JPH0529091A - X-ray generating device - Google Patents

Abstract

PURPOSE:To reduce generation of switching noise and switching loss in supplying high level DC voltage obtained by increasing and rectifying AC voltage after switching DC into AC by the use of inverter system. CONSTITUTION:A plurality of resonant inverter circuits connected to a DC power supply 10 in parallel respectively 11A to 11N are arranged and variable control voltage Vc of frequency (f) corresponding to variation of output voltage Vo is applied to each inverter circuit 11A, 11B,...11N and feed-back controlled. Since respective inverter circuits 11A to 11N perform switching operation with small timing of voltage or current, switching noise can be reduced, whereby switching loss is reduced. Also with the inverter circuits 11A to 11N connected in parallel, it is possible to meet requirements of X-ray tubes having a wide variable range of output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray generator for generating an X-ray by supplying a high-voltage DC voltage obtained by boosting and rectifying a voltage orthogonally converted by using an inverter circuit to an X-ray tube. Regarding

[0002]

2. Description of the Related Art In an apparatus for diagnosing using an X-ray tube such as an X-ray CT apparatus or an X-ray diagnostic apparatus, a high voltage DC voltage must be supplied to generate X-rays from the X-ray tube. I have to.

In recent years, in order to obtain such a high DC voltage, an inverter configured to input a DC voltage, switch the DC voltage to convert the AC voltage into an AC voltage, and then boost and rectify the AC voltage. The high-voltage DC power supply system is widely used. According to such a power supply, by using a semiconductor element having excellent reliability as a circuit component, it is possible to realize an X-ray generator that operates in a small size, light weight, and high efficiency.

FIG. 7 shows the structure of a conventional X-ray generator using such an inverter system. 1 is an AC power supply, 2 is an AC / DC converter for converting an AC voltage into a DC voltage, and 3 is A chopper circuit 4 for switching the DC voltage into an intermittent waveform as shown in FIG. 8 is an inverter circuit for switching the DC voltage and converting it into an AC voltage. 5 is a transformer for boosting the AC voltage output from the inverter circuit 4 to a high voltage AC voltage, 6 is a rectifier circuit that rectifies the high voltage AC voltage to generate a high voltage DC voltage, and 7 is an X-ray tube that supplies the high voltage DC voltage. is there. 8 is the output voltage (high-voltage DC voltage) V
An error detection circuit for monitoring o and comparing it with a preset reference voltage Vr to detect an error therebetween, and a feedback control circuit 9 for controlling the chopper circuit 3 based on the error voltage so as to eliminate this error. Is.

With the above configuration, the output voltage Vo supplied to the X-ray tube 7 is constantly monitored by the error detection circuit 8 and compared with the reference voltage Vr. Here, the comparison result is V
If there is a relationship of o> Vr, the error between them is output to the control circuit 9, and based on this, the control circuit 9 controls the chopper circuit 3 to reduce the pulse width W1 in the waveform of FIG. Apply voltage. As a result, the DC voltage output from the chopper circuit 3 to the inverter circuit 4 is reduced, and as a result, the output voltage Vo is controlled to be reduced.

On the other hand, if the comparison result has a relationship of Vo <Vr, the error between them is output to the control circuit 9, and based on this, the control circuit 9 sends the pulse width to the chopper circuit 3 in the waveform of FIG. A control voltage that increases W1 is applied. As a result, the DC voltage output from the chopper circuit 3 to the inverter circuit 4 is increased, and as a result, the output voltage Vo is increased. By repeating such a control operation, the output voltage Vo is automatically adjusted in the direction such that it is always equal to the reference voltage Vr.

When the output voltage Vo fluctuates in this way, an error from the reference voltage Vr is always detected, and the pulse width W of the output voltage of the chopper circuit 3 is controlled based on this error, so that the input side to the output side are controlled. Feedback control is performed to adjust the power transmitted to the X-ray tube 7.
It is possible to stabilize the high-voltage DC voltage supplied to the.

[0008]

By the way, in the conventional X-ray generator, a relatively large voltage is interrupted when switching the input DC voltage in the chopper circuit 3, which causes a problem that switching noise occurs.
For example, when using a commercial AC power supply, in the case of 100V input, the DC voltage of about 130V output from the AC / DC converter 2 is switched, or 20
In the case of 0V input, a DC voltage of about 250V output from the AC / DC converter 2 is switched, so that switching noise is unavoidable.

Therefore, in a medical institution, the influence of the noise on other medical devices installed close to each other cannot be ignored. Further, by switching a relatively large voltage in this way, switching loss also increases, resulting in a decrease in efficiency.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an X-ray generation device capable of reducing switching noise and switching loss.

[0011]

In order to achieve the above object, the present invention converts a DC voltage into an AC voltage, boosts the AC voltage, and then rectifies the resulting high DC voltage to an X-ray tube. In an X-ray generator for supplying and generating X-rays, a DC power supply and a plurality of resonant inverter circuits connected in parallel to each other for commonly inputting a DC voltage output from the DC power supply and converting the AC voltage into an AC voltage. A high-voltage direct-current generating circuit for boosting the alternating-current voltage output from each resonant-type inverter circuit, converting it to a high-voltage direct-current voltage, adding it to each other, and supplying it to an X-ray tube; An inverter control circuit for generating a clock signal for controlling the circuit in synchronization is provided.

[0012]

The chopper circuit is omitted, and a plurality of resonance type inverter circuits are used to connect in parallel with each other to input a common DC voltage. Each alternating voltage output after being switched is
After being boosted, they are converted into a high voltage DC voltage, added to each other and supplied to the X-ray tube. As a result, the resonant inverter circuit operates so as to switch at a timing of a small voltage or current, so that switching noise can be reduced and switching loss can be reduced accordingly. Further, by connecting a plurality of resonant inverter circuits in parallel, it is possible to meet the demand for an X-ray tube having a wide output variable range. Furthermore, even if a plurality of resonant inverter circuits are connected in parallel, the synchronization of each can be controlled easily.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an X-ray generator according to the present invention, in which 1 is an AC power source composed of a commercial power source, 2
Is an AC / DC converter that converts AC voltage to DC voltage,
DC power supply 10 common to these power supply 1 and converter 2
Is configured.

Reference numeral 11 denotes a resonant inverter circuit composed of a plurality of units 11A, 11B, ... 11N connected in parallel with each other, and each unit is commonly connected to the DC power supply 10. 5 is a transformer for each unit 11A, 11B, ... 1
It is composed of a plurality of 5A, 5B, ... 5N corresponding to 1N. 6 is a rectifier circuit for each transformer 5A, 5B, ... 5N
.. 6N corresponding to. The outputs of the rectifier circuits 6 are commonly connected so as to add each other, and the X-ray tube 7 is connected thereto.

An error detection circuit 8 monitors the output voltage (high voltage DC voltage) Vo supplied to the X-ray tube 7 and compares it with a preset reference voltage Vr to detect an error between the two.
Reference numeral 12 is each resonance type inverter circuit 11 (11A, 11B, ... 11N) so that this error is eliminated based on the error voltage.
Is a feedback control circuit for controlling by adding a control voltage Vc of a variable frequency f to

FIG. 2 shows the configuration of the feedback control circuit 12. The control circuit 12 is provided corresponding to each of the resonance type inverter circuits 11A, 11B, ... 11N and controls the frequency f which operates as a clock signal. Voltage Vc
A plurality of VCOs (voltage controlled oscillator circuits) 14A,
14B, ... 14N, a VCO gain control circuit 15 for controlling the voltage Vco output to each VCO to adjust the oscillation frequency f thereof, and an operation start signal such that the operation of each resonant inverter is performed within the limits. To a VCO gain control circuit 15 and a drive selection circuit 17 that selects only a required VCO according to the output condition of the X-ray tube 7. The feedback control circuit 12 is used to easily synchronize and operate a plurality of resonant inverter circuits 11A, 11B, ... 11N connected in parallel. FIG. 3 illustrates an example of the principle of the VCO. The variable capacitance diode Do and the inductance Lo form a parallel resonance circuit. The control voltage Vco is applied to the variable capacitance diode Do in the polarity shown in the figure.
The capacitance of the diode Do is changed by adding and changing. Therefore, the oscillation frequency f can be changed by changing the control voltage Vco. Further, the soft start control circuit 16 prevents the control voltage Vc from exceeding the upper limit value of the frequency f which restricts the switching operation of each resonance type inverter circuit at the time of start and becomes unstable as described later. It is used to

The resonance type inverter circuit 11 is shown in FIG.
, A diode DA connected in parallel with the transistor TRA, and a capacitor CA connected in series with the transistor TRA. Also this capacitor C
A constitutes a resonance circuit with the inductance L of the transformer 5A.

As shown in FIG. 6, a control voltage Vc having a variable frequency f (= 1 / Tc) with a constant pulse width W2 and a variable period Tc is applied to the transistor TRA. The frequency f is varied to control the turn-on time of the transistor TRA to adjust the power transmitted from the input side to the output side by so-called frequency modulation.

Compared with the time constant determined by the capacitor C and the inductance L, the transistor TRA is turned off when the value of the current I flowing through the transistor TRA becomes sufficiently small by setting the time of the pulse width W2 sufficiently large. be able to. Therefore, switching noise can be reduced.

FIG. 4 also shows an equivalent circuit when the transistor TRA is on. The capacitor CA is gradually charged and the current I of the transistor TRA is gradually increased due to the presence of the inductance L as shown in the positive side of FIG. It is decreasing. The slope of the characteristic N at this time is determined by the time constant of the capacitor CA and the inductance L.

FIG. 5 shows an equivalent circuit when the transistor TRA is off, and the current I of the transistor TRA is shown in FIG.
After being switched to the negative side of, the discharge current of the capacitor CA flows through the diode DA as shown by the arrow Y. The on / off operation as described above is performed by the control voltage V in each unit.
It is repeated for each cycle Tc to which c is added. Next, the operation of this embodiment will be described.

Since the plurality of resonant inverter circuits 11 operate in exactly the same manner, the operation of the unit 11A which is one of the structural examples will be described as a representative. The output voltage Vo supplied to the X-ray tube 7 is constantly monitored by the error detection circuit 8 and compared with the reference voltage Vr. Assuming that the comparison result has a relation of Vo> Vr, the error between the two is output to the feedback control circuit 12, and based on this, the control circuit 12 compares the transistor TRA of the resonance type inverter circuit 11A with that of FIG. A control voltage Vc that lowers the frequency f in the waveform (reduces the number of pulses) is applied. As a result, the transistor T
Since the turn-on time of RA is shortened, the transmitted power is reduced, and as a result, the output voltage Vo is controlled to be reduced.

On the other hand, if the comparison result has a relationship of Vo <Vr, the error between the two is output to the control circuit 12, and based on this, the control circuit 12 causes the resonant inverter circuit 11A.
A control voltage Vc for increasing the frequency f in the waveform of FIG. 6 (increasing the number of pulses) is applied to the transistor TRA of FIG. As a result, the transistor TRA is turned on for a long time, and the power to be transmitted is increased. As a result, the output voltage Vo is controlled to be increased.

When the output voltage Vo fluctuates in this way, an error with respect to the reference voltage Vr is always detected, and based on this error, the transistor TR for the resonant inverter circuit 11A is detected.
By changing the frequency f of the control voltage Vc applied to A, feedback control is performed to adjust the power transmitted from the input side to the output side, so that the high-voltage DC voltage supplied to the X-ray tube 7 is stabilized. Be promoted. Similar control is performed for other units.

When the operation of the resonance type inverter circuit 11 is frequency-modulated and controlled in this way, in particular, according to the present embodiment, by using the resonance type as the inverter circuit,
Since the transistor that performs the switching operation is switched from on to off at a timing when the voltage or current is small, switching noise can be reduced, and accordingly, switching loss can be reduced. Therefore, the improvement of efficiency is expected to reduce the running cost in terms of electric power. Further, it becomes possible to suppress the influence of noise on other medical devices installed in close proximity. Further, according to this embodiment, the following effects can be obtained by connecting a plurality of resonant inverter circuits in parallel. This will be described below.

For example, an X-ray tube used in an X-ray CT apparatus has different X-ray irradiation conditions depending on the region to be imaged of the subject, or even the same portion depending on the thickness of the tissue. It is configured to be variable. As an example, even when the same region is imaged, the image quality obtained by imaging under the same X-ray exposure condition differs between a subject having a large tissue thickness and a subject having a small tissue thickness. Therefore, for an object having a large tissue thickness, radiography is performed under the X-ray exposure condition such that the X-ray dose is large so that an excellent image quality can be obtained while avoiding the influence of noise. The rating of the output, that is, the tube voltage and the tube current set for the X-ray tube that performs such X-ray irradiation is, for example, 120K.
It is set as V, 50 mA or 120 KV, 300 mA.

The variable range of the rated output given to the X-ray tube is determined by the output voltage Vo applied to the X-ray tube, and when the resonance type inverter circuit is used, the frequency of the control voltage Vc added thereto. The range of rated output is determined by the variable range of f. The lower limit of the frequency f is determined by a value that avoids audible frequencies, and for example, 15 KHz is selected.
On the other hand, the upper limit of the frequency f is the switching transistor TR.
For example, 30 KHz is selected depending on the performance of A. These 15 KHz and 30 KHz are selected for easy understanding of the explanation, and do not necessarily reflect the actual situation.

Thus, the switching transistor TR
If the lower limit of the frequency f of the control voltage Vc of A is set to 15 KHz and the upper limit is set to 30 KHz, the ratio between the lower limit and the upper limit is doubled. Therefore, the output voltage V controlled by this
Therefore, the variable range of the rated output of the X-ray tube is also restricted to double. As an example, the variable range is 120K
In the case of an X-ray tube having a performance of V, 50 mA to 120 KV, 300 mA, the variable range is restricted to double that 120 KV, 50 mA to 120 KV, 1
This shows that only the rated output between 00 mA can be obtained, and the performance of this X-ray tube cannot be fully exhibited.

In such a case, according to the present embodiment, when three resonant inverter circuits 11 are connected in parallel, the rated output for the X-ray tube is 3 when compared with the case of one inverter circuit.
Can be doubled, 120KV, 50mA to 1
It will be possible to deal with it so that it will exhibit the full performance of 20 KV and 300 mA.

Further, according to this embodiment, when a plurality of resonant inverter circuits 11A, 11B, ... 11N are connected in parallel and operated, V of the feedback control circuit 12 is increased.
By applying a control voltage Vc that operates as a clock signal to each corresponding inverter circuit from the COs 14A, 14B, ... 14N, each inverter circuit can be easily operated in synchronization. The clock signal is the error detection circuit 8
Since the frequency is controlled according to the error signal output from the inverter circuit, this allows each inverter circuit to operate efficiently.

The number of resonance-type inverter circuits 11 to be connected in parallel can be arbitrarily set according to the purpose, application and the like. The rated output of the X-ray tube is also an example,
It is possible to deal with various rated outputs.

[0033]

As described above, according to the present invention, since the chopper circuit is omitted and a plurality of resonant inverter circuits are connected in parallel, it is possible to reduce switching noise and switching loss. It is possible to meet the demand for an X-ray tube having a wide output variable range.
Furthermore, it is possible to easily synchronize a plurality of resonant inverter circuits connected in parallel.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an X-ray generator of the present invention.

FIG. 2 is a connection diagram showing a configuration of a footback control circuit used in the device of this embodiment.

FIG. 3 is a diagram showing V used in the feedback control circuit of FIG.
It is explanatory drawing of the operating principle of CO.

FIG. 4 is a connection diagram showing a configuration of a resonant inverter circuit used in the device of the present embodiment and an equivalent circuit at the time of turning on.

FIG. 5 is a connection diagram showing an equivalent circuit of a resonant inverter circuit used in the device of the present embodiment when it is off.

FIG. 6 is a waveform diagram for explaining the operating principle of the resonant inverter circuit used in the device of this embodiment.

FIG. 7 is a block diagram showing a configuration of a conventional device.

FIG. 8 is a waveform diagram showing the operating principle of the chopper circuit used in the conventional device.

[Explanation of symbols]

7 X-ray tube 8 Error detection circuit 10 DC power supply 11, 11A, 11B, ... 11N Resonance type inverter circuit 12 Feedback control circuit 14, 14A, 14B, ... 14N VCO (voltage control type oscillation circuit) 15 VCO gain control circuit

Claims (1)

Claim: What is claimed is: 1. A high-voltage DC voltage obtained by converting a DC voltage into an AC voltage, boosting the AC voltage, and then rectifying the AC voltage to an X-ray tube to generate X-rays. In the line generator,
DC power supply, a plurality of resonance type inverter circuits connected in parallel to each other for commonly inputting the DC voltage output from this DC power supply and converting it into an AC voltage, and each AC voltage output from each resonance type inverter circuit Inverter control for generating a clock signal for synchronously controlling a plurality of resonance type inverter circuits connected in parallel to each other An X-ray generator including a circuit.