.
Overshoot can be suppressed.

(Example) The present invention will be specifically explained below using Examples.

FIG. 3 is a circuit diagram showing an embodiment of the device of the present invention. 1, 1° is a switching transistor that can be operated alternately with a duty of 50%, 2 is a DC power supply, 3 is a choke transformer,
A series connection circuit of a resistor 4 and a capacitor 5 is an energy absorption circuit, 6 is an inverter transformer, 7 is a rectifier circuit, 10 is an X-ray tube, a transistor 12 connected in series with the power supply 2 is for chopping the power supply, and 17 is an A smoothing circuit configured by connecting a chiyoke coil 13 and a resistor 14 in parallel to the power supply path, and connecting a resistor 15 and a capacitor 16 in series; 18 is a capacitor 16 in the smoothing circuit 17; charging/discharging control circuit, 19
is a pulse width modulator configured to have an output pulse width changed by a tube voltage setting signal of the X-ray tube 10, and to control the switching duty of the chopping transistor 12 using this output pulse. (PWM), and 20 is an integrator configured to generate an output V0 in synchronization with the X-ray exposure start signal, thereby controlling the output pulse width of the PWM 19. This integrator 20 contributes to overshoot prevention as described later. In addition, 21 is a chopping transistor 12
This is a flywheel diode connected between the emitter of the power source 2 and the negative electrode side of the power source 2. The charge/discharge control circuit 18 includes a switching transistor 22 connected between the upper contact of the resistor 15 in the smoothing circuit 17 and the negative electrode side of the power supply 2, and a capacitor 1.
an error amplifier 23 which compares the voltage V1 between the terminals of 6 and the tube voltage setting signal and sets the difference voltage between the two as an amplified output V2; 2
The inverting amplifier circuit that drives 2 and the error amplifier
The PWM is controlled by V2 and the PWM is controlled by output V4.
19. This charge/discharge control circuit 18 contributes to improving the rising characteristics of the high voltage output section waveform, as will be described later. Since this charge/discharge control circuit 18 is not required during X-ray exposure, the operation of the circuit is stopped by a lock signal generated in synchronization with the X-ray exposure start signal.

Here, the operation of the main parts of the circuit will be explained in detail.

First, control of the tip circuit will be explained.
The chopping transistor 12 switches the current from the DC power supply 2 under the control of the PWM 19 and supplies it to the smoothing circuit 17 . The switched current passes through the choke transformer 3 of the smoothing circuit 17 and is accumulated in the capacitor 16. At the same time, current also flows to the chiyoke coil 3. A resistor 14 connected in parallel with the coil 13 improves the rise characteristics of the output voltage, and compensates for high frequency components at the time of rise that are blocked by the coil 13.

A smoothing circuit is formed by the jumping coil 13 and the capacitor 16, and converts the pulse wave from the jumping transistor 12 into a DC power source. Therefore, the current supplied to the inverter transformer 6 through the choke transformer 3 is the sum of the current from the capacitor 16 and the current directly sent through the coil 13. In FIG. 3, the conventional technology is used for the choke transformer 3, inverter transformer 6, switching transistors 1 and 1' resistor 4, capacitor 5, and rectifier circuit 7.

The PWM 19 sends a pulse signal to the stepping transistor 12 to switch the current from the DC power supply 2. Therefore, by changing the duty ratio of the output pulse signal of PWM19,
The voltage between the coil 13 and the transformer 3 can be changed arbitrarily. The duty ratio of PWM19 is the tube voltage setting value, the start of X-ray irradiation, and the capacitor 1.
It is determined based on the voltage value of 6. In other words, if the voltage value of the capacitor 16 drops below the set value for some reason, the differential amplifier 2
3 and 25, V4 increases and the duty increases. Furthermore, if the tube voltage setting value is large, the overall duty becomes large, so the power supplied to the X-ray tube 10 also becomes large.

In the present invention, overshoot of the X-ray tube voltage can be prevented by changing this duty based on the start of X-ray exposure.

According to FIG. 3, the chopping transistor 1
The duty during the second switching operation is controlled to be gradually increased as shown in FIG. 4 and settled at a desired value. The integrator 20 generates an output V0 that gradually rises in synchronization with the X-ray exposure start signal to control the output of the PWM 19. In this case, each component of the integrator 20 (capacitor C0, resistor R11, R12, etc.) is adjusted so that the output of the PWM 19 can control the duty during the switching operation of the switching transistor 12 as shown in FIG.
Set a constant for . By controlling in this way, the current flowing through the chiyoke transformer 3 does not change suddenly, so that overshoot can be controlled.

Next, the operation of the entire X-ray apparatus will be explained.

First, the tube voltage is set by the tube voltage setting signal, and the PWM 19 is operated to control the switching operation of the switching transistor 12.
At this time, the output pulse width of the PWM 19 is set to a value that controls the chopping transistor 12 with a duty that allows the set tube voltage to be obtained. Due to the conduction of the chopping transistor 12, the capacitor 16 in the smoothing circuit 17 is charged. And the charging voltage is the charging/discharging control circuit 1
8 to maintain a constant value. Thereafter, when an X-ray exposure start signal is applied, the integrator 20 operates and the operation of the charge/discharge control circuit 18 is locked. The PWM 19 is controlled by the output V0 of the integrator 20, and the chopping transistor 12 operates so that the duty gradually increases and eventually settles into a predetermined state. For this reason
The voltage applied to the wire tube has a high voltage output waveform corresponding to the change in duty. Therefore, when used as a diagnostic X-ray apparatus, overshoot can be suppressed by controlling the duty and operating the smoothing circuit even under light load. still,
At heavy loads, the rise characteristics become gentler due to the duty control, but as mentioned above, at the start of X-ray exposure, the capacitor 16 in the smoothing circuit 17
is maintained at a predetermined voltage, the rise characteristics are improved and high speed can be achieved.

[Effects of the Invention] As detailed above, according to the embodiment, overshoot can be reduced by gradually increasing the duty of the chopping pulse when the secondary voltage rises.
It is possible to provide an X-ray apparatus that can suppress fluctuations in X-ray tube voltage and that can always obtain X-ray images with stable image quality.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the basic configuration of an inverter-type X-ray device, Figure 2 is a characteristic diagram showing the relationship between tube voltage and time to explain the problem of overshoot at light loads, and Figure 3 is a diagram showing the relationship between tube voltage and time. 4 is a circuit diagram showing an embodiment of the device of the present invention, and FIG. 4 is a characteristic diagram showing the relationship between duty and time. 1,1'...Switching transistor, 2...
...DC power supply, 3... Chiyoke transformer, 4... Resistor, 5... Capacitor, 6... Inverter transformer, 7... Rectifier circuit, 10... X-ray tube, 11...
Cable capacitance, 12... Chopping transistor, 13... Chopping coil, 14, 15
...Resistor, 16...Capacitor, 17...Smoothing circuit, 18...Charge/discharge control circuit, 19...PWM,
20... Integrator, 21... Diode, 22 Switching transistor, 23... Error amplifier, 2
4,25... Schmitt circuit.

Claims (1)

[Claims] 1. An input power source, a stepping circuit that steps the input power source, an inverter transformer that performs an inverter operation by applying the output of the stepping circuit to the primary coil and generates a high voltage output to the secondary coil; A smoothing circuit inserted and connected between an X-ray tube to which a high voltage output is applied, the input power source and the inverter transformer, and a duty control means for controlling the chopping circuit by gradually increasing the duty from the start of operation. An X-ray device characterized by comprising: