JPH0363200B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an X-ray high voltage device, and more particularly to a high voltage generator using an inverter.

[Background of the invention]

FIG. 1 shows the configuration of a high voltage generator using an inverter. In the figure, 1 is a first rectifier circuit that receives a commercial AC power supply and converts it into DC, 2 to 5 are rectifier elements that constitute this first rectifier circuit, and 6 is a first rectifier circuit.
a DC reactor 7 for smoothing the output of the first rectifier circuit 1, 7 a capacitor for smoothing the output of the first rectifier circuit 1 together with the DC reactor 6;
9 is a high voltage transformer that boosts the output voltage of the inverter 8; 10 is a second rectifier circuit that converts the AC voltage boosted by the high voltage transformer 9 into a DC voltage; 11 12 is a smoothing capacitor for smoothing the output voltage of the second rectifier circuit 10, 12 is an X-ray tube, and 13 is for outputting an exposure signal to the inverter 8 in accordance with an X-ray exposure start signal and an X-ray stop signal. This is a control circuit that controls its operation. In the conventional device, the capacitor 7 is fully charged when the high voltage generator is connected to a commercial power source and X-ray exposure is possible. At this time, when the X-ray exposure signal is output to the control circuit 13, the control circuit 13 outputs the exposure signal to the inverter 8 as shown in FIG. The inverter 8 starts DC-AC conversion according to the exposure signal. FIG. 3 shows an equivalent circuit of the high voltage generator immediately after the inverter 8 starts DC-AC conversion. 21 is a DC power supply equal to the voltage of the capacitor 7, 22 is the leakage inductance of the high voltage transformer 9, 23 is the capacity of the smoothing capacitor 11,
24 is the equivalent resistance of the X-ray tube. The circuit operation immediately after starting DC-AC conversion is the step voltage response of the circuit shown in FIG. The leakage inductance of the high voltage transformer 9 is generally designed to be small, and becomes a capacitive load as shown in FIG. Therefore, immediately after the voltage of the DC power supply 21 is applied, an excessive current flows through the leakage inductance 22, and the voltage of the capacitor 23 overshoots. A similar phenomenon occurs in Fig. 1, so an excessive current flows through the inverter 8 immediately after the inverter 8 starts DC-AC conversion, and the voltage Vout of the smoothing capacitor 11 causes an overshoot as shown in Fig. 2. arise. This overshoot not only adversely affects the X-ray photograph, but also
This must be prevented since there is a risk of exceeding the withstand voltage limit of the wire tube 12 or damaging the inverter 8 due to overcurrent.

[Purpose of the invention]

An object of the present invention is to provide a high-frequency X-ray apparatus that suppresses overcurrent of an inverter and overshoot of voltage applied to an X-ray tube at the start of X-ray exposure.

[Summary of the invention]

The main point of the present invention is to focus on the fact that the overcurrent of the inverter at the start of X-ray exposure and the overshoot of the voltage applied to the X-ray tube are step voltage responses of the equivalent circuit. To prevent direct current from being applied, charging of the capacitor on the power supply side of the inverter is started at the same time as X-ray exposure, and after the exposure is finished, the voltage of the capacitor is set to zero.

[Embodiments of the invention]

FIG. 4 shows an embodiment of the present invention. 31, 33
is a semiconductor switch, 32 is a resistor, and 34 is a signal a that turns on the semiconductor switch 31 from the time when the X-ray exposure start signal is input until the X-ray stop signal is input, and after the X-ray stop signal is input, This is a control circuit that outputs a signal b that turns on the resistor 33 to the semiconductor switches 31 and 33, respectively, for a period in which the voltage of the capacitor 7 is zero or longer.

The operation will be explained using FIG. Even when the device of the present invention is connected to a commercial AC power source, the semiconductor switch 31 is in an off state, so the capacitor 7 is not charged and the voltage is zero. When the X-ray exposure start signal is input to the control circuits 13 and 34, the control circuit 13 outputs the exposure signal to the inverter 8, and the inverter 8 starts DC-AC conversion. At the same time, the control circuit 34 outputs a signal a that turns on the semiconductor switch 31, so that the semiconductor switch 31 is turned on.
Then, the capacitor 7 starts charging through the first rectifier circuit 1, the semiconductor switch 31, and the DC reactor 6, and the voltage Vin of the capacitor 7 becomes the fifth
It rises as shown in the figure. As the capacitor 7, an electrolytic capacitor is normally used to smooth Vin. Electrolytic capacitors deteriorate due to excessive inrush current or pulsating current, so it is necessary to keep the current below the allowable value. Therefore, the inductance of the DC reactor 6 is selected so as to suppress the inrush current and pulsating current of the capacitor 7. As a result, inrush current is suppressed and Vin does not cause a large overshoot. Inverter 8 has an input voltage of Vin
is input, no overcurrent flows to the inverter, and no overshoot occurs at Vout.

When the X-ray stop signal is input to the control circuits 13 and 34, the control circuit 13 stops outputting the exposure signal, and the inverter 8 stops DC-AC conversion, so that the X-ray exposure is completed. On the other hand, the control circuit 34 stops outputting the signal a and outputs a signal b to the semiconductor switch 33 to turn it on. The semiconductor switch 31 is turned off, and the semiconductor switch 3
3 is turned on, the charge accumulated in the capacitor 7 is discharged through the resistor 32 and the semiconductor switch 33, and the voltage becomes zero. semiconductor switch 33
The on-time of is determined according to the resistance value of the resistor 32 so that Vin is sufficiently small.

In this manner, the present invention can suppress overcurrent of the inverter and overshoot of the voltage applied to the X-ray tube.

FIG. 6 shows another embodiment of the invention. In the diagram, 4
1 and 42 are controlled rectifying elements. The difference from FIG. 4 is that a semiconductor switch for controlling the charging of the capacitor 7 is not separately provided, and some of the elements constituting the rectifier circuit for rectifying the AC power source are used as control rectifier elements. In this configuration, the control rectifiers 41 and 42 are controlled by the signal a output from the control circuit 34.
When ignited, an effect similar to that shown in FIG. 4 can be obtained.

FIG. 7 shows yet another embodiment of the present invention. In the figure, 51 is a diode for circulating the energy of the DC reactor 6 when the semiconductor switch 31 is turned off, and 52 is a diode for ensuring that the current flowing through the inverter 8 does not exceed a predetermined value and that the voltage of the X-ray tube 12 is set to a predetermined value. This is a control circuit that controls the energization period of the semiconductor switch 31 so as to satisfy the two conditions that the voltage does not exceed .

The circuit of FIG. 7 differs from that of FIG. 4 or 6 in that the switch for charging the capacitor 7 is turned on and off after the start of exposure until a steady state is reached. This is to shorten the rise time of Vin and Vout. The rise time can be shortened by reducing the inductance of the DC reactor 6. However, then the 8th
As shown in the figure, an overcurrent flows and causes an overshoot, which deviates from the original purpose. Therefore, if the maximum value of the current or voltage is set and the semiconductor switch 31 is turned off when the current or voltage reaches that value, the rise time will be shortened and overcurrent and overshoot will be prevented. Does not occur. FIG. 9 shows how the energization width of the semiconductor switch 31 is changed with respect to the upper limit of the overcurrent. Since the inductance of the DC reactor 6 is small, the current I ₁ becomes oscillatory. However, as shown in FIG. 9, by turning off the semiconductor switch 31 with a predetermined current, the current value can be suppressed and the rise time can be shortened.

The energization period of the semiconductor switch 31 determined by the controller 52 can be determined by directly detecting overcurrent or overvoltage and using feedback control, or by determining the optimum energization period in advance through experiments or simulations, and then determining the optimum energization period for semiconductor memory, etc. There are ways to memorize and follow that data.

Note that the first rectifier circuit 1 and the semiconductor switch 31
In some cases, a filter with an inductance and a capacitor of the same magnitude as that formed by the DC reactor 6 and capacitor 7 may be inserted between them.

〔Effect of the invention〕

According to the present invention, overcurrent of the inverter and overshoot of the voltage applied to the X-ray tube at the start of X-ray exposure can be suppressed. Furthermore, since the capacitor is discharged every time X-ray exposure is completed, there is no unnecessary energy inside the apparatus, and the safety of the apparatus is increased.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a high voltage generator using an inverter, Fig. 2 is a time chart explaining the operation of Fig. 1, Fig. 3 is an equivalent circuit diagram of a part of Fig. 1, and Fig. 4 is A configuration diagram of one embodiment of the high voltage generator of the present invention, FIG. 5 is a time chart explaining the operation of FIG. 4, FIG. 6 is a configuration diagram of another embodiment of the present invention, and FIG. 7 is a diagram of the present invention. A block diagram of still another embodiment of the invention, FIG. 8 is a diagram showing differences in output waveforms due to differences in circuit constants in FIG. 7, and FIG. 9 is an explanatory diagram of the operation of FIG. 7. 1... Rectifier circuit, 6... DC reactor, 7... Smoothing capacitor, 8... Inverter, 9... High voltage transformer,
10... Rectifier, 11... Smoothing capacitor, 12... X
wire tube.

Claims (1)

[Claims] 1. An inverter that converts DC voltage into AC voltage, a capacitor that stabilizes the input voltage of this inverter, a high voltage transformer that boosts the output voltage of this inverter, and a high voltage transformer that boosts the output voltage of this inverter. In an X-ray high voltage device equipped with a rectifier circuit that converts an output voltage into a DC voltage, a series connection body consisting of a first switch that controls charging of the capacitor, a resistor and a second switch in parallel with the capacitor. means for controlling the first switch to start charging the capacitor when the inverter starts operating, and turning on the second switch until the capacitor is completely discharged after the inverter finishes operating. A high-frequency X-ray apparatus characterized by comprising means for: 2. In claim 1, the current flowing through the inverter does not exceed a predetermined value;
A high-frequency X-ray apparatus, comprising means for controlling the first switch so that the output voltage of the rectifier circuit does not exceed a predetermined value.