JP3537117B2 - X-ray tube power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for an X-ray tube, and more particularly, to a power supply device for an X-ray tube having a high-speed start-up characteristic and having no overshoot particularly when a set voltage is changed.

[0002]

2. Description of the Related Art A power supply device for an X-ray tube is a power supply device having a DC high-voltage output, and in recent years, high stability and reduction in size and weight have been realized by combining a high-frequency inverter and a high-voltage rectifier circuit. X-ray tube power supplies of this type are widely used in medical X-ray apparatuses. Incidentally, the medical X-ray apparatus individually and variably sets the applied voltage of the X-ray tube to an optimum value depending on a measurement site of a human body. On the other hand, it is desirable to keep the amount of unnecessary exposure of the X-ray tube to a low level, so that the startup period during which unnecessary exposure is required should be as short as possible. At present, it is required that the time be 1 ms or less.

This X-ray tube power supply has a high voltage output, and has a problem inherent to a high voltage output as compared with a case of a low voltage output. First, the turns ratio of the transformer increases, and leakage magnetic flux is inevitable. The leakage magnetic flux causes a delay element of the main circuit loop. Next, the voltage division ratio of the detection circuit for stabilizing the output voltage increases,
A complicated phase shift is inevitable. The latter phase shift is considerably improved by a phase correcting capacitor, but some phase shift remains.

[0004]

The correspondence between the reference voltage and the high voltage output of the X-ray tube power supply device will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1A is a waveform diagram of a reference voltage, and FIG. 1B is a waveform diagram of a high voltage output. The correspondence between them is as follows: high voltage output
(Uppercase of α) corresponds to the reference voltage β, the high voltage output Β (uppercase of β) corresponds to, the reference voltage γ,
High voltage output Γ (capital of γ) corresponds. 1 in Fig. 1 (b)
If the output set value is reduced while maintaining the high-speed start-up characteristic as shown in FIGS. Although the reason may be variously considered, the output current may be increased when the output voltage is set low. In this case, the output becomes substantially low impedance, which is considered to be the cause of the overshoot. Alternatively, the vicinity of the low setting is a non-linear characteristic as a loop characteristic, so that an overshoot may occur. It is an object of the present invention to prevent an overshoot in a power supply device for an X-ray tube while maintaining a rising characteristic.

[0005]

[Solution cousin] As a solution cousin, the actual measurement is performed with the slope of the rise of the reference voltage being minimized.
As a result, as shown in FIG. 1 (c) for the reference voltage and FIG. 1 (d) for the high voltage output, the high voltage output Α0
The high voltage output Β0 corresponds to the reference voltage β0, and the high voltage output Γ0 corresponds to the reference voltage γ0.

According to the results of the actual measurement, in order to solve the problem, the rising slope of the reference voltage is set to a predetermined value corresponding to the set value of each reference voltage, and when the set value is set to a low value, the predetermined rising is set to the low set value. It turned out that the inclination should be changed so that it rises with time. Therefore, the problem can be solved by automatically associating the set value of the reference voltage with the rising slope.

[0007]

According to the present invention, a high-frequency inverter connected to a primary winding of a transformer and a high-voltage rectifier circuit connected to a secondary winding of the transformer are provided. And a voltage divider for dividing the high voltage output of the high voltage rectifier circuit. The output detection voltage divided by the voltage divider is compared with a reference voltage from a reference voltage source, and these output detection voltages and In the X-ray tube power supply device that controls the high-frequency inverter to be equal to a reference voltage and generates a predetermined output high voltage, the reference voltage source has one input terminal to which a high-voltage output setting signal is input.
An operational amplifier having a base terminal connected to the output of the operational amplifier and an emitter terminal connected through a resistor.
First is connected to the power supply line, a second transistor, a resistor connected to the collector terminal and the series of the first transistor, said collector of said second transistor
And a capacitor charged by a current flowing through the first transistor. The voltage of the resistor generated by the current flowing through the first transistor is connected to the other input terminal of the operational amplifier.
And the operational amplifier is configured to control the voltage of the resistor to be equal to the value of the high voltage output setting signal.
Controlling a second transistor, wherein the capacitor is charged by a current flowing through the second transistor, the current having a magnitude corresponding to the value of the high voltage output setting signal, and the capacitor corresponding to the magnitude of the high voltage output setting signal; A high-frequency inverter that operates such that the high-voltage output rises at the time of rising according to the rising slope of the reference voltage. A tube power supply is proposed.

[0008]

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a power supply device for an X-ray tube according to the present invention will be described with reference to FIG. The X-ray tube power supply device 12 is roughly composed of an inverter and control unit 1 and a high-voltage unit 2. The inverter and control unit 1 includes a rectifier circuit 3, a high-frequency inverter 4,
It comprises a gradient reference voltage generation circuit 5, a drive circuit 6, and an error amplifier 7. In addition, the high-voltage section 2 includes a transformer 1
0, a high voltage rectifier circuit 9 and a voltage divider 8.

To explain the configuration in detail, a voltage of 200 V of a commercial AC power supply is connected to input terminals 311 and 312. The AC 200 V is rectified by the rectifier circuit 3 into a DC voltage of about 400 V. This DC voltage of about 400 V
High frequency inverter 4 consisting of IGBTs 401, 402, 403, 404
Is converted to a high frequency of about 30 kHz and connected to the primary winding of the transformer 10. Here, the driving of the high-frequency inverter 4 is controlled by the drive circuit 6. The turns ratio of the secondary winding of the transformer 10 to the primary winding is 1:70, and the high-frequency high voltage boosted at this ratio is quadrupled by a rectifying circuit 9 comprising diodes 903,905,913,915 and capacitors 901,907,911,917. Is done. This quadruple-voltage rectified DC high voltage reaches a maximum of 150 kV and is supplied between the anode and cathode of the X-ray tube 11.

The stabilization and control of the DC high voltage will be described. Capacitor 907 in high voltage section 2
And 917 are charged to substantially the same value, the voltage across capacitor 907 is detected by voltage divider 8. The voltage divider 8 is configured by connecting a number of resistors in series, and a capacitor is connected in parallel with each resistor. This partial pressure ratio is a ratio that makes 150 kV about 5 V, that is, 30,00
0: 1. At this large voltage division ratio, an ideal voltage division characteristic is not obtained. Therefore, the value of the capacitor is adjusted to approximate the ideal voltage division characteristic as much as possible. This divided voltage signal is sent to the negative input terminal of the error amplifier 7. On the other hand, the output voltage of the reference voltage generating circuit 5 is supplied to the + input terminal of the error amplifier 7. The output of the error amplifier 7 is sent to the drive circuit 6, and generates an inverter control output corresponding to the signal. Therefore, the high-frequency inverter 4 operates so that the detected voltage of the voltage divider 8 and the value from the reference voltage generating circuit 5 become equal to each other.

The reference voltage generation circuit 5 basically generates a constant reference voltage, but is characterized by a rising slope. In the configuration of the reference voltage generating circuit 5, a capacitor 570 having one end connected to a common line is provided, and a charging current is supplied to the capacitor 570 by a constant current circuit 510.
The constant current circuit 510 operates to supply a constant current corresponding to the value of the variable high voltage output setting signal applied to the terminal 512. A limiter 530 is connected between one end of the capacitor 570 and the terminal 512, and the capacitor 570 is charged.
When the voltage value at the terminal 512 is reached, the limiter 530 operates to limit the charging voltage. At both ends of the capacitor 570,
Also, a switch 550 is connected to set the timing of turning on and off the reference voltage.

FIG. 3 is an example of the reference voltage generation circuit 5. The same reference numerals as those in FIG. 2 respectively correspond to the same components. Regarding the constant current circuit 510, the operational amplifier 511, the PNP transistor 515,521 and the resistor 517,
519,523 and a capacitor 513. The negative input terminal of the operational amplifier 511 is connected to the terminal 512 and receives a reference voltage setting signal. The + input terminal of the operational amplifier 511 is connected to a connection point 520 with the resistor 519, and receives a voltage signal across the resistor 519. And an operational amplifier
The output terminal of 511 is connected to the base of a PNP transistor 515. The emitter of PNP transistor 515 is connected to power supply line VD via resistor 517. Another PN
The base of the P-type transistor 521 is commonly connected to the base of the PNP transistor 515. The emitter of the PNP transistor 521 is connected to the power supply line VD via the resistor 523, and the collector is connected to one end of the capacitor 570.

Regarding the operation of the constant current circuit 510,
First, the operation is performed so that the signal voltage at the terminal 512 and the voltage at the connection point 520 become equal to each other. Therefore, the collector current of the PNP transistor 515 acts so as to be a constant current corresponding to the signal voltage at the terminal 512. At this time, the voltage across the resistor 517 becomes a voltage corresponding to the current flowing through the resistor 519. Since the bases of the PNP transistors 515 and 521 are connected in common, the PNP transistors
The 521 operates like a PNP transistor 515, so to speak. Therefore, the collector of the PNP transistor 521 acts so as to have a constant current corresponding to the signal voltage at the terminal 512. That is, when the signal voltage at the terminal 512 is low, a small current corresponding to the low signal voltage flows to charge the capacitor 570. Also, terminal 512
Is high, a large current corresponding to the high signal voltage flows to charge the capacitor 570. Therefore, the rising slope of the charging voltage of the capacitor 570 corresponds to the signal voltage at the terminal 512, and the high voltage output has a rising slope equal to the rising slope of the reference voltage.

The limiter circuit 530 is a voltage follower circuit having a limiter function including an operational amplifier 531 and a diode 533. In general, a voltage follower circuit connected between the negative input terminal and the output terminal of an operational amplifier operates so that the voltage of the positive input terminal and the voltage of the output terminal of the operational amplifier are always equal. The diode 53 connected in series to the output terminal of the operational amplifier 531
By the action of 3, the potential of the connection point 534 is changed to the operational amplifier 531.
If the limiter circuit 530 is turned on without going higher than the + input terminal, the upper limit is limited to the potential of the terminal 512. Note that the resistor 537 is for limiting the current of a low resistance value.

In the switch circuit 550, the drain and source of the FET 553 are connected via a current limiting resistor 555. The logic circuit 551 is connected to the gate of the FET 553. When the signal at the terminal 552 is at the H level, the output terminal of the logic circuit 551 is at the L level,
The gate of 553 is also at the L level, and the switch circuit 550 is turned off. Conversely, when the signal at the terminal 552 is at the L level, the output terminal of the logic circuit 551 is at the H level, the gate of the FET 553 is also at the H level, and the switch circuit 550 is turned on.

As described above, the reference voltage generation circuit 5 shown in FIG. 3 generates a predetermined reference voltage at the terminal 572, rises at an inclination corresponding to the signal voltage at the terminal 512, and The generation of a constant voltage is maintained up to the signal voltage. The reference voltage is stopped, generated, and restarted by the signal of the terminal 552.

[0018]

The present invention has the above-mentioned characteristics, and in a power supply device for an X-ray tube, a high-speed rising characteristic that is always constant and free from overshoot even when a voltage set value is varied. Having. Therefore, there is an effect that the amount of unnecessary exposure to the human body to be measured can be reduced.

[Brief description of the drawings]

FIG. 1 is an illustration for studying characteristics at the time of starting a power supply device for an X-ray tube.

FIG. 2 shows an embodiment of a power supply device for an X-ray tube according to the present invention.

FIG. 3 shows an example of a reference voltage generating circuit in the X-ray tube power supply device according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 inverter and control unit 2 high-voltage unit 3 rectifier circuit 4 high-frequency inverter 5 reference voltage generation circuit 6
... Drive circuit 7 ... Error amplifier 8 ... Voltage divider 9 ... High voltage rectifier circuit 10 ... Transformer 11 ... X-ray tube

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-98 (JP, A) JP-A-8-237037 (JP, A) JP-A-8-31583 (JP, A) JP-A-6-31583 76982 (JP, A) Hiroya Fukuda et al., Application of learning control method to resonant DC-DC converter, IEICE Transactions C, Japan, The Institute of Electrical Engineers of Japan, November 1996, Vol. 116, No. 11 No. pp. 1267-1275 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H05G 1/00-2/00 JTPlus file (JOIS)

Claims (1)

(57) [Claims] A high frequency inverter connected to a primary winding of a transformer, a high voltage rectifier circuit connected to a secondary winding of the transformer, and a voltage divider for dividing a high voltage output of the high voltage rectifier circuit. And comparing the output detection voltage divided by the voltage divider with a reference voltage from a reference voltage source, and controlling the high-frequency inverter so that these output detection voltages and the reference voltage become equal to each other. An X-ray tube power supply device for generating an output high voltage, wherein the reference voltage source receives a high voltage output setting signal.
An operational amplifier having one input terminal, a base terminal connected to the output of the operational amplifier , and an emitter terminal connected to the output terminal.
First and second transistors connected together to a power supply line via a resistor, a resistor connected in series with a collector terminal of the first transistor ,
A capacitor charged by a current flowing through the collector terminal; and a voltage of the resistor generated by a current flowing through the first transistor is input to the other input terminal of the operational amplifier.
And the operational amplifier controls the first and the second so that the voltage of the resistor is equal to the value of the high voltage output setting signal.
Controls of transistors, said capacitor flows through said second transistor,
Outputting a reference voltage having a rising slope and a final value that is charged by a current having a magnitude corresponding to the value of the high-voltage output setting signal and changes in accordance with the magnitude of the high-voltage output setting signal; The power supply device for an X-ray tube, wherein the inverter operates so that the high voltage output rises at the time of rising according to a rising slope of the reference voltage.