JPH05315088A - X-ray generating device - Google Patents

Abstract

PURPOSE:To continue action of generating an X-ray by detecting a tube current to rapidly increase due to a discharge, and controlling switching duty ratio of an inverter temporarily decreased. CONSTITUTION:An AC power supply 1, in which an ignition phase is controlled in an SCR switch circuit 2a by a thyristor control part 3, is smoothed by a smoothing circuit 2b and input to a transformer 7 in a high voltage generating part 6 through an inverted 4. Three voltage-doubler rectifier circuits are connected in series in a secondary side to apply high voltage to an X-ray tube 8. A voltage error signal DELTAv and a current error signal DELTAi are respectively obtained from an error amplifier 15 and an error amplifier 14. The signal DELTAi serves as a PWM control signal of an inverter control part 13 in a filament power supply 10, to feedback control its output. The signal DELTAv serves as a PWM control signal of an inverter control part 5 via a control system of a differentiator 18, comparator 19, monomultivibrator 20 and an adder 17. The signal DELTAv serves as an ignition phase signal of the SCR control part 3 through an LPF16. By double feedback control, a power supply circuit element is protected and automatically returned immediately to a generating mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an X-ray generator comprising an X-ray tube and a power supply for driving the X-ray tube, and more particularly to a technique for coping with the adverse effect of the discharge phenomenon of the X-ray tube. Regarding

[0002]

As is well known, a cathode and an anode are opposed to each other in an X-ray tube, and thermoelectrons generated by heating a cathode filament are accelerated by a high voltage applied between the two electrodes to form an anode. X-rays are generated by the collision. The intensity of the X-ray generated at this time changes depending on the high voltage applied to the X-ray tube and the current flowing through the X-ray tube. Since an X-ray generator used for X-ray analysis is required to maintain stable X-ray output, a high-performance high-voltage generating power supply device that meets the demand is required. The power supply of the conventional X-ray generator is
A large-scale device that combines a slidac or SCR with a high-voltage transformer and a rectifying diode is generally used.
Recently, small switching power supplies have also been used.

[0003]

An X-ray tube has a filament (cathode) for emitting thermoelectrons and a metal target (anode) for receiving electrons arranged in a vacuum, and is commercially available in a sealed state in a glass tube. There are two types, an open type with a vacuum chamber and a vacuum exhaust device. In any case, since a high voltage is applied between the cathode and the anode, a discharge may occur due to a vacuum defect in the tube or a stain in the vacuum chamber. Discharge in the X-ray tube is a current flow different from the usual energization by acceleration of thermoelectrons, and is called a short circuit. Since a much larger current (short-circuit current) than the normal operation flows due to the discharge, the power supply device may be destroyed. Particularly in the case of a switching power supply device, the switching element and the like are easily damaged by overcurrent.

Therefore, in some conventional X-ray generators,
There is one that is provided with an overcurrent relay that detects an overcurrent due to the above-mentioned discharge and shuts off the application of a high voltage to the X-ray tube. However, with such a measure, the X-ray generation operation is completely stopped when discharge occurs, and a troublesome operation is required to restart the stable X-ray generation state, resulting in a long interruption time. was there. Therefore, it has not been possible to substantially continue the X-ray generation operation while protecting the device from overcurrent under the condition that discharge easily occurs.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to promptly interrupt the continuation of discharge when an overcurrent due to the discharge occurs and protect the power supply device from the overcurrent. , A switching power supply type X with a control function that can continue normal operation as much as possible without completely interrupting the X-ray generation operation
It is to provide a line generator.

[0006]

An X-ray generator of the present invention which achieves the above-mentioned object, is a DC power supply section for rectifying and smoothing an AC power supply input, and an output of this DC power supply section is switched to generate a high frequency wave. An inverter that converts to AC, an inverter control unit that changes the output power by changing the switching duty ratio of this inverter, and the output of the inverter is boosted and rectified and smoothed to generate a high DC voltage. A high voltage generator applied to the X-ray tube and an error in the output voltage of the high voltage generator with respect to a target voltage appropriately variably set are detected, and the inverter controller controls the inverter so that the error becomes zero. Voltage stabilization control means for controlling the current, current abnormality detection means for monitoring a change in the tube current of the X-ray tube, and detecting an abnormal sudden rise in the tube current, and this current In which abnormality has a said voltage drop control means for the inverter control unit controls the inverter to lower the output voltage temporarily when it is detected by the atmospheric detection means.

[0007]

When an overcurrent due to discharge occurs, the current abnormality detecting means promptly detects it. Then, the voltage drop control unit works on the inverter control unit to cause X
The voltage applied to the wire tube is temporarily reduced to interrupt the continuation of discharge. After that, the voltage quickly returns to the original value.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic structure of an X-ray generator according to an embodiment of the present invention. The three-phase AC power supply 1 which is the input of this device is a thyristor switch circuit 2 of the DC power supply unit 2.
It is rectified by a (three-phase bridge rectifier circuit), and the rectified output is smoothed by the smoothing circuit 2b including the inductor L1 and the capacitor C1. The control of the gate trigger of the thyristor switch circuit 2a is performed by the thyristor control unit 3 having a well-known configuration. That is, each thyristor is triggered in synchronization with each phase of the three-phase AC power supply 1, and its conduction angle (firing phase) is variably controlled as described below, so that the output voltage of the DC power supply unit 2 is variably adjusted. It

The output of the DC power supply unit 2 is switched by the inverter 4 and converted into high frequency AC power.
The inverter 4 is composed of a bridge of power FETs, is switched by a PWM-type inverter control unit 5 having a well-known configuration, and the switching duty ratio is controlled as described later, so that the AC output power is variably adjusted. .. Although not shown, the PLL (Phase Lo
ck Loop) circuit generates an inverter switching signal synchronized with the AC power supply 1. That is, a feedback loop in which the square wave signal obtained by shaping the waveform of the AC power supply 1 is phase-compared with the frequency-divided signal of the output of the VCO (voltage controlled variable frequency oscillator), and the comparison output is input to the VCO via a low-pass filter. And obtain an inverter switching signal from the VCO. AC power supply 1
It is possible to make the zero-cross point of the above and the rising edge of the switching signal coincide with each other, and it is possible to prevent disturbance of control due to mutual interference between the input power supply frequency and the inverter frequency and adverse effects on the input power supply. In this embodiment, the switching frequency is selected to be 5.1 KHz, which is a common multiple of 50 Hz and 60 Hz.
Whichever power source is used, the same switching frequency of 5.1 KHz can be set only by changing the frequency division ratio of the PLL circuit.

The AC output of the inverter 4 is the high voltage generator 6
Applied to the transformer 7. The transformer 7 includes three secondary windings 7a, 7b and 7c, and each secondary winding 7a, 7b
A voltage doubler rectifying circuit including diodes D1 and D2 and capacitors C1 and C2 is connected to the output sides of b and 7c, respectively. Moreover, the outputs of the three voltage doubler rectifier circuits are connected in series, and the series voltage becomes the output of the high voltage generator 6, and is applied to the cathode and anode of the X-ray tube 8.

The heating power for the cathode filament of the X-ray tube 8 is supplied from the filament power source 10 through the filament transformer 9. The filament power supply 10 includes a rectifier circuit 11 that rectifies and smoothes the AC power supply 1, and a rectifier circuit 1
An inverter 12 for high-frequency switching the output of No. 1 to convert it into AC and apply it to the transformer 9 and an inverter control unit 13 of the PWM control system for variably controlling the switching duty ratio of the inverter 12 to adjust the filament heating power. I have it.

The output voltage (tube voltage) of the high voltage generator 6 applied to the X-ray tube 8 is detected via the voltage dividing resistors R1 and R2 and input to the error amplifier 15. A set value E1 corresponding to a target voltage that is appropriately variably set by a setting circuit (not shown) is also input to the error amplifier 15, and a voltage error signal Δv corresponding to the error of the tube voltage with respect to the target voltage is output from the error amplifier 15. Is output. Further, the current (tube current) flowing through the X-ray tube 8 is detected via the current detection resistor R3 and input to the error amplifier 14. The error amplifier 14 also receives a set value E2 corresponding to a target current that is appropriately variably set by a setting circuit (not shown), and a current error signal Δi corresponding to an error of the tube current with respect to the target current is output from the error amplifier 14. Is output.

The current error signal Δi is the filament power supply 10
The output voltage of the filament power supply 10 is feedback-controlled so that the inverter control unit 13 outputs the PWM control signal and the tube current becomes equal to the set target current.

Similarly, the voltage error signal Δv passes through an adder 17, which will be described later, and the PWM of the inverter control unit 5 of the tube voltage generation system.
It becomes a control signal, and the switching duty ratio of the inverter 4 is controlled so that the tube voltage becomes equal to the set target voltage. This is the first voltage stabilization control means. Although only the duty ratio control of the inverter 4 does not provide very good control response, accuracy, and stability when the tube voltage is changed over a wide range, in the device of this embodiment, the voltage error signal Δv causes the low-pass filter 16 to pass. Is used as an ignition phase control signal for the thyristor control unit 3. That is, if the tube voltage cannot be matched with the target voltage only by controlling the duty ratio of the inverter 4 to some extent, the low-frequency component of the voltage error signal Δv is transmitted to the thyristor control unit 3 via the low-pass filter 16 and the error occurs. The firing phase of the thyristor switch circuit 2a changes according to the polarity of the signal Δv, and as a result, the input voltage of the inverter 4 increases or decreases in the direction of eliminating the error in the tube voltage. This feedback control system is the second voltage stabilization control means.

As described above, the double feedback control for stabilizing the voltage makes it possible to match the tube voltage with the target voltage with high accuracy, and the response and stability of the voltage follow-up control are improved. This dual feedback control mechanism may be adopted in the filament power source 10.

Further, in the X-ray generator of the present invention, the resistance R
The tube current detection signal of the X-ray tube 8 detected via 3 is also input to the differentiating circuit 18, and this circuit 18 detects the rate of change of the tube current. The output of the differentiating circuit 18 is input to the comparing circuit 19, and when the increase rate of the tube current exceeds a reference value set appropriately, an output signal is generated from the comparing circuit 19 to trigger the monostable (monostable multivibrator) 20. Is configured to be. In this embodiment, when the mono-multi 20 is triggered by the comparison circuit 19, the mono-multi 20 outputs a square wave having an amplitude set appropriately in a width of 10 msec. This square wave signal is added by the adder 17 to the voltage error signal Δv to form a PWM control signal for the inverter control unit 5, which acts to reduce the switching duty ratio of the inverter 4 by a constant value.

That is, when a discharge occurs in the X-ray tube 8 and the tube current rises abnormally, the differentiating circuit 18 and the comparing circuit 19 detect it and the monomulti 20 is triggered. Then, the output voltage of the monomulti 20 is added to the PWM control signal supplied from the voltage error amplifier 15 to the inverter control unit 5 for 10 msec, and as a result, the tube voltage applied to the X-ray tube 8 is 10 msec. It decreases by a certain amount only during the period. The value of this voltage drop is chosen so that it interrupts the discharge. When 10 msec has passed, the output of the monomulti 20 is lost, so that the tube voltage returns to the original value and the normal X-ray generation operation is performed.

In the above-mentioned embodiment, the tube voltage is reduced by a constant value by the output of the monomulti 20. However, the present invention is not limited to this embodiment, and the tube voltage can be changed up to that point. It is also possible to reduce the value of the above-mentioned value at a constant rate, and the same operational effect as that of the above-mentioned embodiment is obtained. Needless to say, the configuration of the high voltage generating unit 6 is not limited to the Grainachell booster circuit as shown in the figure, but may be another configuration such as a Cockcroft booster circuit.

[0019]

As described above in detail, in the X-ray generator of the present invention, the switching power supply system for controlling the switching duty ratio of the inverter according to the error between the voltage applied to the X-ray tube and the target voltage. In this device, a control system was added to control the switching duty ratio of the inverter by detecting the sudden rise of the tube current due to discharge, and to temporarily reduce the tube voltage. As soon as the tube voltage drops temporarily, the discharge is immediately interrupted by the drop of the discharge voltage, and there is no danger of damaging the circuit elements of the power supply. Can continue. In other words, even in the situation where discharge is likely to occur, the normal operation can be continued as much as possible without completely interrupting the X-ray generation operation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a schematic configuration of an X-ray generator according to an embodiment of the present invention.

[Explanation of symbols]

 1 Three-phase AC power supply 2 DC power supply part 2a Thyristor switch circuit 2b Smoothing circuit 4 Inverter 6 High voltage generating part 7 Transformer 8 X-ray tube 14 Current error amplifier 15 Voltage error amplifier 16 Low pass filter 17 Adder 18 Differentiator circuit 19 Comparison circuit 20 Mono-multi (monostable multi-vibrator)

Claims (1)

[Claims] 1. A DC power supply unit for rectifying and smoothing an AC power supply input, an inverter for switching an output of the DC power supply unit to convert it into a high-frequency AC, and a switching duty ratio of the inverter. An inverter control unit that changes the output power, a high voltage generation unit that boosts the output of the inverter, rectifies and smoothes it, generates a high DC voltage, and applies it to the X-ray tube, and a target that is appropriately variably set. Voltage stabilization control means for detecting an error in the output voltage of the high voltage generation part with respect to the voltage and controlling the inverter by the inverter control part so that the error becomes zero; and a change in the tube current of the X-ray tube. Current abnormality detection means for detecting an abnormal sudden rise in tube current, and the inverter control section when an abnormality is detected by the current abnormality detection means. An X-ray generator further comprising: a voltage drop control means for controlling the inverter to temporarily reduce the output voltage.